Simultaneous Stabilization and Functionalization of Gold Nanoparticles via Biomolecule Conjugation: Progress and Perspectives

Bonding states of gold/silver plasmonic nanostructures and sulfur-containing active biological ingredients in biomedical applications: a review

As one of the most instrumental components in the architecture of advanced nanomedicines, plasmonic nanostructures (mainly gold and silver nanomaterials) have been paid a lot of attention. This type of nanomaterial can absorb light photons with a specific wavelength and generate heat or excited electrons through surface resonance, which is a unique physical property. In innovative biomaterials, a significant number of theranostic (therapeutic and diagnostic) materials are produced through the conjugation of thiol-containing ingredients with gold and silver nanoparticles (Au and Ag NPs). Hence, it is essential to investigate Au/Ag-S interfaces precisely and determine the exact bonding states in the active nanobiomaterials. This study intends to provide useful insights into the interactions between Au/Ag NPs and thiol groups that exist in the structure of biomaterials. In this regard, the modeling of Au/Ag-S bonding in active biological ingredients is precisely reviewed. Then, the physiological stability of Au/Ag-based plasmonic nanobioconjugates in real physiological environments (pharmacokinetics) is discussed. Recent experimental validation and achievements of plasmonic theranostics and radiolabelled nanomaterials based on Au/Ag-S conjugation are also profoundly reviewed. This study will also help researchers working on biosensors in which plasmonic devices deal with the thiol-containing biomaterials (e.g., antibodies) inside blood serum and living cells.

Effect of Gold Nanoparticle Size on Regulated Catalytic Activity of Temperature-Responsive Polymer-Gold Nanoparticle Hybrid Microgels

Gold nanoparticles (AuNPs) possess attractive electronic, optical, and catalytic properties, enabling many potential applications. Poly(N-isopropyl acrylamide) (PNIPAAm) is a temperature-responsive polymer that changes its hydrophilicity upon a slight temperature change, and combining PNIPAAm with AuNPs allows us to modulate the properties of AuNPs by temperature. In a previous study, we proposed a simpler method for designing PNIPAAm-AuNP hybrid microgels, which used an AuNP monomer with polymerizable groups. The size of AuNPs is the most important factor influencing their catalytic performance, and numerous studies have emphasized the importance of controlling the size of AuNPs by adjusting their stabilizer concentration. This paper focuses on the effect of AuNP size on the catalytic activity of PNIPAAm-AuNP hybrid microgels prepared via the copolymerization of N-isopropyl acrylamide and AuNP monomers with different AuNP sizes. To quantitatively evaluate the catalytic activity of the hybrid microgels, we monitored the reduction of 4-nitrophenol to 4-aminophenol using the hybrid microgels with various AuNP sizes. While the hybrid microgels with an AuNP size of 13.0 nm exhibited the highest reaction rate and the apparent reaction rate constant (kapp) of 24.2 × 10-3 s-1, those of 35.9 nm exhibited a small kapp of 1.3 × 10-3 s-1. Thus, the catalytic activity of the PNIPAAm-AuNP hybrid microgel was strongly influenced by the AuNP size. The hybrid microgels with various AuNP sizes enabled the reversibly temperature-responsive on-off regulation of the reduction reaction.

211At on gold nanoparticles for targeted radionuclide therapy application

Targeted alpha therapy (TAT) is a methodology that is being developed as a promising cancer treatment using the α-particle decay of radionuclides. This technique involves the use of heavy radioactive elements being placed near the cancer target area to cause maximum damage to the cancer cells while minimizing the damage to healthy cells. Using gold nanoparticles (AuNPs) as carriers, a more effective therapy methodology may be realized. AuNPs can be good candidates for transporting these radionuclides to the vicinity of the cancer cells since they can be labeled not just with the radionuclides, but also a host of other proteins and ligands to target these cells and serve as additional treatment options. Research has shown that astatine and iodine are capable of adsorbing onto the surface of gold, creating a covalent bond that is quite stable for use in experiments. However, there are still many challenges that lie ahead in this area, whether they be theoretical, experimental, and even in real-life applications. This review will cover some of the major developments, as well as the current state of technology, and the problems that need to be tackled as this research topic moves along to maturity. The hope is that with more workers joining the field, we can make a positive impact on society, in addition to bringing improvement and more knowledge to science.

Ångstrom-scale gold particles loaded with alendronate via alpha-lipoic acid alleviate bone loss in osteoporotic mice

