Interface-Induced Ag Monolayer Film for Surface-Enhanced Raman Scattering Detection of Water-Insoluble Enrofloxacin

Water-insoluble molecules usually show poor surface-enhanced Raman scattering (SERS) signals, because they are hardly adsorbed on the surface of most commonly used SERS substrates, such as aqueous Ag or Au colloids. In this work, a highly sensitive and reproducible Ag monolayer film (Ag MLF) SERS substrate prepared by self-assembly of Ag nanoparticles (Ag NPs) on water/oil interface can realize the trace SERS detection of water-insoluble enrofloxacin. The positively charged phase transfer catalyst can transfer the negatively charged Ag nanoparticles in aqueous solution to the water/oil interface. At the same time, the water-insoluble enrofloxacin can also be attracted to the interface because of its lipophilic group. The type/volume of the oil phase and phase transfer catalyst and the vortex mixing time were all optimized to maximize the SERS effect of Ag MLF. Results showed that trace water-insoluble enrofloxacin can be identified by Ag MLF and its detection sensitivity was significantly improved. The proposed novel Ag MLF can be further applied to detect other water-insoluble molecules in SERS.

     

Facile fabrication of eco-friendly nano-mosquitocides: Biophysical characterization and effectiveness on neglected tropical mosquito vectors

Mosquito (Diptera: Culicidae) vectors are solely responsible for transmitting important diseases such as malaria, dengue, chikungunya, Japanese encephalitis, lymphatic filariasis and Zika virus. Eco-friendly control tools of Culicidae vectors are a priority. In this study, we proposed a facile fabrication process of poly-disperse and stable silver nanoparticles (Ag NPs) using a cheap leaf extract of Ichnocarpus frutescens (Apocyanaceae). Bio-reduced Ag NPs were characterized by UV–vis spectrophotometry, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The acute toxicity of I. frutescens leaf extract and green-synthesized Ag NPs was evaluated against larvae of the malaria vector Anopheles subpictus, the dengue vector Aedes albopictus and the Japanese encephalitis vector Culex tritaeniorhynchus. Compared to the leaf aqueous extract, Ag NPs showed higher toxicity against A. subpictus, A. albopictus, and C. tritaeniorhynchus with LC₅₀ values of 14.22, 15.84 and 17.26 μg/mL, respectively. Ag NPs were found safer to non-target mosquito predators Anisops bouvieri, Diplonychus indicus and Gambusia affinis, with LC₅₀ values ranging from 636.61 to 2098.61 μg/mL. Overall, this research firstly shed light on the mosquitocidal potential of I. frutescens, a potential bio-resource for rapid, cheap and effective synthesis of poly-disperse and highly stable silver nanocrystals.     

Electrochemical and antibacterial activity of silver nanoparticles synthesized using Mukia madarasapattana leaf extract

In this study, biosynthesis of stable silver nanoparticles (Ag NPs) were prepared using Mukia madarasapattana leaf extract. X-ray diffraction analysis revealed the synthesized silver nanoparticles had face centered cubic crystalline structure. The TEM image showed the silver nanoparticles are not agglomerated, moderately mono dispersed with the size of 15 nm. The high negative zeta potential values indicated the dispersion stability of Ag NPs. Antibacterial activity was carried out against different test microorganisms in silver nanoparticles. The cyclic Voltammetry study showed that Ag NPs have an oxidation peak at 0.61 mV.

     

Magnetic–Plasmonic FePt@Ag Core–Shell Nanoparticles and Their Magnetic and SERS Properties

Magnetic–plasmonic FePt@Ag core–shell nanoparticles (NPs) with different Ag shell thicknesses were successfully synthesized using a seed-mediated method. They presented not only localized surface plasmon resonance in the visible region, but also superparamagnetic behavior at room temperature. When normalized by the weight of FePt, the saturation magnetization of the FePt@Ag NPs was found to be higher than that of FePt NPs, suggesting that the Ag shell effectively passivated the FePt NP surfaces, avoiding the direct interaction between the FePt core and surface capping ligands that typically forms a magnetically dead layer in FePt NPs. Despite the high colloidal stability and the small size of the FePt@Ag NPs, the NPs were easily separated using a permanent magnet. The surface enhanced Raman scattering (SERS) activity of the FePt@Ag NPs was then examined using thiophenol as a Raman reporter molecule and was found to be equivalent to that of Ag NPs. Moreover, the SERS activity of the FePt@Ag NPs was enhanced when a magnetic field was applied during the preparation of the SERS substrate (FePt@Ag NP film). These FePt@Ag NPs hold promise as dual-functional sensing probes for environmental and diagnostic applications.     

