Chitosan-Mediated Synthesis of Gold Nanoparticles on Patterned Poly(dimethylsiloxane) Surfaces

Biotemplated magnetic nanoparticle arrays

Immobilized biomineralizing protein Mms6 templates the formation of uniform magnetite nanoparticles in situ when selectively patterned onto a surface. Magnetic force microscopy shows that the stable magnetite particles maintain their magnetic orientation at room temperature, and may be exchange coupled. This precision-mixed biomimetic/soft-lithography methodology offers great potential for the future of nanodevice fabrication.

Green synthesis and stabilization of gold nanoparticles in chemically modified chitosan matrices

Chitosan-N-2-methylhydroxypyridine-6-methylcorboxylate (Ch-PDC) and chitosan-N-2-methylhydroxypyridine-6-methylhydroxy thiocarbohydrazide (Ch-PDC-Th) were synthesized for the first time using chitosan as precursor. Chitosan, Ch-PDC, Ch-PDC-Th were used in the synthesis of gold nanoparticles (AuNP) in aqueous medium. Chitosan and Ch-PDC-Th possess reducing properties which enabled the 'green' synthesis of AuNPs. The stabilization of the AuNPs was as a result of the thiocarbide (SC) and amine (NH(2)) groups in the chitosan matrix. The modified chitosan, its derivatives and the resulting AuNPs were characterized by Fourier transform infrared (FTIR) spectroscopy, Ultraviolet-visible (UV-vis) spectroscopy, Raman scattering measurements, powder X-ray diffraction (PXRD) and thermo gravimetric analysis (TGA). Particle size, morphology, segregation and individuality of the AuNPs were examined by transmission electron microscope (TEM) and energy dispersion spectroscopy (EDS). An average AuNPs size of 20 nm was observed for chitosan and Ch-PDC-Th while Ch-PDC was 50 nm. In comparison, AuNPs resulting from Ch-PDC-Th precursor has the most enhanced Raman and fluorescent intensities and was stable for over 2 months.

Biological response of hydrogels embedding gold nanoparticles

A nanocomposite hydrogel based on natural polysaccharides and gold nanoparticles (ACnAu) has been prepared and its biological effects were tested in vitro with both bacteria and eukaryotic cells. Antimicrobial tests showed that AC-nAu gels are effective in killing both gram+ (Staphylococcus aureus) and gram- (Pseudomonas aeruginosa) bacteria. LDH assays pointed at a toxic effect towards eukaryotic cell-lines (HepG2 and MG63), in contrast with the case of silver-based hydrogels; cytofluorimetry studies demonstrated an apoptosis-related mechanism induced by increase of ROS intracellular level which leads to cell death after 24 h of direct contact with AC-nAu gels. In vivo biocompatibility has been evaluated in a rat model, investigating the peri-implant soft tissue reaction after 1 month of implantation. The results show that silver-containing samples induced a fibrotic capsule of the same average thickness of the control sample (devoid of nanoparticles) (∼50 μm), while in the case of gold containing materials the fibrotic capsule was thicker (∼100 μm), confirming a higher biocompatibility for silver-based samples than for gold-based ones.

Aptamer-based PDMS-gold nanoparticle composite as a platform for visual detection of biomolecules with silver enhancement

A sensitive colorimetric detection for biomolecules based on aptamer was described. Poly(dimethylsiloxane) (PDMS)-gold nanoparticles (AuNPs) composite film was used as a platform for immobilizing anti-target aptamer. PDMS-AuNPs composite film only covered with aptamer showed high inhibiting ability towards silver reduction, after target molecules were conjugated on the modified surface, the catalytic efficiency of AuNPs for silver reduction was increased. In this system, the darkness density of silver enhancement was applied for target quantitative measurement. Lysozyme and adenosine 5'-triphosphate (ATP) were tested as the models, quantitative measurements with imaging software or semiquantitative measurements with naked eyes were carried out in the range of 1×10(-2)-1 μg/mL and 1×10(-4)-1×10(3) μg/mL, the volume of reagent using in each assay is 15 μL or less. We speculated that aptamer-target conjugates' inhibition ability for AuNPs' catalytic efficiency toward silver reduction might come from charge and spatial effects. This study can offer a completely novel and relatively general approach for colorimetrical aptamer sensors with good analytical properties and potential applications. The sensor could be coupled with digital transmission of images for remote monitoring system in diagnosis, food control, and environmental analysis.

Low molecular weight chitosan in DNA vaccine delivery via mucosa

It is acknowledged that low molecular weight chitosan (LMWC) is advantageous over high molecular weight chitosan (HMWC) in the biodegradability. In this report, the potential of LMWC in DNA vaccine delivery via mucosa was evaluated. Firstly, the effects of molecular weight of chitosan on the physicochemical properties and in vitro transfection efficiency of chitosan/DNA polyplexes were investigated. Secondly, the capabilities of the polyplexes based on LMWC to elicit serum IgG antibodies and to attenuate the development of atherosclerosis after intranasal vaccination were compared with the polyplexes based on HMWC in the rabbit model. Finally, the intramucosal transport of the double-labeled polyplexes was observed by confocal microscopy. The results indicated that LMWC had lower binding affinity to DNA and mediated higher transfection efficiency. Intranasal vaccination with LMWC/DNA polyplexes could elicit significant systemic immune responses, modulate the plasma lipoprotein profile and attenuate the progression of atherosclerosis. Those aspects were comparable to those obtained by HMWC/DNA polyplexes. As revealed by confocal images, LMWC/DNA polyplexes remained stable during interaction with the nasal mucosa, and were internalized by nasal epithelial cells, which was similar to the case of HMWC/DNA polyplexes. In conclusion, LMWCs have potential applications in DNA vaccine delivery via mucosa.

