Plasmonic Annular Nanotrenches with 1 nm Nanogaps for Detection of SARS-CoV-2 Using SERS-Based Immunoassay

This study represents the synthesis of a novel class of nanoparticles denoted as annular Au nanotrenches (AANTs). AANTs are engineered to possess embedded, narrow circular nanogaps with dimensions of approximately 1 nm, facilitating near-field focusing for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via a surface-enhanced Raman scattering (SERS)-based immunoassay. Notably, AANTs exhibited an exceedingly low limit of detection (LOD) of 1 fg/mL for SARS-CoV-2 spike glycoproteins, surpassing the commercially available enzyme-linked immunosorbent assay (ELISA) by 6 orders of magnitude (1 ng/mL from ELISA). To assess the real-world applicability, a study was conducted on 50 clinical samples using an SERS-based immunoassay with AANTs. The results revealed a sensitivity of 96% and a selectivity of 100%, demonstrating the significantly enhanced sensing capabilities of the proposed approach in comparison to ELISA and commercial lateral flow assay kits.

Highly stable electrochemical sensing platform for the selective determination of pefloxacin in food samples based on a molecularly imprinted-polymer-coated gold nanoparticle/black phosphorus nanocomposite

The overuse of pefloxacin (PEF) leaves residues in foods. Therefore, the development of robust analytical techniques for the selective detection of PEF is of great importance. In this study, a highly stable electrochemical sensing platform has been constructed, using molecularly imprinted polymer (MIP)-coated gold nanoparticle/black phosphorus nanocomposites (BPNS-AuNPs), for the selective detection of PEF. BPNS-AuNPs significantly enhance the black phosphorus (BP) stability and electrochemical activity and offer a larger surface area to accommodate more imprinted sites for selective PEF binding. MIP/BPNS-AuNPs exhibit a broad linear detection range (0.005-10 μM), low detection limit (0.80 nM), and high sensitivity (3.199 μA μM-1). The MIP/BPNS-AuNPs show a high binding affinity for PEF, even in the presence of structural analogs, and maintain stable voltammetric signals for at least 35 d. The MIP sensor exhibits consistent high sensitivity in the detection of PEF in real milk and orange juice samples.

Indirect effects of interference of two emerging environmental contaminants on cell health: Radiofrequency radiation and gold nanoparticles

BACKGROUND

The global need for wireless technologies is growing rapidly. So, we have been exposed to a new type of environmental pollution: radiofrequency radiation (RFR). Recent studies have shown that RFR can cause not only direct effects but also indirect or non-targeted effects such as the bystander effect (BE). In this study, we investigated the BE induced by RFR in the present of gold nanoparticles (GNP). Moreover, we studied the expression of cyclooxygenase-2 (COX-2).

METHODS

Non-toxic dose of 15-nm GNP was used to treat the Chinese Hamster Ovary (CHO) cells. After 48 h of incubation, cells were exposed to 900 MHz GSM RFR for 24 h. Then we collected the cell culture medium of these cells (conditioned culture medium, CCM) and transferred it to new cells (bystander cells). Cell deaths, DNA breaks, oxidative stress and COX-2 expression were analyzed in all groups.

RESULTS

The results showed that RFR increased metabolic death in cells treated with GNP. Inversely, the colony formation ability was reduced in bystander cells and RFR exposed cells either in the presence or absence of GNP. Also, the level of reactive oxygen species (ROS) in GNP treated cells showed a significant reduction compared to those of untreated cells. However, RFR-induced DNA breaks and the frequencies of micronuclei (MN) were not significantly affected by GNP. The expression of COX-2 mRNA increased in RFR GNP treated cells, but the difference was not significant.

CONCLUSION

Our results for the first time indicated that RFR induce indirect effects in the presence of GNP. However, the molecular mediators of these effects differ from those in the absence of GNP. Also, to our knowledge, this is the first study to show that COX-2 is not involved in the bystander effect induced by 900 MHz RFR.

M13-Phage-Based Star-Shaped Particles with Internal Flexibility

We report on the construction and the dynamics of monodisperse star-shaped particles, mimicking, at the mesoscale, star polymers. Such multiarm star-like particles result from the self-assembly of gold nanoparticles, forming the core, with tip-linked filamentous viruses (M13 bacteriophages) acting as spines in a sea urchin-like structure. By combining fluorescence and dark-field microscopy with dynamic light scattering, we investigate the diffusion of these hybrid spiny particles. We reveal the internal dynamics of the star particles by probing their central metallic core, which exhibits a hindered motion that can be described as a Brownian particle trapped in a harmonic potential. We therefore show that the filamentous viruses and specifically their tip proteins behave as entropic springs, extending the relevance of the study of such hybrid mesoscopic analogues of star polymers to phage biotechnology.

Morphological Effects of Au Nanoparticles on Electrochemical Sensing Platforms for Nitrite Detection

Au nanoparticles were synthesized in a soft template of pseudo-polyanions composed of polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate (SDS) by the in situ reduction of chloroauric acid (HAuCl₄) with PVP. The particle sizes and morphologies of the Au nanoparticles were regulated with concentrations of PVP or SDS at room temperature. Distinguished from the Au nanoparticles with various shapes, Au nanoflowers (AuNFs) with rich protrusion on the surface were obtained at the low final concentration of SDS and PVP. The typical AuNF synthesized in the PVP (50 g·L^-1)-SDS (5 mmol·L^-1)-HAuCl₄ (0.25 mmol·L^-1) solution exhibited a face-centered cubic structure dominated by a {111} crystal plane with an average equivalent particle size of 197 nm and an average protrusion height of 19 nm. Au nanoparticles with four different shapes, nanodendritic, nanoflower, 2D nanoflower, and nanoplate, were synthesized and used to modify the bare glassy carbon electrode (GCE) to obtain Au/GCEs, which were assigned as AuND/GCE, AuNF/GCE, 2D-AuNF/GCE, and AuNP/GCE, respectively. Electrochemical sensing platforms for nitrite detection were constructed by these Au/GCEs, which presented different detection sensitivity for nitrites. The results of cyclic voltammetry (CV) demonstrated that the AuNF/GCE exhibited the best detection sensitivity for nitrites, and the surface area of the AuNF/GCE was 1.838 times of the bare GCE, providing a linear c(NO₂^-) detection range of 0.01-5.00 µmol·L^-1 with a limit of detection of 0.01 µmol·L^-1. In addition, the AuNF/GCE exhibited good reproducibility, stability, and high anti-interference, providing potential for application in electrochemical sensing platforms.

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.

Rapid nanocatalytic reaction using antibody-conjugated gold nanoparticles for simple and sensitive detection of parathyroid hormone

Biomolecule-conjugated metal nanoparticles (NPs) have been primarily used as colorimetric labels in affinity-based bioassays for point-of-care testing. A facile electrochemical detection scheme using a rapid nanocatalytic reaction of a metal NP label is required to achieve more quantitative and sensitive point-of-care testing. Moreover, all the involved components should be stable in their dried form and solution. This study developed a stable component set that allows for rapid and simple nanocatalytic reactions combined with electrochemical detection and applied it for the sensitive detection of parathyroid hormone (PTH). The component set consists of an indium-tin oxide (ITO) electrode, ferrocenemethanol (FcMeOH), antibody-conjugated Au NPs, and ammonia borane (AB). Despite being a strong reducing agent, AB is selected because it is stable in its dried form and solution. The slow direct reaction between FcMeOH⁺ and AB provides a low electrochemical background, and the rapid nanocatalytic reaction allows for a high electrochemical signal. Under optimal conditions, PTH could be quantified in a wide range of concentrations in artificial serum, with a detection limit of ~0.5 pg/mL. Clinical validation of the developed PTH immunosensor using real serum samples indicates that this novel electrochemical detection scheme is promising for quantitative and sensitive immunoassays for point-of-care testing.

