Sensitive and selective SERS probe for detecting the activity of γ-glutamyl transpeptidase in serum

γ-Glutamyl transpeptidase (GGT) has attracted considerable attention for its regulatory effect on glutathione metabolism in living organisms; further, its close relationship with physiological dysfunctions such as hepatitis and liver cancers has enhanced its applicability. Therefore, the accurate detection of GGT levels is particularly important for the early diagnosis of diseases. Thus, we herein report the development of a surface-enhanced Raman spectroscopic (SERS) probe, namely bis-s,s'-((s)-4,4'-thiolphenylamide-Glu) (b-(s)-TPA-Glu), that comprises of a γ-glutamyl moiety for detection of the GGT activity. In this system, detection was achieved by observing differences in the SERS spectral profiles of the b-(s)-TPA-Glu probe and its corresponding hydrolysis product that resulted from the catalytic action of GGT. This SERS probe system exhibited a high selectivity toward GGT due to a combination of its specific catalytic action and the distinctive spectroscopic fingerprint of the SERS technique. The developed SERS approach was also found to be approximately linear in the range of 0.2-200 U/L, and a limit of detection of 0.09 U/L was determined. Furthermore, the proposed SERS method was suitable for detection of the GGT activity of clinical serum samples and also for evaluation of the inhibitors of GGT. Consequently, this approach is considered to be a promising diagnostic and drug screening tool for GGT-associated diseases.