Osteoporosis is a highly prevalent metabolic disease characterized by low systemic bone mass and deterioration of bone microarchitecture, resulting in reduced bone strength and increased fracture risk. Current treatment options for osteoporosis are limited by factors such as efficacy, cost, availability, side effects, and acceptability to patients. Gold nanoparticles show promise as an emerging osteoporosis therapy due to their osteogenic effects and ability to allow therapeutic delivery but have inherent constraints, such as low specificity and the potential for heavy metal accumulation in the body. This study reports the synthesis of ultrasmall gold particles almost reaching the Ångstrom (Ång) dimension. The antioxidant alpha-lipoic acid (LA) is used as a dispersant and stabilizer to coat Ångstrom-scale gold particles (AuÅPs). Alendronate (AL), an amino-bisphosphonate commonly used in drug therapy for osteoporosis, is conjugated through LA to the surface of AuÅPs, allowing targeted delivery to bone and enhancing antiresorptive therapeutic effects. In this study, alendronate-loaded Ångstrom-scale gold particles (AuÅPs-AL) were used for the first time to promote osteogenesis and alleviate bone loss through regulation of the WNT signaling pathway, as shown through in vitro tests. The in vivo therapeutic effects of AuÅPs-AL were demonstrated in an established osteoporosis mouse model. The results of Micro-computed Tomography, histology, and tartrate-resistant acid phosphatase staining indicated that AuÅPs-AL significantly improved bone density and prevented bone loss, with no evidence of nanoparticle-associated toxicity. These findings suggest the possible future application of AuÅPs-AL in osteoporosis therapy and point to the potential of developing new approaches for treating metabolic bone diseases using Ångstrom-scale gold particles.

HAuCl4-mediated green synthesis of highly stable Au NPs from natural active polysaccharides: Synthetic mechanism and antioxidant property

Polysaccharide-functionalized gold nanoparticles (Polysaccharide-Au NPs) with high stability were successfully prepared by a straightforward method. Notably, the Au (III) ion acts as a strong Lewis acid to facilitate glycosidic bond breaking. Subsequently, the polysaccharide conformation was transformed to an open-chain form, exposing highly reduced aldehyde or ketone groups that reduce Au (III) to Au (0) crystal species, further growing into Au NPs. As-prepared Au NPs displayed excellent stability over a longer storage period (more than 70 days), a wide range of temperatures (25-60 °C), and pH range (3-11), varying concentrations (0-200 mM) and types of salt ions (Na+, K+, Ca2+, Mg2+), and glutathione solutions (5 mM). More interestingly, polysaccharide-Au NPs retained the antioxidant activity of polysaccharides and reduced oxidative damage at the cellular level through decreased reactive oxygen species (ROS) production. The intracellular levels of ROS pretreated with polysaccharide and polysaccharide-Au NPs were decreased 53.12-75.85 % compared to the H2O2 group, respectively. Therefore, the green synthesized Au NPs from natural active polysaccharides exhibit potential applications in biomedical fields.

Biomolecular Corona of Gold Nanoparticles: The Urgent Need for Strong Roots to Grow Strong Branches

Gold nanoparticles (GNPs) are largely employed in diagnostics/biosensors and are among the most investigated nanomaterials in biology/medicine. However, few GNP-based nanoformulations have received FDA approval to date, and promising in vitro studies have failed to translate to in vivo efficacy. One key factor is that biological fluids contain high concentrations of proteins, lipids, sugars, and metabolites, which can adsorb/interact with the GNP's surface, forming a layer called biomolecular corona (BMC). The BMC can mask prepared functionalities and target moieties, creating new surface chemistry and determining GNPs' biological fate. Here, the current knowledge is summarized on GNP-BMCs, analyzing the factors driving these interactions and the biological consequences. A partial fingerprint of GNP-BMC analyzing common patterns of composition in the literature is extrapolated. However, a red flag is also risen concerning the current lack of data availability and regulated form of knowledge on BMC. Nanomedicine is still in its infancy, and relying on recently developed analytical and informatic tools offers an unprecedented opportunity to make a leap forward. However, a restart through robust shared protocols and data sharing is necessary to obtain "stronger roots". This will create a path to exploiting BMC for human benefit, promoting the clinical translation of biomedical nanotools.

Gold Nanoprobes for Detection of a Crucial EGFR Deletion for Early Diagnosis of Non-Small-Cell Lung Cancer

Gold nanoparticles (AuNPs) exhibit improved optical and spectral properties compared to bulk materials, making them suitable for the detection of DNA, RNA, antigens, and antibodies. Here, we describe a simple, selective, and rapid non-cross linking detection assay, using approx. 35 nm spherical Au nanoprobes, for a common mutation occurring in exon 19 of the epidermal growth factor receptor (EGFR), associated with non-small-cell lung cancer cells. AuNPs were synthesized based on the seed-mediated growth method and functionalized with a specific 16 bp thiolated oligonucleotide using a pH-assisted method. Both AuNPs and Au nanoprobes proved to be highly stable and monodisperse through ultraviolet-visible spectrophotometry, dynamic light scattering (DLS), and electrophoretic light scattering (ELS). Our results indicate a detection limit of 1.5 µg mL-1 using a 0.15 nmol dm-3 Au nanoprobe concentration. In conclusion, this work presents an effective possibility for a straightforward, fast, and inexpensive alternative for the detection of DNA sequences related to lung cancer, leading to a potential platform for early diagnosis of lung cancer patients.

