- 1.1 Introduction
- 1.2 Biomarkers
- 1.2.1 Classification of Biomarkers
- 1.3 Sensors for Biomarker Detection and Determination
- 1.3.1 Nanomaterials for Sensor Design
- 1.3.2 Construction and Working of a Biosensor
- 1.3.3 Characteristics of a Biosensor
- 1.3.4 Classification of Biosensors
- 1.4 Conclusion and Future Aspects
- References
Chapter 1: Introduction to Biosensors: An Overview
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Published:20 Dec 2024
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Special Collection: 2024 eBook CollectionSeries: Detection Science Series
S. Kumari, P. Puri, D. Suthar, Kamlesh, S. L. Patel, and Himanshu, in Sensing Materials and Devices for Biomarkers, ed. V. Mutreja, D. Kathuria, S. Sareen, and J. Park, Royal Society of Chemistry, 2024, vol. 28, ch. 1, pp. 1-36.
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Early disease diagnosis and management are crucial aspects of healthcare and research. Biomarker recognition is one of the vital techniques that efficiently provides real-time and precise biological information for early diagnosis. Biomarkers are used as crucial biological indicators in medical exploration and treatment. The examination of biomarkers has evolved into a promising non-invasive means for safe, informal and pain-free monitoring, with the potential to amend the current methods of medical analysis and management. Rapid progress in sensor technology, has led to the development of high-performance sensors for human health monitoring. Since as early as 1867, molecular sensors have been renowned as intelligent devices capable of addressing various issues associated with our environment and health. In the human healthcare system, sensors are garnering interest owing to their high potential to provide incessant and immediate physiological and chemical information, as well as non-invasive measurements of biomarkers in human bio-fluids such as saliva, tears, sweat, interstitial fluid, and human volatiles. In this chapter, we have concisely described numerous types of biosensing units and their operation as well as the role of biosensors in detecting various types of biomarkers in humans.
1.1 Introduction
Human health has always been one of the more intricate issues in contemporary science.1 Diseases are an inherent aspect of human life. However, the diseases that may seem relatively manageable in well-established countries can indeed have devastating consequences in less developed regions across the globe. Some diseases can impose significant physical, emotional and socioeconomic burdens by claiming thousands of lives. The cost, both in material resources and ethical considerations, can be profound throughout the treatment procedure. Cardiac diseases, cerebral diseases, and hypertensive heart diseases collectively contribute significantly to global mortality rates, as highlighted by World Health Organization (WHO) statistics.2 Cancer disease is one of the most dangerous diseases and a noteworthy obstacle for global development. Cardiovascular disease has 100 diverse variants that can affect different major organs in the human body. It is one of the main causes of mortality and disease worldwide.3–5 Human beings are exposed to an escalating number of biological toxicants, some of which have steadily been revealed to be imperative hazard factors for metabolic diseases, such as obesity and diabetes.6 Diabetes mellitus includes both acute and chronic problems, making it a complex and multifaceted condition.7 Kidney diseases are complex and heterogeneous with acute kidney injury (AKI) being common in kids and coupled with increased inpatient death and duration of hospital stay.8 According to WHO, psychological diseases present overwhelming rates of incidence, morbidity, death, and disability. Affliction with a grave psychological illness decreases regular life expectancy by 13 to 32 years.9,10 In most Western countries, despite mortality, mental health disorders are indeed the foremost cause of disability, contributing significantly to chronic sick leave and about 4% of the gross domestic product.11 In total, the analysis and treatment of such severe ailments has been a considerable focus for both academicians and state officials, who have devotedly worked to discover efficient techniques and supplies for earlier and cheaper diagnosis and competent treatment. Human health and performance monitoring (HHPM) is essential for providing inferences crucial for shielding, estimating, supporting and humanizing people in various professional areas, for example, academia, industry, recreation, sports, and military.12 The detection of disease at an early stage plays a pivotal role in disease control and prevention efforts. Early detection allows for prompt medical intervention, which can prevent the progression of disease to more advanced stages. Diseases that are detected early are often more treatable, leading to lower rates of morbidity and mortality.13,14 The traditional screening techniques such as biopsy, blood analysis and clinical imaging have been valuable in diagnosing diseases, but they have limitations, especially when it comes to detecting diseases at very early stages.15 The blood analysis process entails the invasive gathering of blood samples from the human body, generally few micro- or milliliters, which is associated with pain and discomfort and needs trained staff to collect the blood.16 One way to diagnose diseases at an earlier stage is the application of precise molecules entitled biomarkers. Indeed, biomarkers play a crucial role in medical diagnosis and therapy.
Biosensors have the capability to identify a single biomarker or an array of biomarkers with remarkable sensitivity and specificity, even when they are present in low or minute concentrations. These are measurable indicators of normal biological processes, pathogenic processes or responses to therapeutic interventions.17 These biomarkers can be genes, proteins, cells, enzymes, or other measurable substances found in blood, urine, tissue or saliva. These bio-molecules are responsible for various roles in an organism, for example the transmission and storage of hereditary information, regulation of biological activities, catalytic actions or transport of various molecules and they are possibly present in body fluids like blood, urine, or oral fluid and tissues such as tumor tissue.18,19 In individuals who are sick, the level of convinced biomarkers may be found above or below the standard.20 An ideal biomarker should be capable of identifying and monitoring the disease, identifying the particular endotype/phenotype, and detecting the prognosis, effortlessly with minimum distress or threat to the patient. The primary objective of biomarker identification and utilization is to enhance both the diagnosis as well as the treatment of diseases, ideally at the earliest stages possible, to maximize the benefits to patients. Understanding the pathophysiological connection between a biomarker and an investigative and therapeutic endpoint is essential to understand the significance of a biomarker.21,22 There are few important points to consider for a particular molecule to be recognized as a biomarker: (a) there must be substantial confirmation linking the molecule to the disease or condition of interest, (b) the biomarker must be assessable using reliable and validated methods that adhere to appropriate guidelines and standards, and (c) that the results obtained from measurements must be consistent and reproducible across studies conducted in different laboratories.21 Generally, biomarkers are widely used for the early identification of several diseases, including the majority of lethal ones, for example heart disease, cancer and diabetes. Biomarker measurements can help elucidate the empirical outcomes of clinical trials by linking the effects of interventions on cellular and molecular pathways to clinical responses. In recent years, there have been significant efforts to discover biomarkers as promising tools for enhancing prevention, diagnosis, and drug response and development in psychiatric disorders. Currently, no devices or examinations are able to predict critical events, for instance, heart attacks, heat strokes, or epilepsy episodes. Additionally, various health situations, such as lengthy COVID-19 and Alzheimer disease, do not yet have characteristic alarming bio-molecules or biomarkers. For the detection of a biomarker, one should use an explicit appliance termed sensor. A sensor is an apparatus or a device that responds to various stimuli such as changes in temperature, sound, pressure, etc. and responds with an electrical signal. These electrical signals can be measured, analyzed or processed to obtain information about the environment or the target being sensed. The sensors are composed of a recognition element or a bioreceptor that is responsible for recognizing the target analyte and a transducer (e.g., electronic or electrochemical, optical, surface-enhanced Raman scattering (SERS) and heat or mass-based) that translates the detection event into a measurable signal.23 Sensors employ various transduction methods to convert a stimulus into an electrical signal, facilitating the measurement and analysis of the analyte. There are numerous optical and electrochemical transduction methods used for the read out. Potentiometry, voltammetry, colorimetry, and fluorimetry are the most widely established and adopted transduction methods due to their simplicity, cost effectiveness, fast response time, detection of low analyte concentration etc. The electrochemical technique is commonly used for analyzing test samples in aqueous matrices due to its versatility, sensitivity and suitability for real time measurements.22 Optical sensor systems utilize chemical or biological reactions that modify optical detection elements, leading to changes in light emission, absorption or scattering. When sensors are developed using nanotechnological methods and nanomaterials, they are referred to as nanosensors.24 Electrochemical transducers commonly utilize conducting carbon materials like gold and silver surfaces due to their excellent electrochemical stability and high electrical conductivity.25 The availability of metallic nanoparticles in different shapes and sizes, their solubility and long-term stability, as well as their cost effective properties make them generally preferred for various applications.26 Nanomaterials such as carbon nanotubes (CNTs), graphene, MXenes, metal–organic framework (MOFs) are also promising candidates for developing highly sensitive transducer surfaces.27
The main focus of this chapter is to examine how nanosensors contribute to the detection of biomarkers. The initial segment of the chapter is dedicated to exploring the biomarkers and their role in disease diagnosis. However, the latter part of the chapter gives a brief description of the nanomaterials and their classification describing its use as sensing elements, as well as its advantages in sensor design. Finally the detection of biomarkers has been discussed in detail. We have also discussed electrochemical, optical, magneto resistance and surface plasmon resonance (SPR) based sensors and their applications in detail. The chapter concludes with a detail discussion on the future scope of sensors in biomarker detection.
