Thiolated Cyanines Appended to Partially Pegylated Gold Nanoparticles for Fluorescence Quenching of Two-Channel Photothermal Inks.

Following a new approach, we prepared a nanoink with two separate photothermally responsive absorption bands. One is the localized surface plasmon resonance (LSPR) absorption of gold nanoparticles (AuNP, d =17 nm), the second is the absorption band of two cyanine (Cy) dyes, Cy7-C6 or Cy7-C11, grafted to the AuNP surface through thiolated bridges of different lengths: the close proximity to the Au surface induces full quenching of the Cy fluorescence, resulting in thermal relaxation on irradiation. Attempts to full coat AuNP with the lipophilic Cy7-C6 and Cy7-C11 lead to precipitation from aqueous solutions. We thus prepared AuNP with partial pegylation (30, 50, or 70%), using a long chain thiol-terminated PEG bearing a -COOH function. Addition until saturation of either Cy7-C6 or Cy7-C11 to the partially pegylated AuNP gave the AuNP@Cy/PEGX% hybrids (X = 30, 50, 70) that are stable in water and in the water/alcohol mixtures used to prepare the nanoinks. Further overcoating of AuNP@Cy7-C6/PEG50% with PAH (polyallylamine hydrochloride) avoids LSPR hybridization in the dry nanoink printouts, that present two separate bands. When irradiated with laser sources near their absorption maxima, the printouts of the AuNP@Cy7-C6/PEG50%@PAH nanoink respond on two channels, giving different temperature increases depending on the irradiation wavelength.

Gold Nanoparticles Contact with Cancer Cell: A Brief Update.

The fine-tuning of the physicochemical properties of gold nanoparticles has facilitated the rapid development of multifunctional gold-based nanomaterials with diagnostic, therapeutic, and therapeutic applications. Work on gold nanoparticles is increasingly focusing on their cancer application. This review provides a summary of the main biological effects exerted by gold nanoparticles on cancer cells and highlights some critical factors involved in the interaction process (protein corona, tumor microenvironment, surface functionalization). The review also contains a brief discussion of the application of gold nanoparticles in target discovery.

A Supramolecular Approach to Antimicrobial Surfaces.

In this paper, we report on the preparation of Imidazole-functionalized glass surfaces, demonstrating the ability of a dinuclear Cu(II) complex of a macrocyclic ligand to give a "cascade" interaction with the deprotonated forms of grafted imidazole moieties. In this way, we realized a prototypal example of an antimicrobial surface based on a supramolecular approach, obtaining a neat microbicidal effect using low amounts of the described copper complex.

Novel photo-thermally active polyvinyl alcohol-Prussian blue nanoparticles hydrogel films capable of eradicating bacteria and mitigating biofilms.

Antibacterial treatment is an essential issue in many diverse fields, from medical device treatments (for example prostheses coating) to food preservation. However, there is a need of novel and light-weight materials with high antibacterial efficiency (preferably due to the physical activation). Utilization of photo-thermally active nanoparticles can lead to novel and re-usable materials that can be remotely activated on-demand to thermally eradicate bacteria and mitigate biofilm formation, therefore meeting the above challenge. In this study polyvinyl alcohol (PVA) hydrogel films containing non-toxic and highly photo-thermally active Prussian blue (PB) nanoparticles were fabricated. The confocal microscopy studies indicated a uniform nanoparticle distribution and a low degree of aggregation. Upon near-infrared (NIR; 700 and 800 nm) light irradiation of PVA-PB films, the local temperature increases rapidly and reaches a plateau (up to ΔT â‰… 78 °C), within ≈6-10 s under relatively low laser intensities, I â‰… 0.3 W cm-2. The high and localized increase of temperature on the fabricated films resulted in an efficient antibacterial effect on Pseudomonas aeruginosa (P. aeruginosa) bacteria. In addition, the localized photo-thermal effect was also sufficient to substantially mitigate biofilms growth.

Chitosan Oleate Coated Poly Lactic-Glycolic Acid (PLGA) Nanoparticles versus Chitosan Oleate Self-Assembled Polymeric Micelles, Loaded with Resveratrol.