Facile Synthesis of PEGylated Gold Nanoparticles for Enhanced Colorimetric Detection of Histamine

Histamine is among the biogenic amines that are formed during the microbial decarboxylation of amino acids in various food products, posing a significant threat to both food safety and human health. Herein, we present a one-step synthesis of PEGylated gold nanoparticles (PEG-AuNPs) for rapid, simple, and cost-effective colorimetric histamine detection. PEG-AuNPs' surface plasmon resonance (SPR) range at 520-530 nm with a hydrodynamic size distribution of 20-40 nm. Fourier transform infrared (FT-IR) spectra confirmed the reduction of AuNPs at 1645 cm-1 along with the other observed peaks at 2870, 1350, and 1100 cm-1 as a strong evidence for the presence of PEG. Upon the addition of histamine to the PEG-AuNP solution, transmission electron microscopy (TEM) highlighted the aggregation of nanoparticles. In addition, red shifting and a decrease in the absorbance of the SPR peak along with the appearance of an additional peak at ∼690 nm was observed in the PEG-AuNP absorption spectra in the presence of histamine. Increasing the PEG concentration in the gold colloids leads to the formation of a protective barrier around the surface of nanoparticles, which influences the colloidal stability by impeding the aggregation of PEG-AuNPs upon histamine addition. The minimum colorimetric response of PEG-AuNPs to histamine concentration is 30 ppm, as assessed by the naked eye. The absorption ratio (A690/A526) showed a linear dynamic range from 20 to 100 ppm with a limit of detection of 9.357 μM. Additionally, the assay demonstrates a commendable selectivity toward histamine analyte.

Quantified instant conjugation of peptides on a nanogold surface for tunable ice recrystallization inhibition

The adverse effects of recrystallization limit the application of cryopreservation in many fields. Peptide-based materials play an essential role in the antifreezing area because of their excellent biocompatibility and abundant ice-binding sites. Peptide-gold nanoparticle conjugates can effectively reduce time and material costs through metal-thiol interactions, but controlled modification remains an outstanding issue, which makes it difficult to elucidate the antifreezing effects of antifreeze peptides at different densities and lengths. In this study, we developed an instant peptide capping on gold nanoparticles with butanol-assisted dehydration and provided a controllable quantitative coupling within a certain range. This chemical dehydration makes it possible to fabricate peptide-gold nanoparticle conjugates in large batches at minute levels. Based on this, the influence of the peptide density and sequence length on the antifreezing behaviors of the conjugates was investigated. The results evidenced that the antifreezing property of the flexible peptide conjugated on a rigid core is related to both the density and length of the peptide. In a certain range, the density is proportional to the antifreeze, while the length is negatively correlated with it. We proposed a rapidly controllable method for synthesizing peptide-gold nanoparticle conjugates, which may provide a universal approach for the development of subsequent recrystallization-inhibiting materials.

Ultrasmall ATP-Coated Gold Nanoparticles Specifically Bind to Non-Hybridized Regions in DNA

Here we report the synthesis of ultrasmall (2 nm in diameter) ATP-coated gold nanoparticles, ATP-NPs. ATP-NPs can be enlarged in a predictable manner by the surface-catalyzed reduction of gold ions with ascorbate, yielding uniform gold nanoparticles ranging in size from 2 to 5 nm in diameter. Using atomic force microscopy (AFM), we demonstrate that ATP-NPs can efficiently and selectively bind to a short non-hybridized 5A/5A region (composed of a 5A-nucleotide on each strand of the double helix) inserted into a circular double-stranded plasmid, Puc19. Neither small (1.4 nm in diameter) commercially available nanoparticles nor 5 nm citrate-protected ones are capable of binding to the plasmid. The unique ability to specifically target DNA regions characterized by local structural alterations of the double helix can pave the way for applications of the particles in the detection of genomic DNA regions containing mismatches and mutations that are common for cancer cells.

Design and Characterization of pMyc/pMax Peptide-Coupled Gold Nanosystems for Targeting Myc in Prostate Cancer Cell Lines

Myc and Max are essential proteins in the development of prostate cancer. They act by dimerizing and binding to E-box sequences. Disrupting the Myc:Max heterodimer interaction or its binding to E-box sequences to interrupt gene transcription represent promising strategies for treating cancer. We designed novel pMyc and pMax peptides from reference sequences, and we evaluated their ability to bind specifically to E-box sequences using an electrophoretic mobility shift assay (EMSA). Then, we assembled nanosystems (NSs) by coupling pMyc and pMax peptides to AuNPs, and determined peptide conjugation using UV-Vis spectroscopy. After that, we characterized the NS to obtain the nanoparticle's size, hydrodynamic diameter, and zeta potential. Finally, we evaluated hemocompatibility and cytotoxic effects in three different prostate adenocarcinoma cell lines (LNCaP, PC-3, and DU145) and a non-cancerous cell line (Vero CCL-81). EMSA results suggests peptide-nucleic acid interactions between the pMyc:pMax dimer and the E-box. The hemolysis test showed little hemolytic activity for the NS at the concentrations (5, 0.5, and 0.05 ng/µL) we evaluated. Cell viability assays showed NS cytotoxicity. Overall, results suggest that the NS with pMyc and pMax peptides might be suitable for further research regarding Myc-driven prostate adenocarcinomas.

