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Volume-3 Issue-2 | International Journal of Innovative Science and Modern Engineering(TM)
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We do not provide CD and access code. Seller Inventory IN. Publisher: Routledge , Clark, Jr in for oxygen detection. The demonstration of an amperometric enzyme electrode for the detection of glucose by Leland Clark in was followed by the discovery of the first potentiometric biosensor to detect urea in by Guilbault and Montalvo, Jr [ 6 ].
Table 1 shows the historical overview of biosensors in the period — Ever since the development of the i-STAT sensor, remarkable progress has been achieved in the field of biosensors. There are certain static and dynamic attributes that every biosensor possesses. The optimisation of these properties is reflected on the performance of the biosensor.
Selectivity is perhaps the most important feature of a biosensor. Selectivity is the ability of a bioreceptor to detect a specific analyte in a sample containing other admixtures and contaminants. The best example of selectivity is depicted by the interaction of an antigen with the antibody. Classically, antibodies act as bioreceptors and are immobilised on the surface of the transducer.
A solution usually a buffer containing salts containing the antigen is then exposed to the transducer where antibodies interact only with the antigens. To construct a biosensor, selectivity is the main consideration when choosing bioreceptors. Reproducibility is the ability of the biosensor to generate identical responses for a duplicated experimental set-up. The reproducibility is characterised by the precision and accuracy of the transducer and electronics in a biosensor.
Precision is the ability of the sensor to provide alike results every time a sample is measured and accuracy indicates the sensor's capacity to provide a mean value close to the true value when a sample is measured more than once. Reproducible signals provide high reliability and robustness to the inference made on the response of a biosensor. Stability is the degree of susceptibility to ambient disturbances in and around the biosensing system.
These disturbances can cause a drift in the output signals of a biosensor under measurement. This can cause an error in the meas-ured concentration and can affect the precision and accuracy of the biosensor. Stability is the most crucial feature in applications where a biosensor requires long incubation steps or continuous monitoring.
The response of transducers and electronics can be temperature-sensitive, which may influence the stability of a biosensor. Therefore, appropriate tuning of electronics is required to ensure a stable response of the sensor. Another factor that can influence the stability is the affinity of the bioreceptor, which is the degree to which the analyte binds to the bioreceptor.
Bioreceptors with high affinities encourage either strong electrostatic bonding or covalent linkage of the analyte that fortifies the stability of a biosensor.
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Another factor that affects the stability of a measurement is the degradation of the bioreceptor over a period of time. The minimum amount of analyte that can be detected by a biosensor defines its limit of detection LOD or sensitivity. Hence, sensitivity is considered to be an important property of a biosensor.
Linearity of the biosensor can be associated with the resolution of the biosensor and range of analyte concentrations under test. The resolution of the biosensor is defined as the smallest change in the concentration of an analyte that is required to bring a change in the response of the biosensor. Depending on the application, a good resolution is required as most biosensor applications require not only analyte detection but also measurement of concentrations of analyte over a wide working range. Another term associated with linearity is linear range, which is defined as the range of analyte concentrations for which the biosensor response changes linearly with the concentration.
Biosensors have a very wide range of applications that aim to improve the quality of life. This range covers their use for environmental monitoring, disease detection, food safety, defence, drug discovery and many more. One of the main applications of biosensors is the detection of biomolecules that are either indicators of a disease or targets of a drug. For example, electrochemical biosensing techniques can be used as clinical tools to detect protein cancer biomarkers [ 14 — 16 ]. Biosensors can also be used as platforms for monitoring food traceability, quality, safety and nutritional value [ 17 , 18 ].
On the other hand, an application such as pollution monitoring [ 18 , 19 ] requires a biosensor to function from a few hours to several days. Whether it is long-term monitoring or single shot analysis, biosensors find their use as technologically advanced devices both in resource-limited settings and sophisticated medical set-ups: e. A range of electrochemical, optical and acoustic sensing techniques have been utilised, along with their integration into analytical devices for various applications.
