Highly sensitive detection of tryptophan (Trp) in serum based on diazo-reaction coupling with Surface-Enhanced Raman Scattering and colorimetric assay.

Tryptophan plays an important role in the metabolic pathway and tryptophan metabolism is abnormal in tumor tissues. Therefore, Trp and its metabolites in body fluids can be used as tumor markers for cancer monitoring. However, the traditional tryptophan detection method has many shortcomings, such as low sensitivity, time-consuming and so on, which is difficult to meet the clinical needs. Herein, a rapidly, sensitive and reliable method for indirectly detecting Tryptophan (Trp) in serum was proposed by combining diazo-coupling reaction mechanism with surface-enhanced Raman scattering (SERS). The limit of detection (LOD) of Trp can be as low as 20 nM, which is much lower than existing detection methods. In addition, because of obvious change in color in diazo-coupling reaction, a colorimetric detection was applied for convenient determination of Trp in the concentration ranged from 3 × 10 - 10 M. Furthermore, with the support of good results by SERS assay, the presented method was successfully carried out for the determination of Trp in serum that came from healthy people and colorectal cancer patients. Comparing the difference of Trp content in serum between the two groups, it was found that tryptophan metabolism disorder exists in colorectal cancer patients, which suggested that the accurate detection of tryptophan content may provide important reference for the pathogenesis, prediction and prevention of colorectal cancer.