Sensors & Transducers Journal, Vol.76, Issue 2, February 2007, pp.935-936
stranded DNA shows long- range electron transfer through
π
stacks of aromatic rings of base pairs [41-
42]. The first example of a DNA chip, called the eSensorTM, was produced by Motorola Life Sciences
Inc. [43]. eSensor
TM
bioelectric chips also successfully detected 86% of the HPV types contained in
clinical samples[44]. Toshiba’s electrochemical DNA hybridization detection system is called the
Genelyzer
TM
[45]. It contains an electrochemical DNA chip that is able to analyze and type single-
nucleotide polymorphisms (SNPs) and common DNA sequence variations by using the redox-active
dye Hoechst33258 [46].
4. Applications in Food Analyses and Quality Assurance
Safety monitoring and quality control of foods are essential for food industry and the use of biosensors
allows the assessment of food safety in real time. Hence biosensors have been developed for
automated process control and provide a good alternative to other methods which are tedious, time &
energy consuming and may require expensive instruments and reagents in addition to considerable
technical skills
4
. The importance of on-line measurement compared to a laboratory measurement in
terms of process control is firstly its response time. Sampling and subsequent analysis in a laboratory
involves a time delay which can be sometimes several days. Although laboratory instruments have
some inherent advantages, on-line biosensor describes the real time state of the process. Data
generated from the biosensor provide rapid and/or continuous feedback information which can help the
food processor both reduce wastage and increase productivity by incorporating microbiological and
quality control into processing line. Because foods are highly unstable materials and can quickly
undergo rapid and often detrimental changes, process control is an uncertain and doubtful strategy.
Because of this, food industry needs instruments which will simultaneously monitor the parameters of
production lines and report data to the computer for feedback control.
Most of the electrodes used in biosensors are often based on the measurement of O
2
consumption
because there are at least 50 known oxidases acting on fatty acids, hydroxy acids, sugars, amino acids,
aldehydes, etc. Using this concept ethanol, methanol, lactose, lactic and acetic acid, glucose and
galactose on line biosensors have been developed by different researchers.
Beer, wine, bread and dairy industry suffer from lack of monitoring the growth conditions of
microorganisms which must be kept at certain limits. On-line biosensors offer these industries
feedback control of both the component and microbial levels of these and similar processes by
continual on-line monitoring.
A unique situation that recently has come to light in India is the adulteration of milk with materials that
are toxic or production of synthetic milk using ingredients such as urea. Biosensors have already been
developed to check this menace. For example, urea is detected in milk samples by employing the
enzyme unease. Urea and water are converted to ammonium and bicarbonate ions in the aqueous
medium. Bicarbonate ions are weak ions so contribute less to the pH change but the alkaline ions due
to their high alkaline nature contributes maximally to the pH change which is detected by the
potentiometric transducer.
5. Biosensors for Environmental Monitoring
With several countries on the path to acquiring chemical and biological weapons there is now a need to
develop biosensors for the early detection of these agents in accidental release during production and
deliberate use by terrorists. Defense applications have become very prominent, particularly since the
atrocities of September 11
th
2002 and the subsequent anthrax attacks. To circumvent this latest threat
to human health, efforts are underway to develop biosensors that could be used under these situations.
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