Electrochemical Deposition of Nanostructures on a Microelectrode Platform for Surface Enhanced Raman Scattering Applications
The demand for point-of-use sensors continues to increase as the dangers to human health and wellbeing from new bio-chemical hazards, illicit drugs and toxicants continue to rise. To allow for early, cost-effective and decentralized chemical analysis, the next generation of sensors need to be portable, rapid, affordable and user-friendly. Surface-enhanced Raman scattering (SERS) is a water compatible, non-destructive, label-free sensing mechanism that can identify and quantify different chemical compounds in liquid and solid samples. Microelectrodes have previously been shown to produce SERS substrates, albeit with very poor surface coverage and limited to laboratory testing. The objective of this thesis is to study a novel approach for combining microelectrodes and electrochemical deposition, in order to form extensive SERS active structures devoid of said limitations. In this work, we establish that an alternating electrical current can successfully be used to reduce silver ions to form SERS active dendritic nanostructures without damaging the microelectrodes or oxidizing the reduced metal. The nanostructures form in a distinctive manner to standard deposition processes. Here the nanostructures grow along the insulating substrate from all edges of the electrodes, capable of reaching lateral lengths near 300 μm with nm features. The role(s) that electrical parameters, surface interactions and solution composition play in the deposition process are studied to identify the parameters and conditions needed to promote the two-dimensional growth and maximize the SERS enhancement of the nanostructures. Furthermore, it is demonstrated that the formed nanostructures could act as concentration amplification devices, accelerating and localizing analyte adsorption from solution, a unique feature for SERS substrates. The SERS substrates are compatible with a handheld Raman spectrometer, therefore amenable for point-of- need sensing. Finally, it is shown that these SERS substrates can serve as scaffolds for forming Ag/Au bimetallic nanostructures with enhanced chemical stability using a galvanic reaction. The synergy between SERS and chemometrics was explored as the nanostructures were used to identify and quantify toxicants in food and water. The combination of SERS, microelectrodes and chemometrics offers a great deal of promise for point-of-need testing as the nanostructures can be used alone or further augmented to improve compatibility with complex samples.