A microfluidic chip based on an ITO support modified with Ag-Au nanocomposites for SERS based determination of melamine

This article describes a microfluidic SERS chip-based rapid and high-throughput method for the determination of chemical and biological analytes, specifically of melamine. The chip consists of an indium tin oxide (ITO) glass plate modified with silver-gold nanocomposites (Ag-Au NCs) and a polydimethylsiloxane (PDMS) cover plate. The chip has five parallel microfluidic channels. The ITO glass provides electrical conductivity and has a smooth surface which makes it well suited for the deposition of the Ag-Au NC by electrodeposition and galvanic replacement. This technique allows good control of the morphology and composition of the composite. Under optimized conditions, the microfluidic SERS chip provides excellent sensitivity for 4-mercaptobenzoic acid (4-MBA). The detection limit is 0.1 nM and the SERS enhancement factor is 2.7x10(10). The chip exhibits good stability over time and good reproducibility, with a RSD of 8.6 % between the 5 micro-channels. The chip was successfully applied to the determination of melamine in milk with a 10 nM detection limit and an analytical range from 10 nM to 0.1 mM. It is demonstrated that the microfluidic SERS chip developed here shows great promise for use in biochemical assays.