Direct facile approach to the fabrication of chitosan-gold hybrid nanospheres

Chitosan-gold hybrid nanospheres were prepared through a direct facile approach that utilized cross-linked composite nanospheres consisting of low-molecular-weight chitosan (LWCS) and ethylenediaminetetraacetic acid (EDTA) as a precursor reaction system. EDTA was employed not only to construct the counterion interaction-based composite nanospheres with the cationic chitosan but also as the reductant for subsequent in situ gold salt reduction within the LWCS-EDTA composite nanospheres. This approach elegantly ensured that each and every nanosphere was loaded with gold nanoparticles and no nonembedded free gold nanoparticles would exist in the dispersing medium. Moreover, becauseof the noncovalent interaction between LWCS and EDTA, the EDTA reductant can be easily removed from the cross-linked nanospheres, and "pure" chitosan-gold hybrid nanospheres can be obtained. The obtained chitosan-gold hybrid nanospheres were found to have a tunable size and good dispersing stability within a wide pH range. The embedded gold nanoparticles were in the range from several to several tens of nanometers, which may be useful for sensing and imaging. Morphology studies indicated that most of the loaded gold nanoparticles were located in the interior of the hybrid nanospheres. Taking into account the good biocompatibilities of LWCS, abundant functional (amino) groups in chitosan, and the mild preparation conditions, we find that the chitosan-gold hybrid nanospheres prepared here may have tremendous potential in advanced biomedical applications.

In-situ synthesis of poly(dimethylsiloxane)-gold nanoparticles composite films and its application in microfluidic systems

We presented a simple approach for in-situ synthesis of poly(dimethylsiloxane) (PDMS)-gold nanoparticles composite film based on the special characteristics of PDMS itself. It is an environmentally safe synthesis method without the requirement of additional reducing/stabilizing agents. The region where the resulting gold nanoparticles distribute (in the matrix or on the surface of the polymer) and the size of the nanoparticles, as well as the colour of the free-standing films, can be simply controlled by adjusting the ratio of curing agent and the PDMS monomer. The chemical and optical properties of these composite films were studied. Using such a method, gold nanoparticle micropatterns on PDMS surfaces can be performed. And based on the gold nanoparticles micropattern, further modification with antibodies, antigens, enzymes and other biomolecules can be achieved. To verify this ability, an immobilized glucose oxidase (GOx) reactor in microchannels was built and its performance was studied. The experiments have shown that the resulting composite film may have a lot of potential merits in protein immobilization, immunoassays and other biochemical analysis on PDMS microchips.

Mass synthesis of single-crystal gold nanosheets based on chitosan

Single-crystal Au nanosheets with {111} planes as basal surfaces have been synthesized on the basis of the polysaccharide chitosan. The preferential adsorption of polar groups in chitosan molecules on {111} planes of Au nuclei may account for the formation of anisotropic nanosheets. Appropriate precursor (HAuCl(4)) concentrations are vital for the formation of Au nanosheets. The Au nanostructures thus prepared exhibit interesting shape-dependent optical properties. This convenient, environmentally friendly and low-cost route may be amenable to mass production.

The influence of polycaprolactone coating on the internalization and cytotoxicity of gold nanoparticles

The interaction between mesoscopic colloids and cells is largely dependent on the particle size and surface properties. Under a mild reaction condition, gold particles with an average diameter of approximately 100 nm were prepared by incubating poly(dimethylsiloxane) film in HAuCl4/acetic acid solution. The particles were then transferred into a polycaprolactone (PCL) film by thermal pressing. Bare and PCL-coated particles were obtained by control over the extent of rinsing. The bare and PCL-coated gold particles were co-cultured with ECV-304 cells to examine the particle internalization and their influence on the cell morphology and cytotoxicity. Transmission electron microcopy observed the subcellular distribution of the gold particles, which were found in the cell compartments (endosomes or lysosomes), cytoplasm, nucleic envelope, and even nucleus regardless of the existence of PCL coating. However, scanning electron microscopy and beta-tubulin staining revealed a significant change in terms of the cell morphology and cytoskeleton caused by the bare gold particles. Higher cytotoxicity was also determined for the bare gold particles. By contrast, no significant difference of the cell morphology and cytoskeleton change was caused by the PCL-coated gold particles, which have also shown lower cytotoxicity.

Synthesis and electrochemical applications of gold nanoparticles

This review covers recent advances in synthesis and electrochemical applications of gold nanoparticles (AuNPs). Described approaches include the synthesis of AuNPs via designing and choosing new protecting ligands; and applications in electrochemistry of AuNPs including AuNPs-based bioelectrochemical sensors, such as direct electrochemistry of redox-proteins, genosensors and immunosensors, and AuNPs as enhancing platform for electrocatalysis and electrochemical sensors.