Time-dependent, protein-directed growth of gold nanoparticles within a single crystal of lysozyme

Biomacromolecular carriers based hydrophobic natural products for potential cancer therapy

Cancer is the second leading cause of death worldwide. It was estimated that 90 % of cancer-related deaths were attributable to the development of multi-drug resistance (MDR) during chemotherapy, which results in ineffective chemotherapy. Hydrophobic natural products plays a pivotal role in the field of cancer therapy, with the potential to reverse MDR in tumor cells, thereby enhancing the efficacy of tumor therapy. However, their targeted delivery is considered a major hurdle in their application. The advent of numerous approaches for encapsulating bioactive ingredients in the nanodelivery systems has improved the stability and targeted delivery of these biomolecules. The manuscript comprehensively analyses the nanodelivery systems of bioactive compounds with potential cancer therapy applications, including liposomes, emulsions, solid lipid nanoparticles (NPs), and polymeric NPs. Then, the advantages and disadvantages of various nanoagents in the treatment of various cancer types are critically discussed. Further, the application of multiple-compbine delivery methods to overcome the limitations of single-delivery have need critically analyzed, which thus could help in the designing nanodrug delivery systems for bioactive compounds in clinical settings. Therefore, the review is timely and important for development of efficient nanodelivery systems involving hydrophobic natural products to improve pharmacokinetic properties for effective cancer treatment.

Growth Process of Fe-O Nanoclusters with Different Sizes Biosynthesized by Protein Nanocages

All protein-directed syntheses of metal nanoclusters (NCs) and nanoparticles (NPs) have attracted considerable attention because protein scaffolds provide a unique metal coordination environment and can adjust the shape and morphology of NCs and NPs. However, the detailed formation mechanisms of NCs or NPs directed by protein templates remain unclear. In this study, by taking advantage of the ferritin nanocage as a biotemplate to monitor the growth of Fe-O NCs as a function of time, we synthesized a series of iron NCs with different sizes and shapes and subsequently solved their corresponding three-dimensional atomic-scale structures by X-ray protein crystallography and cryo-electron microscopy. The time-dependent structure analyses revealed the growth process of these Fe-O NCs with the 4-fold channel of ferritin as nucleation sites. To our knowledge, the newly biosynthesized Fe35O23Glu12 represents the largest Fe-O NCs with a definite atomic structure. This study contributes to our understanding of the formation mechanism of iron NCs and provides an effective method for metal NC synthesis.

Application of gold nanoclusters in fluorescence sensing and biological detection

Gold nanoclusters (Au NCs) exhibit broad fluorescent spectra from visible to near-infrared regions and good enzyme-mimicking catalytic activities. Combined with excellent stability and exceptional biocompatibility, the Au NCs have been widely exploited in biomedicine such as biocatalysis and bioimaging. Especially, the long fluorescence lifetime and large Stokes shift attribute Au NCs to good probes for fluorescence sensing and biological detection. In this review, we systematically summarized the molecular structure and fluorescence properties of Au NCs and highlighted the advances in fluorescence sensing and biological detection. The Au NCs display high sensitivity and specificity in detecting iodine ions, metal ions, and reactive oxygen species, as well as certain diseases based on the fluorescence activities of Au NCs. We also proposed several points to improve the practicability and accelerate the clinical translation of the Au NCs.

Dentin bond strength and antimicrobial activities of universal adhesives containing silver nanoparticles synthesized with Rosa canina extract

OBJECTIVE

The purpose in the study was to evaluate the effect of biogenic silver nanoparticles (Ag NPs) synthesized by the green synthesis method on dentin bond strength in three different universal adhesives and investigate their antibiofilm activity against Streptococcus mutans (S. mutans).

MATERIALS AND METHODS

Three different universal adhesives (single bond universal, all-bond universal, and clearfil universal) were used in this study. Ag NPs were synthesized using rose hip (Rosa canina) extract as a reducing and stabilizing agent and they were characterized with STEM, UV-vis spectrophotometer, DLS, and zeta potential. Ag NPs were added to the adhesive resins at a rate of 0.05% (w/w), and their homogeneous distribution in the adhesive was determined using EDX spectrometry. Samples in all groups were tested at baseline-after 5000 and 10,000 thermal cycles. Adhesive composite discs were used for the live/dead analysis of S. mutans, MTT metabolic activity test, lactic acid production, and determination of colony-forming unit (CFU) values (n = 3). Ninety extracted caries-free human third molars were used to determine microtensile bond strength (μTBS) (n = 10). After the universal adhesive was applied to the dentin surface, composite resin (Z550 XT, 3 M ESPE, USA) was placed and sections were taken to form a composite-dentin stick of 1 mm × 1 mm wideness and 8-mm length. The sticks were broken at a rate of 1 mm/min under uniaxial tension in a universal testing machine, and the failure modes were determined by SEM. One-way analysis of variance (ANOVA) for antibacterial tests and two-way analysis of variance for μTBS tests were performed (p < 0.05).

