Sensors & Transducers Journal, Vol.76, Issue 2, February 2007, pp.935-936
sandwiches”[7]. This idea was commercially exploited in 1975 with the successful launch of the
Yellow Springs Instrument Company’s glucose analyzer based on the amperometric detection of
hydrogen peroxide (H
2
O
2
). Since then, many biosensors have been developed to detect a wide range of
biochemical parameters, using a number of approaches, each having a different degree of complexity
and efficiency. Recently, the most fascinating and prospective sensors includes Immunosensors [8-9]
and Nucleic acid sensors [10-11], based on affinity reactions between Ab-Ag & hybridization reaction
of complimentary ssDNA oligonucleotides respectively.
In general, a biosensor is an analytical device, which detects, transmit and record the information
regarding the physiological, biochemical change or the presence of a specific analyte (a chemical or
biological substance that needs to be measured) by producing a signal proportional to the concentration
of the target analyte. A basic biosensors assembly includes a receptor, transducer and processor
(amplification and display) as shown in Figure 1.
Fig. 1.
Schematic diagram showing the main components of a biosensor. The biocatalyst (a) converts the
substrate to product. This reaction is determined by the transducer (b) which converts it to a signal. The output
from the transducer is amplified (c), processed (d) and displayed (e).
(Reproduced with permission from ref. 6).
Technically, it is a probe which incorporates a biological/ biologically derived sensing element (e.g.
whole cells/ antibodies/ enzymes/ nucleic acids) forming a recognition layer, that is either integrated
within or intimately associated to the second major component of biosensors that is a transducer via
immobilization, adsorption, cross-linking and covalent bonding so that the close proximity of the
biological component to the transducer is achieved. This is necessary so that the transducer can rapidly
and easily generate the specific signals in response to the undergoing biochemical interactions,
secondly the transmittance should be proportional to the reaction rate of biocatalyst with the measured
analyte for a high range of linearity. The transducer critically acts like a translator, recognizes the
biological/chemical event from the biological component and transforms it into another signal for
interpretation by the processor that converts it in to a readable/ measurable out put. The transducer can
take many forms depending upon the type of parameters being measured. They may be a)
Amperometric:
detect changes in current at constant potential [12], b)
Potentiometer:
detect changes in
potential at constant current [13], c)
Piezoelectric:
detect the changes in mass [14],
d) Thermal:
measures changes in temperature [15], e)
Optical:
detects change in light transmission [16].
Since, these devices offer an excellent combination of the selective biology with the processing power
of nano-electronics to generate rapid, simple and sensitive signal proportional to the target analyte;
they are regarded as potent substitutes to conventional analytical techniques. These low complexity
devices are suited for use at the point of care by healthcare workers with minimal training. By
eliminating a number of steps and much labor, the instrumentation may save a lot of money & time for
laboratories and hospitals. It would therefore in the near future be possible to measure group of
biochemical parameters simultaneously from a single finger prick blood sample. Besides, they allow
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