Two-step biocompatible surface functionalization for two-pathway antimicrobial action against Gram-positive bacteria.

The use of indwelling devices has emerged as a frequent and often life-saving medical procedure. However, infection in prosthetic surgery is one of the most important and devastating complications. Once the biofilm has been formed, its eradication is extremely difficult, due to an increased resistance to host defense and conventional antimicrobials. Thus, the design of novel strategies for inhibiting the bacterial adhesion on implantable devices is a key point for successful surgical procedures. In this work, the development of a simple two-step protocol to prepare surfaces able to prevent the bacterial growth was successfully achieved. The surface-modification design includes a combined approach involving the multi-functionalization of Ti surfaces with silver nanoparticles (AgNPs) and/or ampicillin (AMP). The surface chemistry involved in AMP adsorption on titanium and silver surfaces was elucidated for the first time, thus establishing the basis for the further anchoring of other antibacterial compounds having similar functional groups. Our results show that the antibiotic binds to the titanium surface through covalent interactions between the COOH groups in AMP and the OH groups of the native TiO2 on the surface, although electrostatic interactions between protonated AMP and negatively charged TiO2 can also contribute to the antibiotic anchoring to the surface. The AMP immobilization on the AgNPs is carried out by thiolate-like bonds. The ß-lactam ring functionality is preserved after the adsorption process, since the Ti-AgNPs-AMP surface was able to decrease the bacterial viability in more than 80%. Moreover, the antimicrobial capacity is maintained over time due to a two-pathway antibacterial mechanism: death by contact (AMP) and death by release (AgNPs). The effect of AMP prevails on AgNPs at early stages of bacterial adhesion, while AgNPs are responsible for sustaining the relatively low but steady release of Ag(I), preserving the bacteriostatic activity of the surface over time. This effect would contribute to prevent infections due to sessile cells on indwelling devices, powering the action of the immune system and the conventional antibiotics usually dosed in implanted patients.

Self-assembly of flagellin on Au(111) surfaces.

The adsorption of flagellin monomers from Pseudomonas fluorescens on Au(111) has been studied by Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Surface Plasmon Resonance (SPR), and electrochemical techniques. Results show that flagellin monomers spontaneously self-assemble forming a monolayer thick protein film bounded to the Au surface by the more hydrophobic subunit and exposed to the environment the hydrophilic subunit. The films are conductive and allow allocation of electrochemically active cytochrome C. The self-assembled films could be used as biological platforms to build 3D complex molecular structures on planar metal surfaces and to functionalize metal nanoparticles.

New findings for the composition and structure of Ni nanoparticles protected with organomercaptan molecules.

Here we explore the synthesis of alkanethiol-coated Ni NPs following the one-phase reaction method by Brust et al. The reduction of NiCl2 with NaBH4 in the presence of dodecanethiol (C12SH) yields a complex product that is difficult to identify as illustrated in the figure of merit. We synthesized Ni(II) dodecanethiolate (C12S) (without the addition of NaBH4) for comparison and performed an exhaustive characterization with TEM, HR-TEM, AFM, MFM, XPS, XRD, UV-vis, magnetism, and FT-IR. It is found that the organic coating is not quite a well-organized self-assembled monolayer (SAM) surrounding the Ni cluster as previously reported. XPS and XRD data show slight differences between both syntheses; however, Ni(II) thiolate appears to be more stable than reduced Ni when exposed to ambient air, indicating the propensity of metallic Ni to oxidize. It has been shown that irradiating with TEM electrons over various metal thiolates leads to nanoparticle formation. We irradiated over Ni(II) thiolate and observed no evidence of NP formation whereas irradiating a reduced Ni sample exhibited an ~3.0 nm nanoparticle diameter. Magnetism studies showed a difference between both samples, indicating ferromagnetic character for the reduced Ni sample. According to our results, the product of the synthesis is comprised of ultrasmall metallic clusters embedded in some form of Ni(II) C12S. In this work, we open a discussion of the chemical nature of the core and the shell in the synthesis of Ni NPs protected with organomercaptan molecules.

The complex thiol-palladium interface: a theoretical and experimental study.

