Applications in Surface Enhanced Raman Spectroscopy

Doctoral thesis, 2004

The aim of this thesis is to address specific applications of Raman spectroscopy and specifically surface enhanced Raman spectroscopy, SERS. It includes an introduction to the techniques and several applications. The focus has been on how to achieve high precision SERS measurements, both qualitatively and quantitatively. The overall goal has been to measure biomolecules in complex matrices, such as chemotherapeutic drugs in human blood plasma and in single living cells. The capability to perform these SERS measurements offers exciting possibilities for development of new analytical methodology to be used to improve medical treatment protocols. Surface enhancement was achieved utilising metal colloids, and multivariate statistics have been used throughout this work to aid spectral interpretation. This combination has enabled quantitative studies, and allowed extraction of as much information as possible in spite of the, at times, low signal to noise ratios. Specifically, we have shown that in the complex matrix, blood plasma, with many overlapping spectra, it was possible to identify the spectra of doxorubicin (Paper I). The PCA analysis of spectra led to a feasibility study to quantify doxorubicin in plasma with SERS and PLS modelling (Paper II). The detection limit of doxorubicin in 1 % plasma was 70 nM, which corresponds to 7 µM in whole blood samples. A step towards quantification of chemotherapeutic drugs in lymphocytes was taken when rhodamine 6G was detected simultaneously with the intrinsic components of the cell (Paper III). Rhodamine 6G has the same pathway into and within the cell as doxorubicin, and is also a substrate for glycoprotein The aim of this thesis is to address specific applications of Raman spectroscopy and specifically surface enhanced Raman spectroscopy, SERS. It includes an introduction to the techniques and several applications. The focus has been on how to achieve high precision SERS measurements, both qualitatively and quantitatively. The overall goal has been to measure biomolecules in complex matrices, such as chemotherapeutic drugs in human blood plasma and in single living cells. The capability to perform these SERS measurements offers exciting possibilities for development of new analytical methodology to be used to improve medical treatment protocols. Surface enhancement was achieved utilising metal colloids, and multivariate statistics have been used throughout this work to aid spectral interpretation. This combination has enabled quantitative studies, and allowed extraction of as much information as possible in spite of the, at times, low signal to noise ratios. Specifically, we have shown that in the complex matrix, blood plasma, with many overlapping spectra, it was possible to identify the spectra of doxorubicin (Paper I). The PCA analysis of spectra led to a feasibility study to quantify doxorubicin in plasma with SERS and PLS modelling (Paper II). The detection limit of doxorubicin in 1 % plasma was 70 nM, which corresponds to 7 μM in whole blood samples. A step towards quantification of chemotherapeutic drugs in lymphocytes was taken when rhodamine 6G was detected simultaneously with the intrinsic components of the cell (Paper III). Rhodamine 6G has the same pathway into and within the cell as doxorubicin, and is also a substrate for glycoprotein P-gp. In order to facilitate the spectral interpretation of the mapped cells, multivariate chemical imaging methods in high noise surface enhanced Raman images were developed further to streamline the analysis work (Paper IV).