Biosynthesis of silver nanoparticles by using of the marine brown alga Padina pavonia and their characterization

Silver nanoparticles (AgNPs) are gaining considerable importance due to their attractive physicochemical properties for many applications. In the present study, (Ag NPs) were synthesized by the reduction of aqueous solutions of silver nitrate (AgNO₃) with powder and solvent extracts of Padina pavonia (brown algae). The obtained nanoparticles exhibited high stability, rapid formation of the biogenic process (2 min -3 h), small size (49.58–86.37 nm) (the diameter of formed nanoparticles was measured by TEM and DLS) and variable shapes (spherical, triangular, rectangle, polyhedral and hexagonal). Preliminary characterization of nanoparticles was monitored by using UV–visible spectroscopy (UV–vis), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and finally by Fourier Transform Infrared spectroscopy (FTIR). The ratios of converted Ag NPs were recorded as 88.5; 86.2 and 90.5% in case of P. pavonia powder. extract and chloroform extract, respectively.     

SERS and Antibacterial Active Green Synthesized Gold Nanoparticles

Accurate control of size, composition, morphology, and stability, and the use of environmentally friendly procedures are highly desirable for the synthesis of nanoparticles. Here is a report on the use of Vitis californica leaf broth for the synthesis of gold nanoparticles. The morphology of the particles formed consists of a mixture of gold nanotriangles and spheres with fcc (111) structure. At lower concentrations of the extract, formation of triangular-shaped particles is found to dominate, while at higher concentrations, almost spherical particles alone are observed. The investigations made on the surface enhanced Raman scattering activity of these nanoparticles using 2-aminothiophenol and crystal violet as probe molecules are discussed in detail. The synthesized nanoparticles displayed efficient antibacterial activity against the tested gram-negative bacterium Escherichia coli and gram-positive bacterium Staphylococcus aureus.     

A Real-Time Clinical Endoscopic System for Intraluminal,Multiplexed Imaging of Surface-Enhanced Raman Scattering Nanoparticles

The detection of biomarker-targeting surface-enhanced Raman scattering (SERS) nanoparticles (NPs) in the human gastrointestinal tract has the potential to improve early cancer detection; however, a clinically relevant device with rapid Raman-imaging capability has not been described. Here we report the design and in vivo demonstration of a miniature, non-contact, opto-electro-mechanical Raman device as an accessory to clinical endoscopes that can provide multiplexed molecular data via a panel of SERS NPs. This device enables rapid circumferential scanning of topologically complex luminal surfaces of hollow organs (e.g., colon and esophagus) and produces quantitative images of the relative concentrations of SERS NPs that are present. Human and swine studies have demonstrated the speed and simplicity of this technique. This approach also offers unparalleled multiplexing capabilities by simultaneously detecting the unique spectral fingerprints of multiple SERS NPs. Therefore, this new screening strategy has the potential to improve diagnosis and to guide therapy by enabling sensitive quantitative molecular detection of small and otherwise hard-to-detect lesions in the context of white-light endoscopy.     

Synthesis of Peptide Mediated Au Core–Ag Shell Nanoparticles as Surface-Enhanced Raman Scattering Labels

As the fundamental understanding of metal–light interactions gains solid grounds, further research has been devoted to construct novel structures that take full advantage of such unique interactions, which is called plasmonics. In this report, the preparation of Au–Ag core–shell structures obtained by coating the Au surface with peptide and Raman reporter molecule and depositing an Ag layer on it is reported. The prepared Au–Ag NPs are tested for their surface-enhanced Raman scattering (SERS) performance. The negatively charged peptides with three different lengths, which are 3 (P1), 15 (P2), and 21 (P3) amino acid long, were chemically attached to 13 nm AuNPs along with Raman reporter molecule, carboxytetramethylrhodamine, and these modified AuNPs were coated with three different shell thickness of Ag metal. The prepared Au–Ag NPs were tested for their SERS performance and found that the Au–Ag NPs prepared with P2 and thickest shell performs best as SERS label.     

