Chapter 12 Contemporary Detection Method-Biosensor for Food Safety by Dr. Jerry Teng在线视频

Chapter 12- Biosensor by Jerry

Ladies and Gentlemen, Welcome to the class, today’s topic is biosensors.

Last class we discussed the traditional methods for determination of the food hazards. For most of the chemical hazards, they were based on the chromatography such as HPLC and GC. These methods are very sensitive, selective, and also capable of determining multiple components simultaneously. But at the same time, these methods are very complicated, time-consuming and costly.

Considering the huge amount of food samples need to be detected very quickly, so we need very fast and very simple methods. Before we discuss the biosensors, let’s look at a very common and simple device - pH meter. PH meter is a very simple, fast, easy-to-use, and very reliable device that detect the pH values that is the minus log of hydrogen ion concentration.

The key part of pH meter is the pH electrode; sometimes we call it the glass electrode. This is basically a chemical sensor or specially an electrochemical sensor. This device is converting the concentration of the target analyte, in this case hydrogen ion, to electrical signal. And this sets up a gold standard for lots of those fast detection method.

In theory, all the oxidation-reduction reactions can be transferred into the electrochemical cells. One kind of the sensors that are based on the electrochemical cells, technically, called the ion selective electrodes, has been developed. This is a list of chemical sensors.

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So let’s look back to the sensors. First of all, what is the definition of chemical sensor? The chemical sensor is a device which responds selectively to a chemical concentration or other information and the responds are then transmitted or converted to signals which can be handled by the electronic devices.

There are two key features of any sensor: first one is the interface, or sometimes we call it the sensing element or the recognition element, which selectively responds to the chemical information. The second key part is the transducer. Transducer is responsible for converting chemical information into the electrical signals.

Biosensor is a subclass of chemical sensors. The difference is its recognition element, the part which responsible for the high sensitivity and high selectivity, is based on a biological principles. So there are basically two parts for the biosensor. First one is the biological sensing element and the second part is the transducer, responsible for converting the chemical information or biochemical information to the electoral signal. For the sensing element or the biorecognition, you can use several biological principles. First one the antibody-antigen relationship can be used in this recognition element. Second one is the binding of enzyme and substrate which has higher sensitivity. And also other biological principles can be used in the sensing element.

As for the transducer, the one we have just discussed is an electrochemical transducer; this means it is converting the information into the electrical signal. Such as the one we have been discussed, pH meter, converting the information of concentration into the voltage. Then we can measure the voltage which is relative to the concentration by the Nernst equation.

And also we can use the physical principles, such as the piezoelectric components as the transducer. This is basically the quartz, pure silicon dioxide, placed under a high voltage will be vibrating with characteristic frequencies. If there is mass being deposited on the surface of quarts, there will be change of frequencies. Besides piezoelectric transducer, we can use other transducer such as the optical transducers. And in this case, we use the optical fiber directly as the traducer. And the last one but not the least is the thermal component, thermal transducers such as those that have been used in the environmental sensors which based on variations in resistance because there are changes of temperature.

The mostly popular or the mostly successful commercial available biosensor is the glucose sensor. This one is mostly considered to be the biosensor or chemical sensor. And the principle is based on the selectively catalyzed oxidation of the glucose.

When oxidation-reduction reactions take place, there will be electron transfer. When the electron transferring can be measured directly, the amount of the electron can be related the concentration of glucose.

This is based on the electrochemical sensor. And also this electron transfers can be used to drive another chemical reaction which will resulting in the color changes. Then an optical sensor can be developed. This is the two most popular principles for the glucose biosensors.

Thank you for your attention! This is all for today.