Room-temperature ammonia gas sensing via Au nanoparticle-decorated TiO2 nanosheets

A high-performance gas sensor operating at room temperature is always favourable since it simplifies the device fabrication and lowers the operating power by eliminating a heater. Herein, we fabricated the ammonia (NH₃) gas sensor by using Au nanoparticle-decorated TiO₂ nanosheets, which were synthesized via two distinct processes: (1) preparation of monolayer TiO₂ nanosheets through flux growth and a subsequent chemical exfoliation and (2) decoration of Au nanoparticles on the TiO₂ nanosheets via hydrothermal method. Based on the morphological, compositional, crystallographic, and surface characteristics of this low-dimensional nano-heterostructured material, its temperature- and concentration-dependent NH₃ gas-sensing properties were investigated. A high response of ~ 2.8 was obtained at room temperature under 20 ppm NH₃ gas concentration by decorating Au nanoparticles onto the surface of TiO₂ nanosheets, which generated oxygen defects and induced spillover effect as well.

Amplification-free detection of HBV DNA mediated by CRISPR-Cas12a using surface-enhanced Raman spectroscopy

Nucleic acid markers have been widely used in the detection of various virus-related diseases, including hepatitis B virus (HBV), which is spreading worldwide. The trans-activated CRISPR-Cas system has shown excellent sensitivity and specificity in nucleic acid detection. However, nucleic acid testing usually requires amplification of the target nucleic acid for more accurate and specific detection; furthermore, current nucleic acid assays are time-consuming, costly, and are limited by non-specific cross-reactivity. We developed an amplification-free viral DNA biosensor-based diagnostic method that uses a clustered regularly interspaced short palindromic repeats-associated system (CRISPR/Cas)-based approach with surface enhanced Raman spectroscopy. This method can specifically identify the target site by changing the crRNA sequence. In addition, the incubation period and development of the disease can be determined by quantitative detection of viral DNA. This system could achieve rapid and highly sensitive detection of HBV DNA within 50 min and vast detection range from 0.1 pM to 1 nM. Therefore, a combined CRISPR/Cas12a-SERS-based assay would improve the sensitivity of detection in assays using multiple biomarkers. In conclusion, our CRISPR/Cas12a-based biosensor would enable rapid, simple, and sensitive detection of HBV nucleic acids.

Novel Au Nanoparticle-Modified ZnO Nanorod Arrays for Enhanced Photoluminescence-Based Optical Sensing of Oxygen

Novel optical gas-sensing materials for Au nanoparticle (NP)-modified ZnO nanorod (NR) arrays were fabricated using hydrothermal synthesis and magnetron sputtering on Si substrates. The optical performance of ZnO NR can be strongly modulated by the annealing temperature and Au sputtering time. With exposure to trace quantities of oxygen, the ultraviolet (UV) emission of the photoluminescence (PL) spectra of Au/ZnO samples at ~390 nm showed a large variation in intensity. Based on this mechanism, ZnO NR based oxygen gas sensing via PL spectra variation demonstrated a wide linear detection range of 10-100%, a high response value, and a 1% oxygen content sensitivity detection limit at 225 °C. This outstanding optical oxygen-sensing performance can be attributed to the large surface area to volume ratio, high crystal quality, and high UV emission efficiency of the Au NP-modified ZnO NR arrays. Density functional theory (DFT) simulation results confirmed that after the Au NPs modified the surface of the ZnO NR, the charge at the interface changed, and the structure of Au/ZnO had the lowest adsorption energy for oxygen molecules. These results suggest that Au NP-modified ZnO NR are promising for high-performance optical gas-sensing applications.

Plasmon-enhanced photocatalysis using gold nanoparticles encapsulated in nanoscale molybdenum oxide shell

Using solar energy to enhance the transformation rate of organic molecules is a promising strategy to advance chemical synthesis and environmental remediation. Plasmonic nanoparticles responsive to sunlight show great promise in the catalysis of chemical reactions. In this work, we used a straightforward wet-chemistry method to synthesize plasmonic octahedral gold nanoparticles (NPs) coated with thin molybdenum oxide (MoO_3-x), Au@MoO_3-xNPs, which exhibited strong surface plasmon resonance in a broad wavelength range. The synthesized Au@MoO_3-xNPs were characterized by UV-vis, SEM, TEM, EDS, XPS, and the electrochemical technique of cyclic voltammetry (CV). The catalytic performance of Au@MoO_3-xNPs under visible light irradiation was investigated using the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction. The presence of a thin capping layer of MoO_3-xon our Au NPs contributed to the broadening of their range of absorption of visible light, resulting in a stronger intra-particle plasmonic resonance and the modulation of surface energy and electronic state. Accordingly, the kinetics of plasmon photocatalytic transformation of 4-NP to 4-AP was significantly accelerated (by a factor of 8.1) under visible light, compared to uncapped Au NPs in the dark. Our as-synthesized Au@MoO_3-xNPs is an example that the range of plasmonic wavelengths of NPs can be effectively broadened by coating them with another plasmon-active (semiconducting) material, which substantially improves their plasmonic photocatalytic performance. Meanwhile, the synthesized Au@MoO_3-xNPs can be used to accelerate the transformation of organic molecules under visible light irradiation.

Collision Electrochemical Synthesis of Metal Nanoparticles Using Electrons as Green Reducing Agent

Synthesis of high-quality metal nanoparticles (NPs) is the premise toward their downstream diverse applications. Although some electrochemical synthesis strategies have been developed, the necessary use of high-concentration electrolyte solution as current pathway and reaction medium severely limits the colloidal stability of the growing NPs in the solution and their tunability in size and shape. Herein, we report a collision electrochemical method for the synthesis of metal NPs without the use of electrolyte solution. To this end, we designed an asymmetrical electrochemical cell to control the potential (i.e., to supply electrons) in the reaction system via a separated electrochemical cell, thereby enabling the electrochemical reaction occurring in an electrolyte-free growth solution. Consequently, this collision electrochemical method, using seed-mediated growth of NPs as examples, allows the synthesis of monodisperse homogeneous Au NPs and heterogeneous Pd- and Pt-coated Au NPs at a yield comparable to that achieved in common chemical synthesis. Furthermore, this method allows readily tailoring the morphology of the resultant metal NPs just by changing the concentration of the growth solution. Therefore, our green synthesis method is important for a variety of nanomaterials beyond metal NPs.

Enhanced Gas Sensitivity of Au-Decorated Flowery WSe2 Nanostructures

With the continuous improvement in material life, people are paying more and more attention to air quality; therefore, it is critical to design efficient and stable gas sensor devices. In this work, a flowery WSe₂ nanostructure and its nanocomposite (Au@WSe₂) decorated with Au nanoparticles were fabricated by the hydrothermal method. The performance of a resistive sensor with flowery WSe₂ and Au@WSe₂ sensors was evaluated by detecting volatile organic compounds such as ethanol, isoamylol, n-butyl alcohol, isopropanol, isobutanol and n-propanol. The results show that Au-nanoparticle-decorated flowery WSe₂ can decrease the optimal working temperature from 215 °C to 205 °C and significantly enhance the response of flowery WSe₂. The response values to isoamylol are the highest (as high as 44.5) at a low gas concentration (100 ppm), while the response values to ethanol are the highest (as high as 178.5) at a high gas concentration (1000 ppm) among the six different alcohols. Moreover, the response is steady and repeatable. The results demonstrate that the Au@WSe₂ substrate has good responsiveness and selectivity, which makes it a promising candidate for gas detection.

