Surface-Enhanced Raman Spectroscopy Integrated Centrifugal Microfluidics Platform

This PhD thesis demonstrates (i) centrifugal microfluidics disc platform integrated with Au capped nanopillar (NP) substrates for surface-enhanced Raman spectroscopy (SERS) based sensing, and (ii) novel sample analysis concepts achieved by synergistical combination of sensing techniques and miniaturized fluid handling devices for facile quantitative and qualitative analysis of real-life sample matrices.
A nanofiltration approach based on a wicking (wetting) phenomenon of fluids on nanostructured surfaces was introduced. The method provides purification of complex suspensions by passing it through dense array of NP structures. Furthermore, the wicking assisted nanofiltration procedure was accomplished in centrifugal microfluidics platform and as a result additional sample purification was achieved through the centrifugation process. In this way, the Au coated NP substrate was utilized as nanofilter and SERS active surface at the same time.
To evaluate the efficiency of the nanofiltration technique, a well-known application case, detection of toxic melamine molecules in milk, was selected. According to the statistical SERS map analysis conducted on the purified sample region of the NP surface (2×4 mm²), the spectral response for melamine was 14 times higher as compared to the immersed and non-purified part of the chip. The quantitative study of melamine content with respect to the averaged peak intensity at 687 cm^-1 was in accordance with characteristic Langmuir adsorption curve behavior and the detection limit was estimated to be 10 parts per million (ppm).
The wicking based fluid sample transport was further investigated for simultaneous detection of multiple components in human urine solutions. Using the surface sensitivity of the SERS technique, affinity based chromatographic separation of urine compounds such as creatinine, uric acid and urea was achieved. Additionally, a unique and novel quantification procedure based on spectral profiles was presented.
Lastly, an alternative sensing approach was carried out using Au coated NP like structures on fused silica. By combining the advantages of electrochemical (EC) systems for quantitative analysis and the molecular specificity of SERS, a proof-of-concept study on detection of paracetamol in phosphate-buffered saline (PBS) was performed.