Optical properties of surface-enhanced Raman-active capture matrices

Silver and gold colloidal particles can be immobilized on amine-derivatized magnetic microparticles. Once immobilized, the colloidal particles can be reacted with thiols to form a self-assembled monolayer (SAM). Earlier it was shown that the resultant derivatized magnetic microparticles, i.e., capture matrices, are surface-enhanced Raman (SERS) active and that they can be used to extract trace amounts of analyte from an aqueous sample. In this investigation, the optical properties of the capture matrices are examined. Imaging of these magnetic microparticles shows that the immobilized silver/gold colloidal particles exhibit blinking behavior. An increase in the SERS signals due to the SAM and the continuum is observed with constant laser illumination of these magnetic microparticles. Such an increase can be used to improve sensitivity. This increase in signal is attributed to the electromagnetic enhancement mechanism (EEM).