Lipoic acid capped silver nanoparticles: a facile route to covalent protein capping and oxidative stability within biological systems

Probing the Fluorescence Intermittency of Bimetallic Nanoclusters using Single-Molecule Fluorescence Spectroscopy

Single-molecule spectroscopy (SMS) is a unique and competent technique to study molecule dynamics and sense biomolecules precisely. The design of an ultrahigh-stability single fluorophore probe with excellent photostability and long-lived dark transient states for single-molecule fluorescence microscopy is challenging. Here, we found that the photostability of bimetallic AuAg28 nanoclusters is better than monometallic Ag29 nanoclusters. The photon antibunching experiments unveiled exceptional brightness and remarkable photostability with high survival times of up to 218 s with minimal blinking. AuAg28 NCs exhibited longer "on" times and shorter "off" times as compared to Ag29 NCs. The statistical analysis was performed on at least 100 molecules that showed single-step photobleaching and almost a 5-fold enhancement in intensity on Au doping in Ag29 NCs. The distinctive and tunable photophysics of metal NCs can offer huge potential in pushing single-molecule dynamic measurements to be carried out biologically.

Thermodynamics of the physisorption of capping agents on silver nanoparticles

Nanoscale silver particles have growing applications in biomedical and other technologies due to their unique antibacterial, optical, and electrical properties. The preparation of metal nanoparticles requires the action of a capping agent, such as thiol-containing compounds, to provide colloidal stability, prevent agglomeration, stop uncontrolled growth, and attenuate oxidative damage. However, despite the extensive use of these thiol-based capping agents, the structure of the capping agent layers on the metal surface and the thermodynamics of the formation of these layers remains poorly understood. Here, we leverage molecular dynamics simulations and free energy calculation techniques, to study the behavior of citrate and four thiol-containing capping agents commonly used to protect silver nanoparticles from oxidation. We have studied the single-molecule adsorption of these capping agents to the metal-water interface, their coalescence into clusters, and the formation of complete monolayers covering the metal nanoparticle. At sufficiently high concentrations, we find that allylmercaptan, lipoic acid, and mercaptohexanol spontaneously self-assemble into ordered layers with the thiol group in contact with the metal surface. The high density and ordered structure is presumably responsible for their improved protective characteristics relative to the other compounds studied.

Design, Synthesis, and Characterization of an Amphiphilic Lipoic Acid-Based Ru(III) Complex as a Versatile Tool for the Functionalization of Different Nanosystems

Ru-based chemotherapy is emerging as an effective alternative to the well-established Pt-based one, typically associated with high toxicity. In this context, our recent efforts were devoted to the preparation of nucleolipid-based Ru(III) complexes able to form, under physiological conditions, supramolecular aggregates which can efficiently prevent metal deactivation and convey Ru(III) inside the cells where it exerts its activity. Within an interdisciplinary program for the development of multifunctional nanoparticles for theranostic applications, we here report the design, synthesis, and characterization of a novel functionalized Ru(III) salt, carrying a lipoic acid moiety in the nucleolipid-based scaffold to allow its incorporation onto metal-based nanoparticles.

Analysis of Capped Silver Nanoparticles Combined with Imipenem against Different Susceptibility Profiles of Klebsiella pneumoniae

Klebsiella pneumoniae (K. pneumoniae) is an opportunistic bacterium that has drawn attention due to its resistance to carbapenem antibiotics. The treatment of patients with severe infections has been challenging. Thus, silver nanoparticles (AgNPs) have been applied for their antimicrobial effects. This work aims to analyze the synergistic effect of the carbapenem antibiotic Imipenem with AgNPs against different susceptibility clinical profiles of K. pneumoniae. The silver nanoparticles were synthesized by bottom-up methodology and capped with alpha-lipoic acid. Susceptibility tests were performed using four K. pneumoniae strains with different susceptibility profiles to Imipenem. The strains were induced to form a biofilm for 48 h. Crystal violet and Resazurin assays were performed to determine biofilm formation and minimal inhibitory concentration, respectively. The reduction in Imipenem concentration with the association of nanoparticles was found in all strains studied in planktonic form, and the synergism between silver nanoparticles and Imipenem was demonstrated through the analysis of the fractional inhibitory concentration index. The viability percentage was reduced at rates ≥80% in the biofilm analysis, characterized by the minimal biofilm inhibitory concentration. The study’s proposed association resulted in inhibitory effects on different K. pneumoniae profiles, both in planktonic forms and biofilm, with peculiar behavior in the Imipenem-resistant profile.

Synthesis of Spherical Nanoparticle Hybrids via Aerosol Thiol-Ene Photopolymerization and Their Bioconjugation

Hybrid nanomaterials possess the properties of both organic and inorganic components and find applications in various fields of research and technology. In this study, aerosol photopolymerization is used in combination with thiol-ene chemistry to produce silver poly(thio-ether) hybrid nanospheres. In aerosol photopolymerization, a spray solution of monomers is atomized, forming a droplet aerosol, which then polymerizes, producing spherical polymer nanoparticles. To produce silver poly(thio-ether) hybrids, silver nanoparticles were introduced to the spray solution. Diverse methods of stabilization were used to produce stable dispersions of silver nanoparticles to prevent their agglomeration before the photopolymerization process. Successfully stabilized silver nanoparticle dispersion in the spray solution subsequently formed nanocomposites with non-agglomerated silver nanoparticles inside the polymer matrix. Nanocomposite particles were analyzed via scanning and transmission electron microscopy to study the degree of agglomeration of silver nanoparticles and their location inside the polymer spheres. The nanoparticle hybrids were then introduced onto various biofunctionalization reactions. A two-step bioconjugation process was developed involving the hybrid nanoparticles: (1) conjugation of (biotin)-maleimide to thiol-groups on the polymer network of the hybrids, and (2) biotin-streptavidin binding. The biofunctionalization with gold-nanoparticle-conjugates was carried out to confirm the reactivity of -SH groups on each conjugation step. Fluorescence-labeled biomolecules were conjugated to the spherical nanoparticle hybrids (applying the two-step bioconjugation process) verified by Fluorescence Spectroscopy and Fluorescence Microscopy. The presented research offers an effective method of synthesis of smart systems that can further be used in biosensors and various other biomedical applications.