A novel label-free electrochemical immunosensor for the detection of heat shock protein 70 of lung adenocarcinoma cell line following paclitaxel treatment using l-cysteine-functionalized Au@MnO2/MoO3 nanocomposites

The future trend in achieving precision medicine involves the development of non-invasive cancer biomarker sensors that offer high accuracy, low cost, and time-saving benefits for risk clarification, early detection, disease detection, and therapeutic monitoring. A facile approach for the synthesis of MoO3 nanosheets was developed by thermally oxidizing MoS2 nanosheets in air followed by thermal annealing. Subsequently, Au@MnO2 nanocomposites were prepared using a combined hydrothermal process and in situ chemical synthesis. In this study, we present a novel immunosensor design strategy involving the immobilization of antiHSP70 antibodies on Au@MnO2/MoO3 nanocomposites modified on a screen-printed electrode (SPE) using EDC/NHS chemistry. This study establishes HSP70 as a potential biomarker for monitoring therapeutic response during anticancer therapy. Impedance measurements of HSP70 on the Au@MnO2/MoO3/SPE immunosensor using EIS showed an increase in impedance with an increase in HSP70 concentration. The electrochemical immunosensor demonstrated a good linear response in the range of 0.001 to 1000 ng mL-1 with a detection limit of 0.17 pg mL-1 under optimal conditions. Moreover, the immunosensor was effective in detecting HSP70 at low concentrations in a lung adenocarcinoma cell line following Paclitaxel treatment, indicating its potential for early detection of the HSP70 biomarker in organ-on-a-chip and clinical applications.

Scanning Tunneling Microscopy Study of Lipoic Acid, Mannose, and cRGD@AuNPs Conjugates

The functionalization of AuNPs with different biological elements was achieved to investigate their possibility in biomedical applications such as drug delivery, vaccine development, sensing, and imaging. Biofunctionalized AuNPs are pursued for applications such as drug delivery, vaccine development, sensing, and imaging. In this study, AuNPs with diameters of 20 nm were functionalized with lipoic acid, mannose, or the cRGD peptide. By using UV-vis spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy, and scanning tunneling microscopy techniques, we showed that AuNPs can be functionalized by these biomolecules in a reliable way to obtain conjugates to explore potential biomedical applications. In particular, we demonstrate that the STM technique can be employed to analyze biofunctionalized AuNPs, and the obtained information can be valuable in the design of biomedical applications.

Physicochemical Properties and Route of Systemic Delivery Control the In Vivo Dynamics and Breakdown of Radiolabeled Gold Nanostars

The in vivo dynamics of nanoparticles requires a mechanistic understanding of multiple factors. Here, for the first time, the surprising breakdown of functionalized gold nanostars (F-AuNSs) conjugated with antibodies and 64 Cu radiolabels in vivo and in artificial lysosomal fluid ex vivo, is shown. The short-term biodistribution of F-AuNSs is driven by the route of systemic delivery (intravenous vs intraperitoneal) and long-term fate is controlled by the tissue type in vivo. In vitro studies including endocytosis pathways, intracellular trafficking, and opsonization, are combined with in vivo studies integrating a milieu of spectroscopy and microcopy techniques that show F-AuNSs dynamics is driven by their physicochemical properties and route of delivery. F-AuNSs break down into sub-20 nm broken nanoparticles as early as 7 days postinjection. Martini coarse-grained simulations are performed to support the in vivo findings. Simulations suggest that shape, size, and charge of the broken nanoparticles, and composition of the lipid membrane depicting various tissues govern the interaction of the nanoparticles with the membrane, and the rate of translocation across the membrane to ultimately enable tissue clearance. The fundamental study addresses critical gaps in the knowledge regarding the fate of nanoparticles in vivo that remain a bottleneck in their clinical translation.

Positively Charged-Amylose-Entangled Au-Nanoparticles Acting as Protein Carriers and Potential Adjuvants to SARS-CoV-2 Subunit Vaccines

The COVID-19 pandemic continues to spread worldwide. To protect and control the spread of SARS-CoV-2, varieties of subunit vaccines based on spike (S) proteins have been approved for human applications. Here, we report a new subunit vaccine design strategy that functions as both an antigen carrier and an adjuvant in immunization to elicit high-level immune responses. The complex of 2-hydroxypropyl-trimethylammonium chloride chitosan and amylose entangles Au nanoparticles (HTCC/amylose/AuNPs) forming 40 nm nanocarriers with a positive charge. The obtained positively charged nanoparticles reveal many merits, including the larger S protein loading capacity in PBS buffer, higher cellular uptake ability, and lower cell cytotoxicity, supporting their potential as safe vaccine nanocarriers. Two functionalized nanoparticle subunit vaccines are prepared via loading full-length S proteins derived from SARS-CoV-2 variants. In mice, both prepared vaccines elicit high specific IgG antibodies, neutralize antibodies, and immunoglobulin IgG1 and IgG2a. The prepared vaccines also elicit robust T- and B-cell immune responses and increase CD19⁺ B cells, CD11C⁺ dendritic cells, and CD11B⁺ macrophages at the alveoli and bronchi of the immunized mice. Furthermore, the results of skin safety tests and histological observation of organs indicated in vivo safety of HTCC/amylose/AuNP-based vaccines. Summarily, our prepared HTCC/amylose/AuNP have significant potential as general vaccine carriers for the delivery of different antigens with potent immune stimulation.

