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Lateral flow immunoassay (LFIA) is a convenient tool for rapid field-based control of various bacterial targets. However, for many applications, the detection limits obtained by LFIA are not sufficient. In this paper, we propose enlarging gold nanoparticles’ (GNPs) size to develop a sensitive lateral flow immunoassay to detect Ralstonia solanacearum. This bacterium is a quarantine organism that causes potato brown rot. We fabricated lateral flow test strips using gold nanoparticles (17.4 ± 1.0 nm) as a label and their conjugates with antibodies specific to R. solanacearum. We proposed a signal enhancement in the test strips’ test zone due to the tetrachloroauric (III) anion reduction on the GNP surface, and the increase in size of the gold nanoparticles on the test strips was approximately up to 100 nm, as confirmed by scanning electron microscopy. Overall, the gold enhancement approach decreased the detection limit of R. solanacearum by 33 times, to as low as 3 × 104 cells∙mL–1 in the potato tuber extract. The achieved detection limit allows the diagnosis of latent infection in potato tubers. The developed approach based on gold enhancement does not complicate analyses and requires only 3 min. The developed assay together with the sample preparation and gold enlargement requires 15 min. Thus, the developed approach is promising for the development of lateral flow test strips and their subsequent introduction into diagnostic practice.

We report on the use of poly(allylamine) hydrochloride (PAH) as a reducing agent for the controlled formation of gold nanoparticles (AuNPs) in the size range of 5-50 nm. The formation of AuNPs using this polymer matrix allows for the AuNPs to be imbedded in the polymer matrix, once formed. The kinetics of AuNP formation are shown to be pseudo first-order in [HAuCl^sub 4^] at room temperature. The kinetics of AuNP formation are controlled by the ratio of reducing agent to HAuCl^sub 4^ as well as the overall concentration of the PAH and HAuCl^sub 4^. Additionally, at low PAH:HAuCl^sub 4^ mole ratios, the plasmon resonance wavelength can be controlled through the ratio of the reactants. This plamson resonance shift is shown to be related to AuNP size by means of TEM imaging data on the AuNPs.[PUBLICATION ABSTRACT]

Rapidly growing interest in the nanoparticle-mediated delivery of DNA and RNA to plants requires a better understanding of how nanoparticles and their cargoes translocate in plant tissues and into plant cells. However, little is known about how the size and shape of nanoparticles influence transport in plants and the delivery efficiency of their cargoes, limiting the development of nanotechnology in plant systems. In this study we employed non-biolistically delivered DNA-modified gold nanoparticles (AuNPs) of various sizes (5–20 nm) and shapes (spheres and rods) to systematically investigate their transport following infiltration into Nicotiana benthamiana leaves. Generally, smaller AuNPs demonstrated more rapid, higher and longer-lasting levels of association with plant cell walls compared with larger AuNPs. We observed internalization of rod-shaped but not spherical AuNPs into plant cells, yet, surprisingly, 10 nm spherical AuNPs functionalized with small-interfering RNA (siRNA) were the most efficient at siRNA delivery and inducing gene silencing in mature plant leaves. These results indicate the importance of nanoparticle size in efficient biomolecule delivery and, counterintuitively, demonstrate that efficient cargo delivery is possible and potentially optimal in the absence of nanoparticle cellular internalization. Overall, our results highlight nanoparticle features of importance for transport within plant tissues, providing a mechanistic overview of how nanoparticles can be designed to achieve efficacious biocargo delivery for future developments in plant nanobiotechnology. A study of gold nanospheres and nanorods shows that, even without internalization, they are very efficient for siRNA delivery and inducing gene silencing in mature plant leaves.

The aim of our study was to examine the different concentrations of AuNPs as a new antimicrobial substance to control the pathogenic activity. The extracellular synthesis of AuNPs performed by using Phoma sp. as an endophytic fungus. Endophytic fungus was isolated from vascular tissue of peach trees (Prunus persica) from Baft, located in Kerman province, Iran. The UltraViolet-Visible Spectroscopy (UV–Vis spectroscopy) and Fourier transform infrared spectroscopy provided the absorbance peak at 526 nm, while the X-ray diffraction and transmission electron microscopy images released the formation of spherical AuNPs with sizes in the range of 10–100 nm. The findings of inhibition zone test of Au nanoparticles (AuNPs) showed a desirable antifungal and antibacterial activity against phytopathogens including Rhizoctonia solani AG1-IA (AG1-IA has been identified as the dominant anastomosis group) and Xanthomonas oryzae pv. oryzae. The highest inhibition level against sclerotia formation was 93% for AuNPs at a concentration of 80 μg/mL. Application of endophytic fungus biomass for synthesis of AuNPs is relatively inexpensive, single step and environmentally friendly. In vitro study of the antifungal activity of AuNPs at concentrations of 10, 20, 40 and 80 μg/mL was conducted against rice fungal pathogen R. solani to reduce sclerotia formation. The experimental data revealed that the Inhibition rate (RH) for sclerotia formation was (15, 33, 74 and 93%), respectively, for their corresponding AuNPs concentrations (10, 20, 40 and 80 μg/mL). Our findings obviously indicated that the RH strongly depend on AuNPs rates, and enhance upon an increase in AuNPs rates. The application of endophytic fungi biomass for green synthesis is our future goal.

