Biosensor fundamentals: microbiosensors used for biochemical measurements are commonly built on which transducer principle?

Introduction / Context:
Microbiosensors couple a biological recognition element (enzyme, cell, antibody, nucleic acid) with a microtransducer that converts biochemical changes into electrical signals. Several transducer types exist, but ISFET-based devices are emblematic for miniaturized, ion-responsive biosensing in aqueous media.

Given Data / Assumptions:

• Analytes often induce local pH or ion concentration changes near the sensing surface.
• Microfabrication allows integration of FET structures with biorecognition layers.
• Sensor operation occurs in conductive, buffered solutions.

Concept / Approach:
An ISFET translates changes in ion activity (commonly H+ for pH) at the gate–electrolyte interface into shifts in threshold voltage, producing a measurable electrical response. By immobilizing an enzyme that converts a substrate and releases or consumes ions, the ISFET becomes a selective microbiosensor for that substrate (e.g., urea via urease generating NH4+ and OH-). Other transducers (piezoelectric, optical) are used too, but ISFETs are a canonical microelectronic platform for compact biosensors.

Step-by-Step Solution:

Verification / Alternative check:
ISFET-based glucose, urea, and DNA hybridization sensors are widely documented, underscoring their centrality in microbiosensing.

Why Other Options Are Wrong:

• A: “Ions effect” is vague and not a defined transducer class.
• C/D/E: Piezoelectric, magnetic, and optical methods exist but are not the singular, most typical microelectronic platform referred to in this context.

Common Pitfalls:
Assuming any physical effect equals a biosensor; the key is coupling a biological layer to a sensitive, miniaturizable transducer. ISFETs provide direct electrical readouts ideal for lab-on-chip.

Final Answer:
Ion-sensitive field-effect transistor (ISFET) principle