Interaction of Novel Fluorescent Nanoscale Ionic Silicate Platelets with Biomaterials for Biosensors

The nano silicate platelets (NSPs) of 100 × 100 × 1 nm³ in dimension were previously derived from the exfoliation of naturally occurring sodium montmorillonite clay, and their affinity to the surface of bacteria was revealed. The unique characteristics of ionic charges (Si–O–Na⁺) and the presence of siloxanol functionalities (Si–OH) allowed the organic modification of NSP to form NSP-tethering poly­(hydroxyethyl methacrylate) (PHEMA) pendants through a sol–gel and living polymerization. By attaching nathphalimide-type fluorescence onto NSP-PHEMA, a new class of fluorescent organic–inorganic hybrid (NSP-PHEMA-HA), was prepared and its photoluminescence (PL) and bacterial trapping properties were characterized. The investigation of PL emission revealed that the fluorescent NSP hybrids could be used to detect bacteria and possess the potential for the biosensor applications

Evaluation of the Antibacterial Activity and Biocompatibility for Silver Nanoparticles Immobilized on Nano Silicate Platelets

Silver nanoparticles (AgNPs) are known for their bactericidal abilities. The antibacterial potency is dependent on the particle size and dispersion status. In this study, we synthesized AgNP/NSP nanohybrids in two different weight ratios (1/99 and 8/92) using the fully exfoliated clay, i.e., nanosilicate platelets (NSP), as a dispersing agent and carrier for AgNPs. Due to the size of NSP, the immobilized AgNPs do not enter cells readily, which may lower the risk associated with the cellular uptake of AgNPs. The biocompatibility, immunological response, and antimicrobial activities of AgNP/NSP hybrids were evaluated. The results revealed that AgNP/NSP hybrids elicited merely mild inflammatory response and retained the outstanding antibacterial activity. The hybrids were further embedded in poly­(ether)­urethane (PEU) to increase the biocompatibility. At the same silver content (20 ppm), the PEU-AgNP/NSP nanocomposites were nontoxic to mouse skin fibroblasts, while simultaneously exhibiting nearly complete bacterial growth reduction (99.9%). PEU containing the same amount of free AgNPs did not display such an effect. Our results verify the better biosafety of the AgNPs/NSP hybrids and their polymer nanocomposites for further clinical use

First Observation of Physically Capturing and Maneuvering Bacteria using Magnetic Clays

A new class of nanohybrids composed of structurally exfoliated silicate platelets and magnetic iron oxide nanoparticles was synthesized and shown to be capable of capturing microbes in liquid microbiological media. Nanoscale silicate platelets with an approximate thickness of 1.0 nm were prepared from the naturally occurring mineral clays montmorillonite and mica; these clays yielded platelets with lateral dimensions on the order of 80–100 nm and 300–1000 nm, respectively. The magnetic Fe₃O₄ nanoparticles, approximately 8.3 nm in diameter, were coated in situ onto the silicates during the synthesis process, which involved the coprecipitation of aqueous Fe²⁺/Fe³⁺ salts. Owing to the high surface area-to-volume ratios and the presence of ionically charged groups (i.e., SiO^–Na⁺), the silicate nanoplatelets exhibited intense noncovalent bonding forces between Fe₃O₄ nanoparticles and the surrounding microorganisms. The Fe₃O₄-on-nanoplatelet nanohybrids enabled the entrapment of bacterial cells in liquid microbiological media. These captured bacteria formed bacterial aggregates on the order of micrometers that became physically maneuverable under a magnetic field. This phenomenon was demonstrated with <i>Staphylococcus aureus</i> in liquid microbiological media by physically removing them using a magnetic bar; in two experimental examples, bacterial concentrations were reduced from 10⁶ to 10² and from 10⁴ to 10⁰ CFU/mL (colony formation unit/mL con). Under a scanning electron microscope, these bacteria appeared to have rough and wrinkled surfaces due to the accumulated silicate platelets. Furthermore, the external application of a high-frequency magnetic field completely destroyed these aggregated microbes by the magnetically induced heat. Hence, the newly developed nanohybrids were shown to be viable for physically capturing microbes and also for potential hyperthermia treatment applications

Facile Fabrication of Robust Superhydrophobic Epoxy Film with Polyamine Dispersed Carbon Nanotubes

Nanocomposite films of superhydrophobic surface are fabricated from the dispersion of unmodified carbon nanotubes (CNTs) and hydrophobic poly­(isobutylene)–amine (PIB–amine). The PIB–amine prepared from the amidation of poly­(isobutylene)-succinic anhydride and poly­(oxypropylene)–amines is essential for dispersing the originally entangled CNTs into the debundled CNTs as observed by TEM. A robust CNTs/epoxy nanocomposite film with high dimensional stability is made by subsequent curing with epoxy resin. The self-standing film exhibits a superhydrophobic property, with water droplet contact angle > 152° due to the CNTs controlled alignment on the surface forming micrometer-size plateaus, as observed by SEM. The preparation of PIB–amine/CNTs dispersion and subsequently curing into a superhydrophobic CNTs/epoxy film is relatively simple and can potentially be applied to large surface coating

Selective SERS Detecting of Hydrophobic Microorganisms by Tricomponent Nanohybrids of Silver–Silicate-Platelet–Surfactant

