Silver Nanoparticle Containing Organic/inorganic Thin Films: Preparation, Physical Properties And Biocide Activities

Recently, the physical properties of composite materials consisting of nanometre-sizedclusters of free electron metals in a dielectric have attracted much attention due to theirpotential applications in many areas including heterogeneous catalysis, anti-reflective films,biosensors and nonlinear optical devices. Metal nanoparticles dispersed in dielectricmaterials exhibit a strong characteristic extinction peak, due to plasmon resonance. Theshape, intensity and position of the peak can depend on the size, shape, concentration, andchemical state of the nanoclusters and also the possible interaction between them.Preventing device-related infections in surgical patients is a major concern for thescientific and health care communities. In conjunction with increased bacterial resistance toantibiotics, implant related infections cause serious health, safety, and financial burdens thatcould be prevented. Applying antibacterial coatings to implantable devices would be asimple method of improving existent medical technologies without hindering their overallfunction. A new trend of antibacterial coating includes those designed to actively releaseembedded bactericidal agents. With inimitable functionality and versatility, it’s no surprisethat nanocomposite materials have received a great deal of attention in the scientificcommunity. Silver is historically known to have extensive bactericidal properties withoutotherwise harming mammalian cells. Silver nanoparticles (Ag NPs) afford thesebactericidal properties to nanocomposites via the oxidation of Ag NPs into silver ions. Theions released from these coatings inhibit infection more efficiently than oral antibioticsbecause the antibacterial therapy is concentrated at the implant site, where it is needed.The present dissertation describes the synthesis, characterization, and incorporation ofstabilized silver nanoparticles into different matrices as well as their potential applications.Silver nanoparticles were synthesized into4different matrices and the effect of differentmedium on properties of silver containing coating as well as antibacterial activity ofdifferent coating containing nanosilver was extensively investigated.At the first step, a facile route has been developed to synthesis silver nanoparticles intopolyvinylpyrrolidone (PVP) as an organic storage for silver and silica (SiO2) as aninorganic matrix using sol-gel method. The influence of matrices on the size and opticalproperties of silver nanoparticles were studied. It is found that the particle size can betailored by changing the AgNO3as a nanosilver precursor. It was observed that silvernanoparticle size increases at different rate with silver nitrate (AgNO3) concentration indifferent matrices; there is an up-limit for AgNO3concentration in each given matrix tokeep the particle size below100nm. This limit is8%in silica matrix and can be as high as 50%for PVP matrix. Because the aging time of sol in sol-gel process is significant, theeffects of aging time on the size of nanoparticle and optical absorption spectrum were alsostudied. It is determined that aging time can affect the optical absorption intensity of silvernanoparticles which means that certain time is necessary in the formation of nanoparticles.The absorption peak is varied for different matrix and occurs at425in PVP matrix and at442in SiO2matrix because of the difference in refractive index of these two matrices.Based on Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM)images, Ag nanoparticles are well-dispersed into the film and the mean particle size of thenanosilver increases with the AgNO3content at different rate in different matrix. For thesame1.6%Ag NO3concentration, the mean particle size is65nm in SiO2matrix but only10nm in PVP matrix.Silica-based coatings are interesting substrates for biocide silver because of theirunique properties like chemical durability and biocompatibility.PhTEOS was another silica-based material which was selected for nanosilver storage.In Chapter4, Sol–gel coatings containing biocide silver ions are prepared for the preventionof biofilm formation on implanted surfaces. High-temperature processing of such coatingscan lead to diffusion of nano silver and reduce the amount of available silver for lastingeffect. Here, we present the preparation of silane based matrices, phenyltriethoxysilane(PhTEOS), containing different amount of Ag nanoparticles, using a low-temperature sol–gel method. The incorporation of a silver salt into sol–gel matrix resulted in a desired silverrelease scheme, i.e., with high initial release rate in de-ionized water followed by a lowersustained