3. INTRODUCTION
• A biosensor is an analytical device for the
detection of an analyte that combines a
biological component with a
physicochemical detector component.
8. Electrochemical biosensors
• normally based on enzymatic catalysis of a reaction that
produces or consumes electrons (such enzymes are
rightly called redox enzymes).
• The sensor substrate usually contains three electrodes;
a reference electrode, a working electrode and a counter
electrode.
• The target analyte is involved in the reaction that takes
place on the active electrode surface, and the reaction
may cause either electron transfer across the double
layer (producing a current) or can contribute to the
double layer potential (producing a voltage
10. Photometric
• Many optical biosensors based on the phenomenon of
surface plasmon resonance (SPR) are evanescent wave
techniques.
• This utilises a property of gold and other materials;
specifically that a thin layer of gold on a high refractive
index glass surface can absorb laser light, producing
electron waves (surface plasmons) on the gold surface.
• This occurs only at a specific angle and wavelength of
incident light and is highly dependent on the surface of
the gold, such that binding of a target analyte to a
receptor on the gold surface produces a measurable
signal.
12. Others
• Piezoelectric sensors utilise crystals which
undergo an elastic deformation when an
electrical potential is applied to them. An
alternating potential (A.C.) produces a
standing wave in the crystal at a
characteristic frequency.
14. Applications
• Glucose monitoring in diabetes patients.
• Other medical health related targets.
• Environmental applications.
• Detection of pathogens .
• Determining levels of toxic substances before and after
bioremediation.
• Detection and determining of organophosphate .
• Determination of drug residues in food.
• Drug discovery and evaluation of biological activity of
new compounds.