Nanohybrids consisting of silver nanoparticles (Ag), clay platelets, and a nonionic surfactant were prepared and used as the substrate for surface-enhanced Raman scattering (SERS). The nanoscale silicate platelets (SP) (with dimensions of 100 × 100 nm² and a thickness of ∼1 nm) were previously prepared from exfoliation of the natural layered silicates. The tricomponent nanohybrids, Ag-SP-surfactant (Ag-SP-S), were prepared by in situ reduction of AgNO₃ in the presence of clay and the surfactant. The clay platelets with a large surface area and ionic charge (ca. 18 000 sodium ions per platelet) allowed for the stabilization of Ag nanoparticles in the range of 10–30 nm in diameter. With the addition of a nonionic surfactant such as poly­(oxyethylene) alkyl ether, the tricomponent Ag-SP-S nanohybrids possessed an altered affinity for contacting microorganisms. The particle size and interparticle gaps between neighboring Ag on SP were characterized by TEM. The surface tension of Ag-SP and Ag-SP-S in water implied different interactions between Ag and hydrophobic bacteria (Escherichia coli and Mycobacterium smegmatis). By increasing the surfactant content in Ag-SP-S, the SERS peak intensity was dramatically enhanced compared to the Ag-SP counterpart. The nanohybrids, Ag-SP and Ag-SP-S, with the advantages of varying hydrophobic affinity, floating in medium, and 3D hot-junction enhancement could be tailored for use as SERS substrates. The selective detection of hydrophobic microorganisms and larger biological cells makes SERS a possible rapid, label-free, and culture-free method of biodetection

Novel Polymer Gel Electrolyte with Organic Solvents for Quasi-Solid-State Dye-Sensitized Solar Cells

A cross-linked copolymer was previously synthesized from poly­(oxyethylene) diamine (POE-amine) and an aromatic anhydride and cured to generate an amide-imide cross-linking structure. The copolymer containing several chemical groups such as POE, amido acids, and imide, enabled to absorb liquid electrolytes in methoxypropionitrile (MPN) for suitable uses in dye-sensitized solar cells. To establish the advantages of polymer gel electrolytes (PGE), the same copolymer was studied by using different electrolyte solvents including propylene carbonate (PC), dimethylformamide, and <i>N</i>-methyl-2-pyrrolidone, and shown their long-term stability. The morphology of the copolymer after absorbing liquid electrolytes in these solvents was proven the same as a 3D interconnected nanochannels, evidenced field emission-scanning electron microscopy. Among these solvents, PC was selected as the optimized PGE, which demostrated a higher power conversion efficiency (8.31%) than that of the liquid electrolyte (7.89%). In particular, the long-term stability of only a 5% decrease in the cell efficiency after 1000 h of testing was achieved. It was proven the developed copolymer as PGE was versatile for different solvents showing high efficiency and long-term durability

Controlling Formation of Silver/Carbon Nanotube Networks for Highly Conductive Film Surface

Flexible polymer films with high electrical conductivity were prepared through a simple coating of well-dispersed silver nanoparticle (AgNP) and multiwalled carbon nanotube (CNT) solution. The hybrid film with surface resistance as low as 1 × 10^–2 Ω/sq was prepared by controlling the annealing temperature in air and by using a suitable composition of silver nitrate/CNT/poly­(oxyethylene)-oligo­(imide) (POE-imide) in the ratio 20:1:20 by weight. During the heating, color of the film surface changed from black to golden to milky white, indicating the accumulation of AgNPs through surface migration and melting into CNT-connected networks. Thermogravimetric measurements showed that the transition temperature of 170 °C was responsible for the POE-imide degeneration and the subsequent Ag melting with a decrease in the surface resistance from 2.1 × 10⁵ to 2.0 × 10^–1 Ω/sq, which was able to illuminate light-emitting diode lamps because of the formation of a continuous Ag network

mRNA levels of <i>VEGF-A, TGF-β1</i> and <i>IL-6</i> in different treatment groups during wound healing.

<p>AgNP/NSP treatment also modulates the expression of cytokine mRNAs in wounded skin. The levels of <i>VEGF-A</i>, <i>TGF-β1</i> and <i>IL-6</i> mRNA expression from mice of different treatment groups in both acute thermal injury at day 7 (a) and excision wound at day 15 (b) were examined by RT-PCR. Relative band intensities of different groups were calculated by a densitometer and are demonstrated by the values under the bands. The data shown are representative of three independent experiments.</p

Wound healing rates on (a) acute burn model (b) excision wound model and the photographs of wound appearance on day 5 after (c) acute burn injury and (d) excision injury.

<p>The rate of infected wound healing was compared in animals treated with staphylococcus only (Staph), staphylococcus and NSP (Staph+NSP), staphylococcus and Poly-Ag (Staph+Poly-Ag), staphylococcus and AgNP/NSP (Staph+AgNP/NSP), staphylococcus and Aquacel® (Staph+AQ), staphylococcus and silver sulfadiazine (Staph+SS), and control (untreated). The results are expressed as the mean ± SD from three independent experiments in each group. *<i>P</i><0.05, comparison between AgNP/NSP and the other 6 groups at each time point; † <i>P</i><0.05, comparison between SS treatment with the untreated, Staph, Staph+NSP, and Staph+Poly-Ag groups; ‡ <i>P</i><0.05, comparison between AQ treatment with the untreated, Staph, Staph+NSP, and Staph+Poly-Ag groups; # <i>P</i><0.05, comparison between NSP treatment with untreated, Staph and Staph+Poly-Ag groups; § <i>P</i><0.05, comparison between Poly-Ag treatment with untreated and Staph groups. All the comparisons were confirmed by Student’s <i>t</i> test.</p

Cytokine profile of wound healing.

<p>Serum levels of VEGF-A, TGF-β1 and IL-6 from mice of different treatment groups in both acute thermal injury at day 7 and excision wound at day 15 were examined by ELISA method.</p><p>Results are expressed as the mean (pg/ml) ± standard deviation (SD) from three independent experiments of each group.</p>*<p>Statistically significant as compared to the Staph group (<i>P</i><0.01, Student’s <i>t</i> test).</p