Protocol for synthesis of spherical silver nanoparticles with stable optical properties and characterization by transmission electron microscopy

The synthesis of metallic plasmonic nanoparticles (NPs) faces challenges in stability and reproducibility, especially with silver. Here, we present a protocol for tunable synthesis of spherical silver NPs (AgNPs) with stable optical properties. We describe steps for preparing solutions, morphological characterization of AgNPs by transmission electron microscopy, and testing stability. AgNPs exhibit enduring stability and compatibility with various pH values. Moreover, they can be functionalized for optical biosensing applications, offering versatility in nanomaterial applications.

Polysorbate- and DNA-Mediated Synthesis and Strong, Stable, and Tunable Near-Infrared Photoluminescence of Plasmonic Long-Body Nanosnowmen

Direct photoluminescence (PL) from metal nanoparticles (NPs) without chemical dyes is promising for sensing and imaging applications since this offers a highly tunable platform for controlling and enhancing the signals in various conditions and does not suffer from photobleaching or photoblinking. It is, however, difficult to synthesize metal NPs with a high quantum yield (QY), particularly in the near-infrared (NIR) region where deep penetration and reduced light scattering are advantageous for bioimaging. Herein, we designed and synthesized Au-Ag long-body nanosnowman structures (LNSs), facilitated by polysorbate 20 (Tween 20). The DNA-engineered conductive junction between the head and body parts results in a charge transfer plasmon (CTP) mode in the NIR region. The junction morphology can be controlled by the DNA sequence on the Au core, and polythymine and polyadenine induced thick and thin junctions, respectively. We found that the LNSs with a thicker conductive junction generates the stronger CTP peak and PL signal than the LNSs with a thinner junction. The Au-Ag LNSs showed much higher intensities in both PL and QY than widely studied Au nanorods with similar localized surface plasmon resonance wavelengths, and notably, the LNSs displayed high photostability and robust, sustainable PL signals under continuous laser exposure for >15 h. Moreover, the PL emission from Au-Ag LNSs could be imaged in a deeper scattering medium than fluorescent silica NPs. Finally, highly robust PL-based cell images can be obtained using Au-Ag LNSs without significant signal change while repetitively imaging cells. The results offer the insights in plasmonic NIR probe design, and show that chemical dye-free LNSs can be a very promising candidate with a high QY and a robust, reliable NIR PL signal for NIR sensing and imaging applications.

Preparation of Ag-cellulose nanocomposite for the selective detection and quantification of mercury at nanomolar level and the evaluation of its photocatalytic performance

Mercury is a toxic heavy metal that reaches to the water bodies mainly by coal burning, mining and petrol refining. The study was focused to investigate the application of Ag-cellulose nanocomposite to detect and quantify mercury colorimetrically. The Ag-cellulose nanocomposite was characterized by X-ray diffraction, Transmission electron microscopy, Fourier transform infrared spectroscopy, UV-visible spectroscopy, particle size analyzer and zetasizer. The study identified that the presence of other metal ions did not interfere with the detection of Hg²⁺ ion by the probe. The prepared Ag-cellulose nanocomposite-phenylalanine conjugate incorporated paper strip showed an excellent result in Hg²⁺ detection. The Ag-cellulose nanocomposite was used to quantify the unknown concentration of mercury on real sample (environmental sample) and it was found to be highly accurate by confirming with atomic absorption spectrophotometric analysis. The Ag-cellulose nanocomposite showed effective detection at 45 °C, pH 9 and 0.1% of salinity. The Ag-cellulose nanocomposite showed efficient photocatalytic performance under visible light irradiation. The half-life period of MB by Ag-cellulose nanocomposite under visible light was determined to be 90 min. The study suggests the application of prepared probe in photocatalysis and the detection of Hg²⁺ from various environmental samples.

Chitosan–gold nanocomposite and its functionalized paper strips for reversible visual sensing and removal of trace Hg2+ in practice

To eliminate mercury contamination in aqueous environment, chitosan–gold nanocomposite and its functionalized paper strips were designed and developed for visual sensing and removal of trace Hg²⁺.

