Determination of pyrophosphate and sulfate using polyhexamethylene guanidine hydrochloride-stabilized silver nanoparticles

Simple and rapid method for screening of pyrophosphate using 6,6-ionene-stabilized gold and silver nanoparticles

A colorimetric probe based on desensitized ionene-stabilized gold nanoparticles for single-step test for sulfate ions

Synergistic bactericidal activity of chlorhexidine loaded on positively charged ionic liquid-protected silver nanoparticles as a root canal disinfectant against Enterococcus faecalis: An ex vivo study

Structural and electrical behaviours of PEDOT:PSS thin films in presence of negatively charged gold and silver nanoparticles: A green synthesis approach

Bacterial infections have become a common global health problem, causing a wide range of properties and life loss. The development of a highly efficient, low-toxicity and targeted bacterial agent is urgently needed. As a conventional antibacterial agent, silver nanoparticles have been used for a long time, but they are still unable to achieve targeted bacterial killing. Herein, we have prepared surface positively (Ag(+) nanoparticles) and negatively (Ag(-) nanoparticles) charged silver nanoparticles by reduction of AgNO3 to construct Ag(-)/Ag(+) clusters. The zeta potential of the Ag(-)/Ag(+) nanoclusters could be controlled by changing the ratio of Ag(-) nanoparticles to Ag(+) nanoparticles. The surface negatively changed silver nanoparticles were prepared from the reaction of methyl maleic anhydride with the amino on the surface positively changed silver nanoparticles. In the acidic environment, Ag(-) nanoparticles undergo charge reversal, and Ag(-)/Ag(+) clusters with negatively charged nanoparticles and big-size are transformed into positively charged nanoparticles with small size. The in vitro experimental results demonstrate that the positively charged nanoparticles can be well adsorbed on the negatively charged bacteria, exhibiting a high bactericidal ability. Furthermore, the in vivo skin wound healing experiment showed that the Ag(-)/Ag(+) clusters could serve as an efficient antibacterial agent to combat bacterial infection.

The benzil-cyanide reaction is a cyanide-specific reaction that has been exploited to produce a colorimetric indicator for this toxic anion. This was done by producing a pi-extended analogue of benzil, 7, which is soluble in a 70:30 (v/v) mixture of methanol-water. In this medium, dilute solutions of 7 are yellow but produce colorless products when exposed to low concentrations of cyanide anion (> or = 1.7 microM; added as an aqueous NaCN solution), but no other common anions (e.g., OH(-), F(-), N3(-), benzoate(-), and H2PO4(-)). On the basis of these observations and supporting mechanistic analyses, it is concluded that the modified benzil system 7 is a promising cyanide anion indicator that is attractive in terms of its selectivity, ease-of-use, water compatibility, and the low, naked-eye discernible cyanide detection limit it provides.

Silver nanoparticles (AgNPs) have been extensively used as antibacterial component in numerous healthcare, biomedical and consumer products. Therefore, their adverse effects to biological systems have become a major concern. AgNPs have been shown to be absorbed into circulation and redistributed into various organs. It is thus of great importance to understand how these nanoparticles affect vascular permeability and uncover the underlying molecular mechanisms. A negatively charged mecaptoundeonic acid-capped silver nanoparticle (MUA@AgNP) was investigated in this work. Ex vivo experiments in mouse plasma revealed that MUA@AgNPs caused plasma prekallikrein cleavage, while positively charged or neutral AgNPs, as well as Ag ions had no effect. In vitro tests revealed that MUA@AgNPs activated the plasma kallikrein-kinin system (KKS) by triggering Hageman factor autoactivation. By using specific inhibitors aprotinin and HOE 140, we demonstrated that KKS activation caused the release of bradykinin, which activated B2 receptors and induced the shedding of adherens junction protein, VE-cadherin. These biological perturbations eventually resulted in endothelial paracellular permeability in mouse retina after intravitreal injection of MUA@AgNPs. The findings from this work provided key insights for toxicity modulation and biomedical applications of AgNPs.