1.2 Biomarkers
In the identification of disease, biomarkers are crucial for predicting the onset of certain diseases, thus allowing for early detection, prognosis and personalized treatment strategies. The use of biomarkers for prognostic and diagnostic purposes dates back to the 19th century.28,29 The search for protein cancer biomarkers in urine marked the beginning of research in biomarkers (Bence Jones protein).30 The 1950s marked a significant period in the history when Dr Abraham White and his colleague identified few molecules in the blood which can serve as potential indicators for myocardial infarction and other cardiovascular disease. From then on, the term “biomarker” became evident in the literature.31,32 The United Nations’ World Health Organization (WHO) defines a biomarker as any substance, structure or process measurable within the body or its products, which can influence or predict disease incidence.33 Since 1970s, the detection of cancer biomarkers has marked a significant advancement, paving the way for extensive research in this area. With the advent of human genome sequencing in 2000s, the discovery of gene biomarkers gained momentum. Today, research in biopharmaceutical and biotechnology sectors has expanded significantly to focus on novel biomarkers and their applications. Biomarkers are indispensable tools in modern medicine, serving as biological indicators that reflect various aspects of health and disease. They encompass a wide range of biophysical and biochemical parameters, offering insights into biological processes, physiological functions, and even responses to therapeutic interventions.34,35 In diagnostics, biomarkers can be used to detect the presence of a disease, assess its severity, or monitor its progression. For example, elevated levels of certain proteins in the blood can indicate the presence of specific diseases, such as cardiac troponins for myocardial infarction or prostate-specific antigen (PSA) for prostate cancer. Similarly, biomarkers like blood glucose levels are vital for diagnosing and monitoring diabetes. Biomarkers serve as a comprehensive term encompassing the utilization and advancement of tools and technologies for monitoring drug discovery and development.36 Biomarkers represent crucial cellular or molecular occurrences that significantly contribute to comprehending the interplay between exposure to biological chemicals, the onset of chronic human diseases, and the identification of high risk subgroups.37 Additionally, they serve as notable diagnostic indicators for assessing the presence or risk of disease. Therefore the biomarkers are also referred to as the ‘molecular signature’ of a disease’s physiological state at a specific moment.38 Biomarkers are objectively measured and assessed characteristics that indicate normal pathogenic processes, biological activities, or responses to therapeutic intervention. Biomarkers encompass a variety of molecules found throughout various organs of human bodies such as genes, nucleic acid sequences (RNA, DNA and m-RNA), enzymes/proteins, lipids, circulating lump cells or extracellular vesicles. As personalized medicine gains traction in current therapeutics, the significance of biomarkers is steadily increasing. They enable detailed and objective patient characterization which is a fundamental aspect of personalized medicine.30 Biomarkers serve as invaluable indicators, offering insights not just into present ailments but also provide us information regarding individualized medical condition. In individuals who are unwell, certain biomarkers deviate from standard levels, either dropping below or rising above the normal level.
A perfect biomarker demonstrates high specificity, sensitivity, and predictive value.2 Furthermore, it should prioritize patient safety and ease of detection, ideally through non-invasive means, to enhance accessibility and comfort.39 Choosing the right biomarkers to indicate both healthy and diseased states is crucial for early disease detection and effective treatment, enabling identification before the symptoms become apparent. Analyzing the outcomes obtained from both patient and normal samples offers rapid insights into morbidity, sub-clinical conditions, and other biological information. The detection of biomarkers is imperative and should be carefully evaluated as indicators of normal biological and pathogenic criteria. Biomarkers are developed and confirmed through the process of analytical validation, clinical validation, and the manifestation of clinical utility.40
1.2.1 Classification of Biomarkers
1.2.1.1 On the Basis of Clinical Applications
The US Food and Drug Administration (FDA) and the National Institute of Health (NIH) have categorized biomarkers into various types according to their primary clinical applications including diagnostic, response/pharmacodynamic, monitoring, predictive, safety, prognostic and risk/susceptibility biomarkers.41,42 Clinical biomarkers43 are primary aimed at diagnosing specific disease states, as outlined and exemplified in Table 1.1.
Classification of clinical biomarkers with examples.