RESULTS

All universal adhesive groups containing Ag NPs showed higher antibacterial activity than control groups without Ag NPs (p < 0.05). There was a statistically significant difference in the live/dead assay analysis, MTT metabolic activity test, lactic acid production, and CFU values in the thermal cycled Ag NPs groups (p < 0.05). Antibacterial activity decreased in groups containing Ag NPs subjected to 10,000 thermal cycles. The highest lactic acid production 11.06 (± 0.629) and CFUs 7.61 (± 0.304), live bacteria 31.13 (± 0.466), and S. mutans MTT metabolic activity 0.29 (± 0.376) at AU (All-Bond Universal-Ag NPs) 10,000 thermal cycles group. There was no difference in μTBS values between the initial and 5000 thermal cycle groups, there was a difference between the 10,000 thermal cycle groups. The CU (Clearfil Universal-Ag NPs) group subjected to 10,000 thermal cycles showed lower μTBS 11.1 (± 3.2).

CONCLUSION

In conclusion, universal adhesives containing biogenic Ag NPs showed higher antibacterial activity than the control groups and did not reduce the μTBS.

CLINICAL RELEVANCE

Antibacterial universal adhesives can contribute to restoration success in clinical applications by reducing residual bacteria and preventing secondary caries formation.

Magnetite Mineralization inside Cross-Linked Protein Crystals

Crystallization in confined spaces is a widespread process in nature that also has important implications for the stability and durability of many man-made materials. It has been reported that confinement can alter essential crystallization events, such as nucleation and growth and, thus, have an impact on crystal size, polymorphism, morphology, and stability. Therefore, the study of nucleation in confined spaces can help us understand similar events that occur in nature, such as biomineralization, design new methods to control crystallization, and expand our knowledge in the field of crystallography. Although the fundamental interest is clear, basic models at the laboratory scale are scarce mainly due to the difficulty in obtaining well-defined confined spaces allowing a simultaneous study of the mineralization process outside and inside the cavities. Herein, we have studied magnetite precipitation in the channels of cross-linked protein crystals (CLPCs) with different channel pore sizes, as a model of crystallization in confined spaces. Our results show that nucleation of an Fe-rich phase occurs inside the protein channels in all cases, but, by a combination of chemical and physical effects, the channel diameter of CLPCs exerted a precise control on the size and stability of those Fe-rich nanoparticles. The small diameters of protein channels restrain the growth of metastable intermediates to around 2 nm and stabilize them over time. At larger pore diameters, recrystallization of the Fe-rich precursors into more stable phases was observed. This study highlights the impact that crystallization in confined spaces can have on the physicochemical properties of the resulting crystals and shows that CLPCs can be interesting substrates to study this process.

Atomic Details of Biomineralization Proteins Inspiring Protein Design and Reengineering for Functional Biominerals

Biominerals are extraordinary materials that provide organisms with a variety of functions to support life. The synthesis of biominerals and organization at the macroscopic level is a consequence of the interactions of these materials with proteins. The association of biominerals and proteins is very ancient and has sparked a wealth of research across biological, medical and material sciences. Calcium carbonate, hydroxyapatite, and silica represent widespread natural biominerals. The atomic details of the interface between macromolecules and these biominerals is very intriguing from a chemical perspective, considering the association of chemical entities that are structurally different. With this review I provide an overview of the available structural studies of biomineralization proteins, explored from the Protein Data Bank (wwPDB) archive and scientific literature, and of how these studies are inspiring the design and engineering of proteins able to synthesize novel biominerals. The progression of this review from classical template proteins to silica polymerization seeks to benefit researchers involved in various interdisciplinary aspects of a biomineralization project, who need background information and a quick update on advances in the field. Lessons learned from structural studies are exemplary and will guide new projects for the imaging of new hybrid biomineral/protein superstructures at the atomic level.

Hollow protein microparticles formed through cross-linking by an Au3+ initiated redox reaction

Hollow microparticles (MPs) are of great relevance in the materials industry for a wide range of applications, such as catalysis, coatings, and delivery of theranostics. Here, we report the formation of hollow MPs through the assembly of lipoproteins in CaCO₃ templates. Proteins interact in the pores of CaCO₃ templates through attractive hydrophobic forces and form dense edges of hollow MPs. To further cross-link the proteins, Au³⁺ was added to initiate a redox reaction, where proteins were oxidized forming inter- and intramolecular covalent bonds, while Au³⁺ was reduced and gold nanoparticles (AuNPs) were formed. The obtained protein-based hollow MPs have a diameter of 6 μm and the AuNPs are embedded on their surface. Through this research, we suggest a new route to design biobased Au-protein hollow MPs in simple steps, which can allow new possibilities for carrying functional molecules and bioimaging.

Multilayered Ordered Protein Arrays Self-Assembled from a Mixed Population of Virus-like Particles

Biology shows many examples of spatially controlled assembly of cells and biomacromolecules into hierarchically organized structures, to which many of the complex biological functions are attributed. While such biological structures have inspired the design of synthetic materials, it is still a great challenge to control the spatial arrangement of individual building blocks when assembling multiple types of components into bulk materials. Here, we report self-assembly of multilayered, ordered protein arrays from mixed populations of virus-like particles (VLPs). We systematically tuned the magnitude of the surface charge of the VLPs via mutagenesis to prepare four different types of VLPs for mixing. A mixture of up to four types of VLPs selectively assembled into higher-order structures in the presence of oppositely charged dendrimers during a gradual lowering of the ionic strength of the solution. The assembly resulted in the formation of three-dimensional ordered VLP arrays with up to four distinct layers including a central core, with each layer comprising a single type of VLP. A coarse-grained computational model was developed and simulated using molecular dynamics to probe the formation of the multilayered, core-shell structure. Our findings establish a simple and versatile bottom-up strategy to synthesize multilayered, ordered materials by controlling the spatial arrangement of multiple types of nanoscale building blocks in a one-pot fabrication.

