The development of gold nanorod arrays in alumina as a substrate for multi-analyte SER(R)S sensing

Surface enhanced Raman spectroscopy (SERS) and the closely related surface enhanced resonance Raman spectroscopy (SERRS) play increasingly more important roles in both sensing and optical imaging applications. However, their widespread commercial use has been restricted in part by the lack of suitable substrates. Those currently available provide some but not all of the properties desirable in an ideal SERS substrate. Therefore, there is a need to provide a substrate with substantial signal enhancement with uniformity and repeatability of response over the entire surface. It is also advantageous for certain applications that the nanostructured substrate is also electrically conducting. The ideal substrate would also be capable of both single- and multi-analyte analysis, providing versatility through end user customisation to meet specific needs. In addition to robustness, ease of handling, surface regeneration and cost effectiveness are also desirable. This work details the progress made towards developing such a SERS substrate. The main focus was the electrochemical production of ordered gold nanorod arrays (AuNR) in a porous anodised aluminium oxide (AAO) template that enabled good control of morphology, height, width and the spacing between vertically orientated rods. Optimisation work performed on the AAO template fabrication significantly reduced 'pore branching' that had previously occurred at the top of the AAO template. Comparison studies of electrodeposited AuNR that were formed in the pores to create SERS substrates were carried out. A controlled etching step was developed to partially expose the AuNR while maintaining electrical contact. SERS studies were initially performed using two well-established reporter molecules, one resonant (malachite green) and one non-resonant (4-mercaptobenzoic acid) with the excitation laser. The signal enhancement achieved with the AuNR was vastly superior to that obtained from a commercially available substrate (Klarite®), a monolayer of gold nanoparticles (NP) and a thin gold film. The signal was found to be uniform over the whole surface. A number of cleaning methods were also explored to enable repeat use and surface regeneration over several cycles. An AuNR surface patterning method was also developed to multi-analyte detection on a single substrate. This comprised of AuNR 'dots', which can be individually functionalised. Finally, the application of the substrate for in-situ electrochemical studies was demonstrated in a specially designed flow-cell that allowed for controlled etching, cleaning and surface modification of the SERS substrate to be effected.Surface enhanced Raman spectroscopy (SERS) and the closely related surface enhanced resonance Raman spectroscopy (SERRS) play increasingly more important roles in both sensing and optical imaging applications. However, their widespread commercial use has been restricted in part by the lack of suitable substrates. Those currently available provide some but not all of the properties desirable in an ideal SERS substrate. Therefore, there is a need to provide a substrate with substantial signal enhancement with uniformity and repeatability of response over the entire surface. It is also advantageous for certain applications that the nanostructured substrate is also electrically conducting. The ideal substrate would also be capable of both single- and multi-analyte analysis, providing versatility through end user customisation to meet specific needs. In addition to robustness, ease of handling, surface regeneration and cost effectiveness are also desirable. This work details the progress made towards developing such a SERS substrate. The main focus was the electrochemical production of ordered gold nanorod arrays (AuNR) in a porous anodised aluminium oxide (AAO) template that enabled good control of morphology, height, width and the spacing between vertically orientated rods. Optimisation work performed on the AAO template fabrication significantly reduced 'pore branching' that had previously occurred at the top of the AAO template. Comparison studies of electrodeposited AuNR that were formed in the pores to create SERS substrates were carried out. A controlled etching step was developed to partially expose the AuNR while maintaining electrical contact. SERS studies were initially performed using two well-established reporter molecules, one resonant (malachite green) and one non-resonant (4-mercaptobenzoic acid) with the excitation laser. The signal enhancement achieved with the AuNR was vastly superior to that obtained from a commercially available substrate (Klarite®), a monolayer of gold nanoparticles (NP) and a thin gold film. The signal was found to be uniform over the whole surface. A number of cleaning methods were also explored to enable repeat use and surface regeneration over several cycles. An AuNR surface patterning method was also developed to multi-analyte detection on a single substrate. This comprised of AuNR 'dots', which can be individually functionalised. Finally, the application of the substrate for in-situ electrochemical studies was demonstrated in a specially designed flow-cell that allowed for controlled etching, cleaning and surface modification of the SERS substrate to be effected