Ag nanoparticles on ZnO nanoplates as a hybrid SERS-active substrate for trace detection of methylene blue

Decorating two-dimensional (2D) nanomaterials with nanoparticles provides an effective method to integrate their physicochemical properties. In this work, we present the hydrothermal growth process of 2D zinc oxide nanoplates (ZnO NPls), then silver nanoparticles (AgNPs) were uniformly distributed on the surface of ZnO NPls through the reduction procedure of silver nitrate with sodium borohydride to create a metal–semiconductor hybrid. The amount of AgNPs on the ZnO NPls'' surface was carefully controlled by varying the volume of silver nitrate (AgNO₃) solution. Moreover, the effect of AgNPs on the surface-enhanced Raman scattering (SERS) property of ZnO NPls was thoroughly investigated by using methylene blue (MB) as the target molecule. After calculation, the maximum enhancement factor value for 10⁻⁴ M of MB reached 6.2 × 10⁶ for the peak at 1436 cm⁻¹ and the limit of detection was 10⁻⁹ M. In addition, the hybrid nanosystem could distinguish MB with good reproducibility over a wide range of concentrations, from 10⁻⁹ to 10⁻⁴ M. The SERS mechanism is well elucidated based on the chemical and electromagnetic mechanisms related to the synergism of ZnO and Ag in the enhancement of Raman signal. Abundant hot spots located at the gap between adjacent separate Ag nanoparticles and ZnO nanoplates which formed a strong local electromagnetic field and electron transfer between ZnO and Ag are considered to be the key factors affecting the SERS performance of our prepared ZnO/Ag substrates. In this research, we found high sensitivity of ZnO nanoplates/Ag nanoparticles in detecting MB molecules. This unique metal–semiconductor hybrid nanosystem is advantageous for the formation of Raman signals and is thus suitable for the trace detection of methylene blue.

Decorating two-dimensional (2D) nanomaterials with nanoparticles provides an effective method to integrate their physicochemical properties.     

Facile one-pot synthesis of silver nanoparticles encapsulated in natural polymeric urushiol for marine antifouling

Silver nanoparticle-based coatings have been regarded as promising candidates for marine antifouling. However, current toxic fabrication methods also lead to environment risks. Nanoparticle agglomeration, poor compatibility with polymer, and rapid release of Ag⁺ result in short-term efficacy. In this study, a facile one-pot synthesis method of silver nanoparticles (AgNPs) encapsulated in polymeric urushiol (PUL) was developed. AgNPs were synthesized in situ by natural urushiol, serving as a reductant, dispersant and surfactant. Simultaneously, silver nitrate catalyzed the polymerization of urushiol into PUL. This in situ reduction method made AgNPs uniformly distributed in the polymer matrix. The binding between the AgNPs and the PUL resulted in the stable release of Ag⁺. Results showed the antibacterial rate of a 0.1% AgNPs coating is 100% in laboratory experiments. This environment-friendly coating showed good microbial inhibition performance with long-term (120 days) marine antifouling efficacy. This study shows the potential of preparing an eco-friendly coating with long-term marine antifouling ability.

PUL/AgNPs was developed by a one-step reaction, PUL/AgNPs coatings showed excellent antifouling performance in antimicrobial experiments and marine field tests.     

Antibacterial performance of polymer quaternary ammonium salt–capped silver nanoparticles on Bacillus subtilis in water

In this study, we prepared polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) and investigated their antimicrobial activities. The antimicrobial effectiveness of PQAS–AgNPs on Bacillus subtilis (B. subtilis), and the effect of dose, pH, chloride ion and humic acid (HA) were studied. It was found that PQAS–AgNPs revealed excellent antimicrobial activity to B. subtilis, compared with polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs), which was the reference antimicrobial material. The positive surface, the antimicrobial activity of PQAS, and the synergistic antibacterial effect between PQAS and AgNPs contributed to the significant antibacterial superiority of PQAS–AgNPs. This study demonstrated that the impact of the dose of the material was positive and the microbiocidal efficacy of PQAS–AgNPs was stronger at lower pH. In addition, the antibacterial performance of PQAS–AgNPs decreased in the presence of Cl⁻ and HA. Finally, in combination with the results of FCM and adenosine triphosphate (ATP) content, it was found that PQAS–AgNPs destroyed the respiratory chain of bacterial cells, reduced the synthesis of ATP, and destroyed the cell wall and cell membrane function.

Polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) were synthesized, and they exhibited significant antibacterial capacity against Bacillus subtilis.     

Coated silver nanoparticles: synthesis,cytotoxicity, and optical properties

Coated silver nanoparticles (AgNPs) have recently become a topic of interest due to the fact that they have several applications such as in electronic, antimicrobial, industrial, optical, and medical fields as biosensors and drug delivery systems. However, the use of AgNPs in medical fields remains somewhat limited due to their probable cytotoxic effect. Researchers have succeeded in reducing the toxicity of silver particles by coating them with different substances. Generally, the coating of AgNPs leads to change in their properties depending on the type of the coating material as well as the layer thickness. This review covers the state-of-the-art technologies behind (a) the synthesis of coated AgNPs including coating methods and coating materials, (b) the cytotoxicity of coated AgNPs and (c) the optical properties of coated AgNPs.

Coated silver nanoparticles (AgNPs) have recently become a topic of interest due to the fact that they have several applications such as in electronic, antimicrobial, industrial, optical, and medical fields as biosensors and drug delivery systems.     

Facile synthesis of silver/gold alloy nanoparticles for ultra-sensitive rhodamine B detection

The synthesis of Ag/Au nanoparticles (NPs) in a controlled manner has been a challenge for a long time. The aim of this report is to present a systematic study on the fabrication, characterization of Ag/Au alloy NP-based surface-enhanced Raman spectroscopy (SERS) substrates. Silver (Ag) and gold (Au) colloidal NPs were prepared by chemical reduction route of the corresponding metal salts by trisodium citrate (TSC). Ag/Au alloy nanoparticles with varying molar fractions are prepared in aqueous solution by the simultaneous reduction of AgNO₃ and HAuCl₄ by TSC. The composition of Ag and Au in the alloy samples was controlled by tuning the molar ratio of Ag⁺/Au³⁺ in the mixture solution. The morphologies of the different products were characterized by TEM, and the size of obtained samples was in the range of 40 to 60 nm. The resulting samples were denoted as AgNPs, AuNPs, Ag₃Au, AgAu, and AgAu₃ NPs. In order to compare the optical property of the Ag/Au alloy and Ag/Au mixture, we mixed the pure Ag and Au NPs with different ratios to obtain the aggregated nanoparticles. Ag/Au alloy NPs were demonstrated as an ultrasensitive SERS substrate for the detection of rhodamine B (RhB) molecules. The concentration of RhB ranged from 10⁻¹¹ to 10⁻⁵ M. The effect of the Au content on the optical and SERS properties of the Ag/Au alloys was studied. The obtained results show that the Au content in the Ag/Au alloys play an important role in the physical properties of Ag/Au alloy NPs. The SERS spectra of RhB from the as-prepared Ag/Au alloy NP substrates indicated the superior enhancement with high reproducibility and sensitivity compared to those of Ag or Au samples. Interestingly, the highest SERS activity was achieved for the Ag₃Au sample with an enhancement factor larger than 10¹⁰ for 10⁻¹¹ M RhB and a limit of detection (LOD) at 10⁻¹¹ M, as well as good long-term stability after storage for 1 year. As far as we know, this is the highest sensitivity record of RhB by SERS detection. Furthermore, the composition-dependent SERS activity was explained in detail. These advantages demonstrated the potential for growing Ag/Au alloy NP-based SERS substrates in food safety and bioanalysis.

The synthesis of Ag/Au nanoparticles (NPs) in a controlled manner has been a challenge for a long time.     