Tumor-Microenvironment-Activated NIR-II Nanotheranostic Platform for Precise Diagnosis and Treatment of Colon Cancer

Rational design of tumor-microenvironment (TME)-activated nanoformulation for precisely targeted cancer treatment has recently attracted an enormous attention. However, the all-in-one TME-activated theranostic nanosystems with a simple preparation and high biocompatibility are still rarely reported. Herein, catalase nanocrystals (CatCry) are first introduced as a tumor microenvironment activatable nanoplatform for selective theranostics of colon cancer. They are engaged as (i) a "nanoreactor" for silver nanoparticles (AgNP) synthesis, (ii) a nanovehicle for tumor delivery of anticancer drug doxorubicin (DOX), and (iii) an in situ O2 generator to relief tumor hypoxia. When CatCry-AgNP-DOX nanoformulation is within a tumor, the intratumoral H2S turns AgNP into Ag2S nanoparticles, inducing a photothermal effect and NIR-II emission under 808 nm laser irradiation and also triggering DOX release. Simultaneously, CatCry catalyzes intratumoral H2O2 into O2, relieving hypoxia and enhancing chemotherapy. In contrast, when delivered to healthy tissue without increased concentration of H2S, the developed nanoformulation remains in the "off" state and no theranostic action takes place. Studies with colon cancer cells in vitro and a murine colon cancer model in vivo demonstrated that CatCry-AgNP-DOX delivered a synergistic combination of PTT and enhanced chemotherapy, enabling complete eradication of tumor with minimal side effects. This work not only introduces nanoplatform for theranostics of H2S-rich tumors but also suggests a general strategy for protein-crystal-based nanomedicine.

Design of a gold clustering site in an engineered apo-ferritin cage

Water-soluble and biocompatible protein-protected gold nanoclusters (Au NCs) hold great promise for numerous applications. However, design and precise regulation of their structure at an atomic level remain challenging. Herein, we have engineered and constructed a gold clustering site at the 4-fold symmetric axis channel of the apo-ferritin cage. Using a series of X-ray crystal structures, we evaluated the stepwise accumulation process of Au ions into the cage and the formation of a multinuclear Au cluster in our designed cavity. We also disclosed the role of key residues in the metal accumulation process. X-ray crystal structures in combination with quantum chemical (QC) calculation revealed a unique Au clustering site with up to 12 Au atoms positions in the cavity. Moreover, the structure of the gold nanocluster was precisely tuned by the dosage of the Au precursor. As the gold concentration increases, the number of Au atoms position at the clustering site increases from 8 to 12, and a structural rearrangement was observed at a higher Au concentration. Furthermore, the binding affinity order of the four Au binding sites on apo-ferritin was unveiled with a stepwise increase of Au precursor concentration.

Macromolecular protein crystallisation with biotemplate of live cells

Macromolecular protein crystallisation was one of the potential tools to accelerate the biomanufacturing of biopharmaceuticals. In this work, it was the first time to investigate the roles of biotemplates, Saccharomyces cerevisiae live cells, in the crystallisation processes of lysozyme, with different concentrations from 20 to 2.5 mg/mL lysozyme and different concentrations from 0 to 5.0 × 10⁷ (cfu/mL) Saccharomyces cerevisiae cells, during a period of 96 h. During the crystallisation period, the nucleation possibility in droplets, crystal numbers, and cell growth and cell density were observed and analysed. The results indicated the strong interaction between the lysozyme molecules and the cell wall of the S. cerevisiae, proved by the crystallization of lysozyme with fluorescent labels. The biotemplates demonstrated positive influence or negative influence on the nucleation, i.e. shorter or longer induction time, dependent on the concentrations of the lysozyme and the S. cerevisiae cells, and ratios between them. In the biomanufacturing process, target proteins were various cells were commonly mixed with various cells, and this work provides novel insights of new design and application of live cells as biotemplates for purification of macromolecules.

An unexpected all-metal aromatic tetranuclear silver cluster in human copper chaperone Atox1

Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins. Herein we report the formation and crystal structure of a planar square tetranuclear silver cluster when silver ions were mixed with human copper chaperone Atox1. Quantum chemical studies reveal that two Ag 5s¹ electrons in the tetranuclear silver cluster fully occupy the one bonding molecular orbital, with the assumption that this Ag₄ cluster is Ag₄²⁺, leading to extensive electron delocalization over the planar square and significant stabilization. This bonding pattern of the tetranuclear silver cluster represents an aromatic all-metal structure that follows a 4n + 2 electron counting rule (n = 0). This is the first time an all-metal aromatic silver cluster was observed in a protein.

Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins.

Engineering of protein crystals for use as solid biomaterials

Protein crystals have attracted a great deal of attention as solid biomaterials because they have porous structures created by regular assemblies of proteins. The lattice structures of protein crystals are controlled by designing molecular interfacial interactions via covalent bonds and non-covalent bonds. Protein crystals have been functionalized as templates to immobilize foreign molecules such as metal nanoparticles, metal complexes, and proteins. These hybrid crystals are used as functional materials for catalytic reactions and structural analysis. Furthermore, in-cell protein crystals have been studied extensively, providing progress in rapid protein crystallization and crystallography. This review highlights recent advances in crystal engineering for protein crystallization and generation of solid functional materials both in vitro and within cells.

