Fabrication of Flexible AgNW@R-PDMS SERS Substrates by Sandpaper-Assisted Lithography for Surface Swab Capture of Fungicides

This study presents a cost-effective approach for fabricating flexible SERS substrates with deposited silver nanowires that is achieved through sandpaper-assisted lithography. Silver nanowires (AgNWs) are employed as a sensing element in the sandpaper-assisted soft lithography technique to fabricate a PDMS-based SERS substrate. The SERS activity of these substrates was tested using widely used fungicide molecules, viz., thiabendazole (TBZ) and thiram (TM). The as-fabricated substrate performed admirably in TBZ and TM and demonstrated an enhancement factor of 8.09 × 107 for TBZ and 7.68 × 108 for TM. It also exhibited a low limit of detection of 3.08 × 10–10 M for TBZ and 3.20 × 10–11 M for TM. Further, the uniformity analysis using point-to-point Raman measurements and Raman mapping also have shown promising results. The stability of these substrates was also tested for a period of 60 days with an interval of 10 days, which showed a relative standard deviation (RSD) of 15.77%. Moreover, this substrate not only offers Raman enhancement capabilities but also provides direct surface sampling capacity from fruit surfaces. This study provides a rapid and highly sensitive method for detecting trace amounts of residual fungicides present on fruit surfaces, as evidenced by experiments conducted on apple surfaces with the fabricated substrates.