Engineered nanoparticles are utilized as drug delivery carriers in modern medicine due to their high surface area and tailorable surface functionality. After in vivo administration, nanoparticles distribute and interact with biomolecules, such as polar proteins in serum, lipid membranes in cells, and high ionic conditions during digestion. Electrostatic forces and steric hindrances in a nanoparticle population are disturbed and particles agglomerate in biological fluids. Little is known about the stability of nanoparticles in relation to particle surface charge. Here, we compared three different surface-stabilized silver nanoparticles (50 nm) for intracellular agglomeration in human hepatocellular carcinoma cells (HepG2). Nanoparticles stabilized with branched polyethyleneimine conferred a positive surface charge, particles stabilized with lipoic acid conferred a negative surface charge, and particles stabilized with polyethylene glycol conferred a neutral surface charge. Particles were incubated in fetal bovine serum, simulated lung surfactant fluid, and simulated stomach digestion fluid. Each nanoparticle system was characterized via microscopic (transmission electron, fluorescence, and enhanced darkfield) and spectroscopic (hyperspectral, dynamic light scattering, and ultraviolet-visible absorption) techniques. Results showed that nanoparticle transformation included cellular internalization, agglomeration, and degradation and that these changes were dependent upon surface charge and incubation matrix. Hyperspectral analyses showed that positively charged silver nanoparticles red-shifted in spectral analysis after transformations, whereas negatively charged silver nanoparticles blue-shifted. Neutrally charged silver nanoparticles did not demonstrate significant spectral shifts. Spectral shifting indicates de-stabilization in particle suspension, which directly affects agglomeration intracellularly. These characteristics are translatable to critical quality attributes and can be exploited when developing nano-carriers for nanomedicine.

The bactericidal efficiency of various positively and negatively charged silver nanoparticles has been extensively evaluated in literature, but there is no report on efficacy of neutrally charged silver nanoparticles. The goal of this study is to evaluate the role of electrical charge at the surface of silver nanoparticles on antibacterial activity against a panel of microorganisms. Three different silver nanoparticles were synthesized by different methods, providing three different electrical surface charges (positive, neutral, and negative). The antibacterial activity of these nanoparticles was tested against gram‐positive (i.e., Staphylococcus aureus, Streptococcus mutans, and Streptococcus pyogenes) and gram‐negative (i.e., Escherichia coli and Proteus vulgaris) bacteria. Well diffusion and micro‐dilution tests were used to evaluate the bactericidal activity of the nanoparticles. According to the obtained results, the positively‐charged silver nanoparticles showed the highest bactericidal activity against all microorganisms tested. The negatively charged silver nanoparticles had the least and the neutral nanoparticles had intermediate antibacterial activity. The most resistant bacteria were Proteus vulgaris. We found that the surface charge of the silver nanoparticles was a significant factor affecting bactericidal activity on these surfaces. Although the positively charged nanoparticles showed the highest level of effectiveness against the organisms tested, the neutrally charged particles were also potent against most bacterial species.

SERS-based biosensor with Raman-active external responsive element for rapid determination of adenosine monophosphate

Positively charged silver nanoparticles, Ag [+], obtained by UV-assisted reduction of silver nitrate using branched poly(ethyleneimine) (BPEI) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) solutions as reducing agents, were immobilized on glass surfaces to produce substrates active in surface-enhanced Raman scattering (SERS). Negatively charged silver nanoparticles, Ag [-], synthesized via a modified citrate reduction method, were also investigated for comparison. At a sparse surface coverage of 30 nanoparticles/microm(2), substrates with immobilized Ag [+] showed increasing SERS sensitivity to a variety of anions in water in the order SO(4)(2-) < CN(-) < SCN(-) approximately ClO(4)(-), with corresponding binding constants of 10(5), 3.3 x 10(5), and 10(7) (for both SCN- and ClO(4)(-)) M(-1), respectively. This order followed the Hofmeister series of anion binding in water. Significantly, substrates with Ag [+] allowed limit of detection values of 8.0 x 10(-8) M (8 ppb) and 2.7 x 10(-7) M (7 ppb) for environmentally relevant perchlorate (ClO(4)(-)) and cyanide (CN(-)) anions, respectively. In contrast, substrates with immobilized Ag [-], even upon subsequent modification by a monolayer of BPEI for positive surface charge of the nanoparticles, showed a drastically lower sensitivity to these anions. The high sensitivity of substrates with Ag [+] for anion detection can be attributed to the presence of two types of functional groups, amino and amide, on the nanoparticle surface resulting from UV-assisted fragmentation of BPEI chains. Both amino and amide provide strong binding of anions with Ag [+] nanoparticles due to the synergistic effect through a combination of electrostatic, hydrogen bonding, and dispersive interactions.