π-π conjugation promoted nanocatalysis for cancer therapy based on a covalent organic framework

The production of reactive oxygen species (ROS) to elicit lethal cellular oxidative damage is an attractive pathway to kill cancer cells, but it is still hindered by the low ROS production efficiency of the current methods. Herein, we design a one-dimensional (1D) π-π conjugated ferriporphyrin covalent organic framework on carbon nanotubes (COF-CNT) for activating nanocatalytic and photodynamic cancer therapy. The COF-CNT can catalyze the generation of ROS and O₂ in the tumor microenvironment (TME), and realize a self-oxygen-supplying PDT under near-infrared (NIR) light irradiation, simultaneously. With the full electron delocalization at the atomically dispersed active center, the catalytic activity of COF-CNT with extended π-conjugation is 6.8 times higher than that without the π-conjugated structure. The formation of the COF structure with π-π conjugation also changes the density of states (DOS) profile of its functional building block for improving PDT. Through one single treatment, it successfully achieves complete tumor regression of 4T1 breast carcinoma in mice with immunoregulation.

Investigation of ellagic acid rich-berry extracts directed silver nanoparticles synthesis and their antimicrobial properties with potential mechanisms towards Enterococcus faecalis and Candida albicans

The essential goals of this present study are to elucidate the formation mechanism of ellagic acid rich-blackberry, BBE, (Rubus fruticosus L.) and raspberry, RBE, (Rubus idaeus L.) extracts directed silver nanoparticles and to investigate thier antimicrobial properties towards model dental pathogens E. faecalis and C. albicans compared to BBE, RBE, NaOCl, CHX and EDTA. Both %5 w/w of BBE and RBE reacted with 5 mM Ag ⁺ ions at room temperature (25 °C) under mild-stirring, the formation of BBE and RBE directed b@Ag NP and r@Ag NP was monitored over time by using an Uv-vis spectrophotometer. Both b@Ag and r@Ag NPs were also complementarily characterized with SEM and FT-IR. In terms of the antimicrobial studies, b@Ag NP, r@Ag NP, %5 BBE and RBE, 5 mM AgNO₃, %5 NaOCl, %1,5 CHX and %15 EDTA were separately incubated with E. faecalis and C. albicans suspensions. The results were evaluated with student t-test using GraphPad Prism 8.0.1 statistical software (P < 0.05). While formation of b@Ag NP was confirmed with characteristic absorbance at ~435 nm in 20 min (min) of incubation, r@Ag NP did not give absorbance till 80 min owing to concentration of ellagic acid acted as a reducing and stabilizng agent for formation of the Ag NPs. Intrestingly, 50 ppm r@Ag NP inactivated ∼89% and ∼99% of E. faecalis and C. albicans cell, respectively, ∼25% and ∼40% cell inactivations for E. faecalis and C. albicans were observed respectively with 50 ppm b@Ag NP. We showed that 50 ppm r@Ag NP has effective antimicrobial property as much as mostly used %5 NaOCl and %1,5 CHX solutions.

Au3+-Induced gel network formation of proteins

The formation of protein gel networks in aqueous systems is a result of protein intermolecular interactions after an energy input, like heating. In this research, we report that a redox reaction between Au³⁺ ions and proteins can also lead to the formation of a protein gel network. Amino acids, like cysteine and tyrosine, get oxidized and form covalent bonds with neighboring protein molecules, while Au³⁺ ions get reduced to Au⁺ and Au⁰, nucleate and form gold nanoparticles. The protein gel network formation occurs within 2 h at room temperature and can be tuned by varying Au³⁺/protein ratio and accelerated by increasing the incubation temperature. The proposed Au³⁺-induced gel network formation was applied to different proteins, like egg yolk high-density lipoprotein, bovine serum albumin and whey protein. This research opens new insights for the investigation of the metal-protein interactions and may aid in the design of novel hybrid-soft nanocomposite materials.

Catalase Nanocrystals Loaded with Methylene Blue as Oxygen Self-Supplied, Imaging-Guided Platform for Photodynamic Therapy of Hypoxic Tumors

Photodynamic therapy (PDT) is a well-known method for cancer therapy in the clinic. However, the inherent hypoxia microenvironment of solid tumors enormously restricts the PDT efficiency. Herein, catalase nanocrystals (CatCry) are introduced as in situ oxygen (O₂ )-generating system to relieve tumor hypoxia and enhance PDT efficiency for solid tumors. After loading with photosensitizer methylene blue (MB), a PDT drug platform (CatCry-MB) emerges, allowing for significant increasing PDT efficiency instigated by three factors. First, the high stability and recyclable catalytic activity of CatCry enable a long-term endogenous H₂ O₂ decomposition for continuous O₂ supply for sustained relief of tumor hypoxia. Second, both the produced O₂ and loaded MB are confined within CatCry nanoporous structure, shortening the diffusion distance between O₂ and MB to maximize the production of singlet oxygen (¹ O₂ ). Third, the MB molecules are uniformly dispersed within CatCry lattice, avoiding MB aggregation and causing more MB molecules be activated to produce more ¹ O₂ . With the three complementary mechanisms, tumor hypoxia is eradicated and the resulted enhancement in PDT efficiency is demonstrated in vitro and in vivo. The proposed approach opens up a new venue for the development of other O₂ -dependent tumor treatments, such as chemotherapy, radiotherapy, and immunotherapy.

