Advances in the design of amino acid and peptide synthesized gold nanoparticles for their applications

The field of therapeutics and diagnostics is advanced by nanotechnology-based approaches including the spatial-temporal release of drugs, targeted delivery, enhanced accumulation of drugs, immunomodulation, antimicrobial action, and high-resolution bioimaging, sensors and detection. Various compositions of nanoparticles (NPs) have been developed for biomedical applications; however, gold NPs (Au NPs) have attracted tremendous attention due to their biocompatibility, easy surface functionalization and quantification. Amino acids and peptides have natural biological activities as such, their activities enhance several folds in combination with NPs. Although peptides are extensively used to produce various functionalities of Au NPs, amino acids have also gained similar interests in producing amino acid-capped Au NPs due to the availability of amine, carboxyl and thiol functional groups. Henceforth, a comprehensive review is needed to timely bridge the synthesis and the applications of amino acid and peptide-capped Au NPs. This review aims to describe the synthesis mechanism of Au NPs using amino acids and peptides along with their applications in antimicrobial, bio/chemo-sensors, bioimaging, cancer therapy, catalysis, and skin regeneration. Moreover, the mechanisms of various activities of amino acid and peptide capped-Au NPs are presented. We believe this review will motivate researchers to better understand the interactions and long-term activities of amino acid and peptide-capped Au NPs for their success in various applications.

A Bio-Inspired Nanotubular Na2MoO4/TiO2 Composite as a High-Performance Anodic Material for Lithium-Ion Batteries

A train of bio-inspired nanotubular Na₂MoO₄/TiO₂ composites were synthesized by using a natural cellulose substance (e.g., commercial ordinary filter paper) as the structural template. The TiO₂ gel films were coated on the cellulose nanofiber surfaces via a sol-gel method firstly, followed with the deposition of the poly(diallyldimethylammonium chloride)/Na₂MoO₄ (PDDA/Na₂MoO₄) bi-layers several times, through the layer-by-layer self-assembly route, yielding the (PDDA/Na₂MoO₄)_n/TiO₂-gel/cellulose composite, which was calcined in air to give various Na₂MoO₄/TiO₂ nanocomposites containing different Na₂MoO₄ contents (15.4, 24.1, and 41.4%). The resultant nanocomposites all inherited the three-dimensionally porous network structure of the premier cellulose substance, which were formed by hierarchical TiO₂ nanotubes anchored with the Na₂MoO₄ layers. When employed as anodic materials for lithium-ion batteries, those Na₂MoO₄/TiO₂ nanocomposites exhibited promoted electrochemical performances in comparison with the Na₂MoO₄ powder and pure TiO₂ nanotubes, which was resulted from the high capacity of the Na₂MoO₄ component and the buffering effects of the TiO₂ nanotubes. Among all the nanotubular Na₂MoO₄/TiO₂ composites, the one with a Na₂MoO₄ content of 41.4% showed the best electrochemical properties, such as the cycling stability with a capacity of 180.22 mAh g⁻¹ after 200 charge/discharge cycles (current density: 100 mA g⁻¹) and the optimal rate capability.

Phase Control of Nanocrystalline Inclusions in Bioprecipitated Titania with a Panel of Mutant Silica-Binding Proteins

The biomimetic route to inorganic synthesis presents an opportunity to produce complex materials with superior properties under ambient conditions and from nontoxic precursors. While there has been significant progress in using solid-binding peptides (SBPs), proteins, and organisms to produce a variety of inorganic and hybrid structures, it has been more challenging to understand the interplay of solution conditions and solid-binding peptide (SBP) sequence, structure, and self-association on synthetic outcomes. Here, we show that fusing the Car9 silica-binding peptide-but not the silaffin-derived R5 peptide-to superfolder green fluorescent protein (sfGFP) enhances the ability of micromolar concentrations of protein to induce rapid titania (TiO₂) precipitation from acidified solutions of tetrakis(di-lactato)-oxo-titanate (TiBALDH). TiO₂ is produced stoichiometrically and although predominantly amorphous, contains nanosized anatase and monoclinic TiO₂(B) inclusions. Remarkably, the phase of these nanocrystallites can be tuned from about 80% TiO₂(B) to about 65% anatase by using Car9 mutants impaired in their ability to drive the formation of higher-order sfGFP-Car9 oligomers. Our results suggest that the presentation of multiple basic side chains in an extended plane formed by SBP self-association is critical to template the formation of monoclinic crystallites and underscore the subtle influence that single or dual substitutions in dodecameric SBPs can exert on the yield and crystallinity of biomineralized inorganics.

Characterization of photocatalytic TiO2 powder under varied environments using near ambient pressure X-ray photoelectron spectroscopy

Consecutive eight study phases under the successive presence and absence of UV irradiation, water vapor, and oxygen were conducted to characterize surface changes in the photocatalytic TiO₂ powder using near-ambient-pressure X-ray photoelectron spectroscopy (XPS). Both Ti 2p and O 1s spectra show hysteresis through the experimental course. Under all the study environments, the bridging hydroxyl (OH_br) and terminal hydroxyl (OH_t) are identified at 1.1–1.3 eV and 2.1–2.3 eV above lattice oxygen, respectively. This enables novel and complementary approach to characterize reactivity of TiO₂ powder. The dynamic behavior of surface-bound water molecules under each study environment is identified, while maintaining a constant distance of 1.3 eV from the position of water vapor. In the dark, the continual supply of both water vapor and oxygen is the key factor retaining the activated state of the TiO₂ powder for a time period. Two new surface peaks at 1.7–1.8 and 4.0–4.2 eV above lattice oxygen are designated as peroxides (OOH/H₂O₂) and H₂O₂ dissolved in water, respectively. The persistent peroxides on the powder further explain previously observed prolonged oxidation capability of TiO₂ powder without light irradiation.

Engineered peptides for nanohybrid assemblies

Inspired by biological material synthesis, synthetic biomineralization peptides have been screened through a laboratory evolution using biocombinatorial techniques. In this study, using the fine examples in nature, silica binding peptides and gold binding peptides were fused together to form a hybrid peptide. We designed fusion peptides with different gold binding and silica binding parts. First, we have tested the binding capability of the fusion peptides using quartz crystal microbalance on gold surface and silica surface. Second, S1G1 hybrid peptide enabled assembly of gold nanoparticles on a silica surface was achieved. Finally, nanomaterial synthesis ability of the S1G1 peptide was presented by the formation of a silica film on a gold surface. In this study, we are presenting a hybrid peptide tool for nanohybrid assembly as a promising route for nanotechnology applications.