Highly-efficient SERS detection for E. coli using a microfluidic chip with integrated NaYF4:Yb,Er@SiO2@Au under near-infrared laser excitation

A reliable NaYF4:Yb,Er material assembled from Au (UC@SiO2@Au), as the substrate, was firstly integrated into a microfluidic chip and employed to detect R6G and E. coli by surface enhanced Raman spectroscopy (SERS) under a near-infrared excitation. In this microfluidic SERS chip, NaYF4:Yb,Er can convert near-infrared (NIR) light into visible light to promote localized surface plasmon resonance (LSPR) of gold nanoparticles to enhance the SERS signal. Moreover, a microfluidic chip could provide a good survival environment of bacteria, and NIR laser had a relatively smaller damage to the E. coli to improve stability of SERS signals of bacteria. According to synthesis conditions, the SERS substrate was fabricated and evaluated in a microfluidic chip. It shows uniformity with RSD of 11.5% for the Raman vibrations at 926 cm−1, and sensitivity with detection limits of 10−9 M for R6G under a 785 nm excitation. And it also exhibited an excellent sensitivity and stability for E. coli SERS detection under the near-infrared laser excitation. The advantages of NIR excitation in our SERS sensing expands the application range of the microfluidic SERS chip, and also promise a new research direction for the synthesis and applications of SERS-active nanostructures.