Synthesis of a grape-like conductive carbon black/Ag hybrid as the conductive filler for soft silicone rubber

Conductive silicone rubber (CSR) is an outstanding stretchable conductive composite due to its excellent mechanical properties and stable conductivity. In this paper, silver nanoparticles were deposited on carbon black (CB) through a reduction reaction. The uniform dispersion of silver particles on the surface of CB as well as the grape-like branch structure of hybrid particles was formed by the condensation reaction of the hydroxyl groups of CB with (3-mercaptopropyl) trimethoxysilane (KH-590), along with the interattraction between sulfhydryl groups of KH-590 and silver ions. This sulfhydryl modified conductive carbon black/Ag hybrid filler (SMCB@Ag) avoided the high processing viscosity of CSR caused by the hydroxyl groups of CB. The percolation threshold of CSR made from SMCB@Ag was 5.5 wt% according to the percolation equation. With the addition amount of SMCB@Ag increasing to 10 wt%, the conductivity of CSR increased from 10⁻⁵ to about 10¹. Moreover, the conductivity of this CSR showed excellent stability with extension of storage time and increase of stretching-recovery cycles.

Schematic of the fabrication procedure of SMCB@Ag with the grape-like structure.     

Synthesis,purification and characterization of Plectonema derived AgNPs with elucidation of the role of protein in nanoparticle stabilization

Driven by the need to biosynthesize alternate biomedical agents to prevent and treat infection, silver nanoparticles have surfaced as a promising avenue. Cyanobacteria-derived nanomaterial synthesis is of substantive interest as it offers an eco-friendly, cost-effective, sustainable, and biocompatible route for further development. In the present study optimal conditions for synthesis of silver nanoparticles (AgNPs) were 1 : 9 v/v [cell extract: AgNO₃ (1 mM)], pH 7.4, and 30 °C reaction temperatures. Synthesis of nanoparticles was monitored by UV-vis spectrophotometry and the maximum absorbance was observed at a wavelength of 420 nm. SEM with EDX analysis confirmed 96.85% silver by weight which revealed the purity of AgNPs. TEM & XRD analysis exhibited a particle size of ∼12 nm with crystalline nature. FTIR analysis confirmed the presence of possible biomolecules involved in the synthesis and stabilization of AgNPs. Decapping of AgNPs followed by SDS-PAGE, LCMS and MALDI TOF analysis elucidates the proteinaceous nature of the capping and stabilizing agent. Cyanobacterial-derived capped AgNPs showed more cytotoxicicity towards a non-small cell lung cancer (A549) cell line, free radical scavenger and an antimicrobial than de-capped AgNPs. In addition they showed significant synergistic characteristics with antibiotics and fungicides. The test revealed that the capped AgNPs were biocompatible with good anti-inflammatory properties. The blend of antimicrobial and biocompatible properties, coupled with their intrinsic “green” and facile synthesis, made these biogenic nanoparticles particularly attractive for future applications in nanomedicine.

Illuminating the role of protein on the surface of cyanobacterial derived capped, decapped AgNPs and its biomedical application.     

Synthesis of silver nanoparticles via traditional Chinese medicine and evaluation of their antibacterial activities

Silver nanoparticles (AgNPs) are widely used in antibacterial research, but diverse methods for the green synthesis of AgNPs are still underexplored. Phenols, the major components in traditional Chinese medicines (TCMs), can reduce silver ions (Ag⁺) to prepare AgNPs. The representative phenolic compounds are flavonoids and chlorogenic acid (CA) in TCMs. Herein, we report a new strategy to prepare AgNPs via decoctions and dregs of TCMs as reductants and dispersants. Lonicera japonica flos (LJ), Astragalus membranaceus (AM), and Eucommia ulmoides bark (EU) were chosen due to their high contents of phenols. ¹H-NMR and HPLC were run to monitor the reaction for AgNP synthesis in decoctions, and XRD and TEM analyses were performed to characterize the synthesized TCMs-AgNPs. In addition, AgNPs prepared by spent Chinese medicinal grounds (SCMGs) were characterized by IR and XRD. The antibacterial assessment demonstrated that these TCMs-AgNPs significantly inhibited the growth of S. aureus and P. aeruginosa and effectively protected lettuce leaves against P. aeruginosa infection. Taken together, this study developed a new synthetic strategy that used decoctions and dregs of TCMs to obtain AgNPs with excellent antibacterial activity, which indicated the potential antibacterial application of these new TCM-based AgNP materials.