Effect of a Good buffer on the fate of metastable protein-rich droplets near physiological composition

Metastable protein-rich microdroplets are produced from liquid-liquid phase separation (LLPS) of protein aqueous solutions. These globules can be intermediates for the formation of other protein-rich phases. Lysozyme aqueous solutions undergo LLPS around 0 °C in the presence of NaCl near physiological conditions. Here, it is shown that insertion of small amounts of 4-(2-hydroxyethyl)-1-piperazineethanesulfonate (HEPES, 0.1 M) as a second additive to lysozyme-NaCl-water solutions near physiological ionic strength (0.2 M) is an essential step for triggering conversion of protein-rich droplets into another phase. Specifically, LLPS induced by cooling reproducibly leads to a rapid and high-yield formation of compact tetragonal crystalline microparticles only in the presence of HEPES. These microcrystals exhibit small size (1-3 μm), narrow size distribution and guest-binding properties. The temperature-concentration phase diagram shows a characteristic topology with LLPS boundary metastable with respect to tetragonal microcrystals, which in turn become less stable than rod-shaped orthorhombic crystals above 40 °C. Interestingly, dynamic light scattering, hydrogen-ion titrations and isothermal titration calorimetry reveal that lysozyme-HEPES interactions were found to be weakly attractive and exothermic. Our findings indicate that additives of salting-in type can represent an important factor controlling the fate of metastable protein-rich microdroplets relevant to drug formulations, femtosecond crystallography, and potential implications in protein-driven cytoplasmic compartmentalization.

Spectroscopic investigations of the changes in ligand conformation during the synthesis of soy protein-templated fluorescent gold nanoclusters

In this paper, the potential relationship between fluorescence and changes in the ligand conformation observed during the synthesis of soy protein-templated fluorescent gold nanoclusters (SP-AuNCs) was studied using a series of spectroscopic techniques. The results show that the determinants of the fluorescence effect in SP-AuNCs changed with the reaction time during the synthesis process. In the early stage of the reaction (within 60 min), the fluorescence intensity was dominated by the Au nucleus, followed by the combination of the Au nucleus and protein ligand. The structure of the protein ligand also underwent a transition from ordered to disordered to ordered. At the same time, its role in the reaction also changed from providing the reducing power to protecting the Au nucleus and contributing to the transition of the fluorescence effect in the AuNCs via ligand-to-metal charge transfer (LMCT). Using two-dimensional (2D) photon spectra correlation analysis, the formation and growth of the Au nuclei and the LMCT effect observed during the synthesis of the SP-AuNCs were found to be the major causes for the changes in the conformation of the protein ligand. Our results are an important discovery and can be used to explain the mechanism of protein ligands in the synthesis of gold nanoclusters.

Nanotheranostic Application of Fluorescent Protein-Gold Nanocluster Hybrid Materials: A Mini-review

The gold nanoclusters (Au NCs) are a special kind of gold nanomaterial containing several gold atoms. Because of their small size and large surface area, Au NCs possess macroscopic quantum tunneling and dielectric domain effects. Furthermore, Au NCs fluorescent materials have longer luminous time and better photobleaching resistance compared with other fluorescent materials. The synthetic process of traditional Au NCs is complicated. Traditional Au NCs are prepared mainly by using polyamide amine type dendrites, and sixteen alkyl trimethylamine bromide or sulfhydryl small molecule as stabilizers. They are consequently synthesized by the reduction of strong reducing agents such as sodium borohydride. Notably, these materials are toxic and environmental-unfriendly. Therefore, there is an urgent need to develop more effective methods for synthesizing Au NCs via a green approach. On the other hand, the self-assembly of protein gold cluster-based materials, and their biomedical applications have become research hotspots in this field. We have been working on the synthesis, assembly and application of protein conjugated gold clusters for a long time. In this review, the synthesis and assembly of protein-gold nanoclusters and their usage in cell imaging and other medical research are discussed.

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Recent Advances in Bio-Templated Metallic Nanomaterial Synthesis and Electrocatalytic Applications

Developing metallic nanocatalysts with high reaction activity, selectivity and practical durability is a promising and active subfield in electrocatalysis. In the classical "bottom-up" approach to synthesize stable nanomaterials by chemical reduction, stabilizing additives such as polymers or organic surfactants must be present to cap the nanoparticle to prevent material bulk aggregation. In recent years, biological systems have emerged as green alternatives to support the uncoated inorganic components. One key advantage of biological templates is their inherent ability to produce nanostructures with controllable composition, facet, size and morphology under ecologically friendly synthetic conditions, which are difficult to achieve with traditional inorganic synthesis. In addition, through genetic engineering or bioconjugation, bio-templates can provide numerous possibilities for surface functionalization to incorporate specific binding sites for the target metals. Therefore, in bio-templated systems, the electrocatalytic performance of the formed nanocatalyst can be tuned by precisely controlling the material surface chemistry. With controlled improvements in size, morphology, facet exposure, surface area and electron conductivity, bio-inspired nanomaterials often exhibit enhanced catalytic activity towards electrode reactions. In this Review, recent research developments are presented in bio-approaches for metallic nanomaterial synthesis and their applications in electrocatalysis for sustainable energy storage and conversion systems.

