A simple and universal “turn-on” detection platform for proteases based on surface enhanced Raman scattering (SERS)

• “Turn-on” SERS-based enzymatic assay is newly proposed.
• The method works on catalytic property of trypsin to cleave peptides.
• Ultrasensitive detection of target was achieved together with potential as a SERS-based label-free approach.
• We proved the universality of the method as a general approach for proteases.

We describe herein a novel' “turn-on” SERS-based strategy for protease detection based on surface enhanced Raman scattering (SERS) and the mediation of spacing between 4-mercaptobenzoic acid (4-MBA) labeled gold nanoparticles (AuNPs) through enzyme assays. The method employed non-cross-linking aggregation of 4-MBA-modified AuNPs by peptides after treatment with target protease. Thus, SERS signals of 4-MBA are sharply increased because of the decreased electrostatic stability of AuNPs that initiated gold nanoaggregates incorporating Raman reporter molecules due to the formation of “Hot Spots”. Through this strategy, a novel and facile “turn-on” SERS biosensor for trypsin and thrombin based on enzymatic cleavage activity is established with sensitivity, selectivity and simplicity as AuNPs and peptides are easily accessible. Compared with other methods, this newly proposed method has improved sensitivity. The limit of detection was 85 fM (at the ratio of signal to noise, S/N=3:1) for trypsin. Controlled experiments showed that the method exhibited good selectivity over other proteases. We also proved that this principle could be easily adapted to detection of other proteases such as thrombin. The method demonstrated the capability for application in complex matrix samples. The results also presented the potential and superiority of SERS biosensor as a general approach for proteases based on enzyme activity.