Anisotropic Gold Nanoparticles Research Articles

Nanoscale engineering of gold nanostars for enhanced photoacoustic imaging.

Photoacoustic (PA) imaging is a diagnostic modality that combines the high contrast resolution of optical imaging with the high tissue penetration of ultrasound. While certain endogenous chromophores can be visualized via PA imaging, many diagnostic assessments require the administration of external probes. Anisotropic gold nanoparticles are particularly valued as contrast agents, since they produce strong PA signals and do not photobleach. However, the synthesis of anisotropic nanoparticles typically requires cytotoxic reagents, which can hinder their biological application. In this work, we developed new PA probes based on nanostar cores and polymeric shells. These AuNS were obtained through one-pot synthesis with biocompatible Good's buffers, and were subsequently functionalized with polyethylene glycol, chitosan or melanin, three coatings widely used in (pre)clinical research. Notably, the structural features of the nanostar cores strongly affected the PA signal. For instance, despite displaying similar sizes (i.e. 45nm), AuNS obtained with MOPS buffer generated between 2 and 3-fold greater signal intensities in the region between 700 and 800nm than nanostars obtained with HEPES and EPPS buffers, and up to 25-fold stronger signals than spherical gold nanoparticles. A point source analytical model demonstrated that AuNS synthesized with MOPS displayed greater absorption coefficients than the other particles, corroborating the stronger PA responses. Furthermore, the AuNS shell not only improved the biocompatibility of the nanoconstructs but also affected their performance, with melanin coating enhancing the signal more than 4-fold, due to its own PA capacity, as demonstrated by both in vitro and ex vivo imaging. Taken together, these results highlight the strengths of gold nanoconstructs as PA probes and offer insights into the design rules for the nanoengineering of new nanodiagnostic agents.

Deep Learning-Assisted Automated Multidimensional Single Particle Tracking in Living Cells.

The translational and rotational dynamics of anisotropic optical nanoprobes revealed in single particle tracking (SPT) experiments offer molecular-level information about cellular activities. Here, we report an automated high-speed multidimensional SPT system integrated with a deep learning algorithm for tracking the 3D orientation of anisotropic gold nanoparticle probes in living cells with high localization precision (<10 nm) and temporal resolution (0.9 ms), overcoming the limitations of rotational tracking under low signal-to-noise ratio (S/N) conditions. This method can resolve the azimuth (0°-360°) and polar angles (0°-90°) with errors of less than 2° on the experimental and simulated data under S/N of ∼4. Even when the S/N approaches the limit of 1, this method still maintains better robustness and noise resistance than the conventional pattern matching methods. The usefulness of this multidimensional SPT system has been demonstrated with a study of the motions of cargos transported along the microtubules within living cells.

Silver(I)-induced anisotropy in the plasmon-driven growth of nanoscale gold

ABSTRACT The plasmon-mediated synthesis of anisotropic gold nanoparticles (AuNPs) has only recently been investigated and achieved. This process typically utilizes the surface plasmon resonances (SPRs) of the nanoparticles themselves to drive metal deposition and growth. Many of the traditional methods for shape control, including use of functional surfactants and etchants, have yet to be utilized within the context of light-driven synthesis. Here, the underpotential deposition of Ag(I) is utilized as a shape-controlling strategy in a hot electron-driven photochemical synthesis to grow anisotropic gold nanoparticles. The strategy also relies on L-pyroglutamic acid, a natural amino acid metabolite, as a photochemical relay aiding in the transport and localization of plasmon-generated hot electrons. By carefully adjusting reagent concentrations, the morphologies of the resulting nanoparticles can be facilely tuned from spheres to nanostars and nanoflowers. The high extinction in the NIR region of the ‘ideal’ gold nanostars synthesized advocates their use as photothermal therapy agents, supported by a sufficient photothermal conversion efficiency (η = 30.8%) under 808 nm CW laser irradiation. This contribution expands the repertoire of gold nanostructures accessible to visible-light-driven plasmonic photochemistry. Different gold nanoparticle shapes have been accessed using a plasmon-mediated growth technique. Ag(I) ions induce symmetry breaking, yielding nano-sized gold spheres, stars, and flowers. A specialized photoreactor, equipped with 505 nm LED illumination, facilitates the transfer of hot electrons from a pre-made gold nanocube seed surface. Gold reduction and deposition occur, and anisotropic structures grow with the aid of L-pyroglutamic acid and Triton X-100 as coordinating and shape-directing agents.