Construction of thermally robust and porous shrimp ferritin crystalline for molecular encapsulation through intermolecular arginine-arginine attractions

Protein colloid crystals are considered as high porous soft materials, presenting great potentials in nutrients and drug encapsulation, but protein crystal fabrication usually needs precipitant and high protein concentration. Herein, an easy implemented approach was reported for the construction of protein colloid crystals in diluted solution with shimp ferritin as building blocks by taking advantage of the strength of multiple intermolecular arginine-arginine interactions. The X-ray single-crystal structure reveals that a group of exquisite arginine-arginine interactions between two neighboring ferritin enable them self-assembly into long-range ordered protein soft materials. The arginine-arginine interactions mediate crystal generation favored at pH 9.5 with 200 mM NaCl, and the resulting colloid crystals exhibit high thermal stability (90 °C for 30 min). Importantly, the interglobular cavity in colloid crystals is three times larger in volume than that of intrinsic ferritin cavity in each unit cell, which can be used for molecular encapsulation.

Recent advances in protein metalation: structural studies

Recent advances in structural studies unveiling the basis of the metal compounds/protein recognition process are discussed.

Ultrafast synthesis of carbon quantum dots from fenugreek seeds using microwave plasma enhanced decomposition: application of C-QDs to grow fluorescent protein crystals

Herein, we present the rapid synthesis of mono-dispersed carbon quantum dots (C-QDs) via a single-step microwave plasma-enhanced decomposition (MPED) process. Highly-crystalline C-QDs were synthesized in a matter of 5 min using the fenugreek seeds as a sustainable carbon source. It is the first report, to the best of our knowledge, where C-QDs were synthesized using MPED via natural carbon precursor. Synthesis of C-QDs requires no external temperature other than hydrogen (H2) plasma. Plasma containing the high-energy electrons and activated hydrogen ions predominantly provide the required energy directly into the reaction volume, thus maximizing the atom economy. C-QDs shows excellent Photoluminescence (PL) activity along with the dual-mode of excitation-dependent PL emission (blue and redshift). We investigate the reason behind the dual-mode of excitation-dependent PL. To prove the efficacy of the MPED process, C-QDs were also derived from fenugreek seeds using the traditional synthesis process, highlighting their respective size-distribution, crystallinity, quantum yield, and PL. Notably, C-QDs synthesis via MPED was 97.2% faster than the traditional thermal decomposition process. To the best of our knowledge, the present methodology to synthesize C-QDs via natural source employing MPED is three times faster and far more energy-efficient than reported so far. Additionally, the application of C-QDs to produce the florescent lysozyme protein crystals "hybrid bio-nano crystals" is also discussed. Such a guest-host strategy can be exploited to develop diverse and complex "bio-nano systems". The florescent lysozyme protein crystals could provide a platform for the development of novel next-generation polychrome luminescent crystals.

Gold/alpha-lactalbumin nanoprobes for the imaging and treatment of breast cancer

Theranostic agents should ideally be renally cleared and biodegradable. Here, we report the synthesis, characterization and theranostic applications of fluorescent ultrasmall gold quantum clusters that are stabilized by the milk metalloprotein alpha-lactalbumin. We synthesized three types of these nanoprobes that together display fluorescence across the visible and near-infrared spectra when excited at a single wavelength through optical colour coding. In live tumour-bearing mice, the near-infrared nanoprobe generates contrast for fluorescence, X-ray computed tomography and magnetic resonance imaging, and exhibits long circulation times, low accumulation in the reticuloendothelial system, sustained tumour retention, insignificant toxicity and renal clearance. An intravenously administrated near-infrared nanoprobe with a large Stokes shift facilitated the detection and image-guided resection of breast tumours in vivo using a smartphone with modified optics. Moreover, the partially unfolded structure of alpha-lactalbumin in the nanoprobe helps with the formation of an anti-cancer lipoprotein complex with oleic acid that triggers the inhibition of the MAPK and PI3K-AKT pathways, immunogenic cell death and the recruitment of infiltrating macrophages. The biodegradability and safety profile of the nanoprobes make them suitable for the systemic detection and localized treatment of cancer.

Differential Interaction of Metal Ions with Gold Nanoclusters and Application in Detection of Cobalt and Cadmium

Interest in biosensing platforms using protein fluorescent gold nanoclusters (FGNCs) has grown significantly in the past due to the unique optical properties they offer. This study investigates the interaction of metal ions with FGNCs, and the structural modifications brought about by the interaction resulting in fluorescence changes of the cluster and its successful application in the detection of two heavy metals, cobalt and cadmium. The binding of cobalt and cadmium to FGNCs synthesized from BSA significantly altered the secondary structure of the protein, causing a change in its hydrophobicity. It also resulted in a change in fluorescence properties of FGNCs by intersystem crossing (ICT) and fluorescence resonance energy transfer (FRET). Cobalt and cadmium could successfully be detected in the range of 5-165 ng/mL (R² = 0.95) and 20-1000 ng/ mL (R² = 0.91), respectively, with appreciable sensitivity. The principle was also applied for the detection of Vitamin B₁₂ in commercially available ampoules, validating the proposed method. Graphical Abstract Proposed detection method of cadmium and cobalt using FGNCs.

Genetically fused charged peptides induce rapid crystallization of proteins

We utilized electrostatic interaction to induce rapid crystallization of streptavidin. Simply mixing streptavidins possessing either a positively or negatively charged peptide at their C-terminus generated diffraction-quality crystals in a few hours. We modified the streptavidin crystals with fluorescent molecules using biotin, demonstrating the concept of protein crystals as functional biomaterials.