Category of biomarkers . | Definition . | Example . |
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Diagnostic biomarker | A biomarker used to detect any specific disease at an early stage or identify subtypes. | Carcinoma antigen 125 biomarker may be used as diagnostic biomarker for ovarian cancer.44 |
Response//pharmacodynamic | A biomarker used to access the biological reaction to a medical product or an environmental factor. | Blood pressure and antibodies can serve as response biomarkers in the assessment of patients with hypertension and vaccination effectiveness, respectively.17 |
Monitoring biomarker | A biomarker used to monitor the status of a disease or to quantify exposure to a medical product and the response to the interventions. | During the medical examination for risk of kidney and diabetes malfunction creatinine and glucose are used as monitoring biomarkers, respectively.17 |
Prognostic biomarker | A biomarker utilized to assess the likelihood of a clinical event, disease recurrence or progression in patients who have been diagnosed with the disease. | Elevated levels of PSA can serve as a prognostic biomarker during follow-up assessments with prostate cancer patients, aiding to gauge the probability of cancer progression.45 |
Susceptibility/risk biomarker | A biomarker utilized to assess an individual’s risk of developing a disease or clinically noticeable medical condition. | Breast cancer genes 1 and 2 (BRCA1/2) mutations can serve as a biomarker for assessing the risk of individuals’ predisposition to developing breast cancer.46 |
Predictive biomarker | Predictive biomarkers are employed to evaluate the probability of disease onset, predicting its occurrence before symptoms manifest. | Cytokines, antibodies targeting amyloid-beta protein and homocysteine levels is taken as predictive biomarkers for Alzheimer’s disease.47 |
Safety biomarkers | A biomarker quantified to signal the likelihood, onset or extent of toxicity as an adverse outcome. | Bilirubin and creatinine are safety biomarkers for drugs which affect liver and kidney, respectively.48 |
Category of biomarkers . | Definition . | Example . |
---|---|---|
Diagnostic biomarker | A biomarker used to detect any specific disease at an early stage or identify subtypes. | Carcinoma antigen 125 biomarker may be used as diagnostic biomarker for ovarian cancer.44 |
Response//pharmacodynamic | A biomarker used to access the biological reaction to a medical product or an environmental factor. | Blood pressure and antibodies can serve as response biomarkers in the assessment of patients with hypertension and vaccination effectiveness, respectively.17 |
Monitoring biomarker | A biomarker used to monitor the status of a disease or to quantify exposure to a medical product and the response to the interventions. | During the medical examination for risk of kidney and diabetes malfunction creatinine and glucose are used as monitoring biomarkers, respectively.17 |
Prognostic biomarker | A biomarker utilized to assess the likelihood of a clinical event, disease recurrence or progression in patients who have been diagnosed with the disease. | Elevated levels of PSA can serve as a prognostic biomarker during follow-up assessments with prostate cancer patients, aiding to gauge the probability of cancer progression.45 |
Susceptibility/risk biomarker | A biomarker utilized to assess an individual’s risk of developing a disease or clinically noticeable medical condition. | Breast cancer genes 1 and 2 (BRCA1/2) mutations can serve as a biomarker for assessing the risk of individuals’ predisposition to developing breast cancer.46 |
Predictive biomarker | Predictive biomarkers are employed to evaluate the probability of disease onset, predicting its occurrence before symptoms manifest. | Cytokines, antibodies targeting amyloid-beta protein and homocysteine levels is taken as predictive biomarkers for Alzheimer’s disease.47 |
Safety biomarkers | A biomarker quantified to signal the likelihood, onset or extent of toxicity as an adverse outcome. | Bilirubin and creatinine are safety biomarkers for drugs which affect liver and kidney, respectively.48 |
1.2.1.2 On the Basis of Human Health and Performance
On the basis of secretion location, appearance, molecular weights and physicochemical properties biomarkers vary widely. On the basis of origin, biomarkers can be classified into two categories namely invasive and non-invasive sources. Saliva, breath and urine are the important non-invasive sources. Invasive testing is a medical procedure that is executed by puncturing or cutting of the skin or by inserting a tool into the body. The essential non-invasive sources are blood, intestinal fluid, cerebrospinal fluid and exosomes. Table 1.2 presents few representative examples of biomarkers from exhaled breath samples, physical signatures, and human body fluids as the biomarker types.12
Few examples of biomarkers representing the human health status.12 Reproduced from ref. 12, https://doi.org/10.1002/advs.202104426, under the terms of the CC BY 4.0 license https://creativecommons.org/licenses/by/4.0/.
Category of biomarker . | Biomarkers . | Reflecting human status . |
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Vapor-phase biomarkers |
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Noninvasive physical biomarkers |
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Biomarkers in body fluids |
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Category of biomarker . | Biomarkers . | Reflecting human status . |
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Vapor-phase biomarkers |
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Noninvasive physical biomarkers |
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Biomarkers in body fluids |
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1.2.1.3 Biomarkers of Nutrition and Health
Various biomarkers have been explored in dietary studies to understand the connections between diet/nutrition and health. These biomarkers are utilized to assess the nutritional intake. For instance, urine nitrogen serves as a reliable biomarker for protein intake. Urine/plasma genistein and daidzein are promising biomarkers of soy intake. Elevated levels of homocysteine can indicate deficiencies in certain B vitamins like folate, vitamin B6, and B12, which are crucial for this metabolic pathway. However, it can also be influenced by genetic factors and other health conditions, making it a multifaceted biomarker. Some biomarkers relate directly to the disease risk such as plasma concentration of cholesterol or triglycerides, which suggest a risk of cardiovascular diseases.49,50
1.2.1.4 On the Basis of Nutrigenomic Approach
Omic platforms are particularly adept at uncovering and characterizing novel nutritional markers, defining an individual’s nutritional status and identifying nutritional bioactive compounds responsible for beneficial health effects, as illustrated in Table 1.3.49,50
Nutrigenomic biomarkers with characteristics.
Category of biomarker . | Characteristics . |
---|---|
Genetic biomarkers | Biomarkers based on changes in DNA, predominantly focusing on single nucleotide polymorphisms (SNP). |
Transcriptomic biomarkers | Biomarkers based on RNA expression. |
Proteomic biomarkers | Biomarkers stemming from the examination of proteome. |
Epigenetic biomarkers | Epigenetic regulators: non-coding RNAs and DNA methylation, histone modification. |
Metabolomic biomarkers | Biomarkers derived from the Metabolomics or metabolite profiling. |
Lipidomic biomarkers | Biomarkers based metabolomic analysis of lipids. |
Category of biomarker . | Characteristics . |
---|---|
Genetic biomarkers | Biomarkers based on changes in DNA, predominantly focusing on single nucleotide polymorphisms (SNP). |
Transcriptomic biomarkers | Biomarkers based on RNA expression. |
Proteomic biomarkers | Biomarkers stemming from the examination of proteome. |
Epigenetic biomarkers | Epigenetic regulators: non-coding RNAs and DNA methylation, histone modification. |
Metabolomic biomarkers | Biomarkers derived from the Metabolomics or metabolite profiling. |
Lipidomic biomarkers | Biomarkers based metabolomic analysis of lipids. |
Overall, biomarkers significantly aid in diagnosing and detecting particular diseases or associated risks of a disease at an early stage. In addition, they can also be applied to understand the outcome and prognosis of the disease. Various studies such as genomics, proteomics, metabolomics and lipidomics have been widely used to understand the dynamics of these biomarkers.49,50
1.3 Sensors for Biomarker Detection and Determination
Biomarker detection is a decisive step for both early diagnosis and prognosis of diseases, which assists in improving the quality of patients’ life.5 Two important considerations for biosensors are the sensitivity of detection techniques and selectivity toward biomarkers/bio-molecules. Bio-sensing technologies have shown potential in medical diagnostics and point of care hospitals, multi-specialty clinics and laboratories. Biosensors are compact analytical electronic devices containing biologically derived sensing elements integrated with physio-chemical transducers. “Sensing and biological recognition” are the two elemental functional principles of a biosensor.
