In the present paper, we study the mechanism of antibacterial activity of glutathione (GSH) coated silver nanoparticles (Ag NPs) on model Gram negative and Gram positive bacterial strains. Interference in bacterial cell replication is observed for both cellular strains when exposed to GSH stabilized colloidal silver in solution, and microbicidal activity was studied when GSH coated Ag NPs are (i) dispersed in colloidal suspensions or (ii) grafted on thiol-functionalized glass surfaces. The obtained results confirm that the effect of dispersed GSH capped Ag NPs (GSH Ag NPs) on Escherichia coli is more intense because it can be associated with the penetration of the colloid into the cytoplasm, with the subsequent local interaction of silver with cell components causing damages to the cells. Conversely, for Staphylococcus aureus, since the thick peptidoglycan layer of the cell wall prevents the penetration of the NPs inside the cytoplasm, the antimicrobial effect is limited and seems related to the interaction with the bacterial surfaces. Experiments on GSH Ag NPs grafted on glass allowed us to elucidate more precisely the antibacterial mechanism, showing that the action is reduced because of GSH coating and the limitation of the translational freedom of NPs.

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In the present work, we describe a simple procedure to produce biomimetically coated silver nanoparticles (Ag NPs), based on the postfunctionalization and purification of colloidal silver stabilized by citrate. Two biological capping agents have been used (cysteine Cys and glutathione GSH). The composition of the capped colloids has been ascertained by different techniques and antibacterial tests on GSH-capped Ag NPs have been conducted under physiological conditions, obtaining values of Minimum Inhibitory Concentration (MIC) of 180 and 15 μg/mL for Staphylococcus aureus and Escherichia coli, respectively. The antibacterial activity of these GSH capped NPs can be ascribed to the direct action of metallic silver NPs, rather than to the bulk release of Ag(+).

By replacing cetyltrimethylammonium bromide (CTAB) with the zwitterionic lauryl sulfobetaine (LSB) surfactant in the classical seed-growth synthesis, monocrystalline gold nanostars (m-NS) and pentatwinned gold asymmetric nanostars (a-NS) were obtained instead of nanorods. The main product under all synthetic conditions was a-NS, which have branches with high aspect ratios (AR), thus leading to LSPR absorptions in the 750-1150 nm range. The percentage of m-NS versus a-NS, the aspect ratio of the a-NS branches, and consequently the position of their LSPR absorption can be finely tuned simply by regulating the concentration of reductant, the concentration of surfactant, or the concentration of the "catalytic" Ag(+) cation. The m-NS have instead shorter and larger branches, the AR of which is poorly influenced by synthetic conditions and displays an LSPR positioned around 700 nm. A growth mechanism that involves the direct contact of the sulfate moiety of LSB on the surface of the nano-object is proposed, thereby implying preferential coating of the {111} Au faces with weak interactions. Consistent with this, we also observed the straightforward complete displacement of the LSB surfactant from the surface of the nanostars. This was obtained by the simple addition of thiols in aqueous solution to yield extremely stable coated a-NS and m-NS that are resistant to highly acidic, basic, and in similar to in vivo conditions.

Five-branched gold nanostars are obtained using Triton X-100 in a seed-growth synthesis. They have the uncommon feature of two intense localized surface plasmon resonances (LSPRs) in the 600-900 and 1100-1600 nm ranges. Both LSPRs convert laser radiation into heat, offering two photothermally active channels in the NIR and SWIR ranges.

Fluorescent sensors for 3 d divalent metal ions have been designed by means of a supramolecular approach: an anthracene fragment (the signalling subunit) has been linked to either a cyclic or a noncyclic quadridentate ligand (the receptor). occurrence of the metal-receptor interaction is signalled through the quenching of anthracene fluorescence. When the receptor (i.e., the dioxotetramine subunit of sensors 2 and 3) is able to promote the one-electron oxidation of the metal, quenching takes place through a photoinduced metal-to-fluorophore electron-transfer mechanism. In the case of sensors containing a tetraamine binding subunit (4 and s), quenching proceeds copper complexes electron trattsferenergy transfer fluoreseaE. ~~1 1 8 0~) * by an energy-transfer process. Selective metal binding and recognition can be achieved by varying the pH, and metal ions can be distinguished (e.g., Cu" from Ni") by spectrofluorimetric titration experiments in buffered solutions. Whereas systems 2, 3 and 5 show reversible metal binding behaviour, the cyclam-containing system 4 irreversibly incorporates transition metals (due to the kinetic macrocyclic effect) and cannot work properly as a senIn the supramolecular world, a sensor is a two-component system in which the specific receptor for the intended substrate is connected to a subunit capable of signalling the occurrence of the receptor-substrate interaction. The signal is given by a drastic change of a property: thus sensor eficiency is related to the ease of detecting such a property and measuring its intensity over a substantial concentration range, possibly down to trace level, as well as to receptor specificity. In this context, j7uores-cence is a convenient property to investigate. Fluorescence is visible, can be determined in real time without excessively sophisticated and expensive instrumentation and, if the appropriate fluorophore is chosen, can be safely monitored at a concentration level as low as ~O -' M . Efficient sensing should involve variation of the investigated property by at least two orders of magnitude: in spectrofluorimetric measurements, such a situation would correspond to full quenching or to complete revival of the emission intensity.During the last decade, a number of fluorescent sensors has been designed for s-block metal ions.['] Most of them operate by a photoinduced electron-transfer (PET) mechanism.['] In a classic example from the de Silva group, the binding component of the sensor is an NO, crown, which is linked through the amine nitrogen atom to the powerful light-emitting fragment anthracene by a methylene group.131 The uncomplexed sensor 1 is not fluorescent, as the photoexcited fluorophore is deactivated by a nonradiative mode through the transfer of an electron from the highly re-(e.g., of a K' ion), the metal-ligand interaction decreases the amine oxidation potential drastically and prevents the electron transfer. As a consequence, the intense and characteristic anthracene emission is largely restored.We were interested in dev...

Asymmetric branched gold nanoparticles are obtained using for the first time in the seed-growth approach a zwitterionic surfactant, laurylsulfobetaine, whose concentration in the growth solution allows to control both the length to base-width ratio of the branches and the LSPR position, that can be tuned in the 700-1100 nm near infrared range.