A dual-mode optical sensor for sensitive detection of saxitoxin in shellfish based on three-in-one functional nanozymes

Saxitoxin (STX), one of paralytic shellfish poison neurotoxins with high toxicity, posing a significant threat to seafood safety. Therefore, it is of great need to protect human health by screening STX contaminated seafood samples. In this study, to achieve specificity for STX, molecularly imprinted polymers (MIP) were fabricated on Au-Pt nanoparticles modified Fe3O4 magnetic nanozymes (MS@Au-Pt NZs) with numerous memory cavities (MS@Au-Pt/MIP), which catalyzed the oxidation of 3,3 ',5,5 '-tetramethylbenzidine (TMB). STX will occupy the recognition cavity of MIP and obstruct the catalytic site of MS@Au-Pt, thus hindering the color development reaction, and the oxidized TMB (oxTMB) can be measured by Raman spectroscopy and recorded with Raman signals. Under the optimal conditions, the MIDMs method obtained a wide linear range for colorimetric assay (0.01 mu M to 100 mu M) and Raman detection (0.1 nM to 100 nM), with limits of detection (3 sigma/S, n=3) of 3.1 nM and 0.03 nM, respectively. As a proof-of-concept, the approach showed acceptable recoveries of 78.0 similar to 96.2% in real samples of mussel and clam. The dual-mode optical sensor, therefore, is hopeful to be a potential candidate for sensitive and accurate detection of STX in seafood.