A sensor is a device that measures chemical or biochemical information and convert it into an analytically useful signal.51 Conversely, biosensors are accomplished candidates for the simultaneous and specific detection of biomarkers and the study of their associated reactions, because their components can be easily improved and modified. According to IUPAC nomenclature, a biosensor is a device that employs precise biochemical reactions interceded by isolated immune systems, enzymes, organelles, tissues or whole cells to detect chemical compounds (analyte) usually through optical, electrical and thermal signals. The biosensor comprises four standard components: a bioreceptor, a transducer, a micro-electronics/electronic system/an electronic assembly and a display/readout unit which are connected in a series as shown in Figure 1.1.52 Interactions between the bioreceptor (e.g., enzymes, antigens or antibodies, cells, and nucleic acids) and target analyte generate a change which is detected by the transducer (e.g., optical, electrochemical, heat or mass-based), which significantly transforms the collected information into a measurable output. Sensors are employed to recognize and determine the target analyte present in the matrix under observation. The mutual collaborative development and integration between disciplines have become a trend in present scenario. Therefore, the combination of sensing technology and material science holds extensive promise and very important research significance.
(a) Elements/components of a biosensor and (b) schematic of biosensor components.
(a) Elements/components of a biosensor and (b) schematic of biosensor components.
1.3.1 Nanomaterials for Sensor Design
Nanoscale sensors are based on conjugating the nanoparticles with the targeting ligand where the ligands are tailored to detect the specific marker of interest, providing them high specificity and sensitivity. Nanoparticles impart unmatched fascinating characteristics for detection such as increased reactivity, augmented electrical conductivity and strength, distinctive magnetic properties and a significant surface area to volume ratio.14 For label free recognition, a number of nanomaterials are being implemented such as electro-polymers, quantum dots, etc. The use of nanomaterials offers a more accurate and precise approach for biosensing. Nanomaterials can be classified according to their composition and origin. As per the composition they can be categorized into metal-based (silver or gold nanoparticles and metal oxides), carbon-based (fullerenes, grapheme and its oxide, carbon nanotubes (CNTs), carbon nanoribbons, etc.); semiconductor-based (quantum dots); polymer-based (dendrimers); composite-based (nanoclays); and MOFs-based nanomaterials. Based on their origin, nanomaterials have been classified as natural nanomaterials (milk, blood capsid, protein, claws, skin, feathers, hair, the human bone matrix, etc.); incidental nanomaterials (which are generated from industrial waste stream, for example, vehicle exhaust gases; combustion; etc.); and engineered nanomaterials. The natural and incidental nanomaterials can possess irregular or regular shapes; however, engineered nanomaterials exhibits regular shapes such as nanotubes, nanospheres, and nanorings.53
1.3.2 Construction and Working of a Biosensor
A biosensor is an analytical device consisting of four standard components: a biorecognition element/bioreceptor, a transducer, micro-electronics and a display unit which is used to detect the presence and analyte concentration. In addition to this, they are used to examine cell mechanics, cell physiology, drug analysis, etc.54 The basic design of a biosensor with its components is shown in Figure 1.2. The chemical information associated to the analyte (present in various biological fluids such as sweat, blood, saliva, interstitial fluid, tears, breath and human volatiles) is transformed to a readable output via sensing/recognition and transduction. Specificity and selectivity are crucial aspects of biorecognition elements (BERs), also known as bio-receptors, that identify the target analyte.55,56
Basic design of biosensors.56 Reproduced from ref. 56, https://doi.org/10.3390/s21041109, under the terms of the CC BY 4.0 license, https://creativecommons.org/licenses/by/4.0/.
Basic design of biosensors.56 Reproduced from ref. 56, https://doi.org/10.3390/s21041109, under the terms of the CC BY 4.0 license, https://creativecommons.org/licenses/by/4.0/.
Examples of various biorecognition elements are (i) enzymes; (ii) antibodies; (iii) nucleic acids (iv) molecularly imprinted polymers (MIPs); (v) cells; (vi) aptamers; (vii) DNA, etc. The examples (i–iii) belong to the most widely used bioreceptors. The biorecognition elements immobilize on the biosensor surface, allowing the interaction of the target analyte with the immobilize bioreceptors, which will be conveyed to the transducer that transforms the recognition event into a readable output which can be further analyzed and amplified.57,58 The transducing systems can be optical, electrochemical, piezoelectric, ion-sensitive, thermometric, magnetic or acoustic one.59 Biosensors may comprise various types of display units such as a computer, liquid crystal display (LCD) or a printer, which provide a pictographic demonstration of the measured signal. According to the needs of the users, the format for the output signals can be different, for instance, the final outcome can be either in a tabular form, numeric, an image or graphics.
1.3.3 Characteristics of a Biosensor
In order to be applicable in the diagnostic field, a biosensor must possess the following characteristics (a) repeatability; (b) selectivity and specificity; (c) simplicity; (d) low early detection readings; (e) minimal procedure; (f) observer-independent; (g) target specific); (h) sensitivity and linearity, and (i) stability (Figure 1.3).14,64
1.3.4 Classification of Biosensors
Biosensors can be categorized based on their biological selectivity mechanism (enzyme, nucleic acid, aptamer, and antibody based) or by their transduction mechanism.60–62
1.3.4.1 Classification of Biosensors Based on the Transduction Mechanism
Figure 1.4 suggests the classification of biosensors based on the transduction mechanism.60
1.3.4.1.1 Electrochemical Biosensors (ECBs)
ECBs are primarily a subset of chemical sensors that combine the high specificity of biological recognition procedures and the sensitivity of electrochemical transducers.63,64 According to IUPAC, an ECB is defined as a self-contained integrated device capable of analyzing specific quantitative or semi-quantitative information. These biosensors typically employ a biological recognition element, which is in direct spatial contact with an electrochemical transduction element, usually a working electrode where the biochemical reaction occurs generating an electrical signal proportional to the target analyte concentration.65,66 ECBs operate by detecting alterations in potential, conductance, current or field effect resulting from the interaction between the target molecule and the bioreceptor elements on the sensing surface. The fundamental principle of these biosensors lies in the chemical reactions occurring between the target analyte and immobilized biomolecules, which either consume or produce electrons or ions. This in turn, affects the electrical properties of the analyte. ECBs quantify the current generated by oxidation and reduction reactions within the electrochemical system initiated by specific electroactive species.63
This type of biosensors embraces a set of electrodes, namely, a sensing electrode (SE)/working electrode (WE; glassy carbon electrode or GCE, serves as the transducing element), a reference electrode (RE; Ag/AgCl electrode impart stable potential) and an auxiliary/counter electrode (CE; Pt electrode functions to complete the circuit).64 Mainly, the redox reaction occurs on the WE surface and the potential is synchronized by the RE and sometimes the circuit is completed by the CE. To ensure both chemical stability and conductivity, electrodes commonly utilize materials such as gold, platinum, graphite and silicon compounds, chosen based on the nature of the analyte. Mehrvar et al. have offered a comprehensive review of electrochemical biosensors, detailing characteristics such as detection limits.67 Direct or label-free sensing relies on changes in the electrical signal resulting from the targeted recognition event. In contrast, indirect or labeled sensing involves the use of a secondary compound (such as enzyme tagged secondary antibodies) as a label to facilitate electrochemical events.68 Most biosensors use EC detection for the transducer owing to their remarkable delectability, accessibility, portability, cost effectiveness, selectivity, robustness, sensitivity, analytical performances and simplicity of construction than other biosensors.63 Based on the transducer utilized, ECBs are classified into conductometry, potentiometry, amperometry, voltammetry and electrochemical impedance spectroscopy (EIS).58 All of these measurement techniques will be discussed further, and sample curves for these electrochemical measurements are depicted in Figure 1.5.