Gold nanomakura: nanoarchitectonics and their photothermal response in association with carrageenan hydrogels.

Photothermal conversion of light into heat energy is an intrinsic optical property of metal nanoparticles when irradiated using near-infrared radiation. However, the impact of size and shape on the photothermal behaviour of gold nanomakura particles possessing optical absorption within 600-700 nm as well as on incorporation in hydrogels is not well reported. In this study, nanomakura-shaped anisotropic gold nanoparticles (AuNMs) were synthesized via a surfactant-assisted seed-mediated protocol. Quaternary cationic surfactants having variable carbon tail length (n = 16, 14, 12) were used as capping for tuning the plasmon peak of gold nanomakura within a 600-700 nm wavelength. The aspect ratio as well as anisotropy of synthesized gold nanomakura can influence photothermal response upon near-infrared irradiation. The role of carbon tail length was evident via absorption peaks obtained from longitudinal surface plasmon resonance analysis at 670, 650, and 630 nm in CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM, respectively. Furthermore, the impact of morphology and surrounding milieu of the synthesized nanomakuras on photothermal conversion is investigated owing to their retention of plasmonic stability. Interestingly, we found that photothermal conversion was exclusively assigned to morphological features (i.e., nanoparticles of higher aspect ratio showed higher temperature change and vice versa irrespective of the surfactant used). To enable biofunctionality and stability, we used kappa-carrageenan- (k-CG) based hydrogels for incorporating the nanomakuras and further assessed their photothermal response. Nanomakura particles in association with k-CG were also able to show photothermal conversion, depicting their ability to interact with light without hindrance. The CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM after incorporation into hydrogel beads attained up to ≈17.2, ≈17.2, and ≈15.7 °C, respectively. On the other hand, gold nanorods after incorporation into k-CG did not yield much photothermal response as compared to that of AuNMs. The results showed a promising platform to utilize nanomakura particles along with kappa-carrageenan hydrogels for enabling usage on nanophotonic, photothermal, and bio-imaging applications.

Anisotropic Gold Nanoparticles Synthesized using Litchi chinensis Leaf Extract and their Effect on Breast Cancer

For its medicinal potential, especially in cancer therapy, eco-friendly gold nanoparticles (GNPs) have gained a lot of interest. This investigation used Litchi chinensis leaf extract (LLE) as a reducing agent for the one-step synthesis of regulated-size GNPs. Fourier transform infrared (FTIR) spectrum shows that the bio-molecules act as capping and reducing agents. The formation of GNPs has been confirmed using UV-vis absorption spectra. Effect of various synthesized parameters, i.e., reaction time (5–120 minutes), temperature (25–100°C), solvent quantity (5–45 μL), metal ion concentration (0.25–2 mM) and pH (2–10) has been studied. The size, distribution, and morphology (anisotropic) have been studied using field emission scanning electron microscopy (FESEM) and dynamic light scattering (DLS) techniques in the range of 10 to 70 nm. X-Ray diffraction (XRD) reveals that the particles were crystalline and had face-centered cubic (FCC) structure, and transmission electron microscopy (TEM) images revealed anisotropic morphology (spherical, hexagonal, and triangular). In-vitro studies of GNPs on breast cancer cell lines show cytotoxicity with cellular structural alterations and caused DNA damage without the micronuclei formation.