SERS Properties of Different Sized and Shaped Gold Nanoparticles Biosynthesized under Different Environmental Conditions by Neurospora crassa Extract

Surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces. It is known that metal nanoparticles, especially gold and silver nanoparticles, exhibit great SERS properties, which make them very attractive for the development of biosensors and biocatalysts. On the other hand, the development of ecofriendly methods for the synthesis of metallic nanostructures has become the focus of research in several countries, and many microorganisms and plants have already been used to biosynthesize metallic nanostructures. However, the majority of these are pathogenic to plants or humans. Here, we report gold nanoparticles with good SERS properties, biosynthesized by Neurospora crassa extract under different environmental conditions, increasing Raman signals up to 40 times using methylene blue as a target molecule. Incubation of tetrachloroauric acid solution with the fungal extract at 60°C and a pH value of a) 3, b) 5.5, and c) 10 resulted in the formation of gold nanoparticles of a) different shapes like triangles, hexagons, pentagons etc. in a broad size range of about 10-200 nm, b) mostly quasi-spheres with some different shapes in a main size range of 6-23 nm, and c) only quasi-spheres of 3-12 nm. Analyses included TEM, HRTEM, and EDS in order to corroborate the shape and the elemental character of the gold nanoparticles, respectively. The results presented here show that these ‘green’ synthesized gold nanoparticles might have potential applicability in the field of biological sensing.     

Bioengineered silver nanoparticles using Curvularia pallescens and its fungicidal activity against Cladosporium fulvum

Microorganisms based biosynthesis of nanomaterials has triggered significant attention, due to their great potential as vast source of the production of biocompatible nanoparticles (NPs). Such biosynthesized functional nanomaterials can be used for various biomedical applications. The present study investigates the green synthesis of silver nanoparticles (Ag NPs) using the fungus Curvularia pallescens (C. pallescens) which is isolated from cereals. The C. pallescens cell filtrate was used for the reduction of AgNO₃ to Ag NPs. To the best of our knowledge C. pallescens is utilized first time for the preparation of Ag NPs. Several alkaloids and proteins present in the phytopathogenic fungus C. pallescens were mainly responsible for the formation of highly crystalline Ag NPs. The as-synthesized Ag NPs were characterized by using UV–Visible spectroscopy, X-ray diffraction and transmission electron microscopy (TEM). The TEM micrographs have revealed that spherical shaped Ag NPs with polydisperse in size were obtained. These results have clearly suggested that the biomolecules secreted by C. pallescens are mainly responsible for the formation and stabilization of nanoparticles. Furthermore, the antifungal activity of the as-prepared Ag NPs was tested against Cladosporium fulvum, which is the major cause of a serious plant disease, known as tomato leaf mold. The synthesized Ag NPs displayed excellent fungicidal activity against the tested fungal pathogen. The extreme zone of reduction occurred at 50 μL, whereas, an increase in the reduction activity is observed with increasing the concentration of Ag NPs. These encouraging results can be further exploited by employing the as synthesized Ag NPs against various pathogenic fungi in order to ascertain their spectrum of fungicidal activity.     

Boosting bacteria differentiation efficiency with multidimensional surface-enhanced Raman scattering: the example of Bacillus cereus

Surface-enhanced Raman scattering (SERS) is a powerful tool for constructing biomolecular fingerprints, which play a vital role in differentiation of bacteria. Due to the rather subtle differences in the SERS spectra among different bacteria, artificial intelligence is usually adopted and enormous amounts of spectral data are required to improve the differentiation efficiency. However, in many cases, large volume data acquisition on bacteria is not only technical difficult but labour intensive. It is known that surface modification of SERS nanomaterials can bring additional dimensionality (difference) of the SERS fingerprints. Here in this work, we show that the concept could be used to improve the bacteria differentiation efficiency. Ag NPs were modified with 11-mercaptoundecanoic acid, 11-mercapto-1-undecanol, and 1-dodecanethiol to provide additional dimensionality. The modified NPs then were mixed with cell lysate from different strains of Bacillus cereus (B. cereus). Even by applying a simple PCA process to the resulting SERS spectra data, all the three modified Ag NPs showed superior differentiation results compared with bare Ag NPs, which could only separate Staphylococcus aureus (S. aureus) and B. cereus. It is believed that the multidimensional SERS could find great potential in bacteria differentiation.     

