Colloid filtration: A novel substrate preparation method for surface-enhanced Raman spectroscopy

Abstract

A new method for preparing a monodisperse layer of metal colloid particles is presented. Metal colloid particles are filtered onto the surface of an aluminum oxide capillary pore surface capture membrane using both vacuum and syringe filtration devices. Scanning electron microscope (SEM) images reveal that the metal particles can be deposited with very little aggregation. Electronic absorption spectra show that the concentration of particles on the surface can be controlled by varying the silver colloid solution concentration. The linear dynamic range of absorbance of particles on the surface is demonstrated to be at least one order of magnitude. Surface-enhanced Raman (SER) activity is observed for the compound 9-aminoacridine (AA) at 514.5 nm using a filtered silver colloid solution. The SER activity of AA is observed to be related to the degree of colloid aggregation on the surface. Surfaces with no aggregation have no SER activity at this wavelength. The syringe colloid filtration technique is a fast, inexpensive method for producing surfaces with a highly controlled metal particle geometry, extremely useful for comparisons between theoretical and experimental results. These surfaces are also ideal for theoretical substrate design.