Sample curves for various sensors (a) amperometric, (b) potentiometric, (c) voltammetric, (d) colorimetric, and (e) fluorescence. Adapted from ref. 17 with permission from Springer Nature, Copyright 2022.
Sample curves for various sensors (a) amperometric, (b) potentiometric, (c) voltammetric, (d) colorimetric, and (e) fluorescence. Adapted from ref. 17 with permission from Springer Nature, Copyright 2022.
1.3.4.1.1.1 Amperometry
In amperometric biosensors, a constant potential (V) is applied between the working electrode and the reference electrode, and the resulting current (I) from to the redox reactions of electrochemical species is measured. This applied potential triggers redox reactions of the electrolytes within the solution at the surface of the working electrode, generating electrons at a precise potential determined by the nature of the electrolyte. The maximum current value measured within a linear potential range is directly proportional to the bulk concentration of the analyte.69 This method is less influenced by the electrode’s characteristics, as well as the nature and type of the supporting electrolyte. Additionally, it does not necessitate maintaining a fixed temperature during titration, and the substance being analyzed doesn’t need to be reactive at the electrode. This method allows for continuous measurements with rapid response time and has found application in commercial glucose monitors.70 A practical application of amperometry involves its combination with immunosensing techniques to measure levels of the human chorionic gonadotropin β-subunit (βHCG) in advanced pregnancy testing.71 A summary of recently developed amperometry biosensors for various biomarker detections is shown in Table 1.4.
Biosensors for biomarker detection employing amperometry techniques.
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
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Fe3O4@GO | Prostate specific antigen (PSA) | Prostate cancer | 15 fg mL−1 | 72 |
Fe3O4@GO | Prostate specific membrane antigen (PSMA) | Prostate cancer | 4.8 fg m−1 | 72 |
Redox polymer P(SS-GMA-BA)-Os | para-Hydroxyphenylacetate (p-HPA) | Urinary disease | — | 73 |
V2O5 nanoplates/AuE | Methylglyoxal | Diabetes mellitus | 0.24 µM | 74 |
Ti3C2TX/Pt–Pd | Sarcosine | Cancer | 0.16 µM | 75 |
Ferrocene monocarboxylic acid linked anti-VEGF (Fc-anti-VEGF) | Vascular endothelial growth factor | Cancer | 38 pg m−1 | 76 |
LDH/RGO-AuNPs/SPCE | l-Lactate | Cancer | 0.13 µM | 77 |
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
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Fe3O4@GO | Prostate specific antigen (PSA) | Prostate cancer | 15 fg mL−1 | 72 |
Fe3O4@GO | Prostate specific membrane antigen (PSMA) | Prostate cancer | 4.8 fg m−1 | 72 |
Redox polymer P(SS-GMA-BA)-Os | para-Hydroxyphenylacetate (p-HPA) | Urinary disease | — | 73 |
V2O5 nanoplates/AuE | Methylglyoxal | Diabetes mellitus | 0.24 µM | 74 |
Ti3C2TX/Pt–Pd | Sarcosine | Cancer | 0.16 µM | 75 |
Ferrocene monocarboxylic acid linked anti-VEGF (Fc-anti-VEGF) | Vascular endothelial growth factor | Cancer | 38 pg m−1 | 76 |
LDH/RGO-AuNPs/SPCE | l-Lactate | Cancer | 0.13 µM | 77 |
1.3.4.1.1.2 Voltammetry
Another adaptable and promising electrochemical detection method is voltammetric detection, which involves varying the applied potential with controlled steps and speed. Voltammetry refers to techniques where the potential is swept across a predetermined range, and the current is measured as the potential varies under controlled conditions.69 Voltammetric detection is commonly employed to monitor electroactive molecules such as uric acid and vitamin C by directly detecting their direct redox reactions near a specific redox potential on the electrode surface under an applied potential waveform.78 The current response typically manifests as a plateau or a peak, which is directly proportional to the analyte concentration. Voltammetric methods encompass various techniques such as cyclic voltammetry, linear sweep voltammetry, hydrodynamic voltammetry, square-wave voltammetry, differential pulse voltammetry, AC voltammetry, stripping voltammetry and polarography. These techniques offer a broad dynamic range and are also beneficial for low level quantitation. Stripping voltammetry, which involves an analyte preconcentration step followed by a voltammetric scan, enables the detection of trace levels of heavy metals in body fluids.78 Herein, a summary of recently developed voltammetry biosensors for various biomarker detections is shown in Table 1.5.
Biosensors for biomarker detection employing voltammetry techniques.
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
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Silica nanowires | Interleukin-10 (IL10) | Lung cancer | 1 pg Ml−1 | |
Osteopontin (OPN) | Lung cancer | — | 79 | |
Au/AbCD14-FITC-Fc | Creatine kinase (CK) | Heart disease | 0.5 pg mL−1 | 80 |
Au/Ab-IL10-FITC-Fc | Cytokine interleukin 10 (IL10) | Heart disease | — | 80 |
Anti-IL-8/AuNPs-rGO/ITO | Interleukin (IL)-8 | Oral Cancer | 72.73 pg mL−1 | 81 |
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|
Silica nanowires | Interleukin-10 (IL10) | Lung cancer | 1 pg Ml−1 | |
Osteopontin (OPN) | Lung cancer | — | 79 | |
Au/AbCD14-FITC-Fc | Creatine kinase (CK) | Heart disease | 0.5 pg mL−1 | 80 |
Au/Ab-IL10-FITC-Fc | Cytokine interleukin 10 (IL10) | Heart disease | — | 80 |
Anti-IL-8/AuNPs-rGO/ITO | Interleukin (IL)-8 | Oral Cancer | 72.73 pg mL−1 | 81 |
1.3.4.1.1.3 Potentiometry
1.3.4.1.1.4 Conductometry
Conductometry, a subset of impedimetric devices, monitors alterations in the electrical conductivity of the sample solution as the composition of the solution or medium changes during a chemical reaction process.69 Conductometric biosensors can detect biorecognition events that alter the ionic concentration. Typically, these reactions result in changes in the concentration of the ionic species, which in turn cause variations in current flow or electrical conductivity.90 There is currently heightened interest in conductometric immunosensors, particularly in conjunction with nanostructures, especially nanowires, for biosensing applications.69 Conductometric methods have garnered interest among various research groups due to their ease of use and simplicity, eliminating the need for a specialized reference electrode. A conductometric biosensor has been reported for the detection of apolipoprotein A1, a biomarker crucial for diagnosing bladder cancer. Conductometric sensors have found applications in environmental monitoring, chemical analysis and detection of food borne pathogens such as Salmonella spp. and Escherichia coli.91 A summary of recently developed conductometric biosensors for biomarker detection is listed in Table 1.6.
Biosensors for biomarker detection employing conductometry techniques.