N-hexane-assisted synthesis of plasmonic Au-mediated polymeric carbon nitride photocatalyst for remarkable H2 evolution under visible-light irradiation

Plasmonic Au-mediated polymeric carbon nitride (PCN) has been recognized as one of the promising materials for photocatalytic applications due to its excellent properties in wide visible light spectrum, however it is still hindered by low catalytic efficiency. In this work, it was established that strong metal-support interactions (MSI) at the interface between plasmonic Au nanoparticles (NPs) and PCN nanosheets (PCNS) improves its photocatalytic efficiency. The resulting Au/PCNS_2.5 exhibits excellent photocatalytic activity with H₂ evolution rate up to 4.84 mmol g^-1h^-1 under visible light, 12.4 times higher than that of bulk PCN. Such strong MSI significantly strengthens the localized surface plasmon resonance (LSPR) effect of Au NPs and the charge "pump" role of Schottky junctions at Au-PCNS interface, resulting in broad light absorption range as well as effective separation and transfer of charge carrier. This work provides a new way to design the plasmonic photocatalysts for splitting water as well as other plasmon-driven chemical reactions.

Demonstration of SWIR Silicon-Based Photodetection by Using Thin ITO/Au/Au Nanoparticles/n-Si Structure

Plasmonic photodetection based on the hot-electron generation in nanostructures is a promising strategy for sub-band detection due to the high conversion efficiencies; however, it is plagued with the high dark current. In this paper, we have demonstrated the plasmonic photodetection with dark current suppression to create a Si-based broadband photodetector with enhanced performance in the short-wavelength infrared (SWIR) region. By hybridizing a 3 nm Au layer with the spherical Au nanoparticles (NPs) formed by rapid thermal annealing (RTA) on Si substrate, a well-behaved ITO/Au/Au NPs/n-Si Schottky photodetector with suppressed dark current and enhanced absorption in the SWIR region is obtained. This optimized detector shows a broad detection beyond 1200 nm and a high responsivity of 22.82 mA/W at 1310 nm at -1 V, as well as a low dark current density on the order of 10^-5 A/cm². Such a Si-based plasmon-enhanced detector with desirable performance in dark current will be a promising strategy for realization of the high SNR detector while keeping fabrication costs low.

Ultrafast chiral peptides purification via surface plasmon enhanced spin selectivity

By D-arginine and L-arginine chiral peptides induced spin selectivity and Au NPs enhanced spin polarization, chiral peptides purification has been effectively simplified and the purification performance has raised from a mixture system. The angular momentums of light are operated by the polarizer and wave plates. Au NPs decorated ZnO nanorods electrodes are utilized to modulate the polarization of spintronic. Seed growth methods are for synthesizing spherical Au NPs. UV light reduction methods are for urchin-liked Au NPs. Au NPs are decorated on ZnO nanorods electrodes for rising photon to electron conversion efficiency and enhancing spin polarization rates by surface plasmon effect. From our results, photon to the electron conversion efficiency of ZnO nanorods electrodes has effectively enhanced by urchin-liked Au NPs decorating. Ultrahigh localized plasmon conversion efficiency as high as 60% was also obtained. Besides, density functional theory (DFT) calculations simulated the force on spintronic. Since the D-arginine and L-arginine are on Au substrate, DFT results demonstrate different angular momentum and spin polarization coupling. Along with urchin-liked Au NPs rising chiral induced spin polarization by surface plasmon resonance, the sensitivity of chiral arginine has been raised around 5000% from bare ZnO nanorods electrodes. The purification and separation time of a specific chiral arginine only needs 5 min.

Actuation-Augmented Biohybrid Robot by Hyaluronic Acid-Modified Au Nanoparticles in Muscle Bundles to Evaluate Drug Effects

Biohybrid robots, which comprise soft materials with biological components, have the potential to sense, respond, and adapt to changing environmental loads dynamically. Instead of humans and other living things, biohybrid robots can be used in various fields such as drug screening and toxicity assessment. In the actuation part, however, since a muscle cell-based biohybrid robot is limited in that the driving force is weak, it is difficult to evaluate drug and toxicological effects by distinguishing changes in the biohybrid robot's motion. To overcome this limitation, we introduced hyaluronic acid-modified gold nanoparticles (HA-AuNPs) into a muscle bundle-based biohybrid robot that moves forward in response to electrical stimulation. To enhance the actuation of muscle bundles, HA-AuNPs were embedded into the muscle bundles. The motion of the fabricated biohybrid robot was improved due to the enhanced differentiation and the improved electrical conductivity of muscle bundles by HA-AuNPs. In addition, the fabricated biohybrid robot exhibited huge changes in motion with respect to the addition of positive and negative inotropic drugs. The proposed biohybrid robot has the potential for neuromuscular disease drug screening by incorporating nervous tissues such as motor neuron organoids and brain organoids.

Poly-adenine-mediated spherical nucleic acids for interfacial recognition of kanamycin

Kanamycin fluorescence aptasensors were created using a series of di-block oligonucleotide modified gold nanoparticles with various lengths of poly-adenine. In the presence of kanamycin, the double strand structure of the aptamer-reporter strand complex is disrupted, and the dye-labelled reporter strand detaches from the surface of gold nanoparticles, resulting in fluorescence recovery (Ex/Em = 485/520 nm). By adjusting the number of consecutive adenines, the programable aptamer density can be implemented on the gold nanoparticle surface, and the conformation of nucleic acid changed from lying-down to up-right. The apparent binding constant, binding kinetics, and limit of detection of the prepared aptasensors were carefully examined to explore the influence of surface density. Under the optimum condition, the aptasensor had a tenfold lower limit of detection than the thiolated aptamer modified one, as low as 23.6 nM, when a di-block oligonucleotide with twenty consecutive adenines tailed. In addition, satisfactory recoveries ranging from 96.33 to 99.47% were achieved in spiked milk samples with relative standard deviation of 1.2-6.9% (n = 3). This surface density regulation strategy holds great promise in other aptamer-based interfacial recognition and sensing. Schematic presentation of di-block oligonucleotide modified gold nanoparticle with different surface densities and its kanamycin sensing application.

Highly Ordered, Plasmonic Enhanced Inverse Opal Photonic Crystal for Ultrasensitive Detection of Staphylococcal Enterotoxin B

Although there is considerable interest in self-assembly of ordered, porous "inverse opal" structures for optical, electronic, and chemical applications, uncontrolled defect formation limits the usefulness of such materials. Herein, we develop a highly ordered and plasmonic enhanced sensing inverse opal photonic crystal (IOPC) material. The co-assembly of the colloidal template with the matrix material avoids the need for liquid penetration into the preassembled colloidal crystals and minimizes the associated rupture and inhomogeneity of the resulting IOPC. Au nanoparticles (Au NPs) not only act as a "bridge" between recognition elements (aptamers) and IOPCs, but also can amplify optical signals. Furthermore, the enhancement mechanism of Au NPs is simulated by COMSOL. During the detection process, the optical signal of the sensing Au-Apt IOPC responds to the Staphylococcal enterotoxin B with a concentration ranging from 10^-2 to 10³ pg mL^-1, and the limit of detection is 2.820 fg mL^-1. Spiked real sample detection indicates that the as-proposed method possessed good accuracy. The sensing Au-Apt IOPC provides an extensive biosensor platform to detect a variety of toxic and harmful substances through replacing the aptamer by other recognition elements, such as antibodies or receptors.

