Telomerase Activity Assay via 3,3′,5,5′-Tetramethylbenzidine Dilation Etching of Gold Nanorods

The level and activity of telomerase are often considered as an important tumor biomarker index in clinical diagnosis. In this work, we developed a rapid and sensitive telomerase activity assay based on the 3,3′,5,5′-tetramethylbenzidine dilation (TMB2+) etching of gold nanorods (AuNRs) at a single-particle level. In principle, telomerase primers are triggered by telomerase to extend and form a hemin/G-quadruplex DNAzyme, which then catalyzes the hydroxyl radical oxidation of TMB to TMB2+, which in turn is able to efficiently etch gold nanorods (AuNRs), making the localized plasmonic resonance (LSPR) scattering features change under dark-field microscopy (DFM). Compared to the common strategy of direct etching of AuNRs based on a hydroxyl radical that has a short lifetime (3 μs), the TMB2+ is much more stable and greatly overcomes the drawbacks of the hydroxyl radical that is not able to effectively etch AuNRs owing to its short lifetime. The LSPR DFM scattering intensity reduction was found to have a good linear relationship with the telomerase level in the range of 100–24 000 cells and the limit of detection (LOD) reaching 43 cells. Telomerase extracted from different cancer cells such as MCF-7, HeLa, and HepG2 demonstrated good accuracy of this assay, showing that this TMB2+ etching strategy of AuNRs for the telomerase activity assay is successful and reliable.