Two types of silver nanoparticles were synthesized via traditional Chinese medicine. Both of them exhibited excellent antibacterial activities, which could be promising in the development of new antibacterial agents and materials.     

A hybrid lipid membrane coating “shape-locks” silver nanoparticles to prevent surface oxidation and silver ion dissolution

The controlled synthesis of stable silver nanoparticles (AgNPs), that do not undergo surface oxidation and Ag⁺ ion dissolution, continues to be a major challenge. Here the synthesis of robust hybrid lipid-coated AgNPs, comprised of l-α-phosphatidylcholine (PC) membranes anchored by a stoichiometric amount of long-chained hydrophobic thiols and sodium oleate (SOA) as hydrophobic binding partners, that do not undergo surface oxidation and Ag⁺ ion dissolution, is described. UV-Visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and inductively coupled plasma mass spectrometry (ICP-MS) demonstrate that in the presence of strong oxidants, such as potassium cyanide (KCN), the hybrid lipid-coated AgNPs are stable and do not undergo surface oxidation even in the presence of membrane destabilizing surfactants. UV-Vis studies show that the stability of hybrid lipid-coated AgNPs of various sizes and shapes is dependent on the length of the thiol hydrocarbon chain and can be ranked in the order of increasing stability as follows: propanethiol (PT) < hexanethiol (HT) ≤ decanethiol (DT). UV-Vis and ICP-MS studies show that the hybrid lipid-coated AgNPs do not change in size or shape confirming that the AgNPs do not undergo surface oxidation and Ag⁺ ion dissolution when placed in the presence of strong oxidants, chlorides, thiols, and low pH. Long-term stability studies, over 21 days, show that the hybrid lipid-coated AgNPs do not release Ag⁺ ions and are more stable. Overall, these studies demonstrate hybrid membrane encapsulation of nanomaterials is a viable method for stabilizing AgNPs in a “shape-locked” form that is unable to undergo surface oxidation, Ag⁺ ion release, aging, or shape conversion. More importantly, this design strategy is a simple approach to the synthesis and stabilization of AgNPs for a variety of biomedical and commercial applications where Ag⁺ ion release and toxicity is a concern. With robust and shielded AgNPs, investigators can now evaluate and correlate how the physical features of AgNPs influence toxicity without the confounding factor of Ag⁺ ions present in samples. This design strategy also provides an opportunity where the membrane composition can be tuned to control the release rate of Ag⁺ ions for optimizing antimicrobial activity.

Hybrid lipid membranes shields and protects silver nanoparticles (AgNPs) from surface oxidation, Ag⁺ ion release, aging, and shape conversion.     

Reduction of 4-nitrophenol using green-fabricated metal nanoparticles

Noble metal (silver (Ag), gold (Au), platinum (Pt), and palladium (Pd)) nanoparticles have gained increasing attention due to their importance in several research fields such as environmental and medical research. This review focuses on the basic perceptions of the green synthesis of metal nanoparticles and their supported-catalyst-based reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The mechanisms for the formation of these nanoparticles and the catalytic reduction of 4-NP are discussed. Furthermore, the parameters that need to be considered in the catalytic efficiency calculations and perspectives for future studies are also discussed.

Noble metal (silver (Ag), gold (Au), platinum (Pt), and palladium (Pd)) nanoparticles have gained increasing attention due to their importance in several research fields such as environmental and medical research.     