Effects of silver nanoparticles with different dosing regimens and exposure media on artificial ecosystem

Due to the wide use of silver nanoparticles (AgNPs) in various fields, it is crucial to explore the potential negative impacts on the aquatic environment of AgNPs entering into the environment in different ways. In this study, comparative experiments were conducted to investigate the toxicological impacts of polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) with two kinds of dosing regimens, continuous and one-time pulsed dosing, in different exposure media (deionized water and XiangJiang River water). There were a number of quite different experimental results (including 100% mortality of zebrafish, decline in the activity of enzymes, and lowest number and length of adventitious roots) in the one-time pulsed dosing regimen at high PVP-AgNP concentration exposure (HOE) compared to the three other treatments. Meanwhile, we determined that the concentration of leached silver ions from PVP-AgNPs was too low to play a role in zebrafish death. Those results showed that HOE led to a range of dramatic ecosystem impacts which were more destructive than those of other treatments. Moreover, compared with the continuous dosing regimen, despite the fact that higher toxicity was observed for HOE, there was little difference in the removal of total silver from the aquatic environment for the different dosing regimens. No obvious differences in ecological impacts were observed between different water columns under low concentration exposure. Overall, this work highlighted the fact that the toxicity of AgNPs was impacted by different dosing regimens in different exposure media, which may be helpful for assessments of ecological impacts on aquatic environments.

Colorimetric and optical Hg(ii) ion sensor developed with conjugates of M13-bacteriophage and silver nanoparticles

Hg(ii) produces an AgHg amalgam on a conjugate of Ag nanoparticles and M13-bacteriophage, which effectively quenches the optical absorption of the Ag nanoparticles.

Are silver nanoparticles always toxic in the presence of environmental anions?

Increasing amounts of silver nanoparticles (AgNPs) are expected to enter the ecosystems where their toxicity in the environment is proposed. In this study, we exploited the effect of environmental anions on AgNP toxicity. AgNP were mixed with various environmental anions, and then exposed to Escherichia coli to determine the effect on bacteria growth inhibition. The results demonstrated that AgNP are not always toxic in the presence of sulfide, but can stimulate microbial growth at certain concentrations. Environmental chloride and phosphate anions cannot induce the stimulation because of their weak capacity to control the release of Ag⁺ from AgNP. Ag⁺ that released from AgNP is proven to be responsible for AgNP toxicity. Moreover, we found that AgNP toxicity is dependent on sulfuration rate. At the same sulfuration rate, AgNP shows an identical pattern of toxicity. This study indicates that only sulfide of the tested environmental anions can induce AgNP stimulation to microbial growth in a sulfuration rate dependent pattern and the toxicity originate from Ag⁺ that released from AgNP.

Application of Starch-Stabilized Silver Nanoparticles as a Colorimetric Sensor for Mercury(II) in 0.005 mol/L Nitric Acid

A sensitive and selective Hg2+optical sensor has been developed based on the redox interaction of Hg2+with starch-coated silver nanoparticles (AgNPs) in the presence of 0.005 mol L−1HNO3. The relative intensity of the localized surface plasmon absorption band of AgNPs at 406 nm is linearly dependent on the concentration of Hg2+with positive slope for the concentration range 0–12.5 μg L−1and negative slope for the concentration range 25–500 μg L−1. Experiments performed demonstrated that metal ions (Na+, K+, Mg2+, Ca2+, Pb2+, Cu2+, Zn2+, Cd2+, Fe3+, Co2+, and Ni2+) do not interfere under the same conditions, due to the absence of oxidative activity of these ions, which guarantees the high selectivity of the proposed optical sensor towards Hg2+. The limits of detection and quantification were found to be 0.9 µg L−1and 2.7 µg L−1, respectively, and relative standard deviations varied in the range 9–12% for Hg content from 0.9 to 12.5 μg L−1and 5–9% for Hg levels from 25 to 500 μg L−1. The method was validated by analysis of CRM Estuarine Water BCR505. A possible mechanism of interaction between AgNPs and Hg2+for both concentration ranges was proposed on the basis of UV-Vis, TEM, and SAED analyses.

