Effect of Metal Nanoparticle Aggregate Structure on the Thermodynamics of Oxidative Dissolution

Dual-Role Peptide with Capping and Cleavage Site Motifs in Nanoparticle-Based One-Pot Colorimetric and Electrochemical Protease Assay

A new method for enzyme substrate assembly and its use in proteolytic enzyme assays with colorimetric and electrochemical detection is presented. The novelty of the method is the use of dual-function synthetic peptide containing both gold clustering and protease-sensitive moieties, which not only induces the simple formation of the peptide-decorated gold nanoparticle test substrates but also allows for the detection of proteolysis in the same batch. Protease-treated nanoparticles with a destabilized peptide shell became more prone to electroactivity, and thus, the model enzyme plasmin activity could be quantified with stripping square wave voltammetry analysis as well, giving an alternative method to conduct aggregation-based assays. Spectrophotometric and electrochemical calibration data proved to be linear within the 40-100 nM active enzyme concentration range, with possible extensions of the dynamic range by varying substrate concentration. The simple initial components and the ease of synthesis make the assay substrate preparation economic and easy to implement. The possibility of cross-check analytical results with two independent measurement techniques in the same batch greatly increases the applicability of the proposed system.

Electrochemical Mechanism of Oxidative Dissolution of Silver Nanoparticles in Water: Effect of Size on Electrode Potential and Solubility

For the first time, an electrochemical mechanism of oxidative dissolution of silver nanoparticles in aqueous solutions is suggested and substantiated. The dissolution is caused by the occurrence of two interrelated electrochemical processes: (1) silver oxidation on a microanode and (2) oxygen reduction on a microcathode. According to the suggested model, the standard electrode potential of a nanoparticle decreases with a decrease in its size, which leads to an increase in the electromotive force of the oxidative dissolution of silver. A proportional dependence of the solubility of nanoparticles on their standard potential is revealed. An empirical equation is derived that relates the solubility of AgNPs to their electrode potential and size. In the course of oxidation, silver nanoparticles undergo aggregation with a gradual increase in the potential to the value characteristic of the bulk metal. This leads to the deceleration and practical cessation of the dissolution.

Multiwavelength Photothermal Imaging of Individual Single-Walled Carbon Nanotubes Suspended in a Solvent

Optical imaging of individual single-walled carbon nanotubes (SWCNTs) enables the characterization of heterogeneous SWCNT samples. However, previous measurement methods have targeted SWCNTs fixed on a substrate. In this study, absorption-contrast imaging of individual SWCNTs moving irregularly in a solvent was performed by simultaneous multiwavelength photothermal (PT) microscopy. Using this technique, heterogeneous samples containing semiconducting and metallic SWCNTs were characterized by absorption spectroscopy. The semiconducting and metallic SWCNTs were visualized in different colors in the obtained multiwavelength images due to their different absorption spectra. Statistical analysis of the multiwavelength signals revealed that semiconducting and metallic SWCNTs could be distinguished with more than 90% accuracy. Time-series PT imaging of the nanotube aggregates induced by salt addition was also conducted by performing single-nanotube measurements. Our study demonstrated that PT microscopy is a versatile technique for determining the composition and degree of aggregation of SWCNTs in liquid and polymeric media, which can promote the industrial application of such materials.