Tunable Competitive
Absorption-Induced Signal-On Photoelectrochemical
Immunoassay for Cardiac Troponin I Based on Z‑Scheme Metal–Organic
Framework Heterojunctions
Recently emerged Z-scheme heterostructure-based immunoassays
have
presented new opportunities for photoelectrochemical (PEC) biosensing
development. Here, we described a tunable signal-on PEC biosensor
for the detection of cardiac troponin I (cTnI), which exploited a
competitive absorption effect between Cu(II) ions and a Zr metal–organic
framework (Zr-MOF) constructed on TiO2 nanorods (Cu2+@Zr-MOF@TiO2 NRs). Water-stable Zr-MOF was coated
onto TiO2 NRs on fluorine-doped tin oxide to form a Z-scheme
heterostructure substrate (Zr-MOF@TiO2 NRs), which exhibited
a high photoelectric response. Cu2+@Zr-MOF@TiO2 NRs, constructed by loading Cu(II) ions onto the architecture of
Zr-MOF by electrostatic interaction, demonstrated a low background
signal. After sandwich immunorecognition within a 96-well plate, H2S, generated by confined alkaline phosphatase on zeolitic
imidazolate framework-8, was directed to react with Cu(II) ions to
form CuS. This resulted in an in situ change in the photoelectrode
and an enhanced photoelectric signal. The developed PEC biosensing
platform exhibited high sensitivity and selectivity for the cTnI immunoassay
with a detection limit of 8.6 pg/mL. The Z-scheme-based competition
absorption modulation of photoelectrochemistry provides a new strategy
for general PEC biosensing development.