High mobility of lattice molecules and defects during the early stage of protein crystallization

Protein crystals are expected to be useful not only for their molecular structure analysis but also as functional materials due to their unique properties. Although the generation and the propagation of defects during crystallization play critical roles in the final properties of protein crystals, the dynamics of these processes are poorly understood. By time-resolved liquid-cell transmission electron microscopy, we observed that nanosized crystal defects are surprisingly mobile during the early stages of the crystallization of a lysozyme as a model protein. This highly dynamic behavior of defects reveals that the lattice molecules are mobile throughout the crystal structure. Moreover, the disappearance of the defects indicated that intermolecular bonds can break and reform rapidly with little energetic cost, as reported in theoretical studies. All these findings are in marked contrast to the generally accepted notion that crystal lattices are rigid with very limited mobility of individual lattice molecules.

In Situ Ligand-Directed Growth of Gold Nanoparticles in Biological Tissues

Fundamental understandings and precise control of nanoparticle growth in the complex biological environment are crucial to broadening their potential applications in tissue imaging. Herein, we report that glutathione (GSH), a widely used capping ligand for precise control of the size of gold nanoparticle (AuNP) down to single-atom level in test tubes, can also be used to direct the selective growth of the AuNPs in the mitochondria of renal tubule cells as well as hippocampus cells in the tissues. Precise control of this growth process can lead to the formation of both ultrasmall AuNPs with near-infrared luminescence and large plasmonic AuNPs. The observed selective growth of the AuNPs is likely due to unique GSH storage function of the mitochondria. Using a different ligand, β-glucose thiol, we also found that the brush border of the intestine for glucose absorption became the major site for the growth of luminescent AuNPs. These findings suggest that selective growth of AuNPs in the biological tissues can indeed be directed with specific ligands, opening up a new avenue to tissue labeling and future development of artificial bionano hybrid systems.

Noble Metal Nanostructured Materials for Chemical and Biosensing Systems

Nanomaterials with unique physical and chemical properties have attracted extensive attention of scientific research and will play an increasingly important role in the future development of science and technology. With the gradual deepening of research, noble metal nanomaterials have been applied in the fields of new energy materials, photoelectric information storage, and nano-enhanced catalysis due to their unique optical, electrical and catalytic properties. Nanostructured materials formed by noble metal elements (Au, Ag, etc.) exhibit remarkable photoelectric properties, good stability and low biotoxicity, which received extensive attention in chemical and biological sensing field and achieved significant research progress. In this paper, the research on the synthesis, modification and sensing application of the existing noble metal nanomaterials is reviewed in detail, which provides a theoretical guidance for further research on the functional properties of such nanostructured materials and their applications of other nanofields.

Plasmonic bimetallic nanodisk arrays for DNA conformation sensing

The integration of large-scale 2D bimetallic Ag/Au nanodisk arrays with gold nanoparticles is developed for sensing DNA conformation with the assistance of 3D finite-difference time-domain simulation. The optimized system comprising Ag/Au nanodisk arrays and gold nanoparticles offers a more than 6-fold enhancement in surface plasmon resonance shift, enabling the feasibility for sensitive DNA detection with a detection limit down to 100 femtomolar. Importantly, owing to the distance-dependent nature of the surface plasmon signal, sensitive differentiation of DNA conformations can be achieved with a conventional optical measurement. This platform could provide new exciting capabilities for a reliable, reproducible, and label-free assay analysis for investigating the conformations of DNA and other biological molecules.

Colorimetric Sensor Array for Human Semen Identification Designed by Coupling Zirconium Metal-Organic Frameworks with DNA-Modified Gold Nanoparticles

Rapid and accurate identification of semen is critical for male infertility diagnosis and the arrangement of personalized treatment. However, the complexity and diversity of samples impose lots of restrictions in detection. To solve this problem, we propose a colorimetric sensor array in this work by coupling zirconium metal-organic frameworks (Zr-MOFs) with single-stranded-DNA-decorated gold nanoparticles (ssDNA-AuNPs) for human semen identification. Because of the coordination interactions between the Zr₆ clusters and the DNA phosphate backbone, as well as π-π stacking and H-bonding, Zr-MOFs can absorb and precipitate AuNPs with the aid of single-stranded DNA. What's more, addition of semen samples in the test solution, proteins, or other contents in the samples will affect the co-precipitation of Zr-MOFs and ssDNA-AuNPs. Subsequently, the color of the supernatant will change and a method to identify human semen can be developed. Further studies reveal that the method can completely detect different semen cases based on the differences in inclusions, demonstrating the characteristics of simplicity, feasibility, and sensitivity in the application of male infertility diagnosis.

Design and site-directed compartmentalization of gold nanoclusters within the intrasubunit interfaces of ferritin nanocage

BACKGROUND

Protein nanocages have emerged as popular nanocarriers for either drug delivery or biotemplates for the preparation of nanomaterials. However, only three interfaces, namely exterior surface, intersubunit and inner cavity, have been used as reaction sites for the above purposes with all known protein nanocages. On the other hand, how to control the site of Au NCs formed within a targeted protein template while maintaining the functionality of protein itself remains challenging.

RESULTS

In this work, inspired by compartmentalization in living systems, we firstly come up with the conception of "intrasubunit interfaces", located within subunit of protein nanocage. We built a new, specific compartment for fabrication of gold nanoclusters by genetic modification of the inherent ferroxidase center located within four-α-helix bundle of each ferritin subunit. This newly built compartment not only realizes the site-directed synthesis of gold nanoclusters but also has no effect on the functionality of ferritin itself such as encapsulation by its inner cavity. These redesigned composites can be further applied as fluorescent imaging agent and carriers for preparation of hybrid nanomaterials.