Nanopharmaceuticals (Au-NPs) after use: Experiences with a complex higher tier test design simulating environmental fate and effect

The current environmental hazard assessment is based on the testing of the pristine substance. However, it cannot be excluded that (nano)pharmaceuticals are excreted into sewage during the use phase followed by entry into wastewater treatment plants (WWTPs). Sorption to sewage sludge or release via effluent can result in modified ecotoxicological effects which possibly can only be detected with a modified test approach. The objective of our study was to investigate a realistic exposure scenario for metallic nanoparticles (NPs) in pharmaceutical products, excreted into effluent, and released into the environment after treatment in WWTPs. The test approach was illustrated by using gold (Au) NPs. Effluent from model WWTPs were investigated in aquatic tests (Daphnia magna, fish cell lines). Sewage sludge was used as a sole food source (Eisenia fetida) or mixed with soil and used as test medium (soil microorganisms, Folsomia candida, Enchytraeus crypticus). To cover the aspect of regulation, the test systems described in OECD-test guidelines (OECD TG 201, 211, 220, 232, 249, 317) were applied. Modifications and additional test approaches were included to meet the needs arising out of the testing of nanomaterials and of the exposure scenarios. The results were assessed regarding the suitability of the test design and the toxicity of Au-NPs. Except for activated sludge as a sole food source for E.fetida, the selected test approach is suitable for the testing of nanomaterials. Additional information can be gained when compared to the common testing of the pristine nanomaterials in the standardized test systems. Effects of Au-NPs were observed in concentrations exceeding the modeled environmental.

Incorporation of Au Nanoparticles on ZnO/ZnS Core Shell Nanostructures for UV Light/Hydrogen Gas Dual Sensing Enhancement

ZnO/ZnS nanocomposite-based nanostructures exhibit dual light and gas sensing capabilities. To further boost the light/dual sensing properties, gold nanoparticles (Au NPs) were incorporated into the core-shell structures. Multiple material characterizations revealed that Au NPs were successfully well spread and decorated on ZnO/ZnS nanostructures. Furthermore, our findings show that the addition of Au NPs could enhance both 365 nm UV light sensing and hydrogen gas sensing in terms of light/gas sensitivity and light/gas response time. We postulate that the optimization of gas/light dual sensing capability may result from the induced electric field and inhabitation of electron-hole recombination. Owing to their compact size, simple fabrication, and stable response, ZnO/ZnS/Au NPs-based light/gas dual sensors are promising for future extreme environmental monitoring.

Gold Nanoparticles Produced by Low-temperature Heating of the Dry Residue of a Droplet of an HCl Acidic Solution of HAuCl4·4H2O in a Low Vacuum

An easy method is presented for producing gold nanoparticles. We show that by performing simultaneous low-temperature heating of a quartz glass substrate on which the dry residue of a 10 μL droplet of an HCl acidic solution of HAuCl₄·4H₂O is deposited and a counter substrate using Peltier devices in a low vacuum produced by a rotary pump, gold nanoparticles with sizes ranging from about twenty to one hundred and several tens of nanometers are produced on the counter substrate. In this study, an application of a gold nanoparticle substrate produced by this method to the sample holder for surface-enhanced Raman scattering analysis is also shown.

Enhancement of Scattering and Near Field of TiO2-Au Nanohybrids Using a Silver Resonator for Efficient Plasmonic Photocatalysis

Recently, localized surface plasmon resonances (SPRs) of metallic nanoparticles (NPs) have been widely used to construct plasmonic nanohybrids for heterogeneous photocatalysis. For example, the combination of plasmonic Au NPs and TiO₂ provides pure TiO₂ visible-light activity. The SPR effect induces an electric field and consequently enhances light scattering and absorption, favoring the transfer of photon energy to hot carriers for catalytic reactions. Numerous approaches have been dedicated to the improvement of SPR absorption in photocatalysts. Here, we have designed a core@shell-satellite nanohybrid catalyst whereby an Ag NP core, as a plasmonic resonator featuring unique dual functions of strong scattering and near-field enhancement, is encapsulated by SiO₂ and TiO₂ layers in sequence, with Au NPs on the outer surface, Ag@SiO₂@TiO₂-Au, for efficient plasmonic photocatalysis. By varying the size and number of Ag NP cores, the Au SPR can be tailored over the visible and near-infrared spectral region to reabsorb the scattered photons. In the presence of the Ag core, the incident light is efficiently confined in the reaction suspension by undergoing multiple scattering, thus leading to an increase of the optical path to the photocatalysis. Moreover, using numerical analysis and experimental verifications, we demonstrate that the Ag core also induces a strong near-field enhancement at the Au-TiO₂ interface via SPR coupling with Au. Consequently, the activity of the TiO₂-Au plasmonic photocatalyst is significantly enhanced, resulting in a high H₂ production rate under visible light. Thus, the design of a single structural unit with strong scattering and field enhancement, induced by a plasmonic resonator, is a highly effective strategy to boost photocatalytic activity.

Physical properties of gold nanoparticles affect skin penetration via hair follicles

Drug penetration through the skin is significant for both transdermal and dermal delivery. One mechanism that has attracted attention over the last two decades is the transport pathway of nanoparticles via hair follicle, through the epidermis, directly to the pilosebaceous unit and blood vessels. Studies demonstrate that particle size is an important factor for drug penetration. However, in order to gain more information for the purpose of improving this mode of drug delivery, a thorough understanding of the optimal physical particle properties is needed. In this study, we fabricated fluorescently labeled gold nanoparticles (GNP) with a tight control over the size and shape. The effect of the particles' physical parameters on follicular penetration was evaluated histologically. We used horizontal human skin sections and found that the optimal size for polymeric particles is 0.25 μm. In addition, shape penetration experiments revealed gold nanostars' superiority over spherical particles. Our findings suggest the importance of the particles' physical properties in the design of nanocarriers delivered to the pilosebaceous unit.

Direct Mercury Detection in Landfill Leachate Using a Novel AuNP-Biopolymer Carbon Screen-Printed Electrode Sensor

A novel Au nanoparticle (AuNP)-biopolymer coated carbon screen-printed electrode (SPE) sensor was developed through the co-electrodeposition of Au and chitosan for mercury (Hg) ion detection. This new sensor showed successful Hg2+ detection in landfill leachate using square wave anodic stripping voltammetry (SWASV) with an optimized condition: a deposition potential of -0.6 V, deposition time of 200 s, amplitude of 25 mV, frequency of 60 Hz, and square wave step voltage of 4 mV. A noticeable peak was observed at +0.58 V associated with the stripping current of the Hg ion. The sensor exhibited a good sensitivity of ~0.09 μA/μg (~0.02 μA/nM) and a linear response over the concentration range of 10 to 100 ppb (50-500 nM). The limit of detection (LOD) was 1.69 ppb, which is significantly lower than the safety limit defined by the United States Environmental Protection Agency (USEPA). The sensor had an excellent selective response to Hg2+ in landfill leachate against other interfering cations (e.g., Zn2+, Pb2+, Cd2+, and Cu2+). Fifteen successive measurements with a stable peak current and a lower relative standard deviation (RSD = 5.1%) were recorded continuously using the AuNP-biopolymer-coated carbon SPE sensor, which showed excellent stability, sensitivity and reproducibility and consistent performance in detecting the Hg2+ ion. It also exhibited a good reliability and performance in measuring heavy metals in landfill leachate.

Synergistic Effects of Surface Passivation and Charge Separation to Improve Photo-electrochemical Performance of BiOI Nanoflakes by Au Nanoparticle Decoration

We demonstrate that the photoactivity of bismuth oxyiodide (BiOI) nanoflake (NF) photocathodes in photo-electrochemical (PEC) water splitting can be significantly enhanced by about 24-fold by thermal calcination under an air atmosphere and then surficial decoration of Au nanoparticles (NPs). To understand the key factors affecting the PEC efficiency in Au NP-decorated BiOI NF photoelectrodes, incident photon-to-current conversion efficiency, electrochemical impedance spectroscopy, photovoltage, and electrochemically active surface area measurements were performed. The analytic results presented that thermal calcining could produce mesopores, increasing active sites on the surface of BiOI NFs. In addition, the synergistic effects of surface-state passivation and charge separation were observed for the surficial Au NP decoration on BiOI NFs. Transient absorption spectroscopy coupled with PEC measurements confirmed that the lifetime of photogenerated electrons on the conduction band of BiOI NFs can be prolonged by Au NP decoration, resulting in higher probability to carry out water reduction. The current investigation presents important insights into the mechanism of charge carrier dynamics in metal-semiconductor nano-heterostructures, which is contributive to develop photoelectrode materials in solar fuel production.