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|
Si/SiO2/oxygen-deficient ZnO/Au/Cr | Interleukin-6 (IL 6) and C-reactive protein (CRP) antigens | Cardiac inflammation | 0.5 nm | 92 |
Single site-specific polyaniline (PANI) nanowire | Myoglobin (Myo), cardiac troponin I (cTnI), creatine kinase-MB (CK-MB), and b-type natriuretic peptide (BNP) | Cardiovascular diseases | Myo-100 pg mL−1, cTnI-250 fg mL−1, CK-MB-150 fg mL−1, BNP-50 fg mL−1 | 93 |
Nickel/Si-nanowire/nickel sandwich | Apolipoprotein A1 | Bladder cancer | 1 ng mL−1 | 94 |
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|
Si/SiO2/oxygen-deficient ZnO/Au/Cr | Interleukin-6 (IL 6) and C-reactive protein (CRP) antigens | Cardiac inflammation | 0.5 nm | 92 |
Single site-specific polyaniline (PANI) nanowire | Myoglobin (Myo), cardiac troponin I (cTnI), creatine kinase-MB (CK-MB), and b-type natriuretic peptide (BNP) | Cardiovascular diseases | Myo-100 pg mL−1, cTnI-250 fg mL−1, CK-MB-150 fg mL−1, BNP-50 fg mL−1 | 93 |
Nickel/Si-nanowire/nickel sandwich | Apolipoprotein A1 | Bladder cancer | 1 ng mL−1 | 94 |
1.3.4.1.1.5 Electrochemical Impedance Spectroscopy (EIS)
It was introduced by Lorenz and Schulze in 1975, involving the application of a sinusoidal potential ranging from 2–10 mV to measure the resulting current response (I). This response encompasses both resistive and capacitive properties of materials. The frequency is systematically adjusted across a wide range to achieve the impedance spectrum.63 The capacitive and resistive components of impedance are determined by analyzing the out-of-phase and in-phase current responses, respectively. Impedance techniques are highly effective as they can detect mass transfer at low frequency and electron transfer at high frequency. These methods are primarily employed for affinity biosensors. Impedance sensors were developed for the detection of water in an oil-in-water emulsion as well as for detecting NO2 and tobacco smoke, aiding in odor detection.64 An instance of impedimetric detection involves monitoring immunological binding events of antigens (Ag) and antibodies (Ab) on an electrode surface. This process entails measuring slight changes in impedance, which are directly proportional to the concentration of Ag in measured species.95 EIS serves as a valuable tool in both the development and investigation of materials for biosensor transduction. For example, it is utilized in studying processes such as polymer degradation. An inventory of selected studies in the literature on biomarker detection via nanomaterials by using EIS techniques is presented in Table 1.7.
Biosensors for biomarker detection employing EIS techniques.
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|
Gold screen-printed electrodes modified with a specific thiolated antibody | Triggering Receptor-1 Expressed on Myeloid cells (TREM-1), Matrix MetalloPeptidase 9 (MMP-9), N-3-oxo-dodecanoyl-l-Homo Serine Lactone (HSL) | Infection | 3.3 pM for TREM-1, 1.1 nM for MMP-9, 1.4 nM for HSL | 96 |
Glassy carbon electrode (GCE)/single-walled carbon nanohorns (SCN) | a-fetoprotein (AFP) | Cancer | 0.3 pg mL−1 | 97 |
Ab/core–shell Au–Ag NPs/SPE | Cancer antigen 125 (CA125) | Ovarian cancer | 1.03 IU mL−1 | 98 |
Integrated graphene electrode | Carcinoembryonic antigen (CEA) | Lung cancer | 0.085 ng ml−1 | 99 |
Anti-Mb-IgG/MWCNTs/SPE | Mb | Acute myocardial infarction | 0.08 ng mL−1 | 100 |
Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|
Gold screen-printed electrodes modified with a specific thiolated antibody | Triggering Receptor-1 Expressed on Myeloid cells (TREM-1), Matrix MetalloPeptidase 9 (MMP-9), N-3-oxo-dodecanoyl-l-Homo Serine Lactone (HSL) | Infection | 3.3 pM for TREM-1, 1.1 nM for MMP-9, 1.4 nM for HSL | 96 |
Glassy carbon electrode (GCE)/single-walled carbon nanohorns (SCN) | a-fetoprotein (AFP) | Cancer | 0.3 pg mL−1 | 97 |
Ab/core–shell Au–Ag NPs/SPE | Cancer antigen 125 (CA125) | Ovarian cancer | 1.03 IU mL−1 | 98 |
Integrated graphene electrode | Carcinoembryonic antigen (CEA) | Lung cancer | 0.085 ng ml−1 | 99 |
Anti-Mb-IgG/MWCNTs/SPE | Mb | Acute myocardial infarction | 0.08 ng mL−1 | 100 |
1.3.4.1.2 Optical Biosensors
Following the electrochemical approach, the second most common biosensors are optical biosensors. They have extensive applications in health care, pharmaceuticals, homeland security, monitoring of environmental contaminants, etc.101 The optical recognition of biomarkers occurs when the optical field interacts with the bio-recognition element, leading to changes in optical properties, which can be analyzed and correlated with the analyte concentration. The optical properties include changes in the phase, polarization, or frequency. The optical biosensor integrates the optical transducer intimately with the biosensing element. The working principle of optical biosensors primarily depends on the type of optical transducer employed.101 Depending on the transducer, an optical biosensor is classified into colorimetric/spectrophotometric (based on absorption of light), fluorometric, chemiluminescence and surface plasmon resonance (SPR)-based biosensors.66 Another commonly used approach to categorize optical biosensors is by classifying them as label-free or label-based. In label-free optical sensing, the output signal is generated owing to the on-site interaction between the transducer and analyte, such as in surface plasmon resonance (SPR) sensing. Conversely, in label-based optical sensing, a label is utilized to access the recognition, and the optical signal is generated via mechanisms including colorimetric, fluorescence or luminescence. Labels can be enzymes, nanoparticles, fluorescent materials/luminescent molecules, etc. Optical biosensing methods have gained significant popularity due to their numerous advantages over conventional analytical techniques. These advantages include real-time sensing, remote sensing capabilities, minimally invasive characteristics suitable for in vivo measurements, high specificity and sensitivity, compact size, cost effectiveness and the provision of detailed chemical information on analytes. The fundamental components of optical biosensors include a source of light, an optical-transmission medium such as fiber or a waveguide, immobilized biological recognition elements such as enzymes, antibodies and microbes and the optical sensing platform.101
1.3.4.1.2.1 Colorimetric Sensors
Few reported examples of biomarker detection using colorimetric, fluorescence and luminescence techniques.