Enhanced resonance energy transfer in gold nanoparticles bifunctionalized by tryptophan and riboflavin and its application in fluorescence bioimaging

Gold nanoparticles were functionalized by amino acid tryptophan and vitamin riboflavin - a resonance energy transfer (RET) pair of biomolecules. The presence of the gold nanoparticles resulted in 65% increase in RET efficiency. Because of enhanced RET efficiency, the photobleaching dynamics of the fluorescent molecules at the surface of the nanoparticles is different from that of molecules in solution. The observed effect was used for detection of the functionalized nanoparticles within biological material rich with autofluorescent species. Synchrotron radiation deep-ultraviolet fluorescence microscopy is used to study the photobleaching dynamics of the fluorescence centers within human hepatocellular carcinoma Huh7.5.1 cells incubated with the nanoparticles. The fluorescent centers were classified according to their photobleaching dynamics, which enabled the discrimination of the cell areas where the accumulation of the nanoparticles takes place, even though the particles were smaller than the spatial resolution of the images.

Isolation of organophosphate pesticides from water using gold nanoparticles doped magnetic three-dimensional graphene oxide

Pesticides are a large group of pristine organic contaminants, which are widely discharged into environmental water due to agricultural activities. Hence, extraction, determination, and removal of pesticides from water resources are necessary for human health. In this study, novel adsorbent was developed based on three-dimensional magnetic graphene coated with gold nanoparticles (3D-MG@AuNPs) for extraction of chlorpyrifos, dicrotophos, fenitrothion, and piperophos as four specific organophosphorus pesticides (OPPs) from wastewater and tap water samples. The proposed nanocomposite was characterized; FTIR and EDX are performed for the expected functional groups and elemental analysis, SEM showed the unique and spherical AuNPs are well dispersed over graphene sheets. In this investigation, the important parameters that have effect on the extraction efficiency, including the desorbing solvent, desorbing solvent volume, vortex time, the extraction time, adsorbent dosage, pH of sample solutions, and salt effect were evaluated. In conclusion, the measured amounts of the chosen OPPs were determined using the gas chromatography microelectron capture (μECD-GC) method. Limits of quantification (S/N ratio of 10) and detection (S/N ratio of 3) were attained at concentrations of 0.26-0.43 μg.L^-1 and 0.08-0.14 μg.L^-1, respectively. According to the results of the investigations, the synthesized 3D-MG@AuNPs did not require any complicated sample preparation methods; therefore, it is a very good choice for solid magnetic phase extraction studies.

Ethanol and NaCl-Induced Gold Nanoparticle Aggregation Toxicity toward DNA Investigated with a DNA/GCE Biosensor

Engineered nanomaterials are becoming increasingly common in commercial and consumer products and pose a serious toxicological threat. Exposure of human organisms to nanomaterials can occur by inhalation, oral intake, or dermal transport. Together with the consumption of alcohol in the physiological environment of the body containing NaCl, this has raised concerns about the potentially harmful effects of ingested nanomaterials on human health. Although gold nanoparticles (AuNPs) exhibit great potential for various biomedical applications, there is some inconsistency in the case of the unambiguous genotoxicity of AuNPs due to differences in their shape, size, solubility, and exposure time. A DNA/GCE (DNA/glassy carbon electrode) biosensor was used to study ethanol (EtOH) and NaCl-induced gold nanoparticle aggregation genotoxicity under UV light in this study. The genotoxic effect of dispersed and aggregated negatively charged gold nanoparticles AuNP1 (8 nm) and AuNP2 (30 nm) toward salmon sperm double-stranded dsDNA was monitored by cyclic and square-wave voltammetry (CV, SWV). Electrochemical impedance spectroscopy (EIS) was used for a surface study of the biosensor. The aggregation of AuNPs was monitored by UV-vis spectroscopy. AuNP1 aggregates formed by 30% v/v EtOH and 0.15 mol·L^-1 NaCl caused the greatest damage to the biosensor DNA layer.

Precise Localization and Simultaneous Bacterial Eradication of Biofilms Based on Nanocontainers with Successive Responsive Property toward pH and ATP

The bacterial colonization of surfaces and subsequent biofilm formation are a great threat in medical therapy and clinical diagnosis. The complex internal structure and composition sets an enormous obstacle for the localization and removal of biofilms. In this study, we proposed a novel biofilm-targeted nanocontainer with successive responsive property toward pH and ATP for precise localization and simultaneous bacterial eradication, with an acidic and adenosine triphosphate (ATP)-rich microenvironment within biofilms, formed due to the accumulation of fatty acids and ATP in the three-dimensional enclosed structure, integrated as two successive indicators to improve the precision of biofilm identification and removal. The biofilm-targeted nanocontainer was composed of a ATP-responsive zeolitic imidazolate framework-90 (ZIF-90) core loaded with Rho 6G and doxorubicin hydrochloride (DOX) encapsulated in the pH-responsive amorphous calcium carbonate/poly(acrylic acid) (ACC/PAA) shell. In the presence of biofilms, the ACC/PAA shell and ZIF-90 core were successively degraded by the accumulated H⁺ and ATP within biofilms, resulting in the release of fluorescence indicators and antimicrobial agents. On the other hand, to meet the application requirements of different biofilm scenarios, the pH response ability of the nanocontainers could be adjusted by changing the metallic ions (Ni²⁺, Zn²⁺, and Cu²⁺) doped into the structure of the ACC/PAA shell. Owing to excellent water dispersion of the pH/ATP double-responsive ZIF-90@Zn-ACC/PAA nanocontainer, precise localization and simultaneous bacterial eradication was successfully realized via a simple spray process. The successive pH/ATP two-step unlocking processes endowed the nanocontainers high precision for localization and simultaneous eradication of biofilms, which made the proposed nanocontainers high promising in food safety and medical treatment.