Chitosan oleate (CS-OA), a chitosan salt with amphiphilic properties, has demonstrated the ability to self-assemble in aqueous environment to give polymeric micelles useful to load poorly soluble drugs. More recently, CS-OA was proposed to stabilize nanoemulsions during the preparation by emulsification and solvent evaporation of poly lactic-glycolic acid (PLGA) nanoparticles (NPs) loaded with curcumin. Positive mucoadhesive behavior and internalization properties were demonstrated for these NPs attributable to the presence of positive charge at the NP surface. In the present paper, two CS-OA-based nanosystems, micelles and PLGA NPs, were compared with the aim of elucidating their physico-chemical characteristics, and especially their interaction with cell substrates. The two systems were loaded with resveratrol (RSV), a hydrophobic polyphenol endowed with anti-cancerogenic, anti-inflammatory, and heart/brain protective effects, but with low bioavailability mainly due to poor aqueous solubility. Calorimetric analysis and X-ray spectra demonstrated amorphization of RSV, confirming its affinity for hydrophobic domains of polymeric micelles and PLGA core of NPs. TGA decomposition patterns suggest higher stability of PLGA-NPs compared with polymeric micelles, that anyway resulted more stable than expected, considering the RSV release profiles, and the cell line interaction results.

Prussian Blue Nanoparticles as a Versatile Photothermal Tool.

Prussian blue (PB) is a coordination polymer studied since the early 18th century, historically known as a pigment. PB can be prepared in colloidal form with a straightforward synthesis. It has a strong charge-transfer absorption centered at ~700 nm, with a large tail in the Near-IR range. Irradiation of this band results in thermal relaxation and can be exploited to generate a local hyperthermia by irradiating in the so-called bio-transparent Near-IR window. PB nanoparticles are fully biocompatible (PB has already been approved by FDA) and biodegradable, this making them ideal candidates for in vivo use. While papers based on the imaging, drug-delivery and absorbing properties of PB nanoparticles have appeared and have been reviewed in the past decades, a very recent interest is flourishing with the use of PB nanoparticles as photothermal agents in biomedical applications. This review summarizes the syntheses and the optical features of PB nanoparticles in relation to their photothermal use and describes the state of the art of PB nanoparticles as photothermal agents, also in combination with diagnostic techniques.

Thermal and Chemical Stability of Thiol Bonding on Gold Nanostars.

The stability of thiol bonding on the surface of star-shaped gold nanoparticles was studied as a function of temperature in water and in a set of biologically relevant conditions. The stability was evaluated by monitoring the release of a model fluorescent dye, Bodipy-thiol (BDP-SH), from gold nanostars (GNSs) cocoated with poly(ethylene glycol) thiol (PEG-SH). The increase in the BDP-SH fluorescence emission, quenched when bound to the GNSs, was exploited to this purpose. A maximum 15% dye release in aqueous solution was found when the bulk temperature of gold nanostars solutions was increased to T = 42 °C, the maximum physiological temperature. This fraction reduces 3-5% for temperatures lower than 40 °C. Similar results were found when the temperature increase was obtained by laser excitation of the near-infrared (NIR) localized surface plasmon resonance of the GNSs, which are photothermally responsive. Besides the direct impact of temperature, an increased BDP-SH release was observed upon changing the chemical composition of the solvent from pure water to phosphate-buffered saline and culture media solutions. Moreover, also a significant fraction of PEG-SH was released from the GNS surface due to the increase in temperature. We monitored it with a different approach, that is, by using a coating of α-mercapto-ω-amino PEG labeled with tetramethylrhodamine isothiocyanate on the amino group, that after heating was separated from GNS by ultracentrifugation and the released PEG was determined by spectrofluorimetric techniques on the supernatant solution. These results suggest some specific limitations in the use of the gold-thiolate bond for coating of nanomaterials with organic compounds in biological environments. These limitations come from the duration and the intensity of the thermal treatment and from the medium composition and could also be exploited in biological media to modulate the in vivo release of drugs.

Novel DFO-SAM on mesoporous silica for iron sensing. Part I. Synthesis optimization and characterization of the material.

The synthesis and the physico-chemical characterisation of a novel solid phase, designed for iron(iii) sorption, are presented. The solid (indicated in the following as DFO-SAMMS) is made with a hydroxamate siderophore, the deferoxamine (DFO), covalently bound on a self-assembled monolayer on mesoporous silica (SAMMS). The data demonstrate that the DFO molecules are bound to the solid material, grafted on the surface and do not enter the silica pores. A new one-pot synthesis is presented in which DFO is dissolved in DMSO, and left to react with GPTMS with stirring overnight. In the same mixture, SAMMS is added to get the final product. The optimisation of experimental conditions of this novel one-pot synthesis is presented, with results indicating that a temperature of 90 °C, for the reaction between DFO and GPTMS, and the use of MCM-41 silica are the most convenient conditions. The kinetics of sorption reveals that the iron uptake is relatively fast, around 100 min at pH = 2.5, and from the sorption profile of iron(iii), the estimated capacity of the product obtained under optimized conditions was higher than 0.3 mmol g(-1). The results found in the present research are very promising for application in real biological samples.