Pseudomonas aeruginosa  was used to synthesize anisotropic gold nanoparticles from the unusually reducible aryldiazonium gold (III) salt of the chemical formula [HOOC-4-C 6 H 4 N≡N]AuCl 4 (abbreviated as DS-AuCl 4 ). We investigated the effect of bacterial cell density, temperature, and pH on the AuNP synthesis. The bacterial cell density of 6.0 × 10 8  CFU/mL successfully reduced 0.5 mM DS-AuCl 4 salt to AuNPs after incubation at 37 °C (24 h), 42 °C (24 h), and 25 °C (48 h). Transmission electron microscopy (TEM) images revealed the formation of spherical, triangle, star, hexagon, and truncated triangular morphologies for the AuNPs synthesized using P. aeruginosa bacteria. The average size of AuNPs synthesized at 25 °C (48 h), 37 °C (24 h), and 42 °C (24 h) was 39.0 ± 9.1 nm, 26.0 ± 8.1 nm, and 36.7 ± 7.7 nm, respectively. The average size of AuNPs synthesized at pH 3.7, 7.0, and 12.7 was 36.7 ± 7.7 nm, 14.7 ± 3.8 nm, and 7.3 ± 2.5 nm, respectively, with the average size decreasing at a pH of 12.7. The reduction of the DS-AuCl 4 salt was confirmed using X-ray photoelectron spectroscopy (XPS). The significant peaks for C1s, Au4f doublet, N1s, and O1s are centered at 285, 84–88, 400, and 532 eV. The ability of inactivated bacteria (autoclave-dead and mechanically lysed bacteria), peptidoglycan, and lipopolysaccharides to reduce the DS-AuCl 4 salt to AuNPs was also investigated. Anisotropic AuNPs were synthesized using inactivated bacteria and peptidoglycan but not using lipopolysaccharides. The AuNPs demonstrated biocompatibility with human RBCs and were safe, with no antibacterial activities against Escherichia coli and Staphylococcus aureus . This is the first report demonstrating the synthesis of AuNPs using aryldiazonium gold(III) salts with P. aeruginosa . These AuNPs are promising candidates for exploring potential applications in nanomedicine and drug delivery. Key points • Anisotropic AuNPs were synthesized using P. aeruginosa bacteria. • Dead and lysed bacterial residues synthesized anisotropic AuNPs. • AuNPs are hemocompatible. Graphical Abstract

Epidermal growth factor receptor (EGFR) is estimated to be overexpressed in 60~80% of colorectal cancer (CRC), which is associated with a poor prognosis. Anti-EGFR targeted monoclonal antibodies (cetuximab and panitumumab) have played an important role in the treatment of metastatic CRC. However, the therapeutic response of anti-EGFR monoclonal antibodies is limited due to multiple resistance mechanisms. With the discovery of new functions for gold nanoparticles (AuNPs), we hypothesize that cetuximab-conjugated AuNPs (cetuximab-AuNPs) will not only improve the cytotoxicity for cancer cells, but also introduce expression change of the related biomarkers on cancer cell surface. In this contribution, we investigated the size-dependent cytotoxicity of cetuximab-AuNPs to CRC cell line (HT-29), while also monitored the expression of cell surface biomarkers in response to treatment with cetuximab and cetuximab-AuNPs. AuNPs with the size of 60 nm showed the highest impact for cell cytotoxicity, which was tested by cell counting kit-8 (CCK-8) assay. Three cell surface biomarkers including epithelial cell adhesion molecule (EpCAM), melanoma cell adhesion molecule (MCAM), and human epidermal growth factor receptor-3 (HER-3) were found to be expressed at higher heterogeneity when cetuximab was conjugated to AuNPs. Both surface-enhanced Raman scattering/spectroscopy (SERS) and flow cytometry demonstrated the correlation of cell surface biomarkers in response to the drug treatment. We thus believe this study provides powerful potential for drug-conjugated AuNPs to enhance cancer prognosis and therapy.

Background Gene and chemical therapy has become one of the rising stars in the field of molecular medicine during the last two decades. However, there are still numerous challenges in the development of efficient, targeted, and safe delivery systems that can avoid siRNA degradation and reduce the toxicity and adverse effects of chemotherapy medicine. Results In this paper, a highly efficient AS1411 aptamer modified, dsDNA and MMP-2 cleavable peptide-fabricated gold nanocage vehicle, which could load doxorubicin hydrochloride (DOX) and siRNAs to achieve a combination of tumor responsive genetic therapy, chemotherapy, and photothermal treatment is presented. Our results show that this combined treatment achieved targeted gene silencing and tumor inhibition. After nearly one month of treatment with DOX-loaded Au-siRNA-PAA-AS1411 nanoparticles with one dose every three days in mice, a synergistic effect promoting the eradication of long-lived tumors was observed along with an increased survival rate of mice. The combined genetic, chemotherapeutic, and photothermal treatment group exhibited more than 90% tumor inhibition ratio (tumor signal) and a ~ 67% survival rate compared with a 30% tumor inhibition ratio and a 0% survival rate in the passive genetic treatment group. Conclusions The development of nanocarriers with double-stranded DNA and MMP-2 cleavable peptides provides a new strategy for the combined delivery of gene and chemotherapy medicine. Au-siRNA-PAA-AS1411 exerts high anticancer activities on lung cancer, indicating immense potentials for clinical application.

