The Development of a Composite Thin Film Barrier of Tungsten Fe3O4-rGO (FerGO) for the Radiation Shielding of Medical Personnel.

Tungsten is the most effective eco-friendly material used for radiation shielding in hospitals. However, despite its commendable density and shielding performance, tungsten faces challenges in miscibility with other materials because of its elevated melting point and strength. In this study, to protect medical personnel against scattered rays, which are indirect X-rays, a lightweight material was prepared by mixing graphite oxide material, considering its thinness and flexibility. Tungsten particles were evenly dispersed in the polymer, and nanofibers were prepared using this blended polymer solution via electrospinning. Concurrently, the process technology was explored to craft a thin film sheet and obtain a lead-like shielding effect. A spinning solution was prepared by mixing Fe3O4-rGO (FerGO) and tungsten. At 60 kVp, 0.1 mm was measured as 0.097 mmPb, at 80 kVp, 0.2 mm was measured as 0.196 mmPb, and at 100 kVp, 0.3 mm was measured as 0.279 mmPb, showing similar shielding performance to lead. As density directly affects the shielding effect, graphene oxide played an important role in increasing the density of the material from 1.941 g/cm3 to 2.302 g/cm3. Thus, this study provides an effective process for producing thin film sheets equivalent to lead.

Integration of Gold Nanoparticles into Crosslinker-Free Polymer Particles and Their Colloidal Catalytic Property.

This work demonstrates the incorporation of gold nanoparticles (AuNPs) into crosslinker-free poly(N-isopropylacrylamide), PNIPAM, particles in situ and the examination of their structural and catalytic properties. The formation process of the AuNPs across the crosslinker-free PNIPAM particles are compared to that of crosslinked PNIPAM particles. Given the relatively larger free volume across the crosslinker-free polymer network, the AuNPs formed by the in situ reduction of gold ions are detectably larger and more polydisperse, but their overall integration efficiency is slightly inferior. The structural features and stability of these composite particles are also examined in basic and alcoholic solvent environments, where the crosslinker-free PNIPAM particles still offer comparable physicochemical properties to the crosslinked PNIPAM particles. Interestingly, the crosslinker-free composite particles as a colloidal catalyst display a higher reactivity toward the homocoupling of phenylboronic acid and reveal the importance of the polymer network density. As such, the capability to prepare composite particles in a controlled polymer network and reactive metal nanoparticles, as well as understanding the structure-dependent physicochemical properties, can allow for the development of highly practical catalytic systems.

Rapid vertical flow immunoassay on AuNP plasmonic paper for SERS-based point of need diagnostics.

SERS based immunoassays for point-of-care diagnostics are a promising tool to facilitate biomarker detection for early disease diagnosis and disease control. The technique is based on a sandwiched system in which antigen is first captured by a selective plasmonic paper substrate and then labeled by an extrinsic Raman label (ERL), consisting of a 60 nm gold nanoparticle (AuNP) functionalized with a mixed monolayer of detection antibody and 4-nitrobenezenethiol (NBT) as a Raman reporter molecule. Here, we report on the use of AuNP modified filter paper as a novel capture membrane in a vertical flow format. This vertical flow configuration affords reproducible flow of sample and label through the capture substrate to overcome diffusion limited kinetics and significantly reduced assay time. The filter paper was selected due to its affordability and availability, while the embedded AuNPs maximized plasmonic coupling with the ERLs and SERS enhancement. Additionally, the embedded AuNP served as a scaffold to immobilize capture antibody to specifically bind antigen. In this work, a SERS-based rapid vertical flow (SERS-RVF) immunoassay for detection of mouse IgG was developed to establish proof-of-principle. Optimization of assay conditions led to a limit of detection of 3 ng/mL, which is comparable to more traditional formats carried out in multi-well plates, and significantly reduced assay time to less than 2 min. Additionally, IgG was accurately quantified in normal mouse serum to validate the SERS-RVF assay for application to the analysis of biological samples. These results highlight the potential advantages of the SERS-RVF platform for point-of-need testing.

Comparative Catalytic Properties of Supported and Encapsulated Gold Nanoparticles in Homocoupling Reactions.

This report describes strategies to increase the reactive surfaces of integrated gold nanoparticles (AuNPs) by employing two different types of host materials that do not possess strong electrostatic and/or covalent interactive forces. These composite particles are then utilized as highly reactive and recyclable quasi-homogeneous catalysts in a C-C bond forming reaction. The use of mesoporous TiO2 and poly(N-isopropylacrylamide), PNIPAM, particles allows for the formation of relatively small and large guest AuNPs and provides the greatly improved stability of the resulting composite particles. As these AuNPs are physically incorporated into the mesoporous TiO2 (i.e., supported AuNPs) and PNIPAM particles (i.e., encapsulated AuNPs), their surfaces are maximized to serve as highly reactive catalytic sites. Given their increased physicochemical properties (e.g., stability, dispersity, and surface area), these composite particles exhibit notably high catalytic activity, selectivity, and recyclability in the homocoupling of phenylboronic acid in water and EtOH. Although the small supported AuNPs display slightly faster reaction rates than the large encapsulated AuNPs, the apparent activation energies (Ea) of both composite particles are comparable, implying no obvious correlation with the size of guest AuNPs under the reaction conditions. Investigating the overall physical properties of various composite particles and their catalytic functions, including the reactivity, selectivity, and Ea, can lead to the development of highly practical quasi-homogeneous catalysts in green reaction conditions.