Vibrational Spectra of Nucleotides in the Presence of the Au Cluster Enhancer in MD Simulation of a SERS Sensor

Surface-enhanced Raman scattering (SERS) nanoprobes have shown tremendous potential in in vivo imaging. The development of single oligomer resolution in the SERS promotes experiments on DNA and protein identification using SERS as a nanobiosensor. As Raman scanners rely on a multiple spectrum acquisition, faster imaging in real-time is required. SERS weak signal requires averaging of the acquired spectra that erases information on conformation and interaction. To build spectral libraries, the simulation of measurement conditions and conformational variations for the nucleotides relative to enhancer nanostructures would be desirable. In the molecular dynamic (MD) model of a sensing system, we simulate vibrational spectra of the cytosine nucleotide in FF2/FF3 potential in the dynamic interaction with the Au20 nanoparticles (NP) (EAM potential). Fourier transfer of the density of states (DOS) was performed to obtain the spectra of bonds in reaction coordinates for nucleotides at a resolution of 20 to 40 cm-1. The Au20 was optimized by ab initio density functional theory with generalized gradient approximation (DFT GGA) and relaxed by MD. The optimal localization of nucleotide vs. NP was defined and the spectral modes of both components vs. interaction studied. Bond-dependent spectral maps of nucleotide and NP have shown response to interaction. The marker frequencies of the Au20-nucleotide interaction have been evaluated.

CRISPR-Cas12a-Based Nucleic Acid Amplification-Free DNA Biosensor via Au Nanoparticle-Assisted Metal-Enhanced Fluorescence and Colorimetric Analysis

Cell-free DNA (cfDNA) has attracted significant attention due to its high potential to diagnose diseases, such as cancer. Still, its detection by amplification method has limitations because of false-positive signals and difficulty in designing target-specific primers. CRISPR-Cas-based fluorescent biosensors have been developed but also need the amplification step for the detection. In this study, for the first time CRISPR-Cas12a based nucleic acid amplification-free fluorescent biosensor was developed to detect cfDNA by a metal-enhanced fluorescence (MEF) using DNA-functionalized Au nanoparticle (AuNP). Upon activating the CRISPR-Cas12a complex by the target cfDNA and subsequent single-strand DNA (ssDNA) degradation between AuNP and fluorophore, MEF occurred with color changes from purple to red-purple. Using this system, breast cancer gene-1 (BRCA-1) can be detected with very high sensitivity in 30 min. This rapid and highly selective sensor can be applied to measure other nucleic acid biomarkers such as viral DNA in field-deployable and point-of-care testing (POCT) platform.

Fabrication of a Sensitive Strain and Pressure Sensor from Gold Nanoparticle-Assembled 3D-Interconnected Graphene Microchannel-Embedded PDMS

Manufacture of uniform, sensitive, and durable microtextured sensing materials is one of the greatest challenges for pressure sensors and electronic skins. Reported in this article is a gold nanoparticle-assembled, 3D-interconnected, graphene microchannel-embedded PDMS (3D GMC-PDMS) film for strain and pressure sensors. The film consists of porous nickel foam with its inner walls coated by multilayer graphene. Embedding in PDMS with etching removal of the Ni yields a 3D GMC-PDMS. Coating the inner walls with Au nanoparticles yields an Au nanoparticle-assembled 3D GMC-PDMS (AuNPs-GMC-PDMS) film, which is useful as an ultrasensitive pressure and strain sensor. This sensor exhibits a wide detection range (∼50 kPa) and ultrahigh sensitivity of 5.37, 1.56, and 0.5 kPa^-1 in the ranges of <1, 1-10, and 10-50 kPa, respectively. Its lower detection limit is 4.4 Pa, its response time is 20 ms, and its strain factor is up to 15. Comparison of a AuNPs-GMC-PDMS film with a 3D GMC-PDMS film reveals a sensitivity improvement of 40 times in the 0-1 kPa pressure range and a gauge factor of more than 4 times in the 0-30% tensile strain range. The device has broad applications as a traditional or wearable medical sensor.

TAT-Modified Gold Nanoparticles Enhance the Antitumor Activity of PAD4 Inhibitors

Purpose

Histone citrullination by peptidylarginine deiminases 4 (PAD4) regulates the gene expression of tumor suppressor. In our previously study, YW3-56 (356) was developed as a potent PAD4 inhibitor for cancer therapy with novel function in the autophagy pathway. To enhance the antitumor activity, the PAD4 inhibitor 356 was modified by the well-established cationic penetrating peptide RKKRRQRRR (peptide TAT) and gold nanoparticles to obtain 356-TAT-AuNPs which could enhance the permeability of chemical drug in solid tumor.

Methods

356-TAT-AuNPs were prepared, and their morphology were characterized. The antitumor activity of 356-TAT-AuNPs was evaluated in vitro and in vivo.

Results

356-TAT-AuNPs exhibited higher anticancer activity against HCT-116, MCF-7 and A549 cells than 356 and 356-AuNPs. Compared with 356 and 356-AuNPs, 356-TAT-AuNPs entered the cytoplasm and nuclear, exhibited stronger anticancer activity by increasing apoptosis, inducing autophagy and inhibiting of histone H3 citrullination, and in HCT-116 xenograft mouse model, 356-TAT-AuNPs could improve the antitumor activity.

Conclusion

The modified AuNPs with peptide TAT as drug delivery system are potent in delaying tumor growth and could be a powerful vehicle for profitable anticancer drug development. We believe that peptide TAT modification strategy may provide a simple and valuable method for improving antitumor activity of PAD4 inhibitors for clinical use.

Potential of TiO2 with Various Au Nanoparticles for Catalyzing Mesotrione Removal from Wastewaters under Sunlight

Nowadays, great focus is given to the contamination of surface and groundwater because of the extensive usage of pesticides in agriculture. The improvements of commercial catalyst TiO₂ activity using different Au nanoparticles were investigated for mesotrione photocatalytic degradation under simulated sunlight. The selected system was 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) that was studied by transmission electron microscopy and ultraviolet-visible (UV-Vis) spectroscopy. It was found that TiO₂ particles size was ~20 nm and ~50 nm, respectively. The Au nanoparticles were below 10 nm and were well distributed within the framework of TiO₂. For 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L), band gap energy was 2.45 eV. In comparison to the pure TiO₂, addition of Au nanoparticles generally enhanced photocatalytic removal of mesotrione. By examining the degree of mineralization, it was found that 2.43 × 10⁻³% Au–S–CH₂–CH₂–OH/TiO₂ (0.5 g/L) system was the most efficient for the removal of the mesotrione and intermediates. The effect of tert-butanol, NaF and ethylenediaminetetraacetic acid disodium salt on the transformation rate suggested that the relative contribution of various reactive species changed in following order: h⁺ > ^●OH_ads > ^●OH_bulk. Finally, several intermediates that were formed during the photocatalytic treatment of mesotrione were identified.

