To prepare silver nitrate solution, measure 0.0017 grams of AR grade silver nitrate on a weighing balance. Add the weighed powder to 10 milliliters of deionized water and stir the mixture. Draw one milliliter of AR grade ammonia water using a syringe and add it to the silver nitrate solution while stirring, until the solution becomes clear.
To prepare 0.2 molar glucose solution, weigh 0.36 grams of glucose powder and add it to 10 milliliters of deionized water. Stir the mixture thoroughly. Next, using a pipette gun, add 30 microliters of the silver ammonia complex into the glucose solution at 30 minute intervals.
To synthesize yellow colored silver nanoparticles. To synthesize the PDMS substrate, take five grams of PDMS A solution and add B solution into it, at a ratio of one to 10. Stir the mixture thoroughly.
Transfer the mixed PDMS into a square Petri dish and bake it in an 80 degree Celsius oven for two hours. Once cured, use a scalpel to cut the PDMS along the dark grid of the dish, creating small cubes. Next, move the handheld plasma processor back and forth over the PDMS piece for surface plasma treatment.
For APTES modification, immerse the surface modified PDMS pieces into 10%APTES solution for 10 hours. Finally, immerse the PDMS substrate into the silver nanoparticle solution for 10 hours. ESEM images showed uniformity in synthesized nanoparticles with diameters between 20 and 50 nanometers.
The Surface-Enhanced Raman Scattering signals for fabricated PDMS substrates displayed excellent detection capability, reaching a limit of 10 to the negative 10th molar for R6G with notable enhancement effect. The substrate also showed Thiram detection with clear characteristic peaks, up to 10 to the minus eighth molar. The paste and peel method on the apple surface show the detection of Thiram up to 10 to the minus seventh molar, indicating the effectiveness of the substrate for identifying pesticide residues on fruit surfaces.
