A Versatile Self-Powered Photoelectrochemical-Colorimetric Dual-Mode Immunosensing Platform Based on a 3D BiOI Nanoflower Functionalized by Bi Doping and Morphology Engineering

Photoelectrochemical-colorimetric (PEC-CL) dual-mode detection integrates PEC and CL advantages for bioanalysis but often faces low efficiency, complex conditions, and performance trade-offs due to different signal transduction materials. Here, BiOI was functionalized by Bi0 self-doping and morphology engineering, forming a 3D Bi-doped BiOI nanoflower with excellent PEC and CL properties. This material was innovatively developed as a single transduction material for self-powered PEC-CL dual-mode detection. The synergistic enhancement of photoelectric conversion and peroxidase (POD)-like activity was systematically investigated. Using γH2AX, a genotoxicity biomarker, as a model, a self-powered PEC sandwich immunosensor was constructed with ITO/Au as the photocathode, BiOI-Ab2 as the signal probe, and CdIn2S4 as the photoanode. Upon γH2AX recognition, BiOI was introduced on the photocathode via an immunoreaction. The well-matched energy levels between Au and BiOI, along with the dual-photoelectrode effect, enable a sensitive "signal-on" PEC analysis. Simultaneously, a sandwich immunoreaction involving the BiOI-labeled secondary antibody occurred in the microplate containing H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB), among which BiOI-catalyzed H2O2 produced reactive oxygen species, which further oxidized TMB to produce color, thus achieving the high-throughput visual detection of γH2AX. The PEC-CL dual-mode sensor exhibited broad linear ranges (0.1 pg/mL to 1000 ng/mL for PEC, 1 pg/mL to 500 ng/mL for CL) with ultralow detection limits of 23.9 and 330 fg/mL, respectively. The sensitivity of PEC mode is 100-fold higher than the ELISA method. Moreover, the practicability of the PEC-CL immunosensor was verified in cell lysates exposed to known genotoxic compounds. This sensing platform is versatile, which allows the detection of other biomarkers by changing the recognition element.