Development of SERS-based Solenoid Microfluidic Sensor

Abstract

Optical nanoparticles are extensively used as efficient detection probes in biomedical or environmental science. In this research, we fabricated silver-coated superparamagnetic (Ag@Fe3O4) beads and used them as highly sensitive surface-enhanced Raman scattering (SERS) templates in a solenoid-type microfluidic channel. SERS technique, using core-shell type micro-beads, provides a highly sensitive immunoassay protocol compared to a conventional immunoassay method such as ELISA or SPR. For this purpose, Ag@Fe3O4 beads have been prepared by the following procedures. First, gold nanoparticles (Au NPs) were seeded on the surface of micro-size superparamagnetic spheres by electrostatic interactions. Then, Au seeds on Fe3O4 beads were reduced by Ag ions and they were grown up again. These Ag@Fe3O4 beads have been characterized using the field emission scanning electron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. For a sequential immunoassay in a microfluidic channel, a microfluidic device integrated with solenoids has been fabricated. This solenoid chip allowed manipulates the magnetic field distribution, and the use of magnetic beads allowed the control of substrate beds with simple magnetic field manipulations. Target samples were introduced into the channel and on the surface of immobilized Ag@Fe3O4 beads in the channel wall. Then Raman signals were measured using the confocal Raman microscope. Here, we report a novel analytical technique using the SERS optofluidic sensor and Ag@Fe3O4 beads. We expect this SERS sensor, in combination with a solenoid lab-on-a-chip and superparamagnetic baeds, can be successfully applied to micro-environmental analysis as well as other highly sensitive bio-analyses.