Rapid Detection of Bifidobacterium bifidum in Feces Sample by Highly Sensitive Quartz Crystal Microbalance Immunosensor

In this work, a quartz crystal microbalance (QCM) sensor has been fabricated using immunoassay for sensitive determination of Bifidobacterium bifidum. Au nanoparticle has been used for amplifying sandwich assays. The proposed immunosensor exhibited a linear detection range between 103 and 105 CFU/mL with a limit of detection of 2.1 × 102 CFU/mL. The proposed immunosensor exhibited good selectivity for B. bifidum sensing with low cross reactivity for other foodborne pathogens such as Lactobacillus acidophilus, Listeria monocytogenes, and Escherichia coli. In addition, the proposed immunosensor has been successfully used for B. bifidum detection in feces samples and food samples. The frequency decreases of 12, 17, and 10 Hz were observed from the milk samples consisting of the mixtures of L. acidophilus, L. monocytogenes, and E. coli. The frequency decreases of 8, 15, and 7 Hz were observed from the feces samples consisting of the mixtures of L. acidophilus, L. monocytogenes, and E. coli.

One-pot ultrasonic synthesis of multifunctional Au nanoparticle-ferrocene-WS2 nanosheet composite for the construction of an electrochemical biosensing platform

Structuring of noble metal nanoparticles on transition metal dichalcogenide nanosheets induces significantly enhanced electronic, optical, and catalytic functions. However, the synthesis of multifunctional hybrids is always time-consuming and involves multiple steps. Herein, a ternary Au nanoparticle-ferrocene-WS₂ nanosheet (AFW) composite has been prepared by a facile one-step sonochemical approach. Stripped WS₂ nanosheets were functionalized with ferrocene monocarboxylic acid (FMC) and gold nanoparticles (AuNPs) by making use of the strong coordinative interaction of carboxyl groups with tungsten atoms. The AuNPs decorating the WS₂ nanosheet not only increase the water solubility of WS₂ nanosheet and surface area of the modified electrode, but also act as electron transport bridges to aid the tunneling of electrons from the small redox molecule, FMC, through the space to the electrode on which they are mounted. Furthermore, the ternary AFW nanocomposite could effectively avoid the leaching of FMC from the nanocomposite matrix and provided a suitable environment for the immobilized biomolecules. Combining the immune magnetic beads technology and the AFW nanocomposite with aforementioned advantages, a high-performance electrochemical immunosensor was successfully developed using carbohydrate antigen 72-4 (CA72-4) as a model analyte. A linear relationship in the range of 2-50 U/L for the detection of CA72-4 was found with a low detection limit of 0.6 U/L. In addition, the biosensor showed excellent performance in selectivity, stability, and reproducibility. Thus, this work not only proposes a facile avenue for preparing a 2D WS₂ nanocomposite with multifunctional properties but also opens up a new method to extend the application of WS₂-based materials in biological sensing.

Lateral flow assay using aptamer-based sensing for on-site detection of dopamine in urine

A lateral flow assay using DNA aptamer-based sensing for the detection of dopamine in urine is reported. Dopamine duplex aptamers (hybridized sensor with capture probe) are conjugated to 40-nm Au nanoparticles (AuNPs) with 20T linkers. The detection method is based on the dissociation of the duplex aptamer in the presence of dopamine, with the sensor part undergoing conformational changes and being released from the capture part. Hybridization between the complementary DNA in the test line and the conjugated AuNP-capture DNA produces a red band, whose intensity is related to the dopamine concentration. The minimum detectable concentration obtained by ImageJ analysis was <10 ng/mL (65.2 nM), while the visual limit of detection is estimated to be ~50 ng/mL (normal range of dopamine in urine of 52-480 ng/mL or 0.3-3.13 μM). No cross reactivity to other stress biomarkers in urine was confirmed. These results indicate that this robust and user-friendly point-of-care biosensor has significant potential for providing a cost-effective alternative for dopamine detection in urine.

Au nanozyme-driven antioxidation for preventing frailty

From senescence and frailty that may result from various biological, mechanical, nutritional, and metabolic processes, the human body has its own antioxidant defense enzymes to remove by-products of oxygen metabolism, and if unregulated, can cause several types of cell damage. Herein, an antioxidant, artificial nanoscale enzyme, called nanozyme (NZs), is introduced that is composed of Au nanoparticles (NPs) synthesized with a mixture of two representative phytochemicals, namely, gallic acid (GA) and isoflavone (IF), referred to as GI-Au NZs. Their unique antioxidant and anti-aging effects are monitored using Cell Counting Kit-8 and senescence-associated β-galactosidase assays on neonatal human dermal fibroblasts (nHDFs). Furthermore, alterations in epidermal thickness and SOD activity are measured under ultraviolet light to investigate the effects of the topical application of NZs on the histological structure and antioxidant activity in hairless mice skin. Then, hepatotoxicity and nephrotoxicity in the hairless mice are monitored. It is concluded that the NZs can effectively prevent serial passage-induced senescence in nHDFs, as well as oxidative stress in mice skin, suggesting a range of strategies to further develop novel therapeutics for acute frailty.

Laser ablation in liquids for the assembly of Se@Au chain-oligomers with long-term stability for photothermal inhibition of tumor cells

For the potential use of Au nanoparticles (NPs) in photothermal therapy, it is important and effective to achieve the uniaxial assembly of Au NPs to allow enhanced absorption in the near infrared (NIR) region. Herein, we first presented the construction of amorphous selenium encapsulated gold (Se@Au) chain-oligomers by successive laser ablation of Au and Se targets in sodium chloride solution without other toxic precursors, stabilizers, or templating molecules. Se@Au chain-oligomers showed evidently enhanced NIR absorption and excellent photothermal transduction efficiency (η), which was higher than 47% at 808 nm. After being stored for 1 year, the Se@Au colloids still exhibited outstanding photothermal performance. The cytotoxicity assay demonstrated that there is negligible toxicity of Se@Au chain-oligomers in cells, but cell viability declined to only 1% in phototherapeutic experiments that were implemented in vitro. In intracellular Reactive Oxygen Species (ROS) generation measurements, Se@Au chain-oligomers could trigger a 35.9% increment of ROS upon laser irradiation. The possible synergetic effects between the anticancer function of Se and photothermal behaviors of Se@Au oligomers were intended to increase ROS level in cells. Therefore, such designed Se@Au chain-oligomers of high stability exhibit promising potential for their use as in vivo photothermal therapeutic agents.

One step preparation of stable gold nanoparticle using red cabbage extracts under UV light and its catalytic activity

Herein, we have reported the synthesis, characterization and catalytic activity of highly stable gold nanoparticles (Au NPs) using red cabbage extract (RCE) under UV irradiation. The anthocyanin groups predominantly existing in RCE play an essential role for biosynthesis of stable Au NPs. The reasons for using anthocyanins: 1) they act as chelating agents for preferentially reacting with gold ions (Au³⁺) to form Au³⁺- anthocyanin complexes, 2) as light-active reductants for reduction of Au³⁺ to zero valent Au⁰ under UV irradiation and 3) as stabilizing agent for preventing Au NPs from aggregation in high salt concentration owing to their unique salt tolerance property. We also demonstrate that how reaction time, concentration of RCE, pH value of reaction solutions and using one more reducing agent affected formation of the Au NPs. The stability of RCE Au NPs was comparatively studied with commercial (citrate stabilized) Au NPs against 100 mM salt (NaCl) solution. The RCE-Au NP showed reduction ability for conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). UV-vis spectrometry, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential (ZT) methods were utilized to characterize the Au NPs. We demonstrated that how whole RCE (anthocyanins molecules are major component) can be used as photo-active reducing and stabilizing agents to form Au NPs in a short time under UV irradiation and strong reducing agent without additional agents.

Observation of Single Nanoparticle Collisions with Green Synthesized Pt, Au, and Ag Nanoparticles Using Electrocatalytic Signal Amplification Method

This work describes the tailored design, green synthesis and characterization of noble metal (Pt, Ag and Au) nanoparticles (NPs) using Sapinduss Mukkorossi fruit extract (SMFE) and its signal NP collision signal response, based on the principle of the electrocatatlytic amplication (EA) method. Here, the SMFE can act as both the reducing and the capping agent for the fabrication of noble nanometals. The SMFE-capped NPs was available for the observation of a single NP collision signal. Two general types of current response were observed: a staircase current response for the Pt or Au NPs, and a blip/spike current response for Ag NPs. These results demonstrated that the eco-friendly synthesized SMFE-capped NPs maintained their electrocatalytic activity, therefore they can be used for the single NP experiments and place an arena for future biosensing applications.

