Protein–Silver Nanoparticle Interactions to Colloidal Stability in Acidic Environments

Abstract

We report a kinetic study of Ag nanoparticles (AgNPs) under acidic environments (i.e., pH 2.3 to pH ≈7) and systematically investigate the impact of protein interactions [i.e., bovine serum albumin (BSA) as representative] to the colloidal stability of AgNPs. Electrospray-differential mobility analysis (ES-DMA) was used to characterize the particle size distributions and the number concentrations of AgNPs. Transmission electron microscopy was employed orthogonally to provide visualization of AgNPs. For unconjugated AgNPs, the extent of aggregation, or the average particle size, was shown to be increased significantly with an increase of acidity, where a partial coalescence was found between the primary particles of unconjugated AgNP clusters. Aggregation rate constant, kD, was also shown to be proportional to acidity, following a correlation of log(kD) = -1.627(pH)-9.3715. Using ES-DMA, we observe BSA had a strong binding affinity (equilibrium binding constant, ≈ 1.1 × 10(6) L/mol) to the surface of AgNPs, with an estimated maximum molecular surface density of ≈0.012 nm(-2). BSA-functionalized AgNPs exhibited highly-improved colloidal stability compared to the unconjugated AgNPs under acidic environments, where both the acid-induced interfacial dissolution and the particle aggregation became negligible. Results confirm a complex mechanism of colloidal stability of AgNPs: the aggregation process was shown to be dominant, and the formation of BSA corona on AgNPs suppressed both particle aggregation and interfacial dissolution of AgNP samples under acidic environments.

Rapid Kinetics of Size and pH-Dependent Dissolution and Aggregation of Silver Nanoparticles in Simulated Gastric Fluid

“…29 Cl − has been suggested to play a role in particle aggregation by aiding in the formation of interparticle AgCl bridges. 31 What makes the interpretation of the previous data particularly challenging is that many have used an initial time point of examination greater than 10 min, 26,27 meaning that there is a dearth of data within a key time window during which particles are undergoing their most rapid modification. Additionally, previous work has focused on highly acidic conditions of pH 2 or less, 29,30 which represent only fasted, not fed, stomach conditions.…”

Mechanism and behavior of silver nanoparticles in aqueous medium as adsorbent

“…In addition, recent investigations conferred that the use of ES-DMA benefits from advantages such as discernment of particle aggregation from the dissolution process and high-resolution particle size measurements [66,67]. Moreover, ES-DMA allows for accurate quantification of ligands bound to AgNPs [61].…”

Understanding ligand–nanoparticle interactions for silica, ceria, and titania nanopowders

“…To investigate the primary size and the morphology of individual nanoparticles, positively-charged aerosolized particles were delivered to a home-made electrostatic precipitator and deposited onto a copper grid with carbon film operated at a sample flow rate of %1.5 L/min and À(2-5) kV/cm electric field. Due to the electrostatic repulsion, the deposition-induced aggregation was negligible during sample collection [27,28,33,34]. The drop-cast method was also employed to prepare samples used for the study of surface dissolution of nanoparticles.…”

“…Folded capillary disposal cells were used under an ionic strength of %2 mmol/L NaCl aqueous solution. Results were converted from the measured electrophoretic mobility to zeta potential using the Smoluchowski approximation [33,36].…”

“…Note that TEM imagery (e.g., shape, aspect ratio of particle) is still required to provide the accurate analytical model to the ES-DMA analysis [28,39]. Besides, the counts observed at the lowest end of particle size of PSDs were attributed to the dried salt remnants in solvent generated by electrospray ionization [28,30,33]. Even though TEM is useful in providing direct image analysis, the laborious, time-consuming particle counting process restricts its use in routine characterization.…”