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Figure 3. Principles and techniques of electrochemical biomarker sensing. (A and B) ISF analysis method based on optical (A) and electrochemical reaction (B); (C) Overview of electrochemical biosensing measurement techniques, including CV, CA, DPV, and EIS, along with their characteristic electrical signal outputs; (D-H) Various sensing mechanisms: (D) enzyme-based electrochemical biosensors across different generations, (E) redox-active and non-enzymatic catalytic sensors, (F) aptamer-based sensors, (G) antibody-based immunosensors, and (H) MIP-based biosensors. ISF: Interstitial fluid; MIP: molecularly imprinted polymer; SERS: surface-enhanced Raman spectroscopy.