Lecture ( 6 part- 2) Biosensor

Biotechnology & Genetic Engineering Lecture (6 part- 2) Assi. Prof. Rajaa Al –Anbaqi


Biosensor- part- 2



A- Amperometry


measuring the current resulting from the electrochemical oxidation or reduction of an electroactive species at a constant applied potential. Is a method of analysis in which the signal of interest is a current that is linearly dependent upon the concentration of the analyte ,electrons are transferred from the analyte to the working electrode or to the analyst from the electrode.




C-Conductometry


Conductometric sensors are based on the measurement of electrolyte conductivity, which varies when the cell( or the biological component) is exposed to different environments. The sensing effect is based on the change of the number of mobile charge carriers in the electrolyte. If the electrodes are prevented from polarizing, the electrolyte shows ohmic behavior. Conductivity measurements are generally performed with AC supply


2- Ion-Sensitive Biosensors

These are semiconductor Field Effect Transistor (FETs) having an ion-sensitive surface. The surface electrical potential changes when the ions and the semiconductor interact. This change in the potential can be subsequently measured. The Ion Sensitive Field Effect Transistor (ISFET) can be constructed by covering the sensor electrode with a polymer layer. This polymer layer is selectively permeable to analyst ions. The ions diffuse through the polymer layer and in turn cause a change in the FET surface potential. This type of biosensor is also called an ENFET (Enzyme Field Effect Transistor) and is primarily used for pH detection.

3- Optical-detection Biosensors


The output transducer signal that is measured is light for this type of biosensor. The biosensor can be made based on optical diffraction. In optical diffraction based devices, a silicon wafer is coated with a protein via covalent bonds. The wafer is exposed to UV light through a photo-mask and the antibodies become inactive in the exposed regions. When the diced wafer chips are incubated in an analyst, antigen-antibody bindings are formed in the active regions, thus creating a diffraction grating. This grating produces a diffraction signal when illuminated with a light source such as laser. The resulting signal can be measured or can be further amplified before measuring for improved sensitivity. Optical Biosensors consist of Colorimetric for color Measure change in light adsorption, Photometric for light intensity ,Photon output for a luminescent or fluorescent process can be detected with and photomultiplier tubes or photodiode systems .

Example for this group will be given in the following Fluorescence molecular sensors have been constructed by coupling fluorophores to proteins, in such a way that their fluorescence properties change in response to sensor-target binding. The molecular constructs integrate both the recognition and transducer elements of a biose