Biosensing method . | Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|---|
Colorimetric | MIP/CdTe-MPA-QDs | Myoglobin (Mb) | Acute myocardial infarction | 7.6 fM | 113 |
Colorimetric | AuNPs and Ag enhancement | CA 125 | Ovarian cancer | 30 U mL−1 | 102 |
Colorimetric | Chromogenic substrate | Prostate cancer antigen 3 | Prostate cancer | 0.34 fg µL−1 | 114 |
Fluorescence | Biotin-labeled CNWMINKEC peptide | Kidney injury molecule-1 (KIM-1) | Chronic kidney disease (CKD), acute kidney injury (AKI) and nephrotoxicity | — | 115 |
Fluorescence | CuS NPs as signal tag | CEA | Colorectal, pancreatic, gastric, and cervical cancers | 0.05 pg mL−1 | 116 |
Fluorescence | Qdot-based lateral flow test strip (LFTS) | Nitrated ceruloplasmin | Cardiovascular disease, lung cancer, and stress response | 1 ng mL−1 | 117 |
Fluorescence | DNA capture probe-magnetic silicon microsphere-rGO | miRNA 21 | Different type cancer | 0.098 nM | 118 |
Luminescence | α-NaYF4:Yb3+,Er3+ upconversion NPs | Vascular endothelial growth factor (VEGF) | Cancer | 6 pM | 119 |
Luminescence | Anti-AFP/PPI/AuNPs/GCE | Alpha fetoprotein (AFP) | Teratoblastoma | 0.0022 ng mL−1 | 120 |
Luminescence | Nickel(ii) metal–organic framework (NiMOF) | 3-Nitrotyrosine (3-NT) | Inflammatory disorders, nitrosative stress | 0.165 µM | 121 |
Luminescence | Polyvinylidene fluoride imbibed with poly(3-alkoxy-4-methylthiophene) | 8-Hydroxy-2′-deoxyguanosine (8-OHdG) | Oxidative stress | 300 pM (fluorometric), 350 pM (colorimetric) | 122 |
Electrochemiluminescence | GSH-MXene QD | miRNA221 | Breast cancer | 10 fM | 123 |
Biosensing method . | Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|---|
Colorimetric | MIP/CdTe-MPA-QDs | Myoglobin (Mb) | Acute myocardial infarction | 7.6 fM | 113 |
Colorimetric | AuNPs and Ag enhancement | CA 125 | Ovarian cancer | 30 U mL−1 | 102 |
Colorimetric | Chromogenic substrate | Prostate cancer antigen 3 | Prostate cancer | 0.34 fg µL−1 | 114 |
Fluorescence | Biotin-labeled CNWMINKEC peptide | Kidney injury molecule-1 (KIM-1) | Chronic kidney disease (CKD), acute kidney injury (AKI) and nephrotoxicity | — | 115 |
Fluorescence | CuS NPs as signal tag | CEA | Colorectal, pancreatic, gastric, and cervical cancers | 0.05 pg mL−1 | 116 |
Fluorescence | Qdot-based lateral flow test strip (LFTS) | Nitrated ceruloplasmin | Cardiovascular disease, lung cancer, and stress response | 1 ng mL−1 | 117 |
Fluorescence | DNA capture probe-magnetic silicon microsphere-rGO | miRNA 21 | Different type cancer | 0.098 nM | 118 |
Luminescence | α-NaYF4:Yb3+,Er3+ upconversion NPs | Vascular endothelial growth factor (VEGF) | Cancer | 6 pM | 119 |
Luminescence | Anti-AFP/PPI/AuNPs/GCE | Alpha fetoprotein (AFP) | Teratoblastoma | 0.0022 ng mL−1 | 120 |
Luminescence | Nickel(ii) metal–organic framework (NiMOF) | 3-Nitrotyrosine (3-NT) | Inflammatory disorders, nitrosative stress | 0.165 µM | 121 |
Luminescence | Polyvinylidene fluoride imbibed with poly(3-alkoxy-4-methylthiophene) | 8-Hydroxy-2′-deoxyguanosine (8-OHdG) | Oxidative stress | 300 pM (fluorometric), 350 pM (colorimetric) | 122 |
Electrochemiluminescence | GSH-MXene QD | miRNA221 | Breast cancer | 10 fM | 123 |
1.3.4.1.2.2 Fluorescence Sensor
Fluorescence is indeed a keystone in biosensing owing to its sensitivity and versatility. Its basic principle involves the emission of light by a substance called fluorophore, after it absorbs photons from an external light source known as excitation light. The light emitted is typically of a longer wavelength than the excitation light which enables its separation through filters. In biosensing applications, the intensity of fluorescence emitted by a labeled target molecule can be correlated with its concentration or presence, providing valuable analytical information.104,105 Fluorescent materials/fluorophores can be used as sensing probes owing to their ability to change their intrinsic fluorescence properties when interacting with other elements. The widespread adoption of highly sensitive and selective fluorescent labeling renders fluorescence one of the most commonly utilized optical procedures for biomarker sensing in various microfluidic systems. In contrast to colorimetric detection, one of the disadvantages of this detection is that it is bulky and fairly complex. Furthermore, the fluorescent materials are costly, often influenced by pH and have a limited shelf life. The labeling process involves intricate fluid handling, which poses a challenge to automating rapid assays.106,107 Fluorescence was primarily used for cell imaging to present the growth and viability of cells on a chip, and afterward it was used for the study of cellular components and cell membranes. Fluorescence detection has found diverse applications in areas such as the detection of protein biomarkers for cancer and infectious diseases. Few examples belonging to this class are given in Table 1.8.
1.3.4.1.2.3 Luminescence Sensors
Luminescence is a phenomenon of light emission wherein a compound or sample returns to its original ground-state after being electronically excited. This emission is utilized to measure chemical or biological reactions, either directly or with the enzyme label, whereas, chemiluminescence occurs during a chemical reaction generating an electronically activated state.108 Biosensor based on chemiluminescence was developed to detect lysozyme in human urine matrix, utilizing an aptamer/DNAzyme-GQDs immobilized on carbon fiber composites.109
The benefit of this technique for lab-on-a chip (LOCs) is that emission filters and excitation light sources are not essential, thus minimizing probable background interferences.110 However, the need of the hour is the fabrication of cost effective photodetectors for application in point-of-care (POC) devices. In the present scenario, electrochemiluminescence (ECL) is gaining popularity in sensing and biosensing applications.111 ECL combines the benefits of chemiluminescence while controlling the spatial and temporal aspects of the light emitting reaction. This allows for improved detection limits by rapidly releasing chemiluminescence generated through the electrochemical recycling of reagents. Zhang et al. reported an ECL aptasensor for miRNA-16 recognition in leukemia patients.112 Few examples of luminescence techniques are provided in Table 1.8.
1.3.4.1.2.4 Surface Plasmon Resonance (SPR) Sensors
The label-free optical phenomenon employed for sensing applications is the surface plasmon resonance (SPR) technique. Its first biosensing application was demonstrated by Liedberg et al. in 1983. SPR occurs when the free electrons of a metal are excited by photons, generating an evanescent wave. The SPR method is not just noninvasive, but also a label-free method for studying the binding affinities between two different molecules, i.e., an injected analyte and an immobilized biomolecule in real time. It measures refractive index changes corresponding to the analyte binding at a metal surface (gold, silver or aluminum). They help in studying specificity, binding affinity, and binding kinetics, as well as measuring the concentration of target analytes in complex biological samples (Figure 1.6). The identified objects are generally biomolecules that have receptors and ligands with properties similar to proteins, nuclear acids, antibodies and enzymes. It is mainly suitable for quantification analysis and process monitoring of immunity reactions. SPR takes place only at the nanometer scale in metals (silver and gold are preferred) and is classified into two categories: SPR when it occurs in a metallic film and localized surface plasmon resonance (LSPR) when it takes place in metallic nanoparticles. The plasmon created depends directly on the size of the metal film, nanoparticle and the material used.107 Unlike other traditional methods, SPR directly provides information on biomolecular interactions without the need for prior labeling. However, limitations stemming from restricted mass transfer, nonspecific binding and avidity can sometimes obscure SPR analysis. A list of selected studies in the literature on biomarker discovery via nanoparticles employing the SPR technique is shown in Table 1.9.