Silver Nanoparticles and Nanorings for Surface-Enhanced Raman Scattering

Silver (Ag) nanoparticles (NPs) and Ag nanorings (NRs) have been fabricated. Due to the inherent features of Ag NPs and Ag NRs, strong electromagnetic (EM) near-field distributions were expected, and hence surface-enhanced Raman scattering (SERS) activity was demonstrated. Size and interparticle gaps distribution of Ag NPs were estimated to be 48.14?±?10.14 nm and 14.11?±?5.24 nm respectively along with estimated coverage density of?~?4?×?10¹⁰ cm^?2. On the other hand, Ag NRs were found to consist of Ag clusters and of various shapes and sizes, instead of a perfect ring structure. High-resolution FESEM revealed that the individual constituent clusters were different from each other, particularly in terms of size and shape in addition to the cases how such clusters were connected to form the edge of the NR. However, the coverage density of Ag NRs was estimated to be?~?5.6?×?10⁶ cm^?2. Based on the scenarios, it was speculated that the local EM near-field distribution would excel and thus led to enhanced SERS signals. SERS enhancement of R6G was estimated as high as 2.18?×?10⁴ and 2.78?×?10⁴ at 610 cm^?1 (C???C ring bending mode in phenyl rings) for Ag NPs and Ag NRs respectively. FDTD analysis was carried out to elucidate the EM near-field distributions.

Graphical abstract

Ag NPs and Ag NRs from an ultrathin layer of Ag on ZnO/Glass (middle pane) confirming high EF of R6G adsorbed on Ag NRs (right pane) and Ag NPs (left pane) supported by corresponding EM near-field distributions.

     

Antimicrobial activity of highly stable silver nanoparticles embedded in agar-agar matrix as a thin film

Highly stable silver nanoparticles (Ag NPs) in agar-agar (Ag/agar) as inorganic-organic hybrid were obtained as free-standing film by in situ reduction of silver nitrate by ethanol. The antimicrobial activity of Ag/agar film on Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans) was evaluated in a nutrient broth and also in saline solution. In particular, films were repeatedly tested for antimicrobial activity after recycling. UV-vis absorption and TEM studies were carried out on films at different stages and morphological studies on microbes were carried out by SEM. Results showed spherical Ag NPs of size 15-25 nm, having sharp surface plasmon resonance (SPR) band. The antimicrobial activity of Ag/agar film was found to be in the order, C. albicans > E. coli > S. aureus, and antimicrobial activity against C. albicans was almost maintained even after the third cycle. Whereas, in case of E. coli and S. aureus there was a sharp decline in antimicrobial activity after the second cycle. Agglomeration of Ag NPs in Ag/agar film on exposure to microbes was observed by TEM studies. Cytotoxic experiments carried out on HeLa cells showed a threshold Ag NPs concentration of 60 μg/mL, much higher than the minimum inhibition concentration of Ag NPs (25.8 μg/mL) for E. coli. The mechanical strength of the film determined by nanoindentation technique showed almost retention of the strength even after repeated cycle.     

Green synthesis and structural classification of Acacia nilotica mediated-silver doped titanium oxide (Ag/TiO2) spherical nanoparticles: Assessment of its antimicrobial and anticancer activity

Current exanimation reports, green fabrication of silver doped TiO₂ nanoparticles (Ag/TiO₂) using aqueous extract of Acacia nilotica as bio-reductant and assess its potential as antimicrobial and anticancer agent. The obtained spherical Ag/TiO₂ were characterized by various analytical techniques including FTIR, (XRD), (FE-SEM EDS), and (TEM). Synthesized Ag/TiO₂ demonstrated broad spectrum antibacterial and anticandidal activity. The order of antimicrobial activity was found to be E. coli > C. albicans > MRSA > P. aeruginosa. In addition, cytotoxicity and oxidative stress of Ag/TiO₂ nanoparticles in (MCF-7) cells was also investigated. Outcomes of MTT assay showed concentration dependent reduction in cell viability. Further, synthesized NPs reduced the level of glutathione, induced ROS generation and lipid peroxidation in the treated cells. Therefore, it is envisaged that these spherical nanoparticles may be exploited in drug delivery, pharmaceutical, and food industry.     