Photoelectrochemical detection of breast cancer biomarker based on hexagonal carbon nitride tubes

Photoelectrochemical (PEC) sensor for sensitive detection of breast cancer biomarker human epidermal growth factor receptor 2 (HER2) utilizing hexagonal carbon nitride tubes (HCNT) as photoactive material is reported. The detection is based on suppression of the PEC current intensity of the sensor. HCNT were synthesized via a facile hydrothermal method with large specific surface area and low electron-hole recombination. Au nanoparticles (AuNPs) were deposited onto the surface of the HCNT, which enhanced the photocurrent intensity of the HCNT by one time. For HER2 detection, peptide specific to HER2 was immobilized on the AuNPs surface for capturing HER2 molecules. The following binding of HER2 with HER2 aptamer and the reaction of phosphate groups on aptamer with molybdate can form molybdophosphate precipitate, which sticks to the surface of HCNT and impedes electron transport. Thus, photocurrent intensity of the sensor was suppressed. Under optimal conditions, the linear relationship between the PEC intensity and the logarithm of HER2 concentration was from 0.5 to 1 ng mL^-1 with low limit of detection (LOD) of 0.08 pg mL^-1. Furthermore, the PEC sensor also displayed capability for detecting HER2 in human serum samples. This PEC sensor signal detection strategy can be easily adapted to other PEC sensors involving DNA and find wide applications. Graphical abstract.

The thermoelectric properties of Au nanoparticle-incorporated Al-doped mesoporous ZnO thin films

Mesoporous Al-doped ZnO thin films incorporated with gold nanoparticles (Au NPs) were synthesized using a sol-gel and evaporation-induced self-assembly process. In this study, the complementary effects of Au NP incorporation and Al doping on the thermoelectric properties of mesoporous ZnO thin films were analysed. The incorporated Au NPs induced an increase in electrical conductivity but a detriment in the pore arrangement of the mesoporous ZnO thin film, which was accompanied by a decrease in porosity. However, the addition of the Al dopant minimized the pore structural collapse because of the inhibition of the grain growth in the ZnO skeletal structure, resulting in the enhancement of the pore arrangement and porosity. When the Au NPs and Al dopant were added at the same time, the degradation in the pore structure was minimized and the electrical conductivity was effectively increased, but the absolute value of the Seebeck coefficient was decreased. However, as a result, the thermoelectric power factor was increased by 2.4 times compared to that of the pristine mesoporous ZnO thin film. It was found that co-introducing the Au NPs and Al doping to the mesoporous ZnO structure was effective in preserving the pore structure and increasing the electric conductivity, thereby enhancing the thermoelectric property of the mesoporous ZnO thin film.

Controlled Symmetry Breaking in Colloidal Crystal Engineering with DNA

The programmed crystallization of particles into low-symmetry lattices represents a major synthetic challenge in the field of colloidal crystal engineering. Herein, we report an approach to realizing such structures that relies on a library of low-symmetry Au nanoparticles, with synthetically adjustable dimensions and tunable aspect ratios. When modified with DNA ligands and used as building blocks for colloidal crystal engineering, these structures enable one to expand the types of accessible lattices and to answer mechanistic questions about phase transitions that break crystal symmetry. Indeed, crystals formed from a library of elongated rhombic dodecahedra yield a rich phase space, including low-symmetry lattices (body-centered tetragonal and hexagonal planar). Molecular dynamics simulations corroborate and provide insight into the origin of these phase transitions. In particular, we identify an unexpected asymmetry in the DNA shell, distinct from both the particle and lattice symmetries, which enables directional, nonclose-packed interactions.

A Novel Gold Nanoprobe for a Simple Electrochemiluminescence Determination of a Prostate-specific Antigen Based on a Peptide Cleavage Reaction

A novel gold nanoprobe for a sensitive and simple determination of a prostate-specific antigen (PSA) was designed on the basis of homogeneous detection and a peptide cleavage reaction. The gold nanoprobe (AuNPs-peptide-Ru1) consisted of a specific peptide tagged with a ruthenium(II) complex (Ru1) and gold nanoparticles (AuNPs) conjugated with the peptide via the strong Au-S bond between the AuNPs surface and the thiol group of the peptide. The electrochemiluminescence (ECL) enzymatic-cleavage-reaction-based bioanalytic system based on homogeneous detection has overcome shortcomings from a complicated fabrication process of traditional electrodes. In the presence of the target PSA, it specifically cleaved the peptide of the AuNPs-peptide-Ru1, and the ECL signal substance (Ru1) part dissociated from AuNPs-peptide-Ru1. This resulted in an increase in the ECL intensity. The ECL biosensor could detect PSA concentrations in the range from 1.0 × 10^-12 to 1.0 × 10^-9 g/mL, the detection limit was 4.0 × 10^-13 g/mL. The assay with the advantages of a simple method for PSA was selective and fast. It is superior to the immunoassay, and is a promising strategy to develop biosensors based on enzymatic cleavage including electrochemistry and optics.

Site-Specific Positioning and Patterning of MoS2 Monolayers: The Role of Au Seeding

Monolayers of transition metal dichalcogenides (TMDs) are attractive for various modern semiconductor devices. However, the limited control over the location, yield, and size distribution of the products using current synthesis methods has severely limited their large-scale applicability. Herein, we identify the ability to use metal ( e. g., Au) nanoparticles to seed the growth of MoS₂ monolayers and thereby provide a means to achieve programmable and controllable synthesis. In this study, prepatterned Au seeds are used as heterogeneous nucleation sites to induce the formation of desired geometries of MoS₂ monolayers via chemical vapor deposition. Our experimental and theoretical results shed light on the growth mechanism driving the formation of MoS₂ monolayers at these sites, revealing that the seeding effect originates from the favorable formation energy of MoS₂ on the Au surface. A field-effect transistor with a predesigned channel geometry exhibits electronic performance that compares nicely with previously reported MoS₂ monolayer devices. We believe this study contributes fundamental insights into controlled synthesis of TMD monolayers, making integration of these materials into emerging electronic devices more attainable.

Ni-Doped ZnS Nanospheres Decorated with Au Nanoparticles for Highly Improved Gas Sensor Performance

Novel Ni-doped wurtzite ZnS nanospheres decorated with Au nanoparticles (Au NPs⁻ZnS NSs) have been successfully fabricated using a simple method involving vacuum evaporation followed by an annealing process. This transition metal-doped gas sensor had high responsivity, extremely fast response and recovery time, and excellent selectivity to formaldehyde at room temperature. The response and recovery time are only 29 s and 2 s, respectively. Since ZnS is transformed into ZnO at a high temperature, superior room temperature-sensing performance can improve the stability and service life of the sensor. The improvement in sensing performance could be attributed to the reduced charge-transfer distance resulting from the creation of a local charge reservoir layer, and the catalytic and spillover effect of Au nanoparticles. The rough and porous spherical structure can also facilitate the detection and diffusion of gases. The as-prepared Au NPs⁻ZnS NSs are considered to be an extremely promising candidate material for gas sensors, and are expected to have other potential applications in the future.

