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Detection of thiram on fruit surfaces and in juices with minimum sample pretreatment via a bendable and reusable substrate for surface-enhanced Raman scattering.

BACKGROUND
Surface-enhanced Raman scattering (SERS) substrates based on metallic nanoparticles locked in some flexible materials have great potential for rapid detection of pesticide residues in foods, but these substrates are generally not reusable.


RESULTS
A bendable and reusable sponge based on polydimethylsiloxane (PDMS) and Au nanospheres was synthesized and employed as SERS substrate to analyze thiram on the surfaces of apples and grapes (20-1000 ng cm-2 ) and in their juices (0.5-5.0 mg L-1 ) with minimum sample pretreatments. The lowest detectible concentrations for thiram in fruit juices and on fruit skins were 0.5 mg L-1 and 20 ng cm-2 , respectively. The Au-PDMS substrate had acceptable intro-reproducibility for SERS analysis of thiram in fruit juices and on fruit skins, resulting 3.6-16.9% relative standard deviation (RSD) for the SERS signal of the primary peak of thiram. Moreover, the Au-PDMS substrate exhibited distinguished reusability and stability, which could provide reproducible SERS signal of thiram in apple juice even after the substrate being reused for 10 times (RSDs for the three major characteristic peaks of thiram were 2.7-10.5% during the 10 reused cycles).


CONCLUSIONS
This flexible and reusable Au-PDMS SERS substrate for thiram detection could be readily extended to the analysis of other trace chemicals in a broad range of foods, providing a new possibility of SERS application. This article is protected by copyright. All rights reserved.