Application of Anisotropic Gold Nanomaterials in Plasmonic Sensors for Detection of Glyphosate

The trend of using agrochemicals is increasing, especially glyphosate-based herbicides (GBH). The application of toxic chemicals as pest control in food crops carries a risk to human safety. Therefore, it is important to create a sensor for detection through Localized Surface Plasmon Resonance (LSPR) by utilizing anisotropic gold nanoparticles (AGN) to detect the presence of GBH contaminants in the form of malathion and temephos, with a detection level as low as three-part per million (ppm). AGN-based LSPR is successfully synthesized through an experimental technique using the Seed Mediated Growth Method (SMGM). The UV-Vis response showed two strong absorbances with a peak occurring around 500 to 600 nm, the peak within the transverse surface plasmon resonance range (t-SPR) corresponds to one aspect, while the peak within the spectral range extending from 700 nm to 900 nm corresponds to another aspect, namely Longitudinal Surface Plasmon Resonance (l-SPR). Anlysis of the FESEM photograph shows a structure consisting of two particles with different shapes, pentagonal pyramids and a bone shape. Pentagonal pyramids joined with a surface density of 64.43 ± 1,53 % and bone shape of 32,46 ± 1.53 %. This characterization shows strong and distinctive optical resonance in the near-infrared visible light spectrum, which is very suitable for LSPR sensors. It is necessary to fabricate an LSPR sensor device capable of detecting the presence of GBH by testing sensitivity, stability and repeatability. The sensitivity test results were evaluated by varying the synthesis time and concentration of contaminants in the AGN growth solution. It confirmed that the AGN-based LSPR sensor has a promising potential for GBH residue detection.

Temperature-Modulated Reversible Clustering of Gold Nanorods Driven by Small Surface Ligands.

Temperature-modulated colloidal phase of plasmonic nanoparticles is a convenient playground for resettable soft-actuators or colorimetric sensors. To render reversible clustering under temperature change, bulky ligands are required, especially if anisotropic morphologies are of interest. This study showcases thermoresponsive gold nanorods by employing small surface ligands, bis (p-sulfonatophenyl) phenyl-phosphine dihydrate dipotassium salt (BSPP) and native cationic surfactant. Temperature-dependent analysis in real-time allowed to describe the structural features (interparticle distance and cluster size) as well as thermal parameters, melting and freezing temperatures. These findings suggest that neither covalent Au-S bonds nor bulky ligands are required to obtain a robust thermoresponsive system based on anisotropic gold nanoparticles, paving the way to stimuli-responsive nanoparticles with a wide range of sizes and geometries.

A Spatially Programmable DNA Nanorobot Arm to Modulate Anisotropic Gold Nanoparticle Assembly by Enzymatic Excision.

Programmable assembly of gold nanoparticle superstructures with precise spatial arrangement has drawn much attention for their unique characteristics in plasmonics and biomedicine. Bio-inspired methods have already provided programmable, molecular approaches to direct AuNP assemblies using biopolymers. The existing methods, however, predominantly use DNA as scaffolds to directly guide the AuNP interactions to produce intended superstructures. New paradigms for regulating AuNP assembly will greatly enrich the toolbox for DNA-directed AuNP manipulation and fabrication. Here, we developed a strategy of using a spatially programmable enzymatic nanorobot arm to modulate anisotropic DNA surface modifications and assembly of AuNPs. Through spatial controls of the proximity of the reactants, the locations of the modifications were precisely regulated. We demonstrated the control of the modifications on a single 15 nm AuNP, as well as on a rectangular DNA origami platform, to direct unique anisotropic AuNP assemblies. This method adds an alternative enzymatic manipulation to DNA-directed AuNP superstructure assembly.

A Spatially Programmable DNA Nanorobot Arm to Modulate Anisotropic Gold Nanoparticle Assembly by Enzymatic Excision

AbstractProgrammable assembly of gold nanoparticle superstructures with precise spatial arrangement has drawn much attention for their unique characteristics in plasmonics and biomedicine. Bio‐inspired methods have already provided programmable, molecular approaches to direct AuNP assemblies using biopolymers. The existing methods, however, predominantly use DNA as scaffolds to directly guide the AuNP interactions to produce intended superstructures. New paradigms for regulating AuNP assembly will greatly enrich the toolbox for DNA‐directed AuNP manipulation and fabrication. Here, we developed a strategy of using a spatially programmable enzymatic nanorobot arm to modulate anisotropic DNA surface modifications and assembly of AuNPs. Through spatial controls of the proximity of the reactants, the locations of the modifications were precisely regulated. We demonstrated the control of the modifications on a single 15 nm AuNP, as well as on a rectangular DNA origami platform, to direct unique anisotropic AuNP assemblies. This method adds an alternative enzymatic manipulation to DNA‐directed AuNP superstructure assembly.