Nanomaterials for Photothermal Antimicrobial Surfaces.

Microbial infection diseases are a major threat to human health and have become one of the main causes of mortality. The search for novel antimicrobial strategies is an important challenge for the scientific community, considering also the constant increase of antimicrobial resistance and the rise of new diseases. Among the new strategies to combat microbial infections, the photothermal effect seems to be one of the most promising. Hyperthermia is an effective and broad spectrum strategy for the removal of microbial infections. Among all of the strategies to reduce the diffusion of microbial infections, the preparation of antimicrobial surfaces seems of primary importance. In many cases, in fact, an infection can be diffused through surfaces just by touching them, or by inoculating microbes through an internalizable device, such as an implant, a prosthesis, or a catheter. In this review, we will summarize the recent advances in the preparation of photothermal antibacterial surfaces.

Amphiphilic copolymers based on poly[(hydroxyethyl)-D,L-aspartamide]: a suitable functional coating for biocompatible gold nanostars.

Novel amphiphilic copolymers have been synthesized based on a biocompatible poly(hydroxyethylaspartamide) (PHEA) backbone, bearing both anchoring groups for gold nanoparticles, such as thiols and disulfide, and conjugable moieties, such as amino groups, the latter as points suitable for appending further functional agents. The strategy was to functionalize α,ß-poly[(N-2-hydroxyethyl)-D,L-aspartamide] (PHEA) with PEG2000-NH2 and with ethylenediamine (EDA) obtaining a partially pegylated copolymer with a large number of pendant primary amino groups. A fraction of the latter was conjugated with molecules bearing terminal thiol moieties such as 12-mercaptododecanoic acid (MDA) and disulfide groups such as lipoic acid (LA), obtaining the two amphiphilic derivatives PHEA-PEG2000-EDA-MDA (PPE-MDA) and PHEA-PEG2000-EDA-LA (PPE-LA), which also proved intrinsically able to self-assemble in polymeric micelles. The two copolymers efficiently coated gold nanostars (GNSs, size ≈ 40 nm), wrapping around the surface increasing only slightly the hydrodynamic diameter (reaching ≈ 45 nm), imparting them stability and a pH-switchable surface charge, due to the unreacted amino groups. Remarkably, the poor solvation and the huge steric hindrance experienced by the amino groups lowers the observed logarithmic protonation constants to 5.6-5.7. In vitro experiments demonstrated that PPE-MDA and PPE-LA copolymers have an intrinsic excellent biocompatibility in both the human brain neuroblastoma (SH-SY5Y) and human bronchial epithelial (16-HBE) cell lines. Interaction of the same cell lines with "nude" GNS and GNS coated with PPE-LA was also studied, disclosing a completely satisfactory biocompatibility of the latter.

Localized surface plasmon resonance with five-branched gold nanostars in a plastic optical fiber for bio-chemical sensor implementation.

In this paper a refractive index sensor based on localized surface plasmon resonance (LSPR) in a Plastic Optical Fiber (POF), is presented and experimentally tested. LSPR is achieved exploiting five-branched gold nanostars (GNS) obtained using Triton X-100 in a seed-growth synthesis. They have the uncommon feature of three localized surface plasmon resonances. The strongest LSPRs fall in two ranges, one in the 600-900 nm range (LSPR 2) and the other one in the 1,100-1,600 nm range (LSPR 3), both sensible to refractive index changes. Anyway, due to the extremely strong attenuation (>10(2) dB/m) of the employed POF in the 1,100-1,600 nm range, only LSPR 2 will be exploited for refractive index change measurements, useful for bio-chemical sensing applications, as a proof of principle of the possibility of realizing a compact, low cost and easy-to-use GNS based device.

Dual mode antibacterial surfaces based on Prussian blue and silver nanoparticles.

