biosensors 

Biosensor: An analytical tool or system consisting of an immobilised biological material in intimate contact with a suitable transducer device that converts the biochemical signal into a quantifiable electrical or optical output. Main components:

  1. microbial cells (cheaper to isolate)
  2. enzymes (increased specificity)
  3. animal/ plant tissue (prolonged lifetime) Transducer (electrochemical or optical) Signal recognition Biosensor

Optical Biosensors:

  1. Light emission from biological element or its response to illumination is monitored by fibre optics
  2. Light delivered to immobilised sensing layer at tip of fibre optic
  3. Absorbance, luminescence or fluorescence monitored by second fibre or bifurcation of original fibre

Calorimetric biosensors: Calorimetry is a universal method for monitoring activity of immobilised biological material. can use two methods of detection:

  1. Enzyme thermistor: sample flows consecutively through an injector, the enzyme column and temperature probe
  2. Sample flow is split: one part is pumped through enzyme free column with temperature probe. Therefore, gives measure of background (non-specific) effects

Immunosensors:

  1. ELISA techniques have been combined with biosensors to form immunosensors in order to increase their range, speed & sensitivity.
  2. Biosensor replaces the traditional colorimetric detection system.
  3. More advanced immunosensors are being developed which rely on the direct detection of antigen bound to the Ab coated surface of the biosensor

Amperometric sensors in immunosensors:

  1. Generally use redox enzyme systems.
  2. A redox enzyme is immobilised at electrode surface
  3. Electrode held at fixed potential and adjusted so that electrons arising from an oxidised substrate are transferred to the electrode. The current produced at the electrode is proportional to the rate of modification of substrate by the enzyme.

Microcantilever sensors:

  1. Microcantilevers can sense & quantitate biological proteins, nucleic acids and other organic & inorganic chemicals
  2. The principal mechanism of action is a nanoscopic deflection caused by receptor-ligand induced stress on one face of the cantilever.
  3. Grimzewski at al produced first cantilever array immunosensor, which could distinguish protein A binding to IgG.
  4. Majumdar et al produced a cantilever immunosensor for PSA in 2002.
       Force Atom Microscopy