Organic matrix-entrapped methylene blue as a photochemical reactor applied in chemical synthesis and nanotechnology

Aggregation modulates the photochemical and photophysical properties of methylene blue (MB+). MB+ adsorbed by the anionic polymer Chelex® 100 was characterized by UV–visible absorption spectroscopy and sulfur K-edge X-ray absorption near edge structure (XANES) as H- and J-aggregates. Nuclear magnetic resonance (NMR) indicates that dye molecules bind to the unprotonated carboxylic groups of the polymer via electrostatic interactions and are bridged by water molecules. MB+ also stacks with phenyl rings appended in the Chelex® 100 chain, leading to a gain in the mobility of ordered water displaced around the aromatic rings. Like the blue bottle experiment, MB+ in Chelex® 100 was entirely photoconverted for the leuco form (LMB) by visible and red light and reoxidized by molecular oxygen. Electron paramagnetic resonance (EPR) of MB+ in Chelex® 100 demonstrated the formation of a sulfur-centered free radical during photobleaching. The free radical involvement in MB+ photobleaching is consistent with a type I mechanism in which the stabilization of the products MB2+• and MB• in dye aggregates allows the formation of LMB by MB• dismutation or a second electron abstraction. Chelex® 100 beds loaded with MB+ solutions prepared in H2O and D2O produce H2O2 and D2O2, respectively, after successive cycles of photobleaching and recycling by O2 dissolved in the liquid phase. The formation of hydrogen peroxide is attributed to spontaneous superoxide ion disproportionation in the microenvironment of the polymer lattice. The LMB produced in Chelex® 100 was also able to act as a reducing agent for the synthesis of anisotropic iridescent gold nanoparticles (GNPs). The LMB/Chelex system allows the modulation of the shape and size of GNPs using different dye/Au3+ ratios. GNPs produced using LMB as a reducing agent are also efficient cell delivery systems. The specific properties of LMB confined in solid hosts LMB/Chelex also have potential applications in new solid-state optoelectronic devices such as sensing and imaging.

Contact lenses that transform gold into nanoparticles for prophylaxis of light-related events and photothermal therapy

This work describes for first time how anisotropic gold nanoparticles (AuNPs) can be spontaneously formed inside preformed contact lenses (CLs) avoiding the use of additional reductant agents (reagent-free) through a precise tunning of the monomeric composition, the saline concentration, and the application of steam heat sterilization. Protocols to generate AuNPs in solution using inorganic or small organic reductants are widely available. Differently, gold precursors interactions with polymer networks have been overlooked and, thus, the interest of chemically cross-linked hydrogels as organic reductants is still to be elucidated. In the ocular field, incorporation of AuNPs to CLs may expand their applications in prophylaxis, therapy and diagnosis. To carry out the work, a variety of hydrogels and commercially available CLs were incubated with gold salt solution without any other chemical reagent. AuNPs formation was monitored by changes in localized surface plasmon resonance (LSPR) bands and quantifying the gold sorbed. Only silicone hydrogels induced AuNPs formation at room temperature in few days; methacrylic acid red-shifted the LSPR band (550–600 nm), while monomers bearing F hindered the reduction. Storage of hydrogels in the gold precursor solution allowed a gradual formation of anisotropic AuNPs, which could be stopped at any time by washing the hydrogel with water. The developed CLs behave as efficient filters against highly penetrant light and also exhibit photoresponsiveness as demonstrated as rapid (10 s), focused mild hyperthermia when irradiated with green, red and NIR lasers.

Behind the Optimization of the Sensor Film: Bioconjugation of Triangular Gold Nanoparticles with Hemoproteins for Sensitivity Enhancement of Enzymatic Biosensors.

