Electrochemiluminescence Double Quenching System Based on Novel Emitter GdPO4:Eu with Low-Excited Positive Potential for Ultrasensitive Procalcitonin Detection

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 center dot- 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.