Facile synthesis of a carbon dots and silver nanoparticles (CDs/AgNPs) composite for antibacterial application

Bacterial infections can seriously harm human health, and the overuse of traditional antibiotics and antibacterial agents will increase the resistance of bacteria. Therefore, it is necessary to prepare a new kind of antibacterial material. In this work, a carbon dots and silver nanoparticles (CDs/AgNPs) composite has been synthesized in a one-step facile method without the introduction of toxic chemicals, wherein CDs could serve as a reducing and stabilizing agent. The CDs/AgNPs composite was characterized by UV-vis spectrophotometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), which demonstrate that the silver nanoparticles were successfully synthesized in the composite. The zeta potential of the CDs/AgNPs composite was −15.3 mV, indicating that the composite possesses high stability. Furthermore, the composite also exhibited biocidal effects for both Gram-negative E. coli bacteria and Gram-positive S. aureus bacteria. Thus, the composite is considered to be of great potential in bactericidal and biomedical applications.

One-step facile synthesis of a carbon dots and silver nanoparticles (CDs/AgNPs) composite without the introduction of toxic chemicals.     

Application potential of biogenically synthesized silver nanoparticles using Lythrum salicaria L. extracts as pharmaceuticals and catalysts for organic pollutant degradation

This study was designed to evaluate the optimal conditions for the eco-friendly synthesis of silver nanoparticles (AgNPs) using Lythrum salicaria L. (Lythraceae) aqueous extracts and their potential application and safe use. AgNPs synthesized using L. salicaria aerial parts (LSA-AgNPs) and root extract (LSR-AgNPs) were characterized by UV-Vis spectrophotometry, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM/EDS), and X-ray powder diffraction (XRPD). Dynamic light scattering (DLS) was used for the determination of the size distribution profiles of the obtained nanoparticles. Both L. salicaria extracts showed high phenolic content, while the flavone C-glucosides orientin, vitexin, and isovitexin were detected in extracts using HPLC. The synthesized AgNPs displayed growth inhibition of the tested bacteria and fungi in concentrations between 0.156 and 1.25 mg mL⁻¹. The studied nanoparticles also showed antioxidant potential and gained selectivity at different concentrations on different cancer cell lines. Concentrations of LSA-AgNPs were found to be 20.5 and 12 μg mL⁻¹ towards A431 and SVT2, respectively, while LSR-AgNPs were effective only against A431 cancer cells (62 μg mL⁻¹). The hemolytic activity of LSA-AgNPs in concentrations up to 150 μg mL⁻¹ was not observed, while LSR-AgNPs in the highest applied concentration hemolyzed 2.8% of erythrocytes. The degradation possibility of Congo red and 4-nitrophenol using LSA-AgNPs and LSR-AgNPs as catalysts was also proven. The results indicate that L. salicaria may be used for the eco-friendly synthesis of AgNPs with possible applications as antimicrobial and selective cytotoxic agents towards cancer cell lines, as well as in catalytic degradation of pollutants.

This study was designed to evaluate the optimal conditions for the eco-friendly synthesis of silver nanoparticles (AgNPs) using Lythrum salicaria L. (Lythraceae) aqueous extracts and their potential application and safe use.     

Preparation of triangular silver nanoplates by silver seeds capped with citrate-CTA+

Due to the competitive growth on the crystal face of seed, it is always difficult to control the morphology of the formation of nanoparticles precisely by a seed-mediated growth method. Herein, we provided a simple but effective technique to synthesize silver nanotriangles using a new silver seed that is capped with citrate-CTA⁺ (CTA⁺ is cetyltrimethyl ammonium cation). Compared to the preparation of silver nanoparticles (AgNPs) by a conventional seed-mediated method, in this paper, we presented a growth technique with two distinct innovative changes. First, the concentrations of CTAB that we added in silver seed collosol have a significant impact on the size distribution, and silver nanotriangles, nanorods, and nanospheres could be obtained by adjusting the CTAB concentration. Second, the seed prepared by our method has a longer use time, and silver nanotriangles, nanospheres, and nanorods could be prepared by adjusting the aged time of the seed colloid. We have also shown a simple way to control the morphology of silver nanoparticles in almost the same reactive medium by varying the NaOH concentration. Using the new silver seed capped with citrate-CTA⁺, we obtained triangular silver nanoparticles with relatively high regularity. Based on the limited experimental results and IR analysis, a possible mechanism was preliminarily proposed to explain the formation of the seed and the truncated triangular AgNPs.

