(337g) Analysis of Organophosphate Residue Detection on SOLID Surface Using QCM-D As Sensing Platform

Detection of residual organophosphates in food is of paramount importance in current scenario. The understanding of interaction of pesticides on chemically modified surface is the backbone of biosensor fabrication. Quartz crystal microbalance with dissipation is one of the most efficient techniques to analyze the interaction of organic molecules with silane modified surfaces making it desirable bio-sensing platform.

In this report, we have studied the real time adsorption of pesticide phorate and malathion on silica coated quartz crystal of QCM-D. The interaction study was first monitored on gold coated and unmodified silica coated crystal as reference. Further self-assembled monolayer was created on silica crystal using n-propyltrimethoxy silane (PTMS), octyltrimethoxy silane (OTMS), N-(3-(trimethoxysilyl) propyl) aniline and diethoxymethylphenyl silane. The interaction study was also monitored by using AFM analysis. Amount of pesticide adsorbed on surface was evaluated in terms of the mass and thickness change of quartz crystal which is calculated from frequency and dissipation factor change using Sauerbrey equation. Low value of dissipation factor (∆D) corresponds to stronger binding of pesticide on crystal. The overall results indicates that OTMS modified surfaces contributes mostly to the dissipation changes (∆D) or acoustic ratio (∆D/∆f). This surface shows largest amount of pesticide adsorption for both malathion and phorate which is correlated with the more hydrophobicity of the surface analyzed by contact angle measurements. The adsorbed amount of pesticide increases with increase in hydrophobicity of surface. The diethoxymethylphenyl silane also shows significant interaction as the phenyl group facilitates interaction with sulfur bond of pesticide. Further verification was done using Raman spectroscopy. The interaction study may be utilized further to fabricate sensors for pesticide detection.