Formation of Aggregate-Free Gold Nanoparticles in the Cyclodextrin-Tetrachloroaurate System Follows Finke–Watzky Kinetics

Abstract

Cyclodextrin-capped gold nanoparticles are promising drug-delivery vehicles, but the technique of their preparation without trace amounts of aggregates is still lacking, and the size-manipulation possibility is very limited. In the present study, gold nanoparticles were synthesized by means of 0.1% (w/w) tetrachloroauric acid reduction with cyclodextrins at room temperature, at cyclodextrin concentrations of 0.001 M, 0.002 M and 0.004 M, and pH values of 11, 11.5 and 12. The synthesized nanoparticles were characterized by dynamic light scattering in both back-scattering and forward-scattering modes, spectrophotometry, X-ray photoelectron spectroscopy, transmission electron microscopy and Fourier-transform infrared spectroscopy. These techniques revealed 14.9% Au1+ on their surfaces. The Finke–Watzky kinetics of the reaction was demonstrated, but the actual growth mechanism turned out to be multistage. The synthesis kinetics and the resulting particle-size distribution were pH-dependent. The reaction and centrifugation conditions for the recovery of aggregate-free nanoparticles with different size distributions were determined. The absorbances of the best preparations were 7.6 for α-cyclodextrin, 8.9 for β-cyclodextrin and 7.5 for γ-cyclodextrin. Particle-size distribution by intensity was indicative of the complete absence of aggregates. The resulting preparations were ready to use without the need for concentration, filtration, or further purification. The synthesis meets the requirements of green chemistry.

Optimization of microfluidic synthesis of silver nanoparticles: A generic approach using machine learning

“…The proposed strategy, which used optimal and flexible experiment designs based on uncertainty analysis, can provide more flexibility compared to existing approaches such as design of experiments [33], since the exact values of the initial parameters are not fixed and the training features could be parameters which have been calculated based on physical parameters, such as nucleation and growth constants. The nucleation and growth constants were derived from an independent set of experiments carried out in a beaker using the Finke-Watzky (F-W) two-step mechanism [34] which has been applied previously to describe well a wide range of kinetic processes such as protein aggregation [35], [36] and metal nanoparticle formation including silver [37], gold [38], palladium [39] and rhodium [40]. Only one set of chemicals was used in this study providing several pairs of nucleation and growth constants.…”

Solid-State Formation of a Potential Melphalan Delivery Nanosystem Based on β-Cyclodextrin and Silver Nanoparticles

“…The solvation sphere diameter of the nanosystem was 116 nm with a polydispersity of 0.4, characteristic of ꞵCD-based nanosystems [ 12 , 16 , 17 , 63 , 64 , 65 ]. Therefore, the dissolution process causes the metal nanoparticles to be surrounded by multiple layers of the complex, as has been previously reported for analogous nanosystems using gold nanoparticles [ 13 , 14 , 15 ].…”

Colorimetric Sensing of Gram-Negative and Gram-Positive Bacteria Using 4-Mercaptophenylboronic Acid-Functionalized Gold Nanoparticles in the Presence of Polyethylene Glycol

“…At basic pH, boronic acid can form a reversible complex with cis -diol residues, and the environmental pH affects the affinity between boronic acid and cis -diol. , The color of 4-MPBA@GNPs in the presence of PEG changed from red to pale purple after adding 0.5 M NaOH, indicating the conversion of dispersed 4-MPBA@GNPs and aggregation induction of 4-MPBA@GNPs. The high concentration of NaOH could induce a high ionic strength in the solution of 4-MPBA@GNPs, which resulted in a reduction in the interparticle distance between 4-MPBA@GNPs and inducing aggregation of 4-MPBA@GNPs. In the case of the sample containing bacteria at a high concentration of 2 × 10 7 CFU mL –1 , the adherence of 4-MPBA@GNPs to bacteria through boronate ester and cis -diol on the bacterial surface could help stabilize 4-MPBA@GNPs .…”

“…However, the low bacterial concentration was not sufficient to allow adherence between 4-MPBA@GNPs and bacteria. Therefore, some free 4-MPBA@GNPs in the solution might interact with the high ionic strength of 0.5 M NaOH, resulting in aggregated 4-MPBA@GNP formation . Based on these results, we further investigated the performance of the designed colorimetric probe in the next section.…”

“…Therefore, some free 4-MPBA@GNPs in the solution might interact with the high ionic strength of 0.5 M NaOH, resulting in aggregated 4-MPBA@GNP formation. 42 Based on these results, we further To evaluate the potential of 4-MPBA@GNPs for the detection of Gramnegative and Gram-positive bacteria using the proposed technique, two bacterial strains at different concentrations were prepared. When 4-MPBA@GNPs interacted with different concentrations of E. coli K-12 (0 to 2 × 10 7 CFU mL −1 ) for 15 min and then 0.5 M NaOH was added to trigger the aggregation of 4-MPBA@GNPs, the absorbance spectra of 4-MPBA@GNPs were investigated.…”