Practice question

Electrochemical biosensors dominate commercial diagnostic market, typified by blood glucose strips, due to ease of miniaturization, low cost and compatibility with portable potentiostats. In these devices analyte recognition by oxidoreductase, dehydrogenase, or affinity bioreceptor immobilized on working electrode modifies local redox environment, ion concentration or interfacial electron transfer resistance. Amperometric mode measures current arising from oxidation or reduction of enzymatic product such as hydrogen peroxide at fixed potential following Cottrell equation where current proportional to concentration gradient; potentiometric mode detects Nernstian potential shift due to accumulation of ions like H+ or NH4+ near ion-selective membrane; impedimetric mode tracks charge-transfer resistance change upon binding event at electrode-electrolyte interface using Nyquist plots. Unlike optical biosensors that detect photon emission, fluorescence quenching or plasmon shifts, or thermal sensors measuring reaction enthalpy, electrochemical platforms exclusively monitor electric current or potential enabling integration with microelectronics and wireless readout. Nanomaterial enhancement using graphene, carbon nanotubes or gold nanoparticles increases electroactive surface area and electron shuttle kinetics achieving nanomolar detection limits and fast response.