Unveiling the interaction of protein fibrils with gold nanoparticles by plasmon enhanced nano-spectroscopy

Probing the effect of the molecular interface of gold nanoparticles on the disassembly of insulin amyloid fibrils

Aberrant protein aggregation into amyloid fibrils underlies the onset of several degenerative pathologies, requiring increasing efforts to identify ever newer approaches to prevent their formation and to disassemble toxic amyloid structures. In this context, gold nanoparticles (AuNPs) show great promise, thanks to their ability to chemically interact with proteins while simultaneously serving as local spectroscopic probes due to their peculiar optical properties. Here, we investigate the role of the surface chemistry of AuNPs in the disassembly of insulin amyloid fibrils. By taking advantage of the remarkable sensitivity and spatial resolution of surface enhanced Raman spectroscopy, we elucidate the molecular mechanisms driving fibril-AuNP interaction at the nanoscale, identifying the amino acids directly involved. The obtained results will serve as a benchmark for developing novel diagnostic and therapeutic strategies employing AuNPs for the treatment of amyloid-related diseases.

Nano CaCO3 mediated in vitro and in vivo wound healing characteristics of chitosan films without added drugs

The proposed investigation aims towards introducing a facile and cost-effective chitosan-based material for healing of full thickness wounds via stimulation of keratinocyte at wound junction to yield faster closure. Chitosan (CS) crosslinked polyacrylic acid (PAA) polymeric networks are chosen as the matrix element to incorporate gold nanoparticles (Au Nps) and nano calcium carbonate (CaCO3 Nps) via covalent and electrostatic interactions. The as-synthesized CS/PAA@Au/CaCO3 nanocomposite hydrogels reveal high in vitro and in vivo biocompatibility against human kidney epithelial (HKE) cells and drosophila larvae, with minimum cell viability of 88.45 % at high doses of 87.5 μg/μL. The innate pH responsive swelling behaviour (1450 %) and WVTR (8.451 mg·cm-2·h-1), hemocompatibility, bioadhesivity along with antibacterial and anti-biofilm activity of the nanocomposite hydrogels against S. aureus and E. coli provide prior motivation to escalate the study towards in vivo wound healing in invertebrates (D.melanogaster) and vertebrates (Sprague-Dawley rats). The proposed hydrogels show accelerated healing in invertebrates and vertebrates, i.e., complete recovery in 3 h and 11 days, respectively. The histopathology analysis establishes the deposition of highly aligned collagen fibers on the wound surface supported by the tight keratinocyte junction at wound surface by the action of calcium ions for which the material becomes promising for wound healing applications.

Sustainable Formation of Gold Nanoparticle-Decorated Amyloid Fibrils for the Development of Functional Hybrid Materials

Amyloid fibrils have recently emerged as promising building blocks for functional materials due to their exceptional physicochemical stability and adaptable properties. These protein-based structures can be functionalized to create hybrid materials with a diverse range of applications. Here we report a simple eco-friendly protocol for generating amyloid fibrils from hen egg white lysozyme decorated with gold nanoparticles that can self-assemble in a hydrogel. Reactive oligomeric species act as reducing agents, enabling the efficient and simple formation of small gold nanoparticles without the need of harsh reagents. Furthermore, the protein molecules template the formation of gold nanoparticles, which are stabilized at regular intervals along the fibril axis, preserving gold nanoparticle properties at a macroscopic scale. As an illustration of potential application, we show that the gold nanoparticle functionalized hydrogel can be employed to sense and quantify creatinine using fluorescence detection. These findings reinforce the growing interest in utilizing proteins as foundational elements for functional biomaterials due to their high biocompatibility, availability, and the ability to finely tune supramolecular assemblies.

Raman spectroscopy and its plasmon-enhanced counterparts: A toolbox to probe protein dynamics and aggregation

Protein unfolding and aggregation are often correlated with numerous diseases such as Alzheimer's, Parkinson's, Huntington's, and other debilitating neurological disorders. Such adverse events consist of a plethora of competing mechanisms, particularly interactions that control the stability and cooperativity of the process. However, it remains challenging to probe the molecular mechanism of protein dynamics such as aggregation, and monitor them in real-time under physiological conditions. Recently, Raman spectroscopy and its plasmon-enhanced counterparts, such as surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS), have emerged as sensitive analytical tools that have the potential to perform molecular studies of functional groups and are showing significant promise in probing events related to protein aggregation. We summarize the fundamental working principles of Raman, SERS, and TERS as nondestructive, easy-to-perform, and fast tools for probing protein dynamics and aggregation. Finally, we highlight the utility of these techniques for the analysis of vibrational spectra of aggregation of proteins from various sources such as tissues, pathogens, food, biopharmaceuticals, and lastly, biological fouling to retrieve precise chemical information, which can be potentially translated to practical applications and point-of-care (PoC) devices. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Diagnostic Tools > Diagnostic Nanodevices Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Green Synthesis of Chitosan-Capped Gold Nanoparticles Using Salvia officinalis Extract: Biochemical Characterization and Antimicrobial and Cytotoxic Activities