Prussian Blue (PB) is an inexpensive, biocompatible, photothermally active material. In this paper, self-assembled monolayers of PB nanoparticles were grafted on a glass surface, protected with a thin layer of silica and decorated with spherical silver nanoparticles. This combination of a photothermally active nanomaterial, PB, and an intrinsically antibacterial one, silver, leads to a versatile coating that can be used for medical devices and implants. The intrinsic antibacterial action of nanosilver, always active over time, can be enhanced on demand by switching on the photothermal effect of PB using near infrared (NIR) radiation, which has a good penetration depth through tissues and low side effects. Glass surfaces functionalized by this layer-by-layer approach have been characterized for their morphology and composition, and their intrinsic and photothermal antibacterial effect was studied against Gram+ and Gram- planktonic bacteria.

Enhanced in vitro immersion behavior and antibacterial activity of NiTi orthopedic biomaterial by HAp-Nb2O5 composite deposits.

NiTi is a class of metallic biomaterials, benefit from superelastic behavior, high biocompatibility, and favorable mechanical properties close to that of bone. However, the Ni ion leaching, poor bioactivity, and antibacterial activity limit its clinical applications. In this study, HAp-Nb2O5 composite layers were PC electrodeposited from aqueous electrolytes containing different concentrations of the Nb2O5 particles, i.e., 0-1 g/L, to evaluate the influence of the applied surface engineering strategy on in vitro immersion behavior, Ni2+ ion leaching level, and antibacterial activity of the bare NiTi. Surface characteristics of the electrodeposited layers were analyzed using SEM, TEM, XPS, and AFM. The immersion behavior of the samples was comprehensively investigated through SBF and long-term PBS soaking. Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) infective reference bacteria were employed to address the antibacterial activity of the samples. The results illustrated that the included particles led to more compact and smoother layers. Unlike bare NiTi, composite layers stimulated apatite formation upon immersion in both SBF and PBS media. The concentration of the released Ni2+ ion from the composite layer, containing 0.50 g/L Nb2O5 was ≈ 60% less than that of bare NiTi within 30 days of immersion in the corrosive PBS solution. The Nb2O5-reinforced layers exhibited high anti-adhesive activity against both types of pathogenic bacteria. The hybrid metallic-ceramic system comprising HAp-Nb2O5-coated NiTi offers the prospect of a potential solution for clinical challenges facing the orthopedic application of NiTi.

Prussian Blue nanoparticles: An FDA-approved substance that may quickly degrade at physiological pH.

Prussian blue (PB) is a coordination polymer based on the Fe2+…CN…Fe3+ sequence. It is an FDA-approved drug, intended for oral use at the acidic pH of the stomach and of most of the intestine track. However, based on FDA approval, a huge number of papers proposed the use of PB nanoparticles (PBnp) under "physiological conditions", meaning pH buffered at 7.4 and high saline concentration. While most of these papers report that PBnp are stable at this pH, a small number of papers describes instead PBnp degradation at the same or similar pH values, i.e. in the 7-8 range. Here we give a definitively clear picture: PBnp are intrinsically unstable at pH ≥ 7, degrading with the fast disappearance of their 700 nm absorption band, due to the formation of OH- complexes from the labile Fe3+ centers. However, we show also that the presence of a polymeric coating (PVP) can protect PBnp at pH 7.4 for over 24 h. Moreover, we demonstrate that when "physiological conditions" include serum, a protein corona is rapidly formed on PBnp, efficiently avoiding degradation. We also show that the viability of PBnp-treated EA.hy926, NCI-H1299, and A549 cells is not affected in a wide range of conditions that either prevent or promote PBnp degradation.

Antibacterial activity of glutathione-coated silver nanoparticles against Gram positive and Gram negative bacteria.

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.

Optical method for predicting the composition of self-assembled monolayers of mixed thiols on surfaces coated with silver nanoparticles.

With a simple optical method, based on UV-vis absorption spectra on glass slides, it is possible to predict the composition of self-assembled monolayers of mixed thiols, grafted on monolayers of silver nanoparticles. Glass slides are modified with the layer-by-layer technique, first forming a monolayer of mercaptopropyltrimethoxysilane, then grafting a monolayer of silver nanoparticles on it. These surfaces are further coated by single or mixed thiol monolayers, by dipping the slides in toluene solutions of the chosen thiols. Exchange constants are calculated for the competitive deposition between the colorless 1-dodecanethiol or PEG5000 thiol and BDP-SH, with the latter being a thiol-bearing molecule containing the strongly absorbing BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety, synthesized on purpose. The constants are calculated by determining the fraction of BDP-SH deposited on the surface from a solution with a given molar fraction, directly measuring the absorption spectra of BDP-SH on the slides. Then, the exchange constant for the competitive deposition between 1-dodecanethiol and PEG5000 thiol is calculated by combining their exchange constants with BDP-SH. This allows to predict the fraction of the two colorless thiols coating the silver nanoparticles slides obtained from a toluene solution with a given molar fraction, for example, of PEG5000 thiol. The correctness of the calculated surface fraction is verified by studying the coating competition between 1-dodecanethiol and a PEG5000 thiol remotely modified with a strongly absorbing fluorescein fragment.

