3D multilayered sheet-like nanozyme enables the multiplex, flexible, and ultrasensitive detection of small-molecule drugs by immunochromatographic assay

The direct and sensitive detection of small molecules in complex samples without the use of complex instruments remains a challenge. Herein, we report an ultrasensitive dual-mode immunochromatographic assay (ICA) using a three-dimensional (3D) sheet-like nanozyme (GO/Au–AuPt) to mediate colorimetric–catalytic dual signal amplification. The 3D GO/Au–AuPt is exquisitely designed through the continuous construction of Au nanoparticles (NPs) and AuPt bimetallic NPs on flexible graphene oxide (GO) nanosheets. In the nanozyme, two-dimensional GO provides a massive surface area and high stability, hundreds of large AuNPs supply enhanced colorimetric ability and an extensive area of spherical surfaces, and tens of thousands of AuPt satellites act as spatial catalytic sites and generate superior peroxidase-like activity. The GO/Au–AuPt mediated ICA can simultaneously detect three important drugs, namely, gentamicin, clenbuterol, and ractopamine, in real complex samples (e.g., pork, chicken, lake water, and river water) with low detection limits of 0.011 ng/mL in direct mode (based on colorimetric signals) and achieves at least a 3.4-fold improvement in sensitivity and an 83.3-fold improvement in detection range by using catalytically enhanced signals. In addition, the testing process consists of only 15 min of chromatography time and 3 min of catalytic time. Therefore, the proposed method greatly improves the detection performance of existing colorimetric ICA techniques based on simple catalysis, thus showing considerable utilization potential for the real-time monitoring of small-molecule targets in different situations.