Due to the competitive growth on the crystal face of seed, it is always difficult to control the morphology of the formation of nanoparticles precisely by a seed-mediated growth method.     

Microwave-assisted preparation of a silver nanoparticles/N-doped carbon dots nanocomposite and its application for catalytic reduction of rhodamine B,methyl red and 4-nitrophenol dyes

In the current work, a silver nanoparticles/nitrogen-doped carbon dots (AgNPs/NCDs) nanocomposite was prepared by a microwave-assisted method that does not require additional reducing or stabilizing agents. Multiple analytical techniques were used to characterize the prepared nanocomposite. The nanocomposite exhibited a surface plasmon resonance (SPR) absorption peak at 420 nm, indicating the development of AgNPs with NCDs. Further, HRTEM results confirmed the formation of the nanocomposite with the appearance of lattice fringes of both materials. Additionally, the nanocomposite did not show any precipitation even after two months of storage. The nanocomposite exhibited high catalytic activity towards the reduction of rhodamine B (RhB, 98.83%), methyl red (MR, 97.14%) and 4-nitrophenol (4-NP, 99.95%) at ambient temperature. Besides, the kinetic analysis revealed that the reduction reaction followed pseudo-first-order kinetics and the calculated rate constants (k) for rhodamine B (RhB), methyl red (MR) and 4-nitrophenol (4-NP) were found to be 0.0296 s⁻¹, 0.0233 s⁻¹ and 0.029 s⁻¹, respectively. Moreover, it is a reusable and stable catalyst for reduction reactions up to five cycles without significant loss in catalytic activity. Finally, a plausible mechanism for the reduction of pollutants is also discussed in detail. As a whole, the prepared nanocomposite might display stunning behaviour for wastewater treatment applications.

A silver nanoparticles/nitrogen-doped carbon dots (AgNPs/NCDs) nanocomposite was prepared by a microwave-assisted method, and exhibited high catalytic activity towards the reduction of rhodamine B, methyl red and 4-nitrophenol at ambient temperature.     

Synthesis of controlled-size silver nanoparticles for the administration of methotrexate drug and its activity in colon and lung cancer cells

A controlled synthesis of methotrexate (MTX) silver nanoparticles (AgNPs-MTX) using borohydride and citrate as reduction and reduction/capping agents, respectively, was performed in order to obtain AgNPs-MTX conjugates with a narrow size distribution. Their characterization showed polydispersed spherical shape nanoparticles with a mean size around 13 nm and distribution range between 7–21 nm. The presence of MTX was confirmed by FTIR and EDX analysis. Spectroscopic determinations suggest the chemisorption of MTX through a carboxylic group (–COOH) onto AgNPs via the exchange with a citrate molecule. Drug loading capacities calculated for AgNPs synthesized using different amounts of MTX were 28, 31 and 40%. In vitro drug release tests depicted similar release profiles for all conjugated amounts releasing between 77 to 85% of the initial MTX loaded into the AgNPs. With respect to free MTX, the addition of the nanocarrier delayed its release and also changed its pharmacokinetics. Free MTX is released after 3 hours following a first order kinetic model, whereas in the presence of AgNPs, a fast initial release is observed during the first 5 hours, followed by a plateau after 24 hours. In this case, AgNPs-MTX fitted a Higuchi model, where its solubilization is controlled by a diffusion process. Results obtained from flow cytometry of different cell lines treated with AgNPs-MTX demonstrated the combined anticancer effect of both reagents, decreasing the percentage of living cells in a colon cancer cell line (HTC-116) down to 40% after 48 hours of exposure. This effect was weaker but still significant for a lung cancer cell line (A-549). Finally, a zebrafish assay with AgNPs-MTX did not show any significant cytotoxic effect, confirming thereby the reduction of systemic drug toxicity achieved by coupling MTX to AgNPs. This observed toxicity reduction in the zebrafish model implies also a probable improvement of the usage of AgNPs-MTX in chemotherapy against human cancers.

