Introduction
A biosensor simply means an analytical device that is used to detect the presence or amount of a specific analyte in a solution. Amperometric signifies the use of carbon-electrodes to carry out the process. When the two words are combined, it means that carbon electrodes are used to carry out the process of oxidation and reduction to analyze a particular solution or sample for the presence of a specific carbohydrate or amino acid. Thus, amperometric biosensors are very helpful for the analysts, who have to carry out such tests.
Developmental Phase
In recent years, a lot of development has been observed in this field. A variety of such biosensors are being used for various purposes. e.g. there are amperometric biosensors for the determination of glycolic acid in real samples, few of them are based on the immobilization of enzymes in polymer films electrogenerated from a series of amphiphilic pyrrole derivatives, for apparent direct electron transfer between electrodes and immobilized peroxidases, selective ones for glucose by in situ electropolymerization, screen-printed amperometric biosensors for the rapid measurement of L- and D-amino acids and flow injection analysis of L-lactate in milk and yoghurt by on-line micro dialysis and amperometric detection at a disposable biosensor etc.
The significance of amperometric biosensors which determine glycolic acid in real samples lies in the fact that they are the first enzyme based biosensors which have a lot of potential. They have a power to find out the occurrence of glycolic acid in complex matrix samples such as instant coffee, cosmetics, and urine. It made the work of analysts a lot easier as two methods for this were devised and they were according to the current technology of commercial analyzers.
Both the designs had three-membrane configuration consisting of an inner and an outer membrane. The inner membrane is cellulose acetate membrane (CA) and the outer membrane is polycarbonate membrane (PC). Both of them comprise of a membrane that contains biomolecule(s).
Chemical bonding was used to stop glycolate oxidase onto a modified polyethersulfonate membrane. Physical adsorption is the method that was used for the immobilization of glycolate oxidase/catalase enzyme into a mixed-ester cellulose acetate covering. The result of both the biosensors was successful. Thus, they were used by the analysts for testing glycolic acid in various samples.
Then there are other amperometric biosensors. These one were developed for the immobilization of enzymes in polymer films electrogenerated from a series of amphiphilic pyrrole derivatives. This involves a procedure which is to be of great interest to the chemical analysts.
It would be worthwhile to notice that a series of different ions of amphiphilic were used. These ions were different in terms of their ammonium head sizes and were used to immobilize the horseradish peroxidase, a type of enzyme which occurs in horseradish plants and other various types of enzymes which include galactose oxidase, polyphenol oxidase, glucose oxidase and xanthine oxidase.
The successful conclusion to be drawn from this information is that, the less hydrophobic monomer gave the best immobilization efficiency and that the glucose bioelectrode gives a particular reaction to ascorbate, urate and acetaminophen in a particular concentration.
Another type of amperometric biosensors was developed. These resulted in yet another category of amperometric biosensors that have a basis on apparent direct electron transfer between electrodes and immobilized peroxidases. According to this method, enzymes and electricity play a part in the reduction of hydrogen peroxide starts at about +600mV as compared to a saturated calomel electrode (SCE) at neutral pH.
It was analyzed from this experiment that the efficiency of electrocatalytic current is dependent on the applied potential. As the applied potential or strength of the solution increases or is made more negative up to -200 mV as compared to SCE, the efficiency of the current increases. Such electrodes are very useful for making hydrogen peroxide amperometric biosensors.
New types were introduced as progress in amperometric biosensors took place. The new ones were more advanced and allowed analysts test samples which were not possible with the previous amperometric biosensors. Three methods for these biosensors were formed in which enzymatic determination of glucose was checked. The bilayer polymer coatings consisted of polypyrrole (PPy) and poly (o-phenylenediamine). The electrode substrate was responsible for introducing a significant amount of variation in the process of electrode construction.
These bore significant results as they generated improved selectivity against the interruption from electroactive acids such as ascorbic acid and uric acid. These acids are mostly found in biological samples. This is not only helpful for the analysts, but it is a great source of knowledge and information for those who are interested in scientific experiments. They can include student groups and various analysts. With the help of the development procedures in the amperometric biosensors, they can test the samples and their minute details as they wish.
Development in the amperometric biosensors led to the formation of screen-printed amperometric sensors for the quick measurement of L- and D- amino acids. This was a step further in the development as these could measure the amount of particular type of amino acids plus this procedure took lesser time. The electrode which has to perform the main task is coated with rhodinised carbon. This makes sure that hydrogen peroxide oxidation can take place at a reduced functional level and immobilized enzyme.
Except for the two amino acids i.e L- and D- proline, the device reacted to all the 20 common L- and D-amino acids. These devices were easily reproducible and showed that they were stable for more than 56 day test period. The main benefit however, lies in the fact that they were a basis of good comparison with the standard photometric amino acid test and was also used to control the effects of milk ageing. This experiment is time efficient and very easy.
New type of amperometric biosensors was formed as time gained momentum. We live in a dynamic environment and changes take place as and when need arises for something which can serve in a better way to adjust to the changing environment. Likewise, a method was developed for the flow injection analysis of L-lactate in milk and yoghurt by micodialysis and amperometric detection at a disposable biosensor.
Conclusion
Huge developments took place in the way of amperometric biosensors. These changes and the formation of new ones have continued to remain helpful for the analysts, researchers and students who are fond of carrying out experiments. It also proves that changes and development pave the way for fulfilling certain requirements and this development is caused by need of new things in the first place. These amperometric biosensors are of significant delight to those who are interested in science and the wonders performed in the field of bio-technology.
Progress will continue to take place in the future as well. And hopefully, advanced amperometric biosensors with distinct uses will be cited. There are biosensors of other types as well but they are not amperometric. They are simple and used to work on other processes e.g. biosensors for the determination of environmental inhibitors of enzymes.
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