Electrochemical biosensors are widely used in a multitude of applications, such as medical, nutrition, research, among other fields. These sensors have been historically used and have not undergone many changes in terms of the involved electrochemical processes. In this work, we propose a new approach on the immobilization and enhancement of the electrochemical properties of the sensing layers through the control and bioconjugation of hemoproteins (hemoglobin, myoglobin, and cytochrome C) on anisotropic gold nanoparticles (gold nanotriangles (AuNTs)). The hemeproteins and the AuNTs are mixed in a solution, resulting in stable bioconjugates that are deposited onto the electrode surface to obtain the biosensors. All the systems proposed herein exhibited direct well-defined redox responses, highlighting the key role of the AuNTs acting as mediators of such electron transfers. Several protein layers surrounding the AuNTs are electroactive, as demonstrated from the charge measured by cyclic voltammetry. The retention of the stability of the hemeproteins once they are part of the bioconjugates is evidenced towards the electrocatalytic reduction of hydrogen peroxide, oxygen, and nitrite. The parameters obtained for the proposed biosensors are similar or even lower than those previously reported for similar systems based on nanomaterials, and they exhibit attractive properties that make them potential candidates for the latest developments in the field of sensing devices.

One-Pot Synthesis of Silica-Coated Gold Nanostructures Loaded with Cyanine 5.5 for Cell Imaging by SERS Spectroscopy

Anisotropic gold nanoparticles have been recognized as promising agents for medical diagnostics and cancer therapy due to their wide functionality, photothermal effect, and ability for optical signal amplification in the near-infrared range. In this work, a simple and rapid method for the preparation of bone-shaped gold nanoparticles coated with a dye-impregnated silica shell with an aminated surface is proposed. The possibility of further functionalization the nanostructures with a delivery vector using folic acid as an example is demonstrated. The average size of the resulting tags does not exceed 70 nm, meeting the criteria of cell endocytosis. The prepared tags exhibit surface-enhanced Raman scattering (SERS) spectra at excitation with lasers of 632.8 and 785 nm. Cell imaging is performed on HeLa cells based on the most pronounced SERS bands as a tracking signal. The obtained images, along with scanning electron microscopy of cell samples, revealed the tendency of tags to agglomerate during endocytosis followed by the "hot spots" effect. To evaluate the toxic and proliferative effect of the nanotags, an MTT assay was performed with two HeLa and HEP G2 cell lines. The results revealed higher viability for HEP G2 cells.

Smart Anisotropic Colloidal Composites: A Suitable Platform for Modifying the Phase Transition of Diblock Copolymers by Gold Nanoparticles

Surface modification of metallic nanoparticles (NPs) by stimuli-responsive polymers is a benign method to prepare smart colloidal composites which tune the characteristic properties of individual systems. The temperature-dependent transition of diblock copolymer poly(N-isopropylacrylamide)-block-poly(N-vinylcaprolactam) (PNIPMA-b-PVCL) synthesized using reversible addition-fragmentation chain transfer polymerization was studied by incorporating anisotropic gold NPs (AGPs) such as spheres (AuNSs), rods (AuNRs), cubes (AuNCs), and rhombic dodecahedrals (AuRDs). Shape-dependent physiochemical properties of nanostructures alter the lower critical solution temperature (LCST) of the chemical inhomogeneous diblock copolymer. Heterogeneous nucleation of AuNPs was facilitated by seed-mediated synthesis for incorporating uniformity. In the mixed system, the presence of PNIPAM-b-PVCL modifies the surface of AGPs through physisorption which is supported by transmission electron microscopy and field emission scanning electron microscopy showing the NPs embedding in the polymeric matrix. Furthermore, steady state fluorescence spectroscopy and Fourier transform infrared spectroscopy were performed to examine the phase transition behavior of PNIPAM-b-PVCL in AGPs. The formation of a smart polymer nanocomposite alters the physiochemical properties of the diblock copolymer as demonstrated from the variation of LCST in the dynamic light scattering measurement. Henceforth, functionalizing the surfaces of AGPs with a thermoresponsive diblock copolymer provides combinatorial benefits in the properties of smart polymeric colloidal systems with potential applications in bioimaging and drug delivery.

