Ultrasensitive Antifouling Sensors Based on Bifunctional Signal Probes and Y-Shaped Biopeptides for Dual-Mode Immunoassays

In sensing analysis, strong output signals and interface anti-interference capacity, as well as the combination of multiple analysis modes, can greatly improve the detection sensitivity and accuracy of sensors. In this study, copper-doped carbon dots and Cu-CeO₂ nanozymes were chosen as efficient signal probes, which could generate strong electrochemical (EC) and colorimetric (CL) signals through interface electron transfer and catalysis, achieving significant "signal-on". Meanwhile, the triggering of two different signals enabled a dual-mode analysis of the target, effectively reducing false-positive results. Second, a Y-shaped zwitterionic biopeptide was designed for interface modification, which consisted of an anchoring fragment (C), a supporting fragment (PPPP), and an antifouling fragment (EK(KSRE)DER) with a dual-branched structure, resisting nonspecific adsorption of interfering substances. Furthermore, COF-Au NPs with a high electrochemically active surface area were selected as a sensing substrate for loading ferrocene as internal standards, which not only promoted electron transfer but also eliminated background and environmental interferences, thus further improving detection sensitivity and reliability. On this basis, an antifouling ratiometric biosensor was constructed for dual-mode monitoring of human epidermal growth factor receptor 2 (HER-2), a crucial indicator for early clinical diagnosis and prognosis evaluation of breast cancer. Specifically, the linear ranges of EC and CL modes were 100 fg/mL-100 ng/mL and 10 fg/mL-100 ng/mL, with detection limits of 41 fg/mL and 4.3 fg/mL (3σ/S), demonstrating the enormous potential of the designed dual-mode platform for HER-2 detection in serum.