method of transduction
(a) Optical-detection:
Image 6
Optical detection biosensors are the most diverse class of biosensors because they can be used for many different types of spectroscopy, such as absorption, fluorescence, phosphorescence, Raman, SERS, refraction, and dispersion spectrometry. In addition, these spectroscopic methods can all measure different properties, such as energy, polarization, amplitude, decay time, and/or phase. Amplitude is the most commonly measured as it can easily be correlated to the concentration of the analyte of interest .
(Image ref 6- http://www.nature.com/nrd/journal/v1/n7/fig_tab/nrd838_F2.html)
(Image ref 7- http://www.medgadget.com/2011/09/optical-biosensor-for-continuous-rapid-detection-of-health-threats.html)
(Image ref 6- http://www.nature.com/nrd/journal/v1/n7/fig_tab/nrd838_F2.html)
(Image ref 7- http://www.medgadget.com/2011/09/optical-biosensor-for-continuous-rapid-detection-of-health-threats.html)
(b) Electrochemical:
Image 8
Electrochemical biosensors measure the current produced from oxidation and reduction reactions. This current produced can be correlated to either the concentration of the electroactive species present or its rate of production/consumption.
(Image ref 8- http://softmatter.quimica.unlp.edu.ar/electrontransfer.php)
(Image ref 8- http://softmatter.quimica.unlp.edu.ar/electrontransfer.php)
(c) Mass-sensitive:
Image 9
Biosensors that are based on mass-sensitive measurements detect small mass changes caused by chemical binding to small piezoelectric crystals. Initially, a specific electrical signal can be applied to the crystals to cause them to vibrate at a specific frequency. This frequency of oscillation depends on the electrical signal frequency and the mass of the crystal. As such, the binding of an analyte of interest will increase the mass of the crystal and subsequently change its frequency of oscillation, which can then be measured electrically and used to determine the mass of the analyte of interest bound to the crystal.
(Image ref 9- http://www.springerimages.com/Images/RSS/1-10.1007_s00216-007-1670-8-0)
(Image ref 9- http://www.springerimages.com/Images/RSS/1-10.1007_s00216-007-1670-8-0)
(d) Thermal detection:
Image 10
Thermal biosensors measure the changes in temperature in the reaction between an enzyme molecule and a suitable analyte. This change in temperature can be correlated to the amount of reactants consumed or products formed.
(Ref no 3)
(Image ref 11- http://www.sciencedirect.com/science/article/pii/S0956566312001741)
(Ref no 3)
(Image ref 11- http://www.sciencedirect.com/science/article/pii/S0956566312001741)