Application of Silver-Coated Magnetic Microspheres to a SERS-Based Optofluidic Sensor

Silver-coated magnetic microspheres (Fe3O4/Ag core/shell) were fabricated for use as a surface-enhanced Raman scattering (SEES) substrate. The surface morphology of the microspheres was characterized via field emission scanning electron microscopy and field emission transmission electron microscopy. Energy-dispersive spectroscopy was also employed to analyze the elemental composition of the structures. Malachite green was used as a model analyte to evaluate the performance of the microspheres as a SEES-active substrate and validate the SEES effect. The prepared microspheres possessed both magnetic and SEES properties. In addition, a microfluidic device with solenoids was designed and fabricated for a facile trace analysis. The solenoid chip allowed us to control the alignment of the magnetic microspheres on the wall of the microfluidic channel. Target samples were introduced into the channel and adsorbed on the surface of trapped silver-coated magnetic microspheres. SEES signals were then measured using a confocal Raman microscope. It is believed that a SEES-based optofluidic sensor with silver-coated magnetic microspheres can be successfully applied to microenvironmental analysis and other highly sensitive bioanalyses.