Abstract: Abnormal S-nitrosothiol metabolism is involved in many different diseases, ranging from asthma to septic shock. A critical limitation of current methods for quantifying S-nitrosothiols present in vivo is that samples need to removed be from the body for analysis. The technology of the present disclosure determining S-nitrosothiol levels in situ using ultraviolet light to cleave the S—N bond, releasing the nitric oxide, collecting the nitric oxide, and measuring the nitric oxide.