Core-composite mediated separation of diverse nanoparticles to purity.

A generalized method for sorting nanoparticles based on their cores does not exist; it is an immediate necessity, and an approach incorporating cost-effectiveness and biocompatibility is in demand. Therefore, an efficient method for the separation of various mixed core-compositions or dissimilar metallic nanoparticles to their pure forms at the nano-bio interface was developed. Various simple core-combinations of monodispersed nanoparticles with dual cores, including silver plus gold, iron oxide plus gold and platinum plus gold, to the complex three-set core-combinations of platinum plus gold plus silver and platinum plus iron plus gold were sorted using step-gradient centrifugation in a sucrose suspension. Viscosity mediated differential terminal velocities of the nanoparticles permitted diversified dragging at different gradients allowing separation. Stability, purity and properties of the nanoparticles during separation were evaluated based on visual confirmation and by employing advanced instrumentations. Moreover, theoretical studies validated our experimental observations, revealing the roles of various parameters, such as the viscosity of sucrose, the density of the particles and the velocity and duration of centrifugation, involved during the separation process. This remarkably rapid, cost-efficient and sustainable strategy can be adapted to separate other cores of nanoparticles for various biomedical research purposes, primarily to understand nanoparticle induced toxicity and particle fate and transformations in natural biotic environments.

A Phosphorescent Trinuclear Gold(I) Pyrazolate Chemosensor for Silver Ion Detection and Remediation in Aqueous Media.

We report a phosphorescent chemosensor based on a trinuclear Au(I) pyrazolate complex or [Au(3-CH3,5-COOH)Pz]3 (aka Au3Pz3) stabilized in aqueous chitosan (CS) polymer media. Au3Pz3 is synthesized in situ within aqueous CS media at pH ∼ 6.5 and room temperature (RT). Au3Pz3 exhibits strong red emission (λmax ∼ 690 nm) in such solutions. On addition of silver salt to Au3Pz3/CS aqueous media, a bright-green emissive adduct (Au3Pz3/Ag+) with a peak maximum within 475-515 nm is developed. The silver adduct exhibits a 4-fold increase in quantum yield (0.19 ± 0.02) compared to Au3Pz3 alone (0.05 ± 0.01), along with a corresponding increase in phosphorescence lifetime. With almost zero interference from 15 other metal ions tested, Au3Pz3 exhibits extreme selectivity for Ag+ with nM/ppb detection limits (6.4-72 ppb, depending on %CS and on the sensitivity basis being a signal-to-noise ratio (S/N) = 3 or a baseline-corrected signal change = 10%). Au3Pz3 exhibits sensitivity to higher concentrations (>1 mM) of other metal ions (Tl+/Pb2+/Gd3+). The sensing methodology is simple, fast, convenient, and can even be detected by the naked eye. On addition of ethylenediaminetetraacetic acid (EDTA), the red Au3Pz3 emission can be restored. Au3Pz3 and its silver adduct retain their characteristic photophysical properties in thin film forms. Remarkable photostability with <7% photobleaching after 4 h of UV irradiation is attained for Au3Pz3 solutions or thin films.

Shining Light on Chitosan: A Review on the Usage of Chitosan for Photonics and Nanomaterials Research.

Chitosan (CS) is a natural polymer derived from chitin that has found its usage both in research and commercial applications due to its unique solubility and chemical and biological attributes. The biocompatibility and biodegradability of CS have helped researchers identify its utility in the delivery of therapeutic agents, tissue engineering, wound healing, and more. Industrial applications include cosmetic and personal care products, wastewater treatment, and corrosion protection, to name a few. Many researchers have published numerous reviews outlining the physical and chemical properties of CS, as well as its use for many of the above-mentioned applications. Recently, the cationic polyelectrolyte nature of CS was found to be advantageous for stabilizing fascinating photonic materials including plasmonic nanoparticles (e.g., gold and silver), semiconductor nanoparticles (e.g., zinc oxide, cadmium sulfide), fluorescent organic dyes (e.g., fluorescein isothiocyanate (FITC)), luminescent transitional and lanthanide complexes (e.g., Au(I) and Ru(II), and Eu(III)). These photonic systems have been extensively investigated for their usage in antimicrobial, wound healing, diagnostics, sensing, and imaging applications. Highlighted in this review are the different works involving some of the above-mentioned molecular-nano systems that are prepared or stabilized using the CS polymer. The advantages and the role of the CS for synthesizing and stabilizing the above-mentioned optically active materials have been illustrated.

Bioinspired Synthesis of Silver Nanoparticles for the Remediation of Toxic Pollutants and Enhanced Antibacterial Activity.