Lemon-Juice-Based Microwave Synthesis and Optical Characterization of Anisotropic Gold Nanoparticles

Anisotropic gold nanoparticles (AuNPs) were synthesized using microwave (MW)-assisted route. Lemon extract was used as both reducing and stabilizing agent. Subsequent UV treatment was carried out to modify the particle size and shape. Distribution of triangular and pentagonal-shaped particles were found to increase in number. Moreover, up to 60% increase in particle size was also observed. Change in optical property and appearance of plasmon modes were clear indication of the modification caused. Local density of photonic states (LDOS) and electric field distribution were obtained through computational simulation using MATLAB toolbox. Experimental results were used as the input values for the simulation. Dipolar distribution was observed along the boundaries of the spherical NPs, while for triangular and pentagonal-shaped NPs, they were found to be concentrated along their edges and corners. The results presented here encourage us to choose an alternative eco-friendly, quick and simple route to synthesize gold NPs of various shapes for various application such as in viral detection, nanobiomaterials, biomedical images, detection-therapy, etc.

Controlled synthesis and computational analysis of gold nanostars for the treatment of Fusarium oxysporum.

Fusarium oxysporum (F. oxysporum) is linked to the widespread fusarium wilt in plants affecting the quality and yield of food crops. Management of fusarium wilt by synthetic fertilizers poses safety concerns. Safer-by-design nanomaterials synthesized with a greener approach can meet the needs of commercial antifungal drug resistance. Herein, a simple aqueous reduction method has been adopted for the synthesis of anisotropic gold nanostars (AuNSs) using quercetin-para aminobenzoic acid (QPABA) as both a reducing and stabilizing agent at room temperature for the treatment of F. oxysporum. QPABA was used to control the growth of Au3+ star-shaped nanoparticles at increasing concentrations in the ratio of 2 : 1 (QPABA : Au3+ ions) respectively. Transmission electron microscopy (TEM) analysis of the as-prepared gold nanoparticles confirmed the formation of nanostars with sizes of 40 ± 2 nm. The formation of anisotropic gold nanoparticles was evaluated by UV-vis characterizations which showed longitudinal surface plasmon modes at 540 and 800 nm. The gold nanoparticles exhibit excellent antifungal activity against F. oxysporum with the minimum inhibitory concentration (MIC) of 100 μg mL-1 using an agar well-diffusion assay. AuNSs proved to be efficacious in controlling F. oxysporum, as shown in the SEM analysis with a disintegrated cell membrane upon treatment. Computational analysis was performed to determine the specific binding sites on the QPABA ligand for gold ion interactions using the DFT B3LYP method, with a 6-31+G(d) basis set. Results showed that the interaction between Au3+ and QPABA at the 4 and 3 positions yielded the highest stability and formation of gold nanostars. The results suggest that the synthesized AuNSs act as a promising antifungal agent with great potential in treating frequent fungal infections that affect agricultural production.

Three-dimensional building of anisotropic gold nanoparticles under confinement in submicron capsules.

The low collision rate and contact time of gold nanoparticles (NPs) in solution afford a low welding probability, which hinders their welding structure, orientation, and dimension. Encapsulated anisotropic NPs, gold nanotriangles (AuNTs), were successfully assembled into a three-dimensional structure inside a permeable silica nanocapsule under light illumination to generate localized surface plasmon resonance (LSPR). AuNTs were trapped in the permeable silica nanocapsules and diffused in the nanospace because of copolymer release, which increased the contact probability of AuNTs and promoted the three-dimensional building of AuNTs. Electron energy loss mapping simulations revealed that the obtained three-dimensional AuNT structure exhibited spatially separated multiple LSPR modes with different energies of incident light, which are photophysically attractive beyond the facet-selective chemical growth of NPs, and postmodification for anchoring substances with site-selective attachment to the obtained structure will be applicable to expand the sensing design and class of substances for sensing.

