Electrochemical-Surface Enhanced Raman Spectroscopic (EC-SERS) Study of 6‑Thiouric Acid: A Metabolite of the Chemotherapy Drug Azathioprine

6-Thiouric acid (6-TUA) has the potential to be an important biomarker for the action of 6-mercaptopurine (6-MP), an immunosuppressive drug used in patients suffering from acute lymphoblastic leukemia (ALL). 6-TUA, a nonactive metabolite of 6-MP, is excreted in the urine, and routine monitoring of this metabolite can be useful in assessing the efficacy of 6-MP for immune system suppression in patients who have undergone stem cell replacement. In this work, electrochemical surface-enhanced Raman spectroscopy (EC-SERS) is used for the first time to study the adsorption and electrochemical behavior of 6-TUA at a nanostructured silver electrode surface, in both 0.1 M NaF and synthetic urine as supporting electrolytes. In addition, ab initio calculations were completed in an effort to understand the adsorption behavior. It was found that EC-SERS provided excellent signal for 6-TUA down to μM concentrations in synthetic urine and highlights the future potential of EC-SERS for rapid detection of important urine biomarkers at the patient point-of-care