Detection of Melanoma Cancer Biomarker Dimethyl Disulfide Using Cavity Ringdown Spectroscopy at 266 nm.

Skin cells emit volatile organic compounds (VOCs), and some of them can be used as biomarkers for screening specific diseases. Dimethyl disulfide (DMDS) has been recently reported as a biomarker of melanoma skin cancer (Kwak et al. "Volatile Biomarkers from Human Melanoma Cells". J. Chromatogr. B. 2013. 931: 90-96.). With the motivation of diagnosing melanoma using DMDS as its biomarker, we explore the potential of measuring DMDS using an advanced laser spectroscopic technique as an alternative method. We report on the first DMDS measurements using an experimental system based on cavity ringdown spectroscopy (CRDS). The test samples were mixtures of DMDS vapor and nitrogen in different concentrations. Two sampling methods were investigated to dilute the DMDS sample to low concentrations for ringdown measurements. The results showed that the ringdown system responded to various DMDS concentrations linearly and a theoretical detection limit of sub-ppb (parts per billion) could be achieved at the absorption wavelength of 266 nm. This ringdown system exhibited a high dynamic range for DMDS measurements, from ppm (parts per million) to ppt (parts per trillion) levels, given different laser wavelengths used. The feasibility of developing a portable melanoma screening sensor using the CRDS technique was also demonstrated in this study.