This
work developed a near-infrared (near-IR) light-activated non-enzymatic
signal-off photoelectrochemical (PEC) immunoassay for the ultrasensitive
detection of α-fetoprotein (AFP) on the basis of branched polyethylenimine
(BPEI)-modified upconversion nanoparticle (UCNP)@CdTe quantum dot
(QD) nanostructures by coupling with the synergistic effect of dual-purpose
copper ions. Emission light originated from NaYF4:Yb,Er
UCNP was directly utilized through the electrostatic bonding of CdTe
QDs to excite the separation of electron–hole pairs, resulting
in the generation of obvious photocurrent under a 980 nm laser. By
using polyclonal antibody-labeled cupric oxide nanoparticle as the
secondary antibody, the nanolabel was introduced into the monoclonal
anti-AFP antibody-modified microplates in the presence of target AFP.
After treatment with acid, the as-released copper ion decreased the
photocurrent through the synergistic effect with two issues: one was
initially to form coordination with BPEI on the surface of UCNP, and
then the near-IR excitation light and upconversion luminescence were
attenuated due to the internal filter effect; another was to snatch
the electrons flowing from the valence band of CdTe QD as the exciton
trapping sites. Under optimal conditions, the dual-purpose Cu2+-activated signal-off PEC immunosensing platform exhibited
a dynamic linear range from 10 pg mL–1 to 50 ng
mL–1, accompanying the decreasing photocurrent with
the increment of AFP concentration at an experimental detection limit
of 1.2 pg mL–1. Importantly, good accuracy was achieved
by this method in comparison with the results with human AFP ELISA
kit for analysis of human serum samples. This dual-purpose Cu2+-activated PEC immunoassay brings a promising, enzyme-free
and innovative thinking for the detection of low-abundance biomarkers.
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