Surface plasmon resonance principle.69 Reproduced from ref. 69 with permission from Elsevier, Copyright 2015.
Few examples of SPR and SERS biosensors to detect biomarkers.
Biosensing method . | Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|---|
SPR | Ag nanosphere | Tumor necrosis factor-α | Cancer | 200 ng mL−1 | 131 |
SPR | Gold nanoprisms | MicroRNA | Pancreatic cancer | — | 22 and 132 |
SPR | Ab–Au sensor chip | α-Casein | Food allergy | 57.8 ng mL−1 | 133 |
SERS | Apt-AuNP-WS2 nanohybrid based SERS active platform | Myoglobin | Acute myocardial infarction | 0.5 aM | 134 |
SERS | Ab1-magnetic NPs | CEA | Breast tumors | 10−12 M | 135 |
SERS | LFAS using citratecapped Au@Ag-AuNPs | Cardiac troponin I | Acutemyocardial infarction | 0.09 ng mL−1 | 136 |
Biosensing method . | Biosensor material . | Biomarker . | Disease . | LOD/LOQ . | Ref. . |
---|---|---|---|---|---|
SPR | Ag nanosphere | Tumor necrosis factor-α | Cancer | 200 ng mL−1 | 131 |
SPR | Gold nanoprisms | MicroRNA | Pancreatic cancer | — | 22 and 132 |
SPR | Ab–Au sensor chip | α-Casein | Food allergy | 57.8 ng mL−1 | 133 |
SERS | Apt-AuNP-WS2 nanohybrid based SERS active platform | Myoglobin | Acute myocardial infarction | 0.5 aM | 134 |
SERS | Ab1-magnetic NPs | CEA | Breast tumors | 10−12 M | 135 |
SERS | LFAS using citratecapped Au@Ag-AuNPs | Cardiac troponin I | Acutemyocardial infarction | 0.09 ng mL−1 | 136 |
1.3.4.1.2.5 Surface-enhanced Raman Spectroscopy Sensors (SERS)
Raman spectroscopy (RS) quantifies the elastically scattered photons generated by vibrational frequencies of a molecular structure when excited by monochromatic light, typically from a laser. This method furnishes fingerprint information regarding the bond structure of a molecule. The Raman microscopy is a novel platform for cell pharmacology, cell sorting and pathology studies.124 The surface-enhanced technique boosts the sensitivity of the Raman spectrum, leading to surface-enhanced Raman scattering (SERS) microscopy. This method addresses a major limitation of classical Raman spectroscopy by utilizing surface-enhancement with metals like gold, silver, and copper to enhance sensitivity.125 The SERS sensors emerged in the 1990s and have undergone rapid development in the last two decades, offering an attractive approach for next-generation sensing. They possess unique features compared to other portable devices. SERS has drawn attention as a powerful technology for detecting biomarkers with high selectivity and sensitivity. SERS significantly enhances the Raman signal by over 10 to 14 orders of magnitude through localized surface plasmon resonance at specific sites. This amplification occurs by intensifying the local electric field substantially when the target analytes are positioned within or adjacent to these hot spots. SERS stands out as an exemplary optical detection method and an ultra-sensitive vibrational spectroscopy technique for characterizing and determining analytes/biomarkers. Its distinguished features include fingerprint recognition, robust anti-interference capability, high resolution, non-destructive sampling, high sensitivity, swift operation, and the ability for multiplexed chemical sensing of complex analytes. Importantly, SERS achieves this label-free and noninvasively without requiring prior knowledge of the analytes.126–128 However, despite its promising capabilities, SERS encounters two significant challenges at its current stage, i.e., designing interfaces for capturing targets and overcoming interference from the surrounding matrix. SERS relies on targets being in close proximity to the substrate surface to function effectively. Nonetheless, researchers have made strides in addressing these challenges, with the development of a SERS biosensor for the sensitive and rapid detection of a protein biomarker associated with endocrine-disrupting compounds in an aquatic environment.129 Ju et al. unveiled a groundbreaking SERS biosensor, aimed at detecting glucose levels within the skin. Their creation relies on a micro-needle array crafted from cost-effective poly(methyl methacrylate).130 This development offers a user friendly and affordable approach for monitoring glucose levels directly at the source. Few selected investigations from the literature on biomarker detection via nanoparticles using the SERS technique are shown in Table 1.9.
1.3.4.1.3 Magnetoresistance-based Sensors
1.3.4.1.4 Thermal Biosensors
Thermopiles and thermistors are the two forms of temperature biosensors. Thermopiles gauge temperature fluctuations between two regions, offering a nuanced perspective on thermal changes. Conversely, thermistors rely on alterations in electrical resistance due to temperature shifts, enabling the determination of absolute temperature. However, their sensitivity is somewhat constrained, impacting their efficacy in certain applications. For enzymatic catalysis, ΔH between ∼−10 to −200 kJ mol−1 is adequate for the determination of substrate concentrations in clinically relevant metabolites such as glucose, oxalate, lactate, cholesterol, triglycerides, etc. In recent times, thermal biosensors have garnered notable attention due to their user friendly nature and easy maintenance. Ongoing advancements have propelled the creation of compact thermal biosensor devices, which are instrumental in bioprocessing applications. Thermoelectric biosensors have been reported to detect l-glutamate (a neurotransmitter),138 C-reactive protein (a reactive protein that increases during inflammation, CVS diseases and depression),139 and cortisol.140 Recently, microelectromechanical system (MEMS) thermal biosensors have emerged as valuable tools for examining metabolic processes through temperature detection. These MEMS thermal sensors possess attributes such as low thermal mass and improved thermal isolation. Moreover, the sample volume within MEMS thermal biosensors enhances sensitivity, extends the linear range, minimizes power consumption and reduces measurement time.
1.4 Conclusion and Future Aspects
In this chapter, we delved into the realm of biomarkers and how biosensors play a pivotal role in their detection. Our focus extends to the integration of nanomaterials in sensor fabrication, aiming to illuminate the techniques employed for biomarker determination and detection. Through this exploration, we highlight the strengths and limitations of the methodologies, fostering a deeper understanding of their comparative efficacy. Biosensors present an exciting alternative to traditional methods by combining a living part with a physicochemical identifier part, offering rapid “real-time” and multiple analyses for estimations and diagnosis. In this chapter, we embark on a comprehensive journey through the fundamentals of biosensors, unraveling their intricate design, operation mechanisms, and underlying principles. We explored the diverse types of biosensors and their wide ranging applications, shedding light on recent advancements in biosensor research. Ultimately, biosensors emerge as indispensible analytical instruments, offering swift and cost effective detection and analysis of numerous analytes and biomarkers. Nevertheless, despite the exponential outgrowth in biosensor publications in research and academics centers, the promising market trend is still far behind the corresponding technological developments. Therefore, future work in biosensors should focus on cost effectiveness and addressing the difficulties associated with the technological shift from academics to industries. Other work such as the design of simplified, robust and sensitive biosensing devices for real-world appliances, implementation of superior nano-material-based bio-analysis tools for the mitigation of “noisy” bio-environments and considerable improvements in the throughput rate, long-term stability, specificity and reliability might be an important step for the next generation of biosensors.