Increasing antimicrobial resistance to the action of existing antibiotics has prompted researchers to identify new natural molecules with antimicrobial potential. In this study, a green system was developed for biosynthesizing gold nanoparticles (BAuNPs) using sage (Salvia officinalis L.) leaf extract bioconjugated with non-toxic, eco-friendly, and biodegradable chitosan, forming chitosan/gold bioconjugates (Chi/BAuNPs). Characterization of the BAuNPs and Chi/BAuNPs conjugates takes place using transmission electron microscopy (TEM), X-ray spectra, Fourier transform infrared (FT-IR) spectroscopy, and zeta potential (Z-potential). The chemical composition of S. officinalis extract was evaluated via gas chromatography/mass spectrometry (GC/MS). This study evaluated the antioxidant and antimicrobial activities of human pathogenic multidrug-resistant (MDR) and multisensitive (MS) bacterial isolates using the agar diffusion method. Chi/BAuNPs showed inhibition of the MDR strains more effectively than BAuNPs alone as compared with a positive standard antibiotic. The cytotoxicity assay revealed that the human breast adenocarcinoma cancer cells (MCF7) were more sensitive toward the toxicity of 5-Fu + BAuNPs and 5-Fu + Chi/BAuNPs composites compared to non-malignant human fibroblast cells (HFs). The study shows that BAuNPs and Chi/BAuNPs, combined with 5-FU NPs, can effectively treat cancer at concentrations where the free chemical drug (5-Fu) is ineffective, with a noted reduction in the required dosage for noticeable antitumor action.

Effect of plasmonic excitation on mature insulin amyloid fibrils

Interactions between amyloid protein structures and nanomaterials have been extensively studied to develop effective inhibitors of amyloid aggregation. Limited investigations are reported on the impact of nanoparticles on mature fibrils. In this work, gold nanoparticles are used as photothermal agents to alter insulin fibrils. To this end, gold colloids bearing a negatively charged capping shell, with an average diameter of 14 nm and a plasmon resonance maximum at 520 nm are synthesized. The effects on mature insulin fibril morphology and structure upon plasmonic excitation of the nanoparticles-fibril samples have been monitored by spectroscopic and microscopic methods. The obtained data indicate that an effective destruction of the amyloid aggregates occur upon irradiation of the plasmonic nanoparticles, allowing the development of emerging strategies to alter the structure of amyloid fibrils.

The Ability of Some Polysaccharides to Disaggregate Lysozyme Amyloid Fibrils and Renature the Protein

The deposition of proteins in the form of insoluble amyloid fibril aggregates is linked to a range of diseases. The supramolecular architecture of such deposits is governed by the propagation of β-strands in the direction of protofilament growth. In the present study, we analyze the structural changes of hen egg-white lysozyme fibrils upon their interactions with a range of polysaccharides, using AFM and FTIR spectroscopy. Linear anionic polysaccharides, such as κ-carrageenan and sodium alginate, are shown to be capable to disaggregate protofilaments with eventual protein renaturation. The results help to understand the mechanism of amyloid disaggregation and create a platform for both the development of new therapeutic agents for amyloidose treatment, and the design of novel functional protein-polysaccharide complex-based nanomaterials.

Synthesis of Chitosan-Based Gold Nanoparticles: Antimicrobial and Wound-Healing Activities

The global spread of multidrug-resistant bacteria has become a significant hazard to public health, and more effective antibacterial agents are required. Therefore, this study describes the preparation, characterization, and evaluation of gold nanoparticles modified with chitosan (Chi/AuNPs) as a reducing and stabilizing agent with efficient antimicrobial effects. In recent years, the development of an efficient and ecofriendly method for synthesizing metal nanoparticles has attracted a lot of interest in the field of nanotechnology. Colloidal gold nanoparticles (AuNPs) were prepared by the chemical reduction of gold ions in the presence of chitosan (Chi), giving Chi/AuNPs. The characterization of Chi/AuNPs was carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and X-ray diffraction (XRD). Chi/AuNPs appeared spherical and monodispersed, with a diameter ranging between 20 to 120 nm. The synergistic effects of AuNPs and Chi led to the disruption of bacterial membranes. The maximum inhibitory impact was seen against P. aeruginosa at 500 µg/mL, with a zone of inhibition diameter of 26 ± 1.8 mm, whereas the least inhibitory effect was reported for S. aureus, with a zone of inhibition diameter of 16 ± 2.1 mm at the highest dose tested. Moreover, Chi/AuNPs exhibited antifungal activity toward Candida albicans when the MIC was 62.5 µg/mL. Cell viability and proliferation of the developed nanocomposite were evaluated using a sulphorhodamine B (SRB) assay with a half inhibitory concentration (IC50) of 111.1 µg/mL. Moreover, the in vitro wound-healing model revealed that the Chi/AuNP dressing provides a relatively rapid and efficacious wound-healing ability, making the obtained nanocomposite a promising candidate for the development of improved bandage materials.

Responsivity of Fractal Nanoparticle Assemblies to Multiple Stimuli: Structural Insights on the Modulation of the Optical Properties

Multi-responsive nanomaterials based on the self-limited assembly of plasmonic nanoparticles are of great interest due to their widespread employment in sensing applications. We present a thorough investigation of a hybrid nanomaterial based on the protein-mediated aggregation of gold nanoparticles at varying protein concentration, pH and temperature. By combining Small Angle X-ray Scattering with extinction spectroscopy, we are able to frame the morphological features of the formed fractal aggregates in a theoretical model based on patchy interactions. Based on this, we established the main factors that determine the assembly process and their strong correlation with the optical properties of the assemblies. Moreover, the calibration curves that we obtained for each parameter investigated based on the extinction spectra point out to the notable flexibility of this nanomaterial, enabling the selection of different working ranges with high sensitivity. Our study opens for the rational tuning of the morphology and the optical properties of plasmonic assemblies to design colorimetric sensors with improved performances.