Hierarchy of hybrid materials. Part-II: The place of organics-on-inorganics in it, their composition and applications

Hybrid materials or hybrids incorporating organic and inorganic constituents are emerging as a very potent and promising class of materials due to the diverse but complementary nature of their properties. This complementarity leads to a perfect synergy of properties of the desired materials and products as well as to an extensive range of their application areas. Recently, we have overviewed and classified hybrid materials describing inorganics-in-organics in Part-I (Saveleva, et al., Front. Chem., 2019, 7, 179). Here, we extend that work in Part-II describing organics-on-inorganics, i.e., inorganic materials modified by organic moieties, their structure and functionalities. Inorganic constituents comprise of colloids/nanoparticles and flat surfaces/matrices comprise of metallic (noble metal, metal oxide, metal-organic framework, magnetic nanoparticles, alloy) and non-metallic (minerals, clays, carbons, and ceramics) materials; while organic additives can include molecules (polymers, fluorescence dyes, surfactants), biomolecules (proteins, carbohydtrates, antibodies and nucleic acids) and even higher-level organisms such as cells, bacteria, and microorganisms. Similarly to what was described in Part-I, we look at similar and dissimilar properties of organic-inorganic materials summarizing those bringing complementarity and composition. A broad range of applications of these hybrid materials is also presented whose development is spurred by engaging different scientific research communities.

Curative Effects of Copper Iodide Embedded on Gallic Acid Incorporated in a Poly(vinyl alcohol) (PVA) Liquid Bandage

In daily life, people are often receiving minor cuts due to carelessness, leaving wounds on the skin. If wound healing is interrupted and the healing process does not finish, pathogens can easily enter wounds and cause infection. Liquid bandages are a fast and convenient way to help stop the bleeding of superficial wounds. Moreover, antibacterial agents in liquid bandages can promote wound restoration and fight bacteria. Herein, a poly(vinyl alcohol) (PVA) liquid bandage incorporating copper iodide nanoparticles (CuI NPs) was developed. CuI NPs were synthesized through green synthesis using gallic acid (GA) as a reducing and capping agent. The sizes of the CuI NPs, which were dependent on the concentration of GA, were 41.45, 43.51 and 49.71 nm, with the concentrations of gallic acid being 0, 2.5 mM and 5.0 mM, respectively. CuI NPs were analyzed using FTIR, XRD and SEM and tested for peroxidase-like properties and antibacterial activity. Then, PVA liquid bandages were formulated with different concentrations of stock CuI suspension. The results revealed that PVA liquid bandages incorporating 0.190% CuI synthesized with 5.0 mM of GA can kill bacteria within 24 h and have no harmful effects on human fibroblast cells.

Nanomaterial Gas Sensors for Biosensing Applications: A Review

BACKGROUND

Nanomaterial is one of the most used materials for various gas sensing applications to detect toxic gases, human breath, and other specific gas sensing. One of the most important applications of nanomaterial based gas sensors is biosensing applications. In this review article, the gas sensors for biosensing are discussed on the basis of crystalline structure and different categories of nanomaterial.

METHODS

In this paper, firstly, rigorous efforts have been made to find out research questions by going through a structured and systematic survey of available peer reviewed high quality articles in this field. The papers related to nanomaterial based biosensors are then reviewed qualitatively to provide substantive findings from the recent developments in this field.

RESULTS

In this mini-review article, firstly, classifications of nanomaterial gas sensors have been presented on the basis of the crystalline structure of nanomaterial and different types of nanomaterial available for biosensing applications. Further, the gas sensors based on nanomaterial for biosensing applications are collected and reviewed in terms of their performance parameters such as sensing material used, target gas component, detection ranges (ppm-ppb), response time, operating temperature and method of detection, etc. The different nanomaterials possess slightly different sensing and morphological properties due to their structure; therefore, it can be said that a nanomaterial must be selected carefully for a particular application. The 1D nanomaterials show the best selectivity and sensitivity for gases available in low concentration ranges due to their miniaturised structure compared to 2D and 3D nanomaterials. However, these 2D and 3D nanomaterials also so good sensing properties compared to bulk semiconductor materials. The polymer and nanocomposites which are also discussed in this patent article have opened the door for future research and have great potential for new generation gas sensors for detecting biomolecules.

CONCLUSION

These nanomaterials extend great properties towards sensing the application of different gases for a lower concentration of particular gas particles. Nano polymer and nanocomposites have great potential to be used as gas sensors for the detection of biomolecules.