This research presents a novel and environmentally friendly approach for the synthesis of multifunctional nanobiocomposites for the efficient removal of toxic heavy metal and dye, as well as the disinfection of wastewater microorganisms. The nanobiocomposites (KAC-CS-AgNPs) were prepared by incorporating photochemically generated silver nanoparticles (AgNPs) within a chitosan (CS)-modified, high-surface-area activated carbon derived from kenaf (KAC), using a unique self-activation method. The even distribution of AgNPs was visible in the scanning electron microscopy images and a Fourier transform infra red study demonstrated major absorption peaks. The experimental results revealed that KA-CS-AgNPs exhibited exceptional adsorption efficiency for copper (Cu2+), lead (Pb2+), and Congo Red dye (CR), and showed potent antibacterial activity against Staphylococcus aureus and Escherichia coli. The maximum adsorption capacity (mg g-1) of KAC-CS-AgNPs was 71.5 for Cu2+, 72.3 for Pb2+, and 75.9 for CR, and the adsorption phenomena followed on the Freundlich and Langmuir isotherm models and the second-order kinetic model (R2 > 0.99). KAC-CS-AgNPs also exhibited excellent reusability of up to four consecutive cycles with minor losses in adsorption ability. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic in nature. The bacterial inactivation tests demonstrated that KAC-CS-AgNPs had a strong bactericidal effect on both E. coli and S. aureus, with MIC calculated for E. coli and S. aureus as 32 µg mL-1 and 44 µg mL-1, respectively. The synthesized bioinspired nanocomposite KAC-CS-AgNPs could be an innovative solution for effective and sustainable wastewater treatment and has great potential for commercial applications.

Lignocellulosic-Based Activated Carbon-Loaded Silver Nanoparticles and Chitosan for Efficient Removal of Cadmium and Optimization Using Response Surface Methodology.

The cadmium-contaminated water body is a worldwide concern for the environment and toxic to human beings and the removal of cadmium ions from drinking and groundwater sustainably and cost-effectively is important. A novel nano-biocomposite was obtained by impregnating silver nanoparticles (AgNPs) within kenaf-based activated carbon (KAC) in the presence of chitosan matrix (CS) by a simple, facile photoirradiation method. The nano-biocomposite (CS-KAC-Ag) was characterized by an environmental scanning electron microscope equipped with energy dispersive X-ray spectroscopy (ESEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and Brunauer−Emmett−Teller (BET) method. A Box−Behnken design of response surface methodology (RSM) was used to optimize the adsorption of Cd2+. It was found that 95.1% of Cd2+ (10 mg L−1) was eliminated at pH 9, contact time of 120 min, and adsorbent dosage of 20 mg, respectively. The adsorption of Cd2+ by CS-KAC-Ag is also in agreement with the pseudo-second-order kinetic model with an R2 (coefficient of determination) factor greater than 99%. The lab data were also corroborated by tests conducted using water samples collected from mining sites in Mexico. Along with Cd2+, the CS-KAC-Ag exhibited superior removal efficiency towards Cr6+ (91.7%) > Ni2+ (84.4%) > Co2+ (80.5%) at pH 6.5 and 0.2 g L−1 dose of the nano-adsorbent. Moreover, the adsorbent was regenerated, and the adsorption capacity remained unaltered after five successive cycles. The results showed that synthesized CS-KAC-Ag was a biocompatible and versatile porous filtering material for the decontamination of different toxic metal ions.

Mesoporous activated carbon as a green adsorbent for the removal of heavy metals and Congo red: Characterization, adsorption kinetics, and isotherm studies.

In this study, an effective and green adsorbent was prepared by the self- activation of kenaf fiber and then the kenaf-based activated carbon (KAC) was applied for the removal of lead Pb(II), copper Cu(II), and Congo red (CR) dye from an aqueous solution by the process of adsorption. The surface morphology of mesoporous adsorbent was characterized. The KAC showed good capacity of adsorption of as Pb(II), Cu(II), and anionic dye CR in very short period of agitation. The adsorbent efficiency of metal ions and dye was estimated by varying the adsorbent dose, pH, contact time, initial metals and dye concentration, and temperature. Optimum adsorption of metal ions and CR dye was observed at pH 6, and at pH 4 at 120 min, respectively. The adsorption isotherm was described by the Langmuir and Freundlich isotherm equations. The green adsorbent followed the pseudo-second-order kinetic model with correlation coefficients R2 value >0.99. The increase in adsorption temperature enhanced the adsorption efficiency for both heavy metals and dye. The KAC showed no significant loss of the adsorption capacity after 3 cycles of reuse.

