A Study of The SERS-based Decoding Strategy on Multiplex Suspension Array with Micro Beads

Abstract

This dissertation is focused on a barcoding strategy using Surface-enhanced Raman Scattering (SERS) for bead-based multiplex analysis. Barcoding or the indexing strategy for the probe particle is most important factor to quantify and classify the information for the suspension array assay. In this work, the author shows a practical implementation of the SERS decoding strategy for the suspension array assay that existed only in theory and explored the possibility of SERS as a barcoding strategy for a multiplex suspension array as follow: i) consecutive SERS signal acquisition from micro beads moving in a microfluidic channel

ii) simultaneous detection of SERS and fluorescence signals from micro beads, and iii) fluorescence quantification and SERS decoding with micro beads for the suspension array. First, the micro spherical gold beads were fabricated using electroless plating on PMMA beads and elegantly optimized to produce the effective SERS signals. The achieved beads produced well-defined SERS spectra even at an extremely short exposure time for a single bead combined with Raman tags such as 2-naphthalenethiol (2-NT) and benzenethiol (BT). The consecutive SERS spectra from a variety of combinations of Raman tags were successfully acquired from the beads at static and moving conditions. The proposed Raman tagged micro beads exhibited the potential of an on-chip microfluidic SERS decoding strategy for a micro suspension array. Second, simultaneous detection of SERS and fluorescence signals using a single excitation source was shown with individually functionalized micro beads that can be applied to array-based multiplex analysis. The author chose proper beads that can produce well-defined SERS spectra and carefully engineered micro beads with a biomarker. The functionalized micro beads successfully worked dependently, with not only the decoding function of the Raman tags but also with the probing function for analytes. Above all, author achieved simultaneous detection for SERS and fluorescence signals while avoiding signal overlapping between the two by carefully selecting the detection ranges. Finally, based on the achieved technologies, the author demonstrates the flow cytometer that can measure fluorescence and SERS signals from a single micro bead in the flow. The flow cytometer includes pump controllable microfluidics and a customized Raman and fluorescence system and it can provide two pieces of independent information which is decoding results from the encoded Raman tags and quantifying the results from the fluorescence of the modified bead. Through this, the author shows that the SERS could be a useful decoding strategy for suspension arrays.