(Europe Section Alessandro Volta Medal) Electrochemical SERS on Nanostructured Surfaces and its Application to DNA Detection and Discrimination

Abstract

Electroplating through self-assembled templates formed from close packed arrays of uniform colloidal particles allows the controlled deposition of thin films of metals that contain regular hexagonal arrays of uniform pores. The size of these pores can be systematically varied by varying the size of the colloidal particles and the thickness of the film by controlling the charge passed in the deposition. Removal of the template leaves a supported thin film containing an array of interconnected spherical segment voids. These sphere segment void (SSV) nanostructured films are ideally suited electrode surfaces for SERS because the structures are robust and reproducible and because the plasmonics of the surface are controlled by the geometry. We have investigated the origins of the surface enhancement on SSV surfaces by varying the film thickness and template sphere diameter and by looking at the angular dependence. The intensity of the SER spectra varies with all of these factors indicating that the precise geometry of the structured surface and the excitation of surface plasmons is important [1]. These surfaces can be used for practical applications in SERS, for example in in situ electrochemical studies [2]. Combining the extreme surface sensitivity of SERS with control of the electrode potential we have been able to use these SSV electrodes as a platform for very sensitive detection and discrimination of DNA sequences [3]. This new method uses a probe DNA strand bound to the gold SSV electrode surface and then uses the SERS to detect the presence of double stranded DNA formed when the target DNA binds to the probe strand at the surface. By sweeping the applied potential cathodic the dsDNA strands can be made to separate and the potential at which this separation occurs can be used to discriminate perfectly matched dsDNA from mismatched cases thus allowing discrimination of single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs) [4].