SERS substrates based on flexible and transparent PDMS supports with periodic hierarchical structure for in-situ detection of pesticide residues

In this work, hierarchical structure composed of periodic nanopillars and wrinkles was designed on flexible and transparent PDMS through a strategy combining template method and oxygen plasma treatment. Investigations on the SERS performance of the substrates obtained after Ag thermal deposition reveal both the nanopillars and the wrinkles contributed greatly to the enhancement. The formation of the periodic wrinkles followed the buckling theory. Under the condition of 30 % deformation and 40 W plasma power, by adjusting the deposition time to 30 min, dense distribution of Ag NPs on the hierarchical PDMS support was achieved while avoiding coverage of the nano wrinkles. The obtained substrate named Ag-30/PDMS-PW had an EF of 3.11×10 7 , excellent uniformity and outstanding reproducibility with an RSD of 2.13 % and 4.9 % respectively. Cyclic loading and tensile tests verify the mechanical stability and perfect elasticity of the Ag-30/PDMS-PW substrate. Coupled with the bi-direction excitation ability, the as-prepared substrate was fully qualified for in-situ detection of pesticide residues, which was demonstrated by the in-situ detection of thiram and thiabendazole on apple surface with concentrations lower than the maximum residue limits. The results manifest the proposed substrate has great potential for in-situ food safety monitoring in real-world applications.