A “Four-in-One” Immunochromatographic Strip for Multi-Readout Detection of Diazepam in Lake Water and Fish via Nanozyme-Mediated Colorimetric, Catalytic, and Photothermal Activities

The presence of psychotropic drugs (PDs) in aquatic ecosystems represents an increasing environmental problem, posing a serious threat to human health and aquatic organisms. Lateral flow immunoassays (LFIA) have been widely used in the detection of PD contaminants. However, maintaining signaling tag reporting activity and achieving LFIA's multi-readout capability remain significant challenges to meeting a range of detection scenarios. Here, a rapid multifunctional LFIA has been developed for detecting diazepam (DAP), an emerging environmental and food safety PD contaminant, in lake water and fish samples. Copper hexacyanoferrate nanoparticles doped with Au and Pt (AuPt@Cu-HCF) were designed and manufactured as a multi-signal reporter with exceptional photothermal conversion efficiency and peroxidase-like enzymatic activity. This study integrates the colorimetric, photothermal, catalytic colorimetric, and catalytic photothermal effects of the AuPt@Cu-HCF nanozyme to form a “four-in-one” multi-readout LFIA. The multifunctional detection approach achieved four different detection signal outputs for DAP, with detection limits of 0.82 ng/mL, 12.82 pg/mL, 12.26 pg/mL, and 4.43 pg/mL for the basic colorimetric, photothermal, catalytic colorimetric, and colorimetric photothermal readout modes, respectively. This quadruplex-functional LFIA offers four different options with varying sensitivities and detection ranges, suitable for various application scenarios. It also allows multiple verifications for a single sample, enhancing detection accuracy.