Polyacrylonitrile Nanofiber Membrane Modified with Ag/GO Composite for Water Purification System.

Silver nanoparticle-modified graphene oxide (Ag/GO) was reliably prepared by using sodium borohydride (NaBH4) in the presence of citric acid capping agent via a simple wet chemistry method. This rapidly formed Ag/GO composite exhibited good dispersity in a solution containing hydrophilic polyacrylonitrile (PAN). Subsequent electrospinning of this precursor solution resulted in the successful formation of nanofibers without any notable defects. The Ag/GO-incorporated PAN nanofibers showed thinner fiber strands (544 ± 82 nm) compared to those of GO-PAN (688 ± 177 nm) and bare-PAN (656 ± 59 nm). Subsequent thermal treatment of nanofibers resulted in the preparation of thin membranes to possess the desired pore property and outstanding wettability. The Ag/GO-PAN nanofiber membrane also showed 30% higher water flux value (390 LMH) than that of bare-PAN (300 LMH) for possible microfiltration (MF) application. In addition, the resulting Ag/GO-PAN nanofiber membrane exhibited antibacterial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Furthermore, this composite membrane exhibited outstanding anti-fouling property compared to the GO-PAN nanofiber membrane in the wastewater treatment. Therefore, the simple modification strategy allows for the effective formation of Ag/GO composite as a filler that can be reliably incorporated into polymer nanofiber membranes to possess improved overall properties for wastewater treatment applications.

Mixed Dye Removal Efficiency of Electrospun Polyacrylonitrile-Graphene Oxide Composite Membranes.

Exfoliated graphene oxide (GO) was reliably modified with a cetyltrimethylammonium chloride (CTAC) surfactant to greatly improve the dispersity of the GO in a polyacrylonitrile (PAN) polymer precursor solution. Subsequent electrospinning of the mixture readily resulted in the formation of GO-PAN composite nanofibers containing up to 30 wt % of GO as a filler without notable defects. The absence of common electrospinning problems associated with clogging and phase separation indicated the systematic and uniform integration of the GO within the PAN nanofibers beyond the typical limits. After thoroughly examining the formation and maximum loading efficiency of the modified GO in the PAN nanofibers, the resulting composite nanofibers were thermally treated to form membrane-type sheets. The wettability and pore properties of the composite membranes were notably improved with respect to the pristine PAN nanofiber membrane, possibly due to the reinforcing filler effect. In addition, the more GO loaded into the PAN nanofiber membranes, the higher the removal ability of the methylene blue (MB) and methyl red (MR) dyes in the aqueous system. The adsorption kinetics of a mixed dye solution were also monitored to understand how these MB and MR dyes interact differently with the composite nanofiber membranes. The simple surface modification of the fillers greatly facilitated the integration efficiency and improved the ability to control the overall physical properties of the nanofiber-based membranes, which highly impacted the removal performance of various dyes from water.

Integrating SERS and PSI-MS with Dual Purpose Plasmonic Paper Substrates for On-Site Illicit Drug Confirmation.

Forensic laboratory backlogs are replete with suspected drug samples. Shifting analysis toward the point of seizure would save significant time and public funds. Moreover, a two-tiered identification strategy for controlled substance testing that relies on two independent, discerning methods could entirely circumvent the need for forensic laboratory testing. To this end, we coupled Raman spectroscopy and paper spray ionization mass spectrometry (PSI-MS) on a single instrumental platform. Both methods are capable of ambient analysis with fieldable instruments, yet Raman is often limited to bulk analysis. Critical to this work is the development of a gold nanoparticle (AuNP)-embedded paper swab to extend the capability of Raman spectroscopy to trace evidence via surface-enhanced Raman scattering (SERS). Plasmonic papers are characterized with respect to SERS signals and compatibility with PSI-MS analysis. Proof-of-principle is established with the identification of five representative drugs, and detection limits on the scale of 1-100 ng are achieved for both PSI-MS and SERS. The integrated SERS-PSI-MS system achieved 99.8% accurate chemical identification in a blind study consisting of 500 samples. Additionally, we demonstrate facile discrimination of several JWH-018 isomers via SERS even when MS and MS2 spectra are indistinguishable. Successful coupling of SERS and PSI-MS to enable on-site chemical analysis by two independent methods can potentially lead to a desirable paradigm shift in the handling of drug evidence.

Facile fabrication and characterization of aliphatic polyketone (PK) micro/nano fiber membranes via electrospinning and a post treatment process.