Recent uses of carbon nanotubes & gold nanoparticles in electrochemistry with application in biosensing: A review

The innovation of nanoparticles assumes a critical part of encouraging and giving open doors and conceivable outcomes to the headway of new era devices utilized as a part of biosensing. The focused on the quick and legitimate detecting of specific biomolecules using functionalized gold nanoparticles (Au NPs), and carbon nanotubes (CNTs) has turned into a noteworthy research enthusiasm for the most recent decade. Sensors created with gold nanoparticles or carbon nanotubes or in some cases by utilizing both are relied upon to change the very establishments of detecting and distinguishing various analytes. In this review, we will examine the current utilization of functionalized AuNPs and CNTs with other synthetic mixes for the creation of biosensor prompting to the location of particular analytes with low discovery cutoff and quick reaction.

Nanocapsules of Magnetic Au Self-Assembly for DNA Migration and Secondary Self-Assembly

To endow valuable responsiveness to self-assemblies of Au nanoparticles (Au NPs), the magnetic Au nanoparticles (Au NPs)/C₁₆H₃₃(CH₃)₃N⁺[CeCl₃Br]^- (CTACe) mixtures were first prepared by using an emulsion self-assembly of a magnetic surfactant, C₁₆H₃₃(CH₃)₃N⁺[CeCl₃Br]^-. A versatile morphology of self-assemblies of Au NPs could be controlled by the counterions in surfactants including [CeCl₃Br]^-, [FeCl₃Br]^-, and Br^- as well as solvent. In particular, the magnetic counterion, [CeCl₃Br]^-, can induce self-growth of Au NPs in an emulsion self-assembly process due to the oxidability of [CeCl₃Br]^-. It enhances the rigidity of Au NPs/CTACe scaffolds template compared with Au NPs/hexadecyltrimethylammonium bromide. [CeCl₃Br]^- engaged Au NPs/CTACe with fascinating capability of conglutination and targeted migration of DNA (150 μmol/L) under a magnet field. The conglutination capability of the DNA molecules can increase to 39.8% by adopting the magnetic strategy when using Au NPs/CTACe as a magnetic booster. Au NPs/CTACe mixtures can ideally self-assemble to be scaffolds, providing abundant conjugation sites of surface charges. Magnetic Au NPs/CTACe can serve as a template scaffold to secondary self-assemble with DNA (40 mmol/L) outside, producing smooth-faced and hollow DNA nanocapsules. We believe that the creative Au NPs/CTACe/DNA nanocapsules will extend the biological application field of Au NPs assemblies.

Optical Field Enhancement in Au Nanoparticle-Decorated Nanorod Arrays Prepared by Femtosecond Laser and Their Tunable Surface-Enhanced Raman Scattering Applications

Various Au nanostructures have been demonstrated to have an enhanced local electric field around them because of surface plasmons. Herein, we propose a novel method for fabricating Au nanoparticle-decorated nanorod (NPDN) arrays through femtosecond laser irradiation combined with Au coating and annealing. The nanorod cavities strongly confined light and produced an enhanced optical field in response to Au nanoparticles (NPs) introduction. The nanogap and diameter of the fabricated Au NPs significantly affected the surface-enhanced Raman scattering (SERS) performance and could be simultaneously tuned with thickness-controllable Au films and substrate morphologies. The resulting Au NPDN substrate was observed to have efficient "hot spots" for tunable SERS applications. We experimentally determined that the enhancement factor of the Au NPDN substrate reached up to 8.3 × 10⁷ at optimal parameters. Moreover, the Au NPDN substrate showed superior chemical stability, with the greatest intensity deviation of 3.2% on exposure to air for 2 months. This work provides a promising method to fabricate tunable plasmonic surfaces for highly sensitive, reproducible, and chemically stable SERS applications.

Enhancing T1 magnetic resonance imaging contrast with internalized gadolinium(III) in a multilayer nanoparticle

Multifunctional nanoparticles for biomedical applications have shown extraordinary potential as contrast agents in various bioimaging modalities, near-IR photothermal therapy, and for light-triggered therapeutic release processes. Over the past several years, numerous studies have been performed to synthesize and enhance MRI contrast with nanoparticles. However, understanding the MRI enhancement mechanism in a multishell nanoparticle geometry, and controlling its properties, remains a challenge. To systematically examine MRI enhancement in a nanoparticle geometry, we have synthesized MRI-active Au nanomatryoshkas. These are Au core-silica layer-Au shell nanoparticles, where Gd(III) ions are encapsulated within the silica layer between the inner core and outer Au layer of the nanoparticle (Gd-NM). This multifunctional nanoparticle retains its strong near-IR Fano-resonant optical absorption properties essential for photothermal or other near-IR light-triggered therapy, while simultaneously providing increased T₁ contrast in MR imaging by concentrating Gd(III) within the nanoparticle. Measurements of Gd-NM revealed a strongly enhanced T₁ relaxivity (r₁ ∼ 24 mM^-1⋅s^-1) even at 4.7 T, substantially surpassing conventional Gd(III) chelating agents (r₁ ∼ 3 mM^-1⋅s^-1 at 4.7 T) currently in clinical use. By varying the thickness of the outer gold layer of the nanoparticle, we show that the observed relaxivities are consistent with Solomon-Bloembergen-Morgan (SBM) theory, which takes into account the longer-range interactions between the encapsulated Gd(III) and the protons of the H₂O molecules outside the nanoparticle. This nanoparticle complex and its MRI T₁-enhancing properties open the door for future studies on quantitative tracking of therapeutic nanoparticles in vivo, an essential step for optimizing light-induced, nanoparticle-based therapies.

Gas sensing properties of MWCNT layers electrochemically decorated with Au and Pd nanoparticles

Multiwalled carbon nanotube (MWCNT)-based chemiresistors were electrochemically decorated with Au and Pd nanoparticles (NPs), resulting in an improvement in the detection of gaseous pollutants as compared to sensors based on pristine MWCNTs. Electrophoresis was used to decorate MWCNTs with preformed Au or Pd NPs, thus preserving their nanometer-sized dimensions and allowing the metal content to be tuned by simply varying the deposition time. The sensing response of unmodified and metal-decorated MWCNTs was evaluated towards different gaseous pollutants (e.g., NO2, H2S, NH3 and C4H10) at a wide range of concentrations in the operating temperature range of 45-200 °C. The gas sensing results were related to the presence, type and loading of metal NPs used in the MWCNT functionalization. Compared to pristine MWCNTs, metal-decorated MWCNTs revealed a higher gas sensitivity, a faster response, a better stability, reversibility and repeatability, and a low detection limit, where all of these sensing properties were controlled by the type and loading of the deposited metal catalytic NPs. Specifically, in the NO2 gas sensing experiments, MWCNTs decorated with the lowest Au content revealed the highest sensitivity at 150 °C, while MWCNTs with the highest Pd loading showed the highest sensitivity when operated at 100 °C. Finally, considering the reported gas sensing results, sensing mechanisms have been proposed, correlating the chemical composition and gas sensing responses.

Methyl Orange removal by a novel PEI-AuNPs-hemin nanocomposite

A novel poly(ethyleneimine)/Au nanoparticles/hemin nanocomposite (PEI-AuNPs-Hemin) acting for Methyl Orange (MO) removal has been synthesized. PEI-AuNPs was prepared firstly and it was then linked to hemin through the coupling between carboxyl groups in hemin and amino groups in PEI without the activation of carboxyl groups. The high reactivity and stability of AuNPs contributed greatly in the formation of the amido bonds in the nanocomposite. Fourier transform infrared spectroscopy, transmission electron microscopy and UV-visible spectroscopy were used to characterize the PEI-AuNPs-Hemin. Results show that PEI-AuNPs-Hemin has strong adsorption for MO. Adsorption and degradation experiments were carried out at different pHs, nanocomposite concentrations and UV irradiation times. Removal of MO in acidic solutions was more effective than in basic solutions. The real-time study showed that the MO degradation with the nanocomposite under UV irradiation was a fast process. In addition, the photocatalytic degradation mechanism was proposed. The study suggests that the PEI-AuNPs-Hemin may have promising applications in environmental monitoring and protection.