To enhance the conductivity detection sensitivity of common anions (Na-anions) in electrostatic ion chromatography (EIC) by elution with water, a conductivity enhancement column packed with strong acid cation exchange resin in the H-form was inserted between an octadecyl silane (ODS)-silica separation column modified with zwitterionic surfactant (CHAPS: 3-{(3-cholamidopropyl)-dimethylammonio} propanesulfonate) and a conductivity detector. Specifically, the Na-anion pairing is converted to H-anion pairing after the EIC separation and then detected sensitively by the conductivity detector. The effects of conductivity enhancement and suppression in the EIC by the enhanced conductivity detection were characterized for the common strong acid anions such as SO4(2-), Cl(-), NO3(-), I(-) and ClO4(-) and weak acid anions such as F(-), NO2(-), HCOO(-), CH3COO(-) and HCO3(-). For the conductivity enhancement effect in the EIC, it is found that the conductivity of measured for all strong acid anions (Na-anions) was enhanced according to the theoretical conductivity predicted for H-anions and that of the measured for weak acid anions was suppressed depending on their pKa of H-anions. For the calibration linearity in the EIC, the strong acid anions were linear (r2 = 0.99 - 1.00) because the degree of dissociation is almost 1.0 over all the concentration range and that of the weak acid anions was non-linear because the degree of dissociation decreased by increasing the concentration of the weak acid anions. In conclusion, the EIC by enhanced conductivity detection was recognized to be useful only for the strong acid anions in terms of conductivity detection and calibration linearity.

Constructing Ce–OH groups on CeO2 for enhancing removal and recovery of uranium from wastewater and seawater

A highly selective coumarin-based chemosensor for naked-eye detection of cyanide anions via nucleophilic addition in pure aqueous environment

Manchar Lake is the largest natural freshwater lake in Pakistan. The Lake has received less fresh water in past few years. In addition, drainage water is being discharged in the Lake through Main Nara Valley Drain (MNVD) since many years. Consequently, concern has grown regarding the water quality of the Lake. The aim of this study was to assess the water quality of Manchar Lake and MNVD and the objectives were to determine physiochemical properties and the concentrations of common cations and anions as well as seven trace metals i.e. Cu, Ni, Zn, Co, Fe, Pb and Cd. The concentration of the trace metals were determined by simultaneous preconcentration and solvent extraction using flame atomic absorption spectrometer. Results of physicochemical parameters of Manchar Lake water samples showed mean pH 8.4 (+/-0.2), conductivity 2,310.3 (+/-581.3) muS cm(-1) and hardness (as CaCO3) 213.1 (+/-62.3) mg l(-1). Mean concentrations of cations and anions were Na 521.5 (+/-49.7), Cl(-) 413.6 (+/-225.7), Ca 70.7 (+/-12.9), Mg 56.2 (+/-28.9), K 17.6 (+/-6.5), NO(3-) 0.34 (+/-0.2) and PO4(3-) 0.02 (+/-0.01) mg l(-1). Mean concentrations of trace metals were Zn 15.7 (+/-1), Fe 12 (+/-3.5), Pb 9 (+/-2.7), Cu 8.9 (+/-7.7), Ni 4.3 (+/-3.4), Co 4 (+/-3.4) and Cd 1.1 (+/-1) microg l(-1). MNVD water samples showed mean pH 8.9 (+/-0.8), conductivity 1,735.7 (+/-567.8) muS cm(-1) and hardness (as CaCO3) 184.8 (+/-32.4) mg l(-1). In MNWD, the mean concentrations of cations and anions were Na 482.7 (+/-11.7), Cl(-) 395.7 (+/-271.5), Ca 79.1 (+/-23.5), Mg 54.2 (+/-28.1), K 26.2 (+/-21.3), NO(-3) 0.5 (+/-0.3) and PO4(3-) 0.1 (+/-0.1) mg l(-1). Mean concentrations of trace metals observed in MNWD water were Fe 14.9(+/-3.5), Cd 8.3 (+/-9.4), Pb 6.9 (+/-2.4), Cu 6.6 (+/-3.1), Zn 6.2 (+/-1.8), Co 4.5 (+/-2.7), and Ni 3.5 (+/-2.9) microg l(-1). The pH of both Manchar Lake and MNVD waters and concentration of Pb in Manchar Lake and concentration of Cd in MNVD water were higher than the World Health Organisation's guideline values for the drinking water quality. The water quality of Manchar Lake was found degraded.