In this article, polyketone (PK) micro/nano fiber membranes were successfully fabricated by electrospinning and a post treatment process and the membrane characteristics were investigated. The morphology of the fiber membranes showed that ambient humidity during electrospinning changed the roughness of the fiber surface and the addition of NaCl decreased the fiber diameter. In particular, the changes in surface roughness was a very rare and novel discovery. The effect of this discovery on membrane properties was also analyzed. Additionally, the nanofiber membrane was modified by in situ surface reduction. FT-IR spectroscopy indicated the successful reduction modification and water contact angle results proved the improved wetting ability by this modification process. DSC and TGA analysis showed that the micro/nano fiber membranes possessed a high melting point and thermal decomposition temperature. Mechanical tests showed that as fiber membranes, PK micro/nano fiber membranes had relatively high mechanical strength, furthermore the mechanical strength can be easily enhanced by controlling the fiber morphology. From these results, it was concluded that the PK micro/nano fiber membranes could be a promising candidate for many applications such as organic solvent-resistant membranes, high-safety battery separators, oil-water separation, etc.

In Situ Formation of Gold Nanoparticles within a Polymer Particle and Their Catalytic Activities in Various Chemical Reactions.

Composite materials consisting of nanoscale gold particles and protective polymer shells were designed and tested as catalysts in various chemical reactions. Initially, the systematic incorporation of multiple gold nanoparticles into a poly(N-isopropylacrylamide) particle was achieved by an in situ method under light irradiation. The degree of gold nanoparticle loading, along with the structural and morphological properties, was examined as a function of the amount of initial gold ions and reducing agent. As these gold nanoparticles were physically-embedded within the polymer particle in the absence of strong interfacial interactions between the gold nanoparticles and polymer matrix, the readily-accessible surface of the gold nanoparticles with a highly increased stability allowed for their use as recyclable catalysts in oxidation, reduction, and coupling reactions. Overall, the ability to integrate catalytically-active metal nanoparticles within polymer particles in situ allows for designing novel composite materials for multi-purpose catalytic systems.

Rapid formation of polyimide nanofiber membranes via hot-press treatment and their performance as Li-ion battery separators.

We describe a new strategy to prepare thermally- and electrochemically-stable polyimide (PI) nanofiber membranes by the hot-press treatment of polyamic acid (PAA) nanofiber sheets in situ and examine their performance as Li-ion battery separators. Typical thermal imidization of PAA to PI membranes using sequential high temperature treatments in an oven takes a long time, but our method readily completes this conversion process at a mild temperature in 30 min while generating a high probability of inter-nanofiber imidization. Along with the improved electrolyte uptake capability and uniform distribution of the pore size and porosity caused by the dense and compact arrangements, the hot-press-induced PI membrane exhibits relatively thin sheets and a much greater mechanical strength than the membrane prepared by the thermal treatment. Subsequently, these PI-based membranes are installed in Li-ion full coin cells as battery separators whose C-rate (charging and discharging) performances are comparable to a commercial polyethylene (PE) separator. In addition, the highly improved thermal stabilities of these PI separators over PE separators are observed during thermal shrinkage and hot-box tests. Overall, our strategy can allow for the manufacture of diverse PI-based membranes with minimal preparation time and cost that can be utilized in high power portable devices requiring thermal and electrochemical stability.

Sub-100 nm anisotropic gold nanoparticles as surface-enhanced Raman spectroscopy substrates.

This study describes a reliable preparation of relatively small Ag/Au-based anisotropic nanostructures possessing tunable absorption bands and their use as surface-enhanced Raman spectroscopy (SERS) substrates. These Au nanostructures were prepared via the seed growth process of small Ag-core-Au-shell-type nanoparticles that were obtained by the subsequent reduction of Ag and Au ions by NaBH(4) and L-ascorbic acid at room temperature. The presence of Ag during the transformation process of the Ag-Au core-shell nanoparticles under light irradiation led to the formation of various small anisotropic Au nanoparticles which clearly exhibited different structural and optical properties from those of nanoparticles prepared from typical Ag-Au alloy or bare Ag or Au seeds. As the optimal size of Au-based substrates for SERS applications was reported to be below 100 nm in diameter under a constant concentration, we tested our moderately small anisotropic nanoparticles (∼55 nm in diameter) as a SERS substrate to examine the signal enhancement of 4-nitrobenzenethiol. These nanoparticles exhibited a greatly increased SERS response compared to those of similar sizes of uniform Ag and Au nanoparticles, presumably because of the increased surface area due to the nanoparticles' anisotropic nature (i.e., chemical effect) and partial overlap of their absorption bands with the SERS excitation wavelength (i.e., electromagnetic effect). In addition, these nanoparticles have shown a suitable stability to prevent significant SERS signal fluctuations caused by unpredictable aggregations. Due to our simple synthetic and modification approaches, relatively small Au-based anisotropic nanostructures can be easily designed to serve as attractive SERS templates.