Antibacterial and antibiofilm efficacy of colistin & meropenem conjugated silver nanoparticles against Escherichia coli and Klebsiella pneumoniae.

The progressive increase in infections caused by multidrug-resistant (MDR) Gram-negative bacteria and the emergence of resistance to last-resort antimicrobial drugs in recent years necessitate the development of new therapeutic strategies. This study was conducted to obtain nanostructured antimicrobials by conjugating colistin (COL) and meropenem (MEM) antibiotics with biosynthesized silver nanoparticles (bio-AgNPs) via the green synthesis method using Rosa damascena extract, and to investigate the antibacterial and antibiofilm activity of these nanostructures against Escherichia coli and Klebsiella pneumoniae strains. Ultraviolet-visible spectrophotometry, high-resolution-transmission electron microscopy, atomic force microscopy, X-ray diffraction, and Fourier transform-infrared spectroscopy analyses were performed to determine the physical and chemical properties of synthesized bio-AgNPs, COL@bio-AgNPs, MEM@bio-AgNPs, and COL&MEM@bio-AgNPs. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration of nanoparticles were determined on standard and MDR clinical strains. The antibiofilm efficacy and cytotoxic effect of nanoparticles were evaluated by the crystal violet dye method and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide dye method, respectively. The characterization analyses demonstrated that the synthesized nanoparticles had crystal structure and spherical morphology (5.6-30.2 nm in size). Antibiotic conjugated nanoparticles exhibited better antimicrobial activity and lower MIC values (0.125-4 µg/mL) on the tested strains compared to free antibiotics, and MIC values were decreased up to 1024-fold (p < 0.05). Antibiotic conjugated nanoparticles were found to be more effective in biofilm eradication than free antibiotics and bio-AgNPs and had a less inhibitory effect on peripheral blood mononuclear cell viability. The findings revealed that antibiotic-conjugated nanoparticles have the potential to be used as an effective antimicrobial drug against MDR E. coli and K. pneumoniae strains.

Important role of pore-filling mechanism in separating naproxen from water by micro-mesoporous carbonaceous material.

Commercial micro-mesoporous carbonaceous material (MCM; 56.8% mesopores) was applied for investigating the removal phenomenon of naproxen drug in aqueous solutions through batch adsorption experiments. Results demonstrated that the adsorption capacity of MCM to naproxen was slightly affected by different pHeq (2.0-11) and ionic strength (0-1 M NaCl). Adsorption kinetics, isotherms, thermodynamics, and mechanisms were evaluated at pH 7.0. Adsorption kinetics indicated the rate constants for adsorption (0.2 × 10-3  L/(mg × min) and desorption (0.076/min) and the adsorption equilibrium constant (2.6 × 10-3  L/mg). Adsorption isotherm showed that MCM exhibited a high-affinity adsorption capacity to naproxen (even at low concentrations) and its Langmuir maximum adsorption capacity (Qmax ) was 252.7 mg/g at 25°C. Adsorption thermodynamics proved that the adsorption process was endothermic and physisorption (ΔH° = 9.66 kJ/mol). The analysis result of pore size distribution demonstrated that the internal pore structure of MCM was appropriate for adsorbing naproxen molecules. Pore-filing mechanism (pore diffusion phenomenon) was confirmed by a considerable decrease in BET-surface area (585 m2 /g) and total pore volume (0.417 cm3 /g) of MCM after adsorbing naproxen (~1000 mg/L and pH 7.0) at 5 min (341 and 0.256), 60 min (191 and 0.205), 120 min (183 and 0.193), 360 min (144 and 0.175), and 24 h (71.6 m2 /g and 0.123 cm3 /g, respectively). The pore diffusion occurred rapidly (even at the initial adsorption period of 5 min). The FTIR technique was applied to identify the existence of C-H···π and n-π interaction. π-π interaction (evaluated through ID /IG ratio and C=C band) played a minor contribution in adsorption mechanisms. The ID /IG ratio (determined by the Raman technique) of MCM before adsorption (1.195) was similar to that after adsorption (1.190), and the wavenumber (C=C band; its FTIR spectrum) slightly shifted from 1638 to 1634 cm-1 after adsorption. A decrease in the Qmax value of MCM from 249 to 217 (H2 O2 -oxidized MCM) or to 224 mg/g (HNO3 -oxidized MCM) confirmed the presence of π-π interaction. Electrostatic attraction was a minor contribution. MCM can serve as a promising material for removing naproxen from water environment through a pore-filling mechanism. PRACTITIONER POINTS: Pore-filling mechanism was proposed by comparing textural properties of MCM before and after adsorbing naproxen. C-H···π and n-π interactions were identified via FTIR technique. π-π interaction was observed by FTIR and Raman techniques. Oxidation of MCM with HNO3 or H2 O2 was a helpful method to explore π-π interaction. Electrostatic attraction was explained through studies: effects of pH and NaCl along with desorption.