Concave gold nano-arrows (AuCNAs) for efficient catalytic reduction of 4-nitrophenol

Anisotropic gold nanostructures have attracted great attention in different fields including catalysis. Thermodynamically driven selective surface growth offers a reliable and reproducible method for anisotropic gold nanoparticle synthesis with specific morphologies. Herein, monocrystalline concave gold nano-arrows (AuCNAs) are prepared by the over-growth method using Au nanorods (AuNRs) as seeds. The as-prepared AuCNAs consist of a biconical head and four concave structures. Interestingly, silver ions (Ag+) concentration significantly affects the product morphology by tuning the peak positions of surface plasmon resonance (SPR), aspect ratio, arrow, and concave morphology of AuCNAs. The position of longitudinal SPR peaks is observed at 810, 805 and 782 nm at [Ag+]/[Au3+] molar ratios of 1:2, 1:1, and 2:1, respectively. Diameters and lengths of AuCNAs varied from 25 nm to 36 nm; 104 nm, 78 nm, and 120 nm, respectively. Additionally, the AuCNAs are applied for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in presence of excess NaBH4. Compared to gold nanorods (AuNRs), the prepared AuCNAs catalyst shows excellent catalytic activity, demonstrating that concave structures and sharp corners significantly enhance the catalytic activity. The value of pseudo-first-order reaction kinetic constants (kapp) increased from 0.0051 to 0.0195 s−1 with increasing catalyst valume from 7.5 to 37.5 μL. The highest normalized reaction rate constant (Knor) and turnover frequency (TOF) reach 5.84 × 104 min−1 mmol−1 and 443.47 h−1, respectively, at [Ag+]/[Au3+] ratio of 1:1 in AuCNAs catalyst. This study expands catalytic applications of anisotropic gold nanostructures and widens their potential application areas, such as surface plasmon exciton photonics, biomedical photonics, and photocatalysis.

Exploitation of N-Gene of SARS-CoV-2 to Develop a New Rapid Assay by ASOs@AuNPs.

A naked-eye (equipment-free), label-free (cost-effective), and RNA extraction-free (to speed up) method for SARS-CoV-2 (as a case study of RNA viruses) detection is developed. Here, the DNA is being used as a template for in situ formation of anisotropic gold nanoparticles (AuNPs) without any chemical modification or DNA labeling. In this study, synthesized AuNPs for the direct detection of N-gene (nucleocapsid phosphoprotein) of SARS-CoV-2 are exploited. To this aim, antisense oligonucleotides (ASOs) with an extra poly guanine tail (G12) were designed. Thus, in the presence of its viral target RNA gene and ASOs@AuNPs-RNA hybridization, there was a red shift in its localized surface plasmon resonance (LSPR), and the intensity of the LSPR peak at 690 nm of throat swab samples was compared to the threshold cycle (Ct) of a reverse-transcriptase real-time polymerase chain reaction (RT-qPCR) (as a gold standard). Results suggested that the plasmonic biosensor can detect a very low amount of SARS-CoV-2 with a detection limit close to RT-qPCR. Simplicity of the new conjugation method with hybridization and annealing without amplification and denaturation steps enabled it to perform in a microfluidic paper-based analytical device.

TiB2 derived nanosheets co-immobilized with triangular gold nanoparticles elicit fast and stable photocatalytic hydrogen evolution

Transition metal diborides are recently being revisited from the viewpoint of yielding 2D nanostructures owing to their layered topology and the inherent presence of boron honeycomb planes. In this report, we show that nanosheets derived from titanium diboride (TiB2), when co-immobilized with anisotropic gold nanoparticles, demonstrate an impressive photocatalytic behavior towards hydrogen evolution. We found that this novel nano construct could achieve H2 evolution rates of up to 1.13 mmol g−1h−1 at neutral pH and simulated light irradiation. This production rate is significant considering the fact that we neither employed any co-catalyst or electron/hole scavenging chemical species nor applied any external bias. In addition, the catalyst could continuously produce H2 for at least 30 h. We also found that the construct was active under direct sunlight exposure. The co-immobilized construct also showed photocatalytic activity under UV and NIR irradiations. This is the first report wherein TiB2 derived nanosheets have been employed towards catalyzing the HER. We attribute the mechanism of photocatalytic H2 evolution to either better electron/hole pair separation or direct electron transfer from the photosensitive gold nanoparticles to the nanosheets (through the formation of a Schottky barrier). This report showcases the rich potential of functionalized metal diboride nanosheets and their constructs for next-generation photocatalysts.