Table 2.

Biomarker sensing principles and their characteristics

Sensing principles	Detectable biomarkers	Characteristics/notes
Direct detection of redox active analytes	Redox‐active small molecule Neurotransmitters (e.g., serotonin, epinephrine, norepinephrine, serotonin, dopamine) Specific hormone (e.g., melatonin)	Detection using direct oxidation/reduction Detection without biorecognition element (BRE)
Potential‐based measurements	Ions (e.g., Na+, K+, Ca2+) pH	Selective detection using ionophores‐based ion‐selective electrodes
Current‐based measurement	Metabolites (e.g., lactate, glucose, ethanol)	Use of enzyme BREs to detect byproduct of catalytic conversion of biomarkers Need of compensations for the salinity, pH, or temperature for accurate measurement
Impedimetric measurements	Cortisol, Neuropeptide Y Volatile organic compounds (e.g., acetone, isopropyl alcohol, and isoprene)	Use of immunoprecipitation BREs (e.g., protein, antibody) Challenges with reliable biofunctionalization, thermal stability, and shelf‐life
Direct detection of noninvasive physical biomarkers	Skin temperature/conductance Mechanical properties of skin Blood circulation Sweat rate	Measured by several conventional electrical, thermal, mechanical, optical, or fluidic sensing principles