MEMBRANES USED IN BIOSENSORS

A variety of membranes can be used in the construction of biosensors depending on the need. The membranes are constructed from a variety of sources/materials; hydrophilic, hydrophobic, conducting, non-conducting and so on.


Various types of membranes used in the construction of biosensors include :

• Membranes made from synthetic polymers with high water regaining capacity. eg: hydrogels like Polyacrylamides
  
• Hydrophobic Membranes that are impermeable to high molecular weight watersoluble compounds, but are permeable to ions and gases. Polytetrafluoroethylene, Polyvinylchloride membranes are used in the making of Ion Selective Electodes (ISE's).
  
• Membranes constructed from biologically derived materials such as cellulose, collagen etc. Membranes derived from these materilas posses good properties for immobilizing biological materilas (such as porosity).
  
• Non-Conducting Polymer Films such as Polyphenol are used as membranes for biosensors.
• Conducting Polymer Films such as Polypyrrole and Polyaniline are also used as membranes in biosensors.
  
• Heterogenous multilayer membranes are used in certain cases. They contain multiple membranes. Each membrane has a different biological material and thus a different function.
• Microfiltrarion membranes such as Polycarbonate membranes are also used in Biosensors

The choice of the membrane used for a biosensor is made taking into consideration, the analyte, the method of detection of the reaction/signal at/from the biological element.

For example :

1. Ion selective membranes are used in the making of Potentiometric biosensors.
2. PolyTetraFluoroEthylene and Teflon membranes are used in the glucose biosensor for seperating the electrode from the bulk reaction mixture.

Making of PolyVinylAlcohol membrane for Glucose and Lactate Biosensors:

Polyvinylalchohol membranes are made and are then activated with cyanogen bromides and coupled with ethylene diamines. Later the membrane is treated with glutaraldehyde after which glucose oxidase and lactate oxidase enzymes are immobilized onto the membrane. Coupled with the O2 Electrode this membrane with either Glucose oxidase or Lactete oxidase functions as Glucose biosensor or a Lactate biosensor.