Synthesis of Silver and Gold Nanoparticles Using Cashew Nut Shell Liquid and Its Antibacterial Activity Against Fish Pathogens

This study reveals a green process for the production of multi-morphological silver (Ag NPs) and gold (Au NPs) nanoparticles, synthesized using an agro-industrial residue cashew nut shell liquid. Aqueous solutions of Ag⁺ ions for silver and chloroaurate ions for gold were treated with cashew nut shell extract for the formation of Ag and Au NPs. The nano metallic dispersions were characterized by measuring the surface plasmon absorbance at 440 and 546 nm for Ag and Au NPs. Transmission electron microscopy showed the formation of nanoparticles in the range of 5–20 nm for silver and gold with assorted morphologies such as round, triangular, spherical and irregular. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analyses of the freeze-dried powder confirmed the formation of metallic Ag and Au NPs in crystalline form. Further analysis by Fourier transform infrared spectroscopy provided evidence for the presence of various biomolecules, which might be responsible for the reduction of silver and gold ions. The obtained Ag and Au NPs had significant antibacterial activity, minimum inhibitory concentration and minimum bactericidal concentration on bacteria associated with fish diseases.     

Size-Dependent Toxicity of Silver Nanoparticles to Bacteria,Yeast, Algae,Crustaceans and Mammalian Cells In Vitro

The concept of nanotechnologies is based on size-dependent properties of particles in the 1–100 nm range. However, the relation between the particle size and biological effects is still unclear. The aim of the current paper was to generate and analyse a homogenous set of experimental toxicity data on Ag nanoparticles (Ag NPs) of similar coating (citrate) but of 5 different primary sizes (10, 20, 40, 60 and 80 nm) to different types of organisms/cells commonly used in toxicity assays: bacterial, yeast and algal cells, crustaceans and mammalian cells in vitro. When possible, the assays were conducted in ultrapure water to minimise the effect of medium components on silver speciation. The toxic effects of NPs to different organisms varied about two orders of magnitude, being the lowest (∼0.1 mg Ag/L) for crustaceans and algae and the highest (∼26 mg Ag/L) for mammalian cells. To quantify the role of Ag ions in the toxicity of Ag NPs, we normalized the EC₅₀ values to Ag ions that dissolved from the NPs. The analysis showed that the toxicity of 20–80 nm Ag NPs could fully be explained by released Ag ions whereas 10 nm Ag NPs proved more toxic than predicted. Using E. coli Ag-biosensor, we demonstrated that 10 nm Ag NPs were more bioavailable to E. coli than silver salt (AgNO₃). Thus, one may infer that 10 nm Ag NPs had more efficient cell-particle contact resulting in higher intracellular bioavailability of silver than in case of bigger NPs. Although the latter conclusion is initially based on one test organism, it may lead to an explanation for “size-dependent“ biological effects of silver NPs. This study, for the first time, investigated the size-dependent toxic effects of a well-characterized library of Ag NPs to several microbial species, protozoans, algae, crustaceans and mammalian cells in vitro.     

Zur Abbaubeschleunigung von Pflanzenschutzmittel-Wirkstoffen im Boden

In the current investigation, we report the biosynthesis of silver nanoparticles (Ag NPs) employing extract of Alternaria alternata, which is an eco-friendly process for the synthesis of metallic nanoparticles. Ag NPs were synthesised through the reduction of aqueous Ag⁺ ion using the cell extract of fungus A. alternata in the dark conditions. The synthetic process was relatively fast and Ag NPs were formed within 24 h. UV–visible spectrum of the aqueous medium containing silver ion showed a peak at 435?nm corresponding to the plasmon absorbance of Ag NPs and another peak at 280?nm refers to tyrosine amino acid. The nanoparticles were characterised by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The morphology of nanoparticles is found to be spherical mostly, with ranging size of 27–79?nm; as revealed by SEM. The FTIR spectrum analysis indicated that biomolecules were involved in the synthesis of Ag NPs. The presence of the amino groups is expected to pack differently around the Ag NPs. This in turn will influence the self-assembly of nanoparticles on substrates as well as their stability. The present study demonstrates the possible use of biologically synthesised Ag NPs in the field of agriculture, when A. alternata could be used for simple, nonhazardous and efficient synthesis of Ag NPs.     