Au Nanorods on Carbon-Based Nanomaterials as Nanohybrid Substrates for High-Efficiency Dynamic Surface-Enhanced Raman Scattering

Gold nanorods (AuNRs) with different aspect ratios were prepared by the seed-mediated growth method and combined with three carbon-based nanomaterials of multiple dimensions (i.e., zero-dimensional (0D) carbon black (CB), one-dimensional (1D) carbon nanotubes (CNTs), and two-dimensional (2D) graphene oxide (GO)). The AuNR/carbon-based nanomaterial hybrids were utilized in dynamic surface-enhanced Raman scattering (D-SERS). First, cetyltrimethylammonium bromide (CTAB) was used to stabilize and coat the AuNRs, enabling them to be dispersed in water and conferring a positive charge to the surface. AuNR/carbon-based nanomaterial hybrids were then formed via electrostatic attraction with the negatively charged carbon-based nanomaterials. Subsequently, the AuNR/carbon-based nanomaterial hybrids were utilized as large-area and highly sensitive Raman spectroscopy substrates. The AuNR/GO hybrids afforded the best signal enhancement because the thickness of GO was less than 5 nm, which enabled the AuNRs adsorbed on GO to produce a good three-dimensional hotspot effect. The enhancement factor (EF) of the AuNR/GO hybrids for the dye molecule Rhodamine 6G (R6G) reached 1 × 10⁷, where the limit of detection (LOD) was 10^-8 M. The hybrids were further applied in D-SERS (detecting samples transitioning from the wet state to the dry state). During solvent evaporation, the system spontaneously formed many hotspots, which greatly enhanced the SERS signal. The final experimental results demonstrated that the AuNR/GO hybrids afforded the best D-SERS signal enhancement. The EF value for R6G reached 1.1 × 10⁸ after 27 min, with a limit of detection of 10^-9 M at 27 min. Therefore, the AuNR/GO nanohybrids have extremely high sensitivity as molecular sensing elements for SERS and are also very suitable for the rapid detection of single molecules in water quality and environmental management.

Functionalized Silver and Gold Nanomaterials with Diagnostic and Therapeutic Applications

The functionalization of nanomaterials with suitable capping ligands or bioactive agents is an interesting strategy in designing nanosystems with suitable applicability and biocompatibility; the physicochemical and biological properties of these nanomaterials can be highly improved for biomedical applications. In this context, numerous explorations have been conducted in the functionalization of silver (Ag) and gold (Au) nanomaterials using suitable functional groups or agents to design nanosystems with unique physicochemical properties such as excellent biosensing capabilities, biocompatibility, targeting features, and multifunctionality for biomedical purposes. Future studies should be undertaken for designing novel functionalization tactics to improve the properties of Au- and Ag-based nanosystems and reduce their toxicity. The possible release of cytotoxic radicals or ions, the internalization of nanomaterials, the alteration of cellular signaling pathways, the translocation of these nanomaterials across the cell membranes into mitochondria, DNA damages, and the damage of cell membranes are the main causes of their toxicity, which ought to be comprehensively explored. In this study, recent advancements in diagnostic and therapeutic applications of functionalized Au and Ag nanomaterials are deliberated, focusing on important challenges and future directions.

Synthesis and Characterization of Dendronized Gold Nanoparticles Bearing Charged Peripheral Groups with Antimicrobial Potential

Dendronized gold nanoparticles (AuNPs) were synthesized bearing charged peripheral groups. Two novel AB3-type dendrons were synthesized with a thiol group at the focal point followed by their attachment to AuNPs. Dendrons were designed to have nine charged peripheral groups (carboxyl or amine), glycol solubilizing, units and one thiol moiety at the focal point. Both dendrons and all intermediates were synthesized in high yields and characterized by nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). The amine- and carboxyl-terminated dendrons were used to functionalize gold nanoparticles (AuNPs) previously stabilized with citrate. The nanoparticles’ diameters and their colloidal stability were investigated using dynamic light scattering (DLS). The size and morphology of the dendronized AuNPs were evaluated by scanning electron microscopy (SEM), which revealed individual particles with no aggregation after replacement of citrate by the dendrons, in agreement with the DLS data. The absorption spectroscopy reveals a prominent plasmonic band at 560 nm for all AuNPs. The zeta potential further confirmed the expected charged structures of the dendronized AuNPs. Considering all the physical–chemical properties of the charged dendronized AuNPs developed in this work, these AuNPs might be used as a weapon against multi-drug resistant bacterial infections.

