Fiber Optic SERS Sensor with Silver Nanocubes Attached Based on Evanescent Wave for Detecting Pesticide Residues

Surface-enhanced Raman scattering(SERS) has great potentialinthe field of rapid detection of pesticide residues in food. In thispaper, a fiber optic SERS sensor excited by evanescent waves was proposedfor efficient detection of thiram. Silver nanocubes (Ag NCs) wereprepared as SERS active substrates, which had much stronger electromagneticfield intensity than nanospheres under laser excitation due to muchmore "hot spots". By using the method of electrostaticadsorption and laser induction, Ag NCs were uniformly assembled atthe fiber taper waist (FTW) for enhancing the Raman signal. Differentfrom the traditional way of stimulation, evanescent wave excitationgreatly increased the interaction area between the excitation andanalyte, while reducing the damage of the excited light to the metalnanostructures. The methods proposed in this work have been successfullyused to detect the pesticide residues of thiram and showed good detectionperformance. The detection limits for 4-Mercaptobenzoic acid (4-MBA)and thiram were determined to be 10(-9) and 10(-8) M, the corresponding enhancement factor could be1.64 x 10(5) and 6.38 x 10(4). Low concentrationof thiram was detected in the peels of tomatoes and cucumbers, indicatingits feasibility in actual sample detection. The combination of evanescentwaves and SERS provides a new direction for the application of SERSsensors, which had great application potential in the field of pesticideresidue detection.