Sonication enhances the stability of MnO2 nanoparticles on silk film template for enzyme mimic application

We have developed an in-situ method using sonication (3 mm probe sonicator, 30 W, 20 kHz) and auto-reduction (control) to study the mechanism of the formation of manganese dioxide (MnO2) on a solid template (silk film), and its resulting enzymatic activity on tetramethylbenzidine (TMB) substrate. The fabrication of the silk film was first optimized for stability (no degradation) and optical transparency. A factorial approach was used to assess the effect of sonication time and the initial concentration of potassium permanganate (KMnO4). The result indicated a significant correlation with a fraction of KMnO4 consumed and MnO2 formation. Further, we found that the optimal process conditions to obtain a stable silk film with highly catalytic MnO2 nanoparticles (NPs) was 30 min of sonication in the presence of 0.5 mM of KMnO4 at a temperature of 20–24 °C. Under the optimal condition, we monitored in-situ the formation of MnO2 on the silk film, and after thorough rinsing, the in-situ catalysis of 0.8 mM of TMB substrate. For control, we used the auto-reduction of KMnO4 onto the silk film after about 16 h. The result from single-wavelength analysis confirmed the different kinetics rates for the formation of MnO2 via sonication and auto-reduction. The result from the multivariate component analysis indicated a three components route for sonication and auto-reduction to form MnO2-Silk. Overall, we found that the smaller size, more mono-dispersed, and deeper buried MnO2 NPs in silk film prepared by sonication, conferred a higher catalytic activity and stability to the hybrid material.