Seed geometry and hydrogen bonding dependent plasmonic tuning of silver nanocrystals in a citrate–hydrazine matrix and SERS spectroscopic detection of chromium

Red-shift and blue-shift in the plasmon wavelength has been observed depending on the seed geometry. Further, these Ag nanocrystals have been used to develop a SERS-spectroscopic method for enhanced detection of chromium upto a limit of 30 ppb.

A reusable multichannel anthraimidazoledione-based receptor for Hg2+and Cu2+ions: ultrasensitive, economical and facile detection of Hg2+in real water sources through fluorescence readout

A multichannel, ultrasensitive and selective receptor (1) has been developed for practical detection of Hg²⁺in various drinking waters.

Cysteine-induced hormesis effect of silver nanoparticles

The toxicity of silver nanoparticles (AgNPs) is widely exploited, but their hormesis effect has, so far, received little attention. This study reports the hormesis effect at low AgNPs concentrations of 0.34 mg L-1, with a 29.9% increase in bacterial viability compared with the control. Cysteine can induce a hormesis effect at a higher concentration. 12.5 mg L-1 cysteine induced a hormesis effect in the AgNP concentration range of 1.7-5.1 mg L-1. Results suggest that this cysteine-induced hormesis effect is concentration-dependent; the concentration that make sulfuration rate (ns/nAg) of 6.15 shows strong excitation to cells.

Activity Variation of Phanerochaete chrysosporium under Nanosilver Exposure by Controlling of Different Sulfide Sources

Due to the particular activation and inhibition behavior of silver nanoparticles (AgNPs) on microbes at various concentrations, it’s crucial to exploit the special concentration effect in environment. Here, we studied the viability variation of Phanerochaete chrysosporium (P. chrysosporium) under exposure to citrate-coated AgNPs (Citrate-AgNPs) in the presence of different sulfide sources (an inorganic sulfide, NaHS and an organic sulfide, thioacetamide (TAA)). The results indicated that both NaHS and TAA can promote activation of P. chrysosporium by Citrate-AgNPs at a higher concentration, which was initial at toxic level. Treatment with various concentrations of Citrate-AgNPs (0–9 mg/L) demonstrated a maximum activation concentration (MAC) at 3 mg/L. With the increase in sulfide concentration, MAC transferred to higher concentration significantly, indicating the obvious “toxicity to activation” transformation at a higher concentration. Ag⁺ testing exhibited that variations in sulfide-induced Ag⁺ concentration (3−7 μg/L Ag⁺) accounted for the “toxicity to activation” transformation. In addition, the similar results were observed on antibacterial application using Escherichia coli as the model species. Based on the research results, the application of this transformation in improving antibacterial activity was proposed. Therefore, the antibacterial activity of AgNPs can be controlled, even at concentration, via adjusting for the sulfide concentration.

Development of an eco-friendly immunochromatographic test strip and its application in detecting Hg2+ without chelators

The schematic diagram of an eco-friendly immunochromatographic test strip (EFITS) and a competitive immunoreaction on the EFITS.

Green-emitting fluorescence Ag clusters: facile synthesis and sensors for Hg2+ detection

Bovine serum albumin directed synthesis of Ag clusters for Hg²⁺ detection.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Highly sensitive fluorescent sensor for mercury based on hyperbranched rolling circle amplification

A label-free hyperbranched rolling circle amplification (HRCA) based fluorescent sensor has been developed for Hg²⁺detection.

Facile synthesis of silver submicrospheres and their applications

Silver submicrospheres fabricated under an ambient condition can catalyze the reduction of 4-nitrophenol and improve significantly the Raman signal of crystal violet as surface-enhanced Raman scattering (SERS) substrate.