Dual-Mode Photoelectrochemical/ColoriMetric Biosensor with a Broad Linear Range for the Sensitive Detection of Enrofloxacin in Aquatic Products

In this study, an integrated dual-mode biosensor combining photoelectrochemical (PEC) and colorimetric (CL) methods was proposed to broaden the linear detection range of enrofloxacin (ENR), thus enabling sensitive detection of ENR in aquatic products. Compared to traditional PEC/CL dual-mode biosensors that rely on the same sensitizer for both PEC and CL signals, this biosensor expanded the linear range and enhanced sensitivity by separating the sensitizer of PEC and the signal label of CL. Specifically, the PEC detection platform employed a Z-type heterojunction of iron indium sulfide (FeIn₂S₄) and cadmium sulfide (CdS) to significantly improve the photoelectric conversion efficiency for the sensitivity of PEC detection. Furthermore, based on an entropy-driven catalytic nucleic acid circuit (ETSD) strategy mediated by aptamers, ENR was converted into a mass of output DNA. Subsequently, the output DNA triggered a strand displacement reaction mediated by a palindrome-catalyzed DNA assembly (NEPA) to form a three-dimensional gold nanoparticle-DNA nanocomposite for the adsorption of methylene blue (3D Au-DNA NC-MB). The resulting 3D Au-DNA NC-MB biomolecular nanocarrier was then used in PEC detection for trace ENR with a linear detection range of 10^–5–10² ng·mL^–1. Concurrently, the unadsorbed MB solution was used in CL detection for a high level of ENR with a linear detection range from 10^–1 to 10⁴ ng·mL^–1. Finally, the method was successfully applied to detect ENR in aquatic products with higher sensitivity and a wider linear range than most reported detection methods, which is anticipated for use in food safety and environmental surveillance.