Bimetallic silver/gold nanosystems are expected to significantly improve therapeutic efficacy compared to their monometallic counterparts by maintaining the general biocompatibility of gold nanoparticles (AuNPs) while, at the same time, decreasing the relatively high toxicity of silver nanoparticles (AgNPs) toward healthy human cells. Thus, the aim of this research was to establish a highly reproducible one-pot green synthesis of colloidal AuNPs and bimetallic Ag/Au alloy nanoparticles (NPs; Ag/AuNPs) using starch as reducing and capping agent. The optical properties, high reproducibility, stability and particle size distribution of the colloidal NPs were analyzed by ultraviolet (UV)-visible spectroscopy, dynamic light scattering (DLS) and -potential. The presence of starch as capping agent was determined by Fourier transform infrared (FT-IR) spectroscopy. The structural properties were studied by X-ray diffraction (XRD). Transmission electron microscopy (TEM) imaging was done to determine the morphology and size of the nanostructures. The chemical composition of the nanomaterials was determined by energy-dispersive X-ray spectroscopy (EDS) and inductively coupled plasma mass spectrometry (ICP-MS) analysis. To further study the biomedical applications of the synthesized nanostructures, antibacterial studies against multidrug-resistant (MDR) and methicillin-resistant (MRSA) were conducted. In addition, the NPs were added to the growth media of human dermal fibroblast (HDF) and human melanoma cells to show their cytocompatibility and cytotoxicity, respectively, over a 3-day experiment. UV-visible spectroscopy confirmed the highly reproducible green synthesis of colloidal AuNPs and Ag/AuNPs. The NPs showed a face-centered cubic crystal structure and an icosahedral shape with mean particle sizes of 28.5 and 9.7 nm for AuNPs and Ag/AuNPs, respectively. The antibacterial studies of the NPs against antibiotic-resistant bacterial strains presented a dose-dependent antimicrobial behavior. Furthermore, the NPs showed cytocompat-ibility towards HDF, but a dose-dependent anticancer effect was found when human melanoma cells were grown in presence of different NP concentrations for 72 hours. In this study, mono- and bimetallic NPs were synthesized for the first time using a highly reproducible, environmentally friendly, cost-effective and quick method and were successfully characterized and tested for several anti-infection and anticancer biomedical applications.

Multidrug-resistant (MDR) bacteria constitute a global health issue. Over the past ten years, interest in nanoparticles, particularly metallic ones, has grown as potential antibacterial candidates. However, as there is no consensus about the procedure to characterize the metallic nanoparticles (MNPs; i.e., metallic aggregates) and evaluate their antibacterial activity, it is impossible to conclude about their real effectiveness as a new antibacterial agent. To give part of the answer to this question, 12 nm gold and silver nanoparticles have been prepared by a chemical approach. After their characterization by transmission electronic microscopy (TEM), Dynamic Light Scattering (DLS), and UltraViolet-visible (UV-vis) spectroscopy, their surface accessibility was tested through the catalytic reduction of the 4-nitrophenol, and their stability in bacterial culture medium was studied. Finally, the antibacterial activities of 12 nm gold and silver nanoparticles facing Staphylococcus aureus and Escherichia coli have been evaluated using the broth microdilution method. The results show that gold nanoparticles have a weak antibacterial activity (i.e., slight inhibition of bacterial growth) against the two bacteria tested. In contrast, silver nanoparticles have no activity on S. aureus but demonstrate a high antibacterial activity against Escherichia coli, with a minimum inhibitory concentration of 128 µmol/L. This high antibacterial activity is also maintained against two MDR-E. coli strains.

Designing chiral materials to manipulate the biological activities of cells has been an important area not only in chemistry and material science, but also in cell biology and biomedicine. Here, we introduce monolayer plasmonic chiral Au nanoparticle (NP) films modified with l - or d -penicillamine (Pen) to be developed for cell growth, differentiation, and retrieval. The monolayer films display high chiroptical activity, with circular dichroism values of 3.5 mdeg at 550 nm and 26.8 mdeg at 775 nm. The l-P en-NP films accelerate cell proliferation, whereas the d -P en-NP films have the opposite effect. Remote irradiation with light is chosen to noninvasively collect the cells. The results demonstrate that left circularly polarized light improves the efficiency of cell detachment up to 91.2% for l -Pen-NP films. These findings will facilitate the development of cell culture in biomedical application and help to understand natural homochirality. Chiral surfaces are emerging as important biomaterial components, as they can modulate cell behavior. Here, the authors modify plasmonic nanoparticle films with amino acid isomers, and find that the chirality of the film remarkably affects cell proliferation, adhesion, and directional differentiation.