CONCLUSIONS

The designing strategy of intrasubunit interfaces opens a new way for future applications of cage-like proteins.

Identifying Reducing and Capping Sites of Protein-Encapsulated Gold Nanoclusters

The reducing and capping sites along with their local structure impact photo properties of the red bovine serum albumin-capped Au nanocluster (BSA-AuNC), however, they are hard to identify. We developped a workflow and relevant techniques using mass spectrometry (MS) to identify the reducing and capping sites of BSA-AuNCs involved in their formation and fluorescence. Digestion without disulfide cleavages yielded an Au core fraction exhibiting red fluorescence and [AunSm] ion signals and a non-core fraction exhibiting neither of them. The core fraction was identified to mainly be comprised of peptides containing cysteine residues. The fluorescence and [AunSm] signals were quenched by tris(2-carboxyethyl)phosphine, confirming that disulfide groups were required for nanocluster stabilization and fluorescence. By MS sequencing, the disulfide pairs, C75-C91/C90-C101 in domain IA, C315-C360/C359-C368 in domain IIB, and C513-C558/C557-C566 in domain IIIB, were identified to be main capping sites of red AuNCs. Peptides containing oxidized cysteines (sulfinic or cysteic acid) were identified as reducing sites mainly in the non-core fraction, suggesting that disulfide cleavages by oxidization and conformational changes contributed to the subsequent growth of nanoclusters at nearby intact disulfide pairs. This is the first report on precise identification of the reducing and capping sites of BSA-AuNCs.

Ferritin-based anticancer metallodrug delivery: Crystallographic, analytical and cytotoxicity studies

The encapsulation of anticancer metal-based drugs within a protein nanocage represents a valuable strategy to improve the efficacy and selectivity of these compounds towards cancer cells. The preparation, characterization of the in vitro cytotoxicity and X-ray structures of several ferritin-metallodrug nanocomposites (mainly containing platinum-, ruthenium- and gold-based anticancer agents) are here reviewed. The molecular mechanisms of action of these Ft-metallodrug adducts are discussed and future directions in the field are outlined.

Critical role of tyrosine-20 in formation of gold nanoclusters within lysozyme: a molecular dynamics study

Lysozyme is one of the most commonly used proteins for encapsulating gold nanoclusters, yielding Ly-AuNC complexes. While possible applications of Ly-AuNCs in environmental, biological and trace metal sensing in solution have been demonstrated, there is currently a poor understanding of the physical characteristics of the Ly-AuNC complex. In this study we have employed fully atomistic molecular dynamics simulations to gain an understanding of the formation of Au clusters within the protein. It was found that in order to form AuNCs in the simulations, an approach of targeted insertion of Au atoms at a critical surface residue was needed. Tyrosine is known to be crucial for the reduction of Au salts experimentally, and our simulations showed that Tyr20 is the key residue for the formation of an AuNC beneath the protein surface in the α-helical domain. It is hoped these observations will aid future improvements and modification of Ly-AuNCs via alterations of the alpha-helix domain or Tyr20.

Protein-mediated disproportionation of Au(i): insights from the structures of adducts of Au(iii) compounds bearingN,N-pyridylbenzimidazole derivatives with lysozyme

Structural data of protein/gold adducts suggest protein-mediated reduction of Au(iii) into Au(i) and disproportionation of Au(i) into Au(iii) and Au(0).

Computational design of symmetrical eight-bladed β-propeller proteins

β-Propeller proteins form one of the largest families of protein structures, with a pseudo-symmetrical fold made up of subdomains called blades. They are not only abundant but are also involved in a wide variety of cellular processes, often by acting as a platform for the assembly of protein complexes. WD40 proteins are a subfamily of propeller proteins with no intrinsic enzymatic activity, but their stable, modular architecture and versatile surface have allowed evolution to adapt them to many vital roles. By computationally reverse-engineering the duplication, fusion and diversification events in the evolutionary history of a WD40 protein, a perfectly symmetrical homologue called Tako8 was made. If two or four blades of Tako8 are expressed as single polypeptides, they do not self-assemble to complete the eight-bladed architecture, which may be owing to the closely spaced negative charges inside the ring. A different computational approach was employed to redesign Tako8 to create Ika8, a fourfold-symmetrical protein in which neighbouring blades carry compensating charges. Ika2 and Ika4, carrying two or four blades per subunit, respectively, were found to assemble spontaneously into a complete eight-bladed ring in solution. These artificial eight-bladed rings may find applications in bionanotechnology and as models to study the folding and evolution of WD40 proteins.

Principles and methods used to grow and optimize crystals of protein-metallodrug adducts, to determine metal binding sites and to assign metal ligands

The characterization of the interactions between biological macromolecules (proteins and nucleic acids) and metal-based drugs is a fundamental prerequisite for understanding their mechanisms of action. X-ray crystallography enables the structural analysis of such complexes with atomic level detail. However, this approach requires the preparation of highly diffracting single crystals, the measurement of diffraction patterns and the structural analysis and interpretation of macromolecule-metal interactions from electron density maps. In this review, we describe principles and methods used to grow and optimize crystals of protein-metallodrug adducts, to determine metal binding sites and to assign and validate metal ligands. Examples from the literature and experience in our own laboratory are provided and key challenges are described, notably crystallization and molecular model refinement against the X-ray diffraction data.