Sensitive colorimetric and fluorescence dual-mode detection of thiophanate-methyl based on spherical Fe3O4/GONRs composite nanozyme

Pesticide detection based on nanozyme is largely limited in terms of the variety of pesticides. Herein, a spherical and well-dispersed Fe 3 O 4 /graphene oxide nanoribbons (Fe 3 O 4 /GONRs) composite nanozyme was applied to firstly develop an enzyme-free and sensitive colorimetric and fluorescence dual-mode detection of thiophanate-methyl (TM). The synthesized Fe 3 O 4 /GONRs possess excellent dual enzyme-like activities (peroxidase and catalase) and can catalyze H 2 O 2 to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB). We found that Fe 3 O 4 /GONRs can adsorb TM through the synergistic effect of multiple forces, thereby inhibiting the catalytic activities of nanozyme. This inhibition can modulate the transformation of TMB to oxTMB, producing dual responses of absorbance decrease (oxTMB) and fluorescence enhancement (TMB). The limits of detection (LODs) of TM were 28.1 ng/mL (colorimetric) and 8.81 ng/mL (fluorescence), respectively. Moreover, the developed method with the recoveries of 94.8–100.8% also exhibited a good potential application in the detection of pesticides residues in water and food samples.