Nowadays, the electrochemiluminescence (ECL) immunosensor with
the unique superiority of tunable luminescence and ultrahigh sensitivity
has become one of the most promising immunoassay techniques, especially
for low-abundance biomarkers analysis. However, the use of signal
probes with high excited potential and applied emitters which owned
good intensity but biotoxicity limited its application. Herein, an
ECL resonance energy transfer strategy was developed based on protein
bioactivity protection utilizing europium-doped phosphoric acid gadolinium
(GdPO4:Eu) as novel low-potential luminophor (donor) and
Pd@Cu2O as the quenching probe (acceptor). Specifically,
GdPO4:Eu was first prepared by using the hydrothermal synthesis
method to apply in ECL, and when it coexisted with K2S2O8, cathode, a strong ECL signal would be generated
at a low potential of −1.15 V (vs Ag/AgCl), where the immunocompetence
of antigens and antibodies can be maintained well. Electrical pair
Eu3+/Eu2+, as the coreactant promoter, produced
by potential excitation could produce more SO4
•– to accelerate the oxidation process of GdPO4:Eu. Meanwhile,
Cu2O coated onto Pd (Pd@Cu2O), as a dual-quencher,
enhanced the quenching effect of Pd alone and controlled the ECL intensity
of the “signal on” state within a reasonable range.
As a result, the proposed biosensor for detection of trace procalcitonin,
a biomarker of systemic inflammatory response syndrome, exhibited
a far low detection limit, 0.402 fg/mL (S/N = 3). Importantly, this
work not only utilized a promising ECL emitter for biosensing platform
construction but also had momentous potential in biomarker detection
of disease diagnosis and clinical analysis.