Highly Reliable Surface-Enhanced Raman Scattering Sensors

Compared to infrared (IR) absorption spectroscopy, recently, researchers have recognized effective applications in various studying-fields by using Raman vibrational spectroscopy. Raman spectroscopy can be conveniently applied not only to in situ measurements of solid-liquid interfaces in fundamental as well as practical studies, but also to the porous and rough surfaces with high surface areas that are very difficult to study using many other surface techniques. With development of technologies of surface-enhanced Raman scattering (SERS), Raman signals of analytes now can be significantly enhanced by fourteen orders of magnitudes. Theses enhancements come not only from the increased surface areas of noble metals (Au, Ag and Cu), but also from the surface plasmon resonance of noble metals. Moreover, with development of technologies of laser sources used in Raman measurement, surface-enhanced resonance Raman spectroscopy (SERRS) can be developed by combining SERS effect with resonance-enhanced Raman scattering (RRS) effect. It results in significantly improving the obtained Raman enhancement factor (EF). Thus, SERRS has emerged as a promising spectroscopy for detections of probe molecules, even for single molecule, in various studying-fields. However, the accompanied disadvantage is its low reliability on spectrum. Existing electrochemical techniques generally have a very high sensitivity capable of detecting a molecular or atomic change in the interface at the submonolayer quantity. However, they have a poor time resolution at milliseconds unless microelectrodes or ultra-microelectrodes are used. Therefore, development on SERS technologies would be positioned on a higher level by using in situ EC-SERS measurements. In spite of the fact that thousands of papers on improvement of SERS enhancement have been published, the development of SERS technologies into a widely used tool has been slow. This phenomenon can be ascribed to the bad spectrum reliability in case of high SERS enhancement, which severely limited the range of SERS’s practical applications in sensors. Nowadays, many techniques are developed to obtain rough metals substrates with SERS activities. However, a controllable and reproduced surface roughness can be generated through control of conventional electrochemical oxidation-reduction cycles (ORC) procedure. In our laboratory, we got bounteous experiment experiences and satisfactory relative results on the preparations of noble metal nanoparticles (NPs) and SERS-active metal substrates based on EC methods. Recently, we are developing sonoelectrochemically pulsed dissolution-deposition cycles (SEPDDC) for preparation of SERS-active substrate. Primarily experimental results indicate that the corresponding EF is high. We also develop micro-treatment technology on glass substrate for its corresponding SERS reliability based on small water clusters (SWC), which are prepared from water in vicinity of illuminated noble metal NPs. Further applications based on these developing technologies are worthy of study. This plan aims to develop SERS-active substrates with both high EF and high reliability for SERS sensors based on EC methods in combinations with other technologies used in preparation of SERS substrates and with strategies used in increasing hot spots in SERS. In the first year, SEPDDC and micro-treatment based on SWC will be developed to prepare SERS-active substrates with both high EF and high reliability. In the second year, strategies on SERS sample preparations regarding increase of hot spots in SERS for molecules with and without S or N element will be developed for reducing their limit of detection (LOD). Also, structure variations of probe molecules will be examined in combination with in situ SERS measurements. In the third year, the developed SERS techniques in the first two years are combined and applied in SERS sensors, such as sensors on prostate cancer and monosodium urate (MSU)-containing solution in gouty arthritis. (1) Establishment of the key technique in preparation of SERS-active substrate with high EF and high reliability by using SEPDDC method. (2) Establishment of the mechanisms of improved reproducibility of SERS-active substrate by using micro-treatment based on SWC. (3) Establishment of the key technique in preparation strategy on SERS sample for increasing hot spots and improving reliability in SERS. (4) Development of in situ SERS measurement technique for effectively reducing LOD of analytes. (5) Combining the developed techniques in preparing SERS-active substrate with high EF and high reliability for sensor application. (6) Using developed SERS techniques in sensor on cancer cell, and development of in situ EC-SERS technique for label-free biosensor.