This paper presents a theoretical study of the surface structures and thermodynamic stability of different thiol and sulfide structures present on the palladium surface as a function of the chemical potential of the thiol species. It has been found that as the chemical potential of the thiol is increased, the initially clean palladium surface is covered by a (√3 × âˆš3)R30° sulfur lattice. Further increase in the thiol pressure or concentration leads to the formation of a denser (√7 × âˆš7)R19.1° sulfur lattice, which finally undergoes a phase transition to form a complex (√7 × âˆš7)R19.1° sulfur + thiol adlayer (3/7 sulfur + 2/7 thiol coverage). This transition is accompanied by a strong reconstruction of the Pd(111) surface. The formation of these surface structures has been explained in terms of the catalytic properties of the palladium surface. These results have been compared with X-ray photoelectron spectroscopy results obtained for thiols adsorbed on different palladium surfaces.

Synthesis and characterization of gold at gold(i)-thiomalate core at shell nanoparticles.

In this paper, the synthesis of gold at gold(I)-thiolate core at shell nanoparticles is described for the first time. The chemical nature and structure of these nanoparticles were characterized by a multi-technique approach. The prepared particles consist of gold metallic cores, about 1 nm in size, surrounded by stable gold(I)-thiomalate shells (Au at Au(I)-TM). These nanoparticles could be useful in medicine due to the interesting properties that gold(I)-thiomalate has against rheumatoid arthritis. Furthermore, the described results give new insights in the synthesis and characterization of metallic and core at shell nanoparticles.

Self-assembly of alkanedithiols on Au(111) from solution: effect of chain length and self-assembly conditions.

A comparative study on the adsorption of buthanedithiol (BDT), hexanedithiol (HDT), and nonanedithiol (NDT) on Au(111) from ethanolic and n-hexane solutions and two different preparation procedures is presented. SAM characterization is based on reflection-absorption infrared spectroscopy, electrochemistry, X-ray photoelectron spectroscopy, and time of flight direct recoil spectroscopy. Results indicate that one can obtain a standing-up phase of dithiols and that the amount of the precursor lying-down phase decreases from BDT to NDT, irrespective of the solvent and self-assembly conditions. A good ordering of the hydrocarbon chains in the standing-up configuration is observed for HDT and NDT when the system is prepared in degassed n-hexane with all operations carried out in the dark. Disulfide bridges at the free SH terminal groups are formed for HDT and to a lesser extent for NDT prepared in ethanol in the presence of oxygen, but we found no evidence of ordered multilayer formation in our experiments. No disulfides were observed for BDT that only forms the lying-down phase. Our results demonstrate the key role of the chain length and the procedure (solvent nature and oxygen presence) in controlling the surface structure and chemistry of SAMs dithiols on Au(111).

Self-assembled dithiothreitol on Au surfaces for biological applications: phospholipid bilayer formation.

Self-assembly of dithiothreitol (DTT) on Au(111) from solution deposition has been studied by X-ray photoelectron spectroscopy and electrochemical data. DTT molecules self-assemble on Au(111) in a lying-down configuration irrespective of the concentration and temperature. XPS and electrochemical data indicate a DTT surface coverage of theta approximately 0.16 with two S-head-Au covalent bonds per DTT molecule. The DTT monolayer turns the Au surface hydrophilic enough to allow the formation of fluid dimyristoylphosphatidylcholine (DMPC) bilayer domains by vesicle fusion as revealed by in situ atomic force imaging. Methylene blue (MB) and flavin adenine dinucleotide (FAD) have been used as probes to study molecule transport across the bilayer.

Electrochemical deposition onto self-assembled monolayers: new insights into micro- and nanofabrication.

Pattern transfer with high resolution is a frontier topic in the emerging field of nanotechnologies. Electrochemical molding is a possible route for nanopatterning metal, alloys and oxide surfaces with high resolution in a simple and inexpensive way. This method involves electrodeposition onto a conducting master covered by a self-assembled alkanethiolate monolayer (SAMs). This molecular film enables direct surface-relief pattern transfer from the conducting master to the inner face of the electrodeposit, and also allows an easy release of the electrodeposited film due their excellent anti-adherent properties. Replicas of the original conductive master can be also obtained by a simple two-step procedure. SAM quality and stability under electrodeposition conditions combined with the formation of smooth electrodeposits are crucial to obtain high-quality pattern transfer with sub-50 nm resolution.