In Situ Self-Assembled Formation of Nitrogen-Rich Ag@Ti3C2 Film for Sensitive Detection and Spatial Imaging of Pesticides with Laser Desorption/Ionization Mass Spectrometry (LDI-MS)

Pesticide residues are hazardous to human health; thus, developing a rapid and sensitive method for pesticide detection is an urgent need. Herein, novel nitrogen-rich Ag@Ti3C2 (Ag@N-Ti3C2) was synthesized via an ecofriendly, ultraviolet-assisted strategy, followed by in situ formation of a highly homogeneous film on target carriers via a facile water evaporation-induced self-assembly process. Ag@N-Ti3C2 shows greater surface area, electrical conductivity, and thermal conductivity than Ti3C2. This Ag@N-Ti3C2 film overcomes the limitations of conventional matrixes and allows laser desorption/ionization mass spectrometry (LDI-MS) to provide fast and high-throughput analysis of pesticides (e.g., carbendazim, thiamethoxam, propoxur, dimethoate, malathion, and cypermethrin) with ultrahigh sensitivity (detection limits of 0.5-200 ng/L), enhanced reproducibility, extremely low background, and good salt tolerance. Furthermore, the levels of pesticides were quantified with a linear range of 0-4 μg/L (R2 > 0.99). This Ag@N-Ti3C2 film was used for high-throughput analysis of pesticides spiked in traditional Chinese herbs and soft drink samples. Meanwhile, high-resolution Ag@N-Ti3C2 film-assisted LDI-MS imaging (LDI MSI) was used to successfully explore spatial distributions of xenobiotic pesticides and other endogenous small molecules (e.g., amino acids, saccharides, hormones, and saponin) in the roots of plants. This study presents the new Ag@N-Ti3C2 self-assembled film equably deposits on the ITO slides and provides a dual platform for pesticide monitoring and has the advantages of high conductivity, accuracy, simplicity, rapid analysis, minimal sample volume requirement, and an imaging function.