Rapid, one-step preparation of SERS substrate in microfluidic channel for detection of molecules and heavy metal ions.

On-chip fabrication of surface-enhanced Raman spectroscopy (SERS)-active materials enables continuous, real-time sensing of targets in the microfluidic chip. However, the current techniques require the time-consuming, complicated process and costly, bulky facilities. In this work, we present a novel method for synthesis of Ag nanostructures in a microfluidic channel via one-step electroless galvanic replacement reaction. The whole reaction could be achieved <10 mins, while the traditional methods take hours. The microfluidic channel has a Cu base, which can reduce Ag ions to Ag nanoparticles in the presence of AgNO3 solution. The new technique enables the label-free sensing of chemical molecules (i.e., methylene blue) and biomolecules (i.e., urea). Two proof-of-concept experiments are performed to verify the utilization of the prepared SERS substrate. First, the microfluidics-assisted SERS sensor is used to detect Hg ions in aqueous solution with high sensitivity and good selectivity. Second, the fabricated SERS-active material can couple with a concentration gradient generator for continuous SERS detection. This simple technique can be used in any laboratory without any bulky equipment and can realize numerous lab-on-a-chip applications with the integration of other microfluidic networks.