A highly reliable, integration-time and laser-power independent, self-referenced SERS sensor with an extended dynamic range for the detection of melamine in milk

Abstract

An ultrasensitive nanosculptured thin film (nSTF) based self-referenced SERS sensing platform for the detection of melamine in milk samples is developed. The self-referenced SERS platform consists of a monolayer of 4-aminothiophenol (4-ATP), sandwiched between Ag nSTF and Ag nanoislands (NIs), deposited over a Si substrate. The SERS signal from the sandwiched 4-ATP monolayer acts as a self-referenced signal. The self-referenced platform offers the advantage of independence of Raman signal on the laser power, integration time of the detector of the spectrometer, or ambient conditions. The dynamic range of the sensor, mostly limited by the limits on laser power and integration time of spectrometer, can now be extended due to the independence of the sensor from these two parameters. A significant enhancement in the Raman signal of rhodamine 6G of the order of 1013 is achieved for the SERS active substrate. The self-referenced SERS sensor offers a linear response over the extended dynamic range from 0.001 to 10 ppm for melamine in spiked milk samples. The achieved limit of detection for melamine in spiked milk samples is 1 ppb. The self-referenced sensor will be of great value for real-time detection of melamine in milk samples, and food safety.