Plasmonic Graphene–Gold Nanostar Heterojunction for Red-Light Photoelectrochemical Immunosensing of C-Reactive Protein

The development of red-light photoelectrochemical (PEC) nanoimmunosensors offers new avenues for detecting clinically relevant biomarkers with high sensitivity and specificity. Herein, the first PEC nanoimmunosensor based on a plasmonic graphene and gold nanostar (AuNS) heterojunction excited with 765 nm red light is presented for label-free detection of C-reactive protein (CRP), a key biomarker of inflammation. This platform leverages the unique localized surface plasmon resonance effect of AuNSs in combination with in situ generated graphene to enhance photoelectrical conversion efficiency under 765 nm monochromatic light. This wavelength minimizes photodamage and interference from biological samples. By optimizing the nanoarchitecture and utilizing a bifunctional photoactive transduction platform, a linear detection range of 25–800 pg/mL is achieved, with a limit of detection as low as 13.3 pg/mL. The low-energy red-light activation, effective electron–hole pair separation, and signal amplification allow CRP’s rapid, selective, and sensitive detection in real clinical samples from patients with low-grade chronic inflammation. The nanoimmunosensor demonstrated consistent analytical performance across multiple samples, showing potential for accurate biomarker monitoring in inflammatory disorders. This work highlights plasmonic nanomaterials to develop robust PEC immunosensors that provide scalable, noninvasive, automated, low-background noise as a highly sensitive alternative for clinical diagnostics.