A controlled synthesis of methotrexate (MTX) silver nanoparticles (AgNPs-MTX) using borohydride and citrate as reduction and reduction/capping agents, respectively, was performed in order to obtain AgNPs-MTX conjugates with a narrow size distribution.     

Magnetic polymer bowl for enhanced catalytic activity and recyclability

This work introduces the fabrication of a magnetic polymer bowl for enhanced catalytic activity and recyclability, which involves the synthesis of silica-coated Fe₃O₄ magnetic clusters, seeded dispersion polymerization using the magnetic clusters, and transformation into a bowl-like structure via a phase separation route. The additional treatment with tannic acid (TA) on the bowls allows the in situ formation of silver nanoparticles (AgNPs) on their surfaces. The openness and larger surface area of the bowls, as compared with those of other structured particles, such as spheres and flowers, enable a considerably higher immobilization of AgNPs, thus leading to an excellent catalytic reduction for 4-nitrophenol (4-NP), methylene blue (MB), and rhodamine B. Furthermore, the strong magnetic response originating from the magnetic clusters inside the bowls endows a good magnetic recovery and an excellent reusability for the repeated reduction of the organic dyes without loss of catalytic activity.

The fabrication of a magnetic polymer bowl with a considerably higher immobilization of AgNPs was demonstrated for enhanced catalytic activity and recyclability.     

Tyndall-effect-based colorimetric assay with colloidal silver nanoparticles for quantitative point-of-care detection of creatinine using a laser pointer pen and a smartphone

Herein, this paper initially reports a new colorimetric Tyndall effect-inspired assay (TEA) for simple, low-cost, sensitive, specific, and point-of-care detection of creatinine (an important small biomolecule) by making use of silver nanoparticles (AgNPs) as model colloidal nanoprobes for visual light scattering signaling. The naked-eye TEA method adopts negatively-charged citrate-capped AgNPs (Cit-AgNPs) prepared by sodium citrate reduction. In the presence of alkaline conditions, the creatinine analyte can form carbanion/oxoanion amino tautomers which in turn crosslink with carboxylate groups on the Cit-AgNPs via a hydrogen bonding network to mediate the aggregation of such colloidal nanoprobes showing a significantly-enhanced TE signal that was created and quantified by a hand-held laser pointer pen and a smartphone, respectively. The results demonstrate that the resulting equipment-free method with the TE readout could enable the portable quantification of creatinine with a detection limit of ∼55 nM, which was ∼90–2334 times lower than that obtained from AgNP-based colorimetric approaches with the most common localized surface plasma resonance signaling. Moreover, it shows a larger analytical sensitivity up to ∼580.8227 signal per nM, offering ∼2.4–232-fold improvement in comparison with many of the recent instrumental creatinine nanosensors. The accuracy and practicality of the developed nanosensing system was additionally confirmed with satisfactory recovery results ranging from ca. 98.52 to 100.36% when analyzing a set of real complex human urine samples.

This work describes a new nanosensor for one-step ultrasensitive naked-eye detection of creatinine based on the target-triggered aggregation of silver nanoparticles showing dramatically enhanced Tyndall effect.     

