Abstract
Raman spectroscopy as a fast, highly selective and information-rich detection technique has been widely used in the field of analytics and bio-analytics. Surface enhanced Raman spectroscopy (SERS) has attracted considerable research interest, since it provides additionally high sensitivity by enhancing the Raman signal in the electromagnetic field near the metal nanostructures. SERS substrates with high uniformity are desired to guarantee reliable and reproducible quantitative analysis. Conventional metal-nanoparticle SERS systems employing randomly formed inter-particle nano-gaps as hot spots suffer from poor signal reproducibility. Consequently, for application especially in the quantitative measurements, nanogap-based SERS systems are usually associated with complementary techniques, such as microfluidic techniques and the introduction of internal standards.In order to develop SERS substrates with high uniformity and easy operation, we utilize the surface plasmons from the silver silicon core shell nanowire array for chemical and biological detection. The performances of the substrate in quantitative and multiplex detections are improved. Compared with the nanogap-based SERS substrate, Ag/SiNWs are hexagonally packed with an inter-wire distance of 150 nm, and the whole surface of silver film functions as an enhancing site. Therefore, analytes can easily enter the wide inter-wire open spaces and be uniformly adsorbed on the Ag/SiNW surface, leading to much improved spot-to-spot reproducibility of Raman signals over the substrate.
The incorporation of SERS detection into microfluidic channels enables fast, damage-free and information-rich sensing and analysis, and it thereby triggers considerable research interest. Ag/Si nanowire (NW) array embedded microfluidic chips were fabricated as an in-situ SERS monitoring platform. This on-chip SERS system not only provides highly reproducible SERS signals in liquid-based detection, but also is capable of large bio molecule detection, demonstrated by the detection of R6G and natural source double strand DNA, respectively. Such excellent SERS performances are attributed to the wide range and uniform enhancement field yielded by the propagating surface plasmons on ordered Ag/SiNW structure upon laser illustration.
The optical property of bare silicon nanowire array was also investigated. Finite Difference Time Domain (FDTD) simulation was carried out to predict the optical behaviour of silicon nanowire array with a diameter of around 100 nm. Experimentally, silicon Raman intensity and the fluorescence of dye molecules decorated on SiNW surface was used as an indicator of the energy inside and outside the SiNW respectively, to verify the existence of leaky mode. By utilizing the leaky mode excited by incident light on the silicon nanowire, the enhancement of the fluorescence signal of dyes and quantum dots was achieved, indicating the possibility of fabrication of metal-free fluorescent enhancement substrates.
| Date of Award | 27 Oct 2015 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Wenjun ZHANG (Supervisor) & Xianfeng CHEN (Supervisor) |