release for more than15days, as determined by inductively coupled plasma massspectrometry (ICP-MS). Scanning Electron Microscopy (SEM) has been employed toinvestigate the morphology of the film surfaces before and after immersion in a nutrient-rich bacterial suspension of approximately108CFU/ml, which was incubated for15and30days at37°C. From SEM images, it was found that thin films containing35nm particlescould prevent formation of biofilm for over30days. The presence of surface silver beforeand after3,9and15days immersion was confirmed by X-ray photoelectron spectroscopy(XPS).In chapter5, two different silica-based coatings containing biocide silver nanoparticleshave been synthesized using low temperature sol-gel method. Two different silane basedmatrices, were synthesized by applying phenyltriethoxysilane (PhTEOS) and tetraethylorthosilicate (TEOS) as precursor to prepare silica-based film. The films were analyzed byusing UV–visible spectrophotometry, atomic force microscopy (AFM) and scanningelectron microscopy (SEM) for their optical, surface morphological as well as structuralproperties. Optical properties of nanosilver in these two matrices showed that the peak absorption occurred at different wavelengths because; optical absorption of nanoparticles isaffected by the surrounding medium. It was also found that the silver absorption has higherintensity in PhTEOS than in TEOS matrix, indicating higher concentration of silvernanoparticles being loaded into the coating. To study silver release property, the films wereimmersed in water for12and20days. AFM and SEM analyzes showed that higherconcentration of silver nanoparticles and smaller particle sizes were synthesized intoPhTEOS coating and consequently, more particles remains on the surfaces after20dayswhich leads to longer antibacterial activity of PhTEOS coating.Graphene, a one-atom-thick planar sheet of sp2bonded carbon atoms densely packedin a honeycomb crystal lattice, has grabbed appreciable attention due to its exceptionalproperties including high current density, ballistic transport, chemical inertness, highthermal conductivity, optical transmittance, high surface area, biocompatibility and superhydrophobicity at nanometer scale. Decorating silver nanoparticles on the surface ofgraphene improves its antibacterial activity. In chapter6, we show the successfulpreparation of silver nanopartcle decorated graphene oxide sheets and embed them intoPVP film. Optical absorption spectra of PVP film containing Ag-GO shows that thepresents of graphene leads the shift of absorption peak of Ag-PVP film in the presence ofGO. The appearance of characteristic surface plasmon band at420nm, leads to a blue-shiftfor the absorption peak at the same concentration of silver in PVP without GO. TEMmicrograph of silver nanoparticles deposited on grapheme oxide sheets shows a wide sizedistribution of particles ranging from5–25nm and the particles are hexagonal in shape thatcould be the result of the deposition of the particles on the graphene sheets. Base on thefringe pattern of the HRTEM images, the lattice spacing of Ag nanoparticle deposited onthe GrO sheets is0.236nm, which corresponds to the (111) crystal plane.Atomic Force Microscopy (AFM) was employed to study the surface topography ofPVP film containing GO decorated by different amount of AgNO3dried at100°C and heat-treated at200°C. AFM images of the dried films containing higher Ag concentrationsdemonstrate that surface concentration and the mean particle size are increased by raisingthe Ag concentration. The mean particle size was measured to be about12nm for0.025and16nm for0.08gr AgNO3concentrations, respectively. It was observed that heat-treatmentcauses surface particles diffusion into the coating. This diffusion was also observed for Ag-Silica based coating. PVP coating containing grapheme oxide sheets embedded silvernanoparticles with0.02AgNO3was also dried at100°C and annealed at200°C for2hours.Previous studies showed that, heat-treatment leads diffusion of nanosilver into the coatingwhich causes surface particles reduction. Reduction of surface particle is undesired forantibacterial activity of biocide nanosilver. Here, we found silver nanoparticles concentration varies when embedded in different matrices, GO matrix causes silvernanoparticles to sustain on the surface of coating even being treated at200°C.Through this thesis work, we have successfully fabricated high concentration,silver nano-composite antibacterial coatings, which can be used in bio-medicalapplications. Based on structural analyses, property evaluation and biocide tests,we have given the correlation between physical properties and biocidecharacteristics, which laid the foundation for new bio-coating materials.