Effects of rice root exudates on aggregation,dissolution and bioaccumulation of differently-charged Ag nanoparticles

The biological toxicity and eco-environmental risk of metal nanoparticles (MNPs) is closely related to their stability. The stability of MNPs not only depends on their own properties but also on the effects of biological and environmental factors. To better understand the interaction between biological factors and MNPs in aquatic environments, the effects of total rice root exudates (T-RRE) on the aggregation, dissolution and bioaccumulation of Ag nanoparticles (AgNPs) with different surface charges were investigated in detail. Results indicated that T-RRE can induce the aggregation and sedimentation, and hinder the dissolution of polyethyleneimine-coated AgNPs (AgNPs@PEI) with positive surface charges as well as reducing the bioaccumulation of Ag in rice roots. T-RRE had no obvious effect on the dispersion stability of AgNPs@Cit (negatively charged citrate-coated AgNPs) and AgNPs@PVP (near electrically neutral polyvinylpyrrolidone-coated AgNPs), although T-RRE could induce the dissolution of AgNPs@Cit and AgNPs@PVP. In the molecular fractions of T-RRE, high-molecular-weight root exudates (H-RRE) play a key role in inducing the aggregation of AgNPs@PEI and hindering the bioaccumulation of Ag in rice roots. Compared with H-RRE, low-molecular-weight root exudates (L-RRE) can promote the dissolution of AgNPs@Cit and AgNPs@PVP, but it can obviously promote silver accumulation in rice roots. The difference in charge intensity between L-RRE and T-RRE plays a key role in inducing the aggregation and dissolution of AgNPs with different charges. These findings provide a foundation for investigation of the interactions between rice root exudates and nanoparticles with different surface charges in complex environmental systems.

The biological toxicity and eco-environmental risk of metal nanoparticles (MNPs) is closely related to their stability.     

Enhanced bactericidal efficacy of polymer stabilized silver nanoparticles in conjugation with different classes of antibiotics

The paper presents the interaction mechanism of silver nanoparticles (AgNPs) with different antibiotics and the antibacterial efficacy of the formed conjugates. The AgNPs used in this study were synthesized from silver nitrate using sodium borohydride as a reducing agent, in the presence of PVP as a protecting agent. Two antibiotics, amikacin and vancomycin with different modes of action, were used to functionalize the synthesized PVP-capped AgNPs. The formation of antibiotic-AgNPs conjugate was confirmed by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and X-ray diffraction (XRD) and the results suggest the conjugation of both drugs to silver nanoparticle surfaces. FTIR results indicate that intermolecular hydrogen bonding exists between PVP-coated AgNPs and antibiotics. The oxygen atom coordinated with PVP was available for interaction with either amine or amide groups of drugs. Further, the antibacterial efficacy of these PVP-capped AgNPs with selected antibiotics was evaluated against Escherichia coli and Staphylococcus aureus by agar well diffusion test. Synergetic bactericidal activity for antibiotic-AgNPs conjugate was observed against both microbes.

The paper presents the interaction mechanism of silver nanoparticles (AgNPs) with different antibiotics and the antibacterial efficacy of the formed conjugates.     

Biosynthesis of silver nanoparticles using endophytic bacteria and their role in inhibition of rice pathogenic bacteria and plant growth promotion

The biosynthesis of silver nanoparticles (AgNPs) through the use of endophytic bacteria is a safe replacement for the chemical method. The study aimed to synthesize AgNPs using endophytic bacterium Bacillus siamensis strain C1, which was isolated from the medicinal plant Coriandrum sativum. The synthesized AgNPs with the size of 25 to 50 nm were further confirmed and characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy with EDS profile. The synthesized AgNPs at 20 μg mL⁻¹ showed a strong antibacterial effect against the pathogen of rice bacterial leaf blight and bacterial brown stripe, while an inhibition zone of 17.3 and 16.0 mm was observed for Xanthomonas oryzae pv. oryzae (Xoo) strain LND0005 and Acidovorax oryzae (Ao) strain RS-1, respectively. Furthermore, the synthesized AgNPs significantly inhibited bacterial growth, biofilm formation and swimming motility of Xoo strain LND0005 and Ao strain RS-1. In addition, the synthesized AgNPs significantly increased root length, shoot length, fresh weight and dry weight of rice seedlings compared to the control. Overall, this study suggests that AgNPs have the potential to protect rice plants from bacterial infection and plant growth promotion.

The mechanism of silver nanoparticles (AgNPs) to inhibit rice pathogenic bacteria.