Plant Extract Synthesized PLA Nanoparticles for Controlled and Sustained Release of Quercetin: A Green Approach

Background

Green synthesis of metallic nanoparticles (NPs) has been extensively carried out by using plant extracts (PEs) which have property of stabilizers/ emulsifiers. To our knowledge, there is no comprehensive study on applying a green approach using PEs for fabrication of biodegradable PLA NPs. Conventional methods rely on molecules like polyvinyl alcohol, polyethylene glycol, D-alpha-tocopheryl poly(ethylene glycol 1000) succinate as stabilizers/emulsifiers for the synthesis of such biodegradable NPs which are known to be toxic. So, there is urgent need to look for stabilizers which are biogenic and non-toxic. The present study investigated use of PEs as stabilizers/emulsifiers for the fabrication of stable PLA NPs. Synthesized PLA NPs through this green process were explored for controlled release of the well known antioxidant molecule quercetin.

Methodology/Principal Findings

Stable PLA NPs were synthesized using leaf extracts of medicinally important plants like Syzygium cumini (1), Bauhinia variegata (2), Cedrus deodara (3), Lonicera japonica (4) and Eleaocarpus sphaericus (5). Small and uniformly distributed NPs in the size range 70±30 nm to 143±36 nm were formed with these PEs. To explore such NPs for drugs/ small molecules delivery, we have successfully encapsulated quercetin a lipophilic molecule on a most uniformly distributed PLA-4 NPs synthesized using Lonicera japonica leaf extract. Quercetin loaded PLA-4 NPs were observed for slow and sustained release of quercetin molecule.

Conclusions

This green approach based on PEs mediated synthesis of stable PLA NPs pave the way for encapsulating drug/small molecules, nutraceuticals and other bioactive ingredients for safer cellular uptake, biodistribution and targeted delivery. Hence, such PEs synthesized PLA NPs would be useful to enhance the therapeutic efficacy of encapsulated small molecules/drugs. Furthermore, different types of plants can be explored for the synthesis of PLA as well as other polymeric NPs of smaller size.     

Complete green synthesis of silver-nanoparticles applying seed-borne Penicillium duclauxii

Seed-borne fungus Penicillium duclauxii was examined in this study to investigate its capability of synthesizing silver nanoparticles (Ag-NPs). In vitro experiments were conducted using corn-grain contaminating fungal isolate. Ag-NPs detection and characterization were assayed by the aid of spectroscopic techniques. Spectroscopy (energy dispersive), X-ray diffraction, transmission electron-microscope and optical absorption dimensions were employed.Ag-NPs with biosynthesized were used to test invitro against Bipolaris sorghicola; the cause of target leaf spot disease on sorghum plants. The myco-synthesis of Ag NPs using Penicillium duclauxii was proved in this study. Moreover, Bipolaris sorghicola was successfully inhibited by such Ag NPs in vitro.     

Antibacterial effect and proteomic analysis of graphene-based silver nanoparticles on a pathogenic bacterium Pseudomonas aeruginosa

Graphene-based silver nanoparticles (Ag NPs–GE) material has been developed and demonstrated antibacterial effect against Escherichia coli and Pseudomonas aeruginosa. In this study, the antibacterial activity and mechanism on P. aeruginosa were investigated. The experiments results showed the minimum bactericidal concentration of Ag NPs–GE to P. aeruginosa is 20 μg/ml. When P. aeruginosa were exposed to 20 μg/ml Ag NPs–GE for 1 h, the cell wall was breakdown. In order to study the mechanism of antibacterial effect of Ag NPs–GE, two-dimensional electrophoresis was carried out to compare the protein expressional profiles of P. aeruginosa exposed to 5 μg/ml Ag NPs–GE or 5 μg/ml AgNO₃ with the untreated bacteria. Identification of differentially expressed protein was performed by MALDI–TOF/TOF MS. The change of proteomic profile induced by Ag NPs–GE was distinct from that induced by AgNO₃. Seven identified proteins were found induced and nine proteins were suppressed by Ag NPs–GE. Five identified proteins were found induced and twenty proteins were suppressed by AgNO₃. In addition, either Ag NPs–GE or AgNO₃ suppressed the expression of eight proteins, amidotransferase, 30S ribosomal protein S6, bifunctional proline dehydrogenase/pyrroline-5-carboxylate dehydrogenase, arginyl-tRNA synthetase, nitroreductase, acetolactate synthase 3, methionyl-tRNA synthetase and periplasmic tail-specific protease. Furthermore, gene ontology analysis and KEGG pathway analysis were used to characterize the functions of those proteins.