Formula-Driven, Size-Tunable Synthesis of PMMA Nanoparticles by Varying Surfactant Concentration.

In this communication, we present a streamlined, reproducible synthetic method for the production of size-tunable poly(methyl methacrylate) (PMMA) nanoparticles (PMMANPs) and amine-functionalized block-copolymer PMMANPs (H2N-PMMANPs) by varying subcritical concentrations (i.e., below the concentration required to form micelles at 1 atm and 20 °C) of sodium dodecyl sulfate (SDS). We plotted the Z-average size data against SDS concentration, which revealed a second-order exponential decay function, expressed as [...] .

Ratiometric Phosphorescent Silver Sensor: Detection and Quantification of Free Silver Ions within Silver Nanoparticles.

Silver nanoparticles (AgNPs) have well-known antibacterial properties that have stimulated their widespread production and usage, which nonetheless concomitantly raises concerns regarding their release into the environment. Understanding the toxicity of AgNPs to biological systems, the environment, and the role that each silver species (Ag+ ions vs AgNPs) plays in that toxicity has received significant attention. One of the critical objectives of this research is the development of a reliable method that can sense and differentiate free silver ions from AgNPs and is able to characterize silver ions leaching from nanosilver. A number of analytical methods described in the literature that are available for sensing silver ions are costly, time consuming, tedious, and, more importantly, destroy the AgNP sample. To address these issues, a phosphorescent gold(I)-pyrazolate cyclic trinuclear complex (AuT) known to detect free silver ions was employed to detect and differentiate silver ions from AgNPs within an AgNP sample. The advantage of the proposed silver sensor is its ratiometric emission capability that undermines any background interference. The sensor exhibits a strong red emission (λmax = ∼690 nm) that, in the presence of Ag+ ions, will form a bright-green emissive adduct with a blue-shifted peak maximum near 475 nm yet red-shifted excitation peak. The presence of AgNPs did not inhibit the silver detection and quantification ability of the phosphorescent silver sensor. To understand the chemical transformation of nanosilver, the leaching of silver ions from AgNPs over a period of 35 days was monitored and quantified by measuring the I/ Io changes of the sensor. Furthermore, through adduct formation, the AuT molecular system was able to remediate free silver ions from the solution. The stronger affinity of the AuT complex to "sandwich" free silver ions than AgNPs was demonstrated in the presence of KCl salt that is well documented to form AgCl in the presence of silver ions. To our knowledge, this is the only ratiometric luminescence-based silver sensor able to successfully differentiate between Ag+ ions and AgNPs, sense the silver leakage from AgNPs, and remediate toxic silver ions from an aqueous solution. The synthesis and characterization of this sensor is a simple, single-step process-anticipating its viability for various applications.

Facile Photochemical Syntheses of Conjoined Nanotwin Gold-Silver Particles within a Biologically-Benign Chitosan Polymer.

A simple photochemical method for making conjoined bi-metallic gold-silver (Au/Ag) nanotwins, a new breed of nanoparticles (NPs), is developed. To the best of our knowledge, the photochemical method resulted in distinct, conjoined, bimetallic nanotwins that are different from any well-established alloyed or core-shell nanostructures in the literature. The conjoined Au-Ag NPs possessed surface plasmon resonance (SPR) properties of both metals. The bimetallic nanostructures possessing distinctive optical properties of both metals were obtained using Au NPs as seeds in the first step, followed by the addition of a silver precursor as feed in the second step during a photochemical irradiation process. In the first step, small, isotropic or large, anisotropic Au NPs are generated by photoinduced reduction within a biocompatible chitosan (CS) polymer. In the second step, a silver precursor (AgNO3) is added as the feed to the AuNPs seed, followed by irradiation of the solution in the ice-bath. The entire photochemical irradiation process resulting in the formation of bimetallic Au-AgNPs did not involve any other reducing agents or stabilizing agents other than the CS polymer stabilizer. The small, conjoined Au-Ag bi-metallic NPs exhibited SPR with peak maxima centering at ~400 nm and ~550 nm, whereas the large conjoined nanoparticles exhibited SPR with peak maxima centering at ~400 nm, 550 nm, and 680 nm, characteristic of both gold and silver surface plasmons in solution. The tunability in the SPR and size of the bimetallic NPs were obtained by varying the reaction time and other reaction parameters, resulting in average sizes between 30 and 100 nm. The SPR, size, distribution, and elemental composition of the bi-metallic NPs were characterized using UV-Vis absorption, electron microscopy, and energy dispersive X-ray spectroscopy (EDS) studies.