Controlled Synthesis of Platinum and Silver Nanoparticles Using Multivalent Ligands

Here, the controlled formation of platinum nanoparticles (PtNPs) and silver nanoparticles (AgNPs) using amine-functionalized multivalent ligands are reported. The effects of reaction temperature and ligand multivalency on the growth kinetics, size, and shape of PtNPs and AgNPs were systematically studied by performing a stepwise and a one-step process. PtNPs and AgNPs were prepared in the presence of amine ligands using platinum (II) acetylacetonate and silver (I) acetylacetonate, respectively. The effects of ligands and temperature on the formation of PtNPs were studied using a transmission electron microscope (TEM). For the characterization of AgNPs, additionally, ultraviolet-visible (UV-Vis) absorption was employed. The TEM measurements revealed that PtNPs prepared at different temperatures (160–200 °C, in a stepwise process) are monodispersed and of spherical shape regardless of the ligand multivalency or reaction temperature. In the preparation of PtNPs by the one-step process, ligands affect the shape of the PtNPs, which can be explained by the affinity of the ligands. The TEM and UV-Vis absorption studies on the formation of AgNPs with mono-, di-, and trivalent ligands showed narrower size distributions, while increasing the temperature from 80 °C to 120 °C and with a trivalent ligand in a one-step process.

Floating synthesis with enhanced catalytic performance via acoustic levitation processing

Acoustic levitation supplies a containerless state to eliminate natural convection and heterogeneous crystal nucleation and thus provides a highly uniform and ultra clean condition in the confined levitating area. Herein, we attempt to make full use of these advantages to fabricate well dispersed metal nanoparticles. The gold nanoparticles, synthesized in an acoustically levitated droplet, exhibited a smaller size and improved catalytic performance in 4-nitrophenol reduction were synthesized in an acoustically levitated droplet. The sound field was simulated to understand the impact of acoustic levitation on gold nanoparticle growth with the aid of crystal growth theory. Chemical reducing reactions in the acoustic levitated space trend to occur in a better dispersed state because the sound field supplies continuous vibration energy. The bubble movement and the cavitation effect accelerate the nucleation, decrease the size, and the internal flow inside levitated droplet probably inhibit the particle fusion in the growth stage. These factors lead to a reduction in particle size compared with the normal wet chemical synthetic condition. The resultant higher surface area and more numerous active catalytic sites contribute to the improvement of the catalytic performance.

Green Synthesis of Gold and Silver Nanoparticles Using Leaf Extract of Capsicum chinense Plant

So far, several studies have focused on the synthesis of metallic nanoparticles making use of extracts from the fruit of the plants from the genus Capsicum. However, as the fruit is the edible, and highly commercial, part of the plant, in this work we focused on the leaves, a part of the plant that is considered agro-industrial waste. The biological synthesis of gold (AuNPs) and silver (AgNPs) nanoparticles using aqueous extracts of root, stem and leaf of Capsicum chinense was evaluated, obtaining the best results with the leaf extract. Gold and silver nanoparticles synthesized using leaf extract (AuNPs-leaf and AgNPs-leaf, respectively) were characterized by UV-visible spectrophotometry (UV-Vis), Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection (FTIR-ATR), X-ray Photoelectron Spectroscopy (XPS), Ultra Hight Resolution Scanning Electron Microscopy coupled to Energy-Dispersive X-ray spectroscopy (UHR-SEM-EDX) and Transmission Electron Microscopy (TEM), and tested for their antioxidant and antimicrobial activities. In addition, different metabolites involved in the synthesis of nanoparticles were analyzed. We found that by the use of extracts derived from the leaf, we could generate stable and easy to synthesize AuNPs and AgNPs. The AuNPs-leaf were synthesized using microwave radiation, while the AgNPs-leaf were synthesized using UV light radiation. The antioxidant activity of the extract, determined by ABTS, showed a decrease of 44.7% and 60.7% after the synthesis of the AuNPs-leaf and AgNPs-leaf, respectively. After the AgNPs-leaf synthesis, the concentration of polyphenols, reducing sugars and amino acids decreased by 15.4%, 38.7% and 46.8% in the leaf extract, respectively, while after the AuNPs-leaf synthesis only reducing sugars decreased by 67.7%. These results suggest that these groups of molecules are implicated in the reduction/stabilization of the nanoparticles. Although the contribution of these compounds in the synthesis of the AuNPs-leaf and the AgNPs-leaf was different. Finally, the AgNPs-leaf inhibited the growth of S. aureus, E. coli, S. marcescens and E. faecalis. All of them are bacterial strains of clinical importance due to their fast antibiotic resistance development.

Gold-Polymer Nanocomposites for Future Therapeutic and Tissue Engineering Applications

Gold nanoparticles (AuNPs) have been extensively investigated for their use in various biomedical applications. Owing to their biocompatibility, simple surface modifications, and electrical and unique optical properties, AuNPs are considered promising nanomaterials for use in in vitro disease diagnosis, in vivo imaging, drug delivery, and tissue engineering applications. The functionality of AuNPs may be further expanded by producing hybrid nanocomposites with polymers that provide additional functions, responsiveness, and improved biocompatibility. Polymers may deliver large quantities of drugs or genes in therapeutic applications. A polymer alters the surface charges of AuNPs to improve or modulate cellular uptake efficiency and their biodistribution in the body. Furthermore, designing the functionality of nanocomposites to respond to an endo- or exogenous stimulus, such as pH, enzymes, or light, may facilitate the development of novel therapeutic applications. In this review, we focus on the recent progress in the use of AuNPs and Au-polymer nanocomposites in therapeutic applications such as drug or gene delivery, photothermal therapy, and tissue engineering.