Peanut shells-derived biochars prepared from different carbonization processes: Comparison of characterization and mechanism of naproxen adsorption in water.

The ubiquitous appearance of nonsteroidal anti-inflammatory drugs (i.e., naproxen) in water bodies has raised enormous concerns among general public. Development of promising materials for eliminating such contaminants from water environment has attracted much attention in the scientific community. In this study, three (direct, post-treated and pre-treated) methods were developed to prepare biochars (800-PSB, 800-800-PSB, and 190-800-PSB, respectively) derived from the wastes of peanut shells (PS). They were thoroughly characterized by various important properties (i.e., porosity and superficial functional group) and applied to remove naproxen drug from water. Results indicated that although the pre- and post-treatments had a slight effect on the surface area of biochars (i.e., 571 m2/g for 800-PSB, 596 m2/g for 800-800-PSB, and 496 m2/g for 190-800-PSB), such treatments remarkably improved the adsorption capacity of biochar. The maximum adsorption capacity of biochar (obtained from the Langmuir model) towards naproxen in solution at 25 decreased in the following order: 800-800-PSB (324 mg/g) > 190-800-PSB (215 mg/g) > 800-PSB (105 mg/g). The thermodynamic study demonstrated that the adsorption was spontaneous and exothermic. Depending the preparation process, the contribution of each mechanism in the adsorption process was dissimilar. The overall adsorption mechanism was regarded as pore filling, π-π interaction, hydrogen bonding formations, n-π interaction, van der Waals force, and electrostatic attraction. Two methods used to identify the important role of π-π interaction were proposed herein. The possible desorption and reuse of laden-biochars were investigated by the chemical and thermal methods. The prepared biochar samples can serve as potential carbonaceous porous adsorbents for effectively removing naproxen from water media.

Ultrasonic Gas Sensing by Two-Dimensional Surface Phononic Crystal Ring Resonators.

An acoustic ring resonator employing a two-dimensional surface phononic crystal is proposed for high-sensitivity detection in binary gas mixtures. Band analyses and frequency-domain simulations via the finite-element method reveal that a single band for spoof surface acoustic waves appears at ultrasonic frequencies around 58 kHz where modification of its dispersion due to varying gas composition results in a linear shift of the resonance frequency. The shift rate is -17.3 and 8.8 mHz/ppm for CO2 and CH4, respectively. The linear shift of resonance frequency is experimentally validated. In addition, the ring resonator can also be employed to track acoustic intensity variation with gas concentration, where exponentially decaying intensity for low concentrations leverages high-sensitivity operation.

Separation and Preconcentration of Nickel(II) from Drinking, Spring, and Lake Water Samples with Amberlite CG-120 Resin and Determination by Flame Atomic Absorption Spectrometry.

In this study, Amberlite CG-120 adsorbent was used for the separation/preconcentration of Ni(II) ions in commercial drinking, spring and lake water samples before detection by flame atomic absorption spectrometry. Various optimization parameters for Ni(II) determination, such as pH, eluent type and concentration, sample and eluent flow rates, amount of adsorbent, were investigated to obtain better sensitivity, accuracy, precision and quantitative recovery. Furthermore, the interference effects of some ions on the recovery efficiency of Ni(II) were also investigated. The optimum experimental parameters were obtained in the case of pH 1; 5 mL of 4 mol L-1 HCl for eluent and 0.3 g for the adsorbent amount. The limit of detection was found to be 0.58 µg L-1 and linearity ranged from 5 to 50 µg L-1. The accuracy of the method was tested by the certified reference material of TMDA-70.2 Ontario Lake Water at a 95% confidence level.

A Novel Method Using Solid-Phase Extraction with Slotted Quartz Tube Atomic Absorption Spectrometry for the Determination of Manganese in Walnut Samples.

Mn(2+) was separated and preconcentrated using both solid-phase extraction (SPE) and a slotted quartz tube (SQT), and detected by a flame atomic absorption spectrometry (FAAS) system. Firstly, Mn(2+) was retained on a column filled with Amberlite CG-120 resin, and then retained Mn(2+) ions on the Amberlite CG-120 resin eluted with 5 mL of 4 mol/L HNO3. This part was called the "first preconcentration step". Furthermore, to determine the Mn(2+) in a walnut sample, the SQT device was also used after the separation and preconcentration of Mn(2+) from the Amberlite CG-120 resin so as to further improve the sensitivity of system. This part was called the "second preconcentration step" in this study. The enrichment factor and limit of detection values were found to be 360 fold and 0.22 µg/L, in turn, after a two-step preconcentration method. The good accuracy of method was confirmed with the use of standard reference material (spinach leaves, NIST-1570a).