Figure 2 indicates different areas of research where biosensors have been used. Irrespective of the field, miniaturisation has always proved to be beneficial for varied reasons. For instance, reducing the size of the biosensor to the micro- or nano-scale can result in a better signal-to-noise ratio as well as the possibility of using smaller sample volumes, which means lower assay costs.
Moreover, when going towards nanoscale dimensions, the surface-to-volume ratio of the sensing active area increases and the sizes of the detecting electrode and that of the target biomarker become comparable. This causes both reduced non-specific binding and increased binding efficiency towards the target molecule. As a result, the bioreceptor becomes an active transducer for the sensing system and it becomes possible to perform single-molecule detection [ 27 ].
An interesting fact in an electrochemical system is that towards nanoscale dimensions the double layer capacitance dramatically decreases because of its dependence on the electrode area. As a result, the extremely low R s C dl time constant where R s is the solution resistance, and C dl is the double layer capacitance allows ultra-fast electron-transfer kinetics and short-life intermediate species can also be investigated. As the time constant decreases, the time required to accomplish a measurement also diminishes towards the nanosecond domain.
Moreover, when C dl decreases dramatically, a further interesting consequence is the possibility of performing measurements in media with a high solution resistance where normal macroelectrodes are not usable. In fact, by keeping the R s C dl factor constant, it is possible to perform measurements even without the need of a supporting electrolyte [ 28 ]. In terms of nanomaterials, the discovery of graphene and its oxidised form, graphene oxide, opened new frontiers in biosensors as well as in other research areas.
Graphene is a pure form of carbon organised into single atom-thick sheets. This feature gives graphene exceptional chemical and physical properties. The integration of graphene, graphene oxide and carbon nanotubes single or multiple one atom-thick carbon concentric tubes as well as nanoparticles and nanowires of different materials are widely reported in the literature for electrode fabrication.
Biosensors so fabricated can nowadays allow limits of detection lower than previously possible, enabling even single-molecule detection. Looking at the never-ending literature related to biosensors over the last few decades, it undoubtedly reveals that biosensors are attractive not only in academia but also in industry. Biosensor technology exploits the unique properties of a biological recognition event on a transducing device.
In such an event, the interaction of the analyte with the bioreceptor is converted into a suitable output that is easily readable by the user. This approach not only exploits the molecular binding event, but also brings researchers from different areas of science and engineering to bridge their skills. Similar practices have created an immense impact on early-stage researchers in the field of biosensors. In addition it has opened new frontiers in scientific research where considerable attention has been drawn towards the development of technologies to benefit different areas including healthcare.
Working in an interdisciplinary field helps to think out of the box and work together with distinct professionals where every idea contributes to make something substantial. A simple example is a pregnancy test biosensor where researchers from biology highlighted the biological aspects and co-operated with engineers to work on the electronics of the system for the read-out. Finally, research from the laboratory is being transferred to customers worldwide because of management professionals. Recently, there has been a gradual increase in start-up companies based on biosensor technology worldwide, which is having a profound impact on the healthcare industrial sector.
In general, it can be said that biosensors have found an important place in our society as they aim to improve the quality of life in diverse areas such as homeland defence and security, agriculture, food safety, environment, medicine and pharmacology. Biosensors have been under development for around 50 years and the research in this field has made tremendous contributions in academia over the last 10 years.
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However, besides lateral flow pregnancy tests and electrochemical glucose biosensors, very few biosensors have achieved global commercial success at the retail level. There are several factors for this: difficulties in translating academic research into commercially viable prototypes by industry; complex regulatory issues in clinical applications; and it has not always been trivial to either find researchers with a background in biosensor technology or engage researchers from different disciplines of science and engineering to work together.
Another reason is that academic research is driven by propositions of peer review of science, and funding agencies and politics that are sometimes characterised by various conflicts of interest. It is often a jury of academics who determine the priorities of funding agencies with legislators who seek considerable warrants for the funding they approve.
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