Surface-Enhanced Raman Spectroscopy Chips Based on Silver Coated Gold Nanostars.

Surface-enhanced Raman scattering (SERS) is becoming widely used as an analytical tool, and the search for stable and highly responsive SERS substrates able to give ultralow detection of pollutants is a current challenge. In this paper we boosted the SERS response of Gold nanostars (GNS) demonstrating that their coating with a layer of silver having a proper thickness produces a 7-fold increase in SERS signals. Glass supported monolayers of these GNS@Ag were then prepared using simple alcoxyliane chemistry, yielding efficient and reproducible SERS chips, which were tested for the detection of molecules representative of different classes of pollutants. Among them, norfloxacin was detected down to 3 ppb, which is one of the lowest limits of detection obtained with this technique for the analyte.

Gold Nanostars Embedded in PDMS Films: A Photothermal Material for Antibacterial Applications.

Bacteria infections and related biofilms growth on surfaces of medical devices are a serious threat to human health. Controlled hyperthermia caused by photothermal effects can be used to kill bacteria and counteract biofilms formation. Embedding of plasmonic nano-objects like gold nanostars (GNS), able to give an intense photothermal effect when irradiated in the NIR, can be a smart way to functionalize a transparent and biocompatible material like polydimethylsiloxane (PDMS). This process enables bacteria destruction on surfaces of PDMS-made medical surfaces, an action which, in principle, can also be exploited in subcutaneous devices. We prepared stable and reproducible thin PDMS films containing controllable quantities of GNS, enabling a temperature increase that can reach more than 40 degrees. The hyperthermia exerted by this hybrid material generates an effective thermal microbicidal effect, killing bacteria with a near infrared (NIR) laser source with irradiance values that are safe for skin.

Fast dissolution of silver nanoparticles at physiological pH.

While silver nanoparticles (AgNP) are used in topical treatments and medical devices for humans, no smooth, safe remedy exists to remove them and avoid possible post-treatment uptake in the body. We show here that cysteamine hydrochloride (CYS∙HCl), a simple FDA and EMA approved molecule, is able to dramatically accelerate the otherwise extremely slow oxidation of citrate-coated AgNP by O2 in a wide range of pH, including the physiological 7.4 value, obtaining the halving of AgNP concentration in t < 10 min. The dependence of oxidation kinetics on CYS concentration and pH is studied, finding faster processes on increasing CYS and basicity, despite the decrease of O2 reduction potential. Complexation and electrochemical studies demonstrate that CYS adhesion to AgNP surface followed by formation of 1:2 Ag+:CYS complex is the driving force for the AgNP oxidation, this also giving a definitive explanation to the otherwise still unclear phenomenon of AgNP etching by thiols. The efficacy of CYS∙HCl is verified also on AgNP coated with pectin and PEG-SH, and on AgNP immobilized on surfaces.

Nanocomposite Sprayed Films with Photo-Thermal Properties for Remote Bacteria Eradication.

Currently there is a strong demand for novel protective materials with efficient antibacterial properties. Nanocomposite materials loaded with photo-thermally active nanoparticles can offer promising opportunities due to the local increase of temperature upon near-infrared (NIR) light exposure capable of eradicating bacteria. In this work, we fabricated antibacterial films obtained by spraying on glass slides aqueous solutions of polymers, containing highly photo-thermally active gold nanostars (GNS) or Prussian Blue (PB) nanoparticles. Under NIR light irradiation with low intensities (0.35 W/cm2) these films demonstrated a pronounced photo-thermal effect: ΔTmax up to 26.4 °C for the GNS-containing films and ΔTmax up to 45.8 °C for the PB-containing films. In the latter case, such a local temperature increase demonstrated a remarkable effect on a Gram-negative strain (P. aeruginosa) killing (84% of dead bacteria), and a promising effect on a Gram-positive strain (S. aureus) eradication (69% of dead bacteria). The fabricated films are promising prototypes for further development of lightweight surfaces with efficient antibacterial action that can be remotely activated on demand.