Sensitive and label-free quantification of cellular biothiols by competitive surface-enhanced Raman spectroscopy

A label-free surface-enhanced Raman spectroscopy (SERS)-based method for the rapid quantification detection of cellular biothiols at picomolar levels was developed by using a mechanism of binary competitive adsorption to regulate the plasmon coupling behavior of gold nanoparticles (Au NPs). 4,4'-Dipyridyl (Dpy), a small organic ligand with two symmetrically located pyridine rings, was used to shorten the inter-particle space and generate a multitude of "hot spots", which in turn amplified the fingerprint signals of Dpy molecules. When biothiols were introduced into the Dpy-containing solution of Au NPs, they competitively adsorbed to the metal surface through the much stronger S-Au linkage, leading to the disaggregation of Au NPs and SERS quenching of Dpy molecules. The change of SERS responses was quantitatively related to biothiols added to the solution, and the detection limit down to 0.14 pM for GSH was facilely achieved without any pre-concentration. The total assay time, including data analysis was within 8 min. Finally, the SERS-based method was successfully applied to measure cellular biothiols, indicating its potential applicability in biological and biomedical research.