Electrochemical SERS study of some endogenous components of human biofluids

The work describes electrochemical (EC) protocol suitable for preparation of copper electrodes which can be used as substrates in surface-enhanced Raman spectroscopy (SERS). These SERS-active electrodes have been used for electrospectral studies based on the combination of electrochemical and SERS analysis (EC-SRS analysis). Several endogenous bodyfluid components (urea, creatinine, uric acid, bilirubin) have been selected for the study because they can significantly affect the SERS-based determination of other analytes in bodyfluids (for example, drugs). The influence of the SERS-active electrode polarization (applied potential) and the pH level of the analyte solutions on the SERS signal and current value have been investigated. The polarization values corresponded to the maximum SERS signal are observed at negative values for all analytes (below −0.2 V vs. copper pseudo-reference electrode). The maximal SERS signal has been observed for most of the analytes in a neutral medium (at the optimum polarization value of the SERS-active electrode), and the weakest signal has been in an alkaline medium. The diminishing of EC-SERS signal at high pH values is explained by deprotonation of analyte molecules that deteriorates analyte adsorption onto the negatively polarized SERS-active electrodes. Analysis of the current-voltage curves has been used to estimate the possible influence of EC changes of the studied molecules on their EC-SERS signal. The results obtained in this work will be useful for the development of EC-SERS systems suitable for the determination of various endo- and exogenous compounds in human biofluids.