Label-free protamine-assisted colorimetric sensor for highly sensitive detection of S1 nuclease activity
A label-free, sensitive, simple and general colorimetric method was reported to monitor S1 nuclease activity based on protamine-assisted aggregation of gold nanoparticles (AuNPs). Here, protamine, a linear polycation, was used as a medium for causing the aggregation of negatively charged AuNPs by electrostatic interaction, which resulting in the changes of surface plasmon resonance (SPR) absorption bands as well as color of AuNPs. Here, the AuNPs was employed as an indicator to report the level of S1 nuclease in the solution. Substrate DNA could be cleaved into small fragments by specific S1 nuclease, which effectively prevents the electrostatic interaction between DNA and protamine and thus facilitate the interaction between protamine and AuNPs. The quantitative analysis of S1 nuclease activity can be done via direct measuring the changes of absorption spectra of AuNPs. Using S1 nuclease as a model analyte, the limit of detection was estimated to be 1.0×10-4 U/mL. Furthermore, the proposed concept has been successfully applied in S1 nuclease analyzing from serum samples, offered ultrasensitive strategy for speedy detection of nuclease activity and revealed a new avenue for high-throughput screening of nucleases and drug with potential inhibition properties.