BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 o Electrode may be selective for certain ions or gase E.g. F- I, CN-, Nat, K+, Ca2+, H+, NH4 CO2 NH3 o Amperometric o Measure current generated by electrochemical oxidation or reduction of electroactive species at a constant applied potential Electrochemical detection ISFET-ion-sensitive field-effect transistors As Se Ni membrane ep --群 0H一 Common pH-modifying enzymatic reactions glucose oxidase ource D-glucose+02-+ D-glucono-1, 5-lactone H2O2- D-gluconate H [6.31 penicillinase penicillin→ penicilloic acid+H’[6.4 enz ane pH-FET H2 NCONH2+H2O+2H一2NH4·+cO2I65] Fig. 2. Biosensor based on a pH-sensitive FET. ease(pH 9.5)D H2NCONH2+ 2H20-+ 2NH3+ HCO3+H (6.61 neutral lipids+H2o-) glycerol+ fatty acids+H[6.71 (Mulchandani and Rogers, 1998) Advantages/disadvantages Pros o Fast measurements Sensitive ow detection limits typically- 10M on Ability to perform measurements on turbid/opaque solution o PH-sensing mechanisms require weakly buffered or non-buffered solutions Calorimetric Calorimetric readouts o Measurement of heat generated by an enzymatic reaction o Typically utilize thermistors to transform heat into an electrical signal Lecture 19-BiosensorsBEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Electrode may be selective for certain ions or gases ƒ E.g. F-, I-, CN-, Na+, K+, Ca2+, H+, NH4+ ƒ CO2, NH3 o Amperometric o Measure current generated by electrochemical oxidation or reduction of electroactive species at a constant applied potential Electrochemical detection: ISFET - ion-sensitive field-effect transistors Common pH-modifying enzymatic reactions: (Mulchandani and Rogers, 1998) Advantages/disadvantages ƒ Pros o Fast measurements o Sensitive ƒ Low detection limits typically ~ 10-9 M o Ability to perform measurements on turbid/opaque solutions ƒ Cons o PH-sensing mechanisms require weakly buffered or non-buffered solutions Calorimetric Calorimetric readouts o Measurement of heat generated by an enzymatic reaction o Typically utilize thermistors to transform heat into an electrical signal Lecture 19 – Biosensors