The mechanism of the adsorption of dsDNA on citrate-stabilized gold nanoparticles and a colorimetric and visual method for detecting the V600E point mutation of the BRAF gene

A study is presented on the binding kinetics and mechanism of the adsorption of dsDNA on citrate-capped gold nanoparticles (AuNPs). Methods include fluorescence titration, isothermal calorimetry (ITC) titration, dynamic light scattering and gel electrophoresis. It is found that the fluorescence of probe DNA (labeled with Rhodamine Green and measured at excitation/emission peaks of 498/531 nm) is quenched by addition of AuNPs. The Stern-Volmer quenching constant (Ksv) is 1.67 × 10^{^}9 L·mol^-1 at 308 K and drops with increasing temperature. The quenching mechanism is mainly static. The results of both fluorescence titrations and ITC show negative values for ΔH and ΔS values. This shows ion-induced dipole-dipole interaction to be the main attractive forces between dsDNA and AuNPs, while electrostatic interactions result in repulsion. The repulsive forces lead to a lower affinity between dsDNA and AuNPs (compared to single-strand DNA). It is also found that dsDNA can prevent the aggregation of AuNPs which is accompanied by a color change from red into blue. The visual detection limit with bare eyes for dsDNA₁ is 36 pM. Based on these findings, a colorimetric method was developed to detect the proto-oncogene of serine/threonine-protein kinase B-Raf V600E point mutation in HT29, Ec109, A549, Huh-7 and SW480 cell lines. Graphical abstract Schematic of the salt-induced aggregation of uncapped gold nanoparticles (AuNPs) which leads to a color change from red to blue. If the AuNPs are coated with dsDNA, aggregation is suppressed.

Identification of tyrosinase inhibitors from traditional Chinese medicines for the management of hyperpigmentation

The inhibition of tyrosinase is the most effective method to decrease melanin synthesis during the process of pigmentation. We aimed to find compounds from traditional Chinese medicines (TCM) that are more effective than the most commonly used tyrosinase inhibitor, arbutin. First, we employed homology modeling to construct a tyrosinase-modeled structure, and structure-based virtual screening to screen from 61,000 TCM compounds. We also adopted the following quantitative structure-activity relationship (QSAR) models for ligand-based validation: support vector machine, multiple linear regression, and Bayesian network. Molecular dynamics (MD) simulation was used to confirm the stability of ligand binding. We found that merresectine C might more effectively bind and inhibit the activity of tyrosinase than arbutin. This study provides useful evidence for the potential development of a novel non-toxic bleaching or whitening ingredient.