Monolayers of gold nanostars with two near-IR LSPRs capable of additive photothermal response.

Monolayers of photothermally responsive gold nanostars on PEI-coated surfaces display two localized surface plasmon resonances (LSPRs) in the near-IR region that can be laser-irradiated either separately, obtaining two different T jumps, or simultaneously, obtaining a T jump equal to the sum of those obtained with separate irradiations.

Gold nanostars coated with neutral and charged polyethylene glycols: A comparative study of in-vitro biocompatibility and of their interaction with SH-SY5Y neuroblastoma cells.

Gold nanostars (GNS) have been coated with four different polyethylene glycols (PEGs) equipped with a -SH function for grafting on the gold surface. These PEGs have different chain lengths with average MW=2000, 3000, 5000 and average number of -O-CH2-CH2 - units 44, 66, and 111, respectively. Two are neutral and two are terminated with -COOH and -NH2 functions, thus bearing negative and positive charges at physiological pH, thanks to the formation of carboxylate and ammonium groups. The negative charge of the GNS coated with PEG carboxylate has also been exploited to further coat the GNS with the PAH (polyallylamine hydrochloride) cationic polymer. Vitality tests have been carried out on SH-SY5Y cells treated with the five differently coated GNS for 4, 24, and 48 h, at Au concentrations ranging from 1.25 to 100 µg/mL. The same tests have been repeated with the pure PEGs and PAH. Excellent biocompatibility was found for all PEGs, independently on charge and chain length, both for coated GNS and for the pure polymers. On the contrary, poor biocompatibility was found for PAH overcoated GNS and for pure PAH, although the latter only at high concentrations. Exploiting the two-photon luminescence of GNS, we have found by confocal laser scanning microscopy that when GNS are coated with PEGs they do not enter SH-SY5Y cells, while when overcoated with PAH they massively penetrate into the cytoplasm. This causes cell death by dramatically changing cell morphology, as demonstrated also by atomic force microscopy.

Gold nanostars co-coated with the Cu(II) complex of a tetraazamacrocyclic ligand.

The twelve-membered tetraazamacrocyclic ligand L1 bears an appended lipoic acid unit, whose disulphide ring is an efficient grafting moiety for the surface of gold nanostars (GNS). The GNS that were used featured a localized surface plasmon resonance (LSPR) absorption at ∼800 nm, i.e. in the near infrared (NIR). We investigated different approaches for coating them with the Cu(2+) complex of L1. While the direct reaction of [CuL1](2+) with as-prepared GNS led to aggregation, an initial coating step with polyethyleneglycol-thiol (PEG-SH) was found to be advantageous. Displacement reactions were carried out on pegylated GNS either with [CuL1](2+), directly generating [Cun(L1@GNS)](2n+), or with void L1, thus obtaining @GNS that coordinates Cu(2+) in a second step. In both cases, even with a large excess of the competing disulphide moiety, only partial displacement of PEG-SH is observed, obtaining ca. 500-1500 [CuL1](2+) per GNS depending on the conditions, with PEG-SH remaining in the [Cun(L1@GNS)](2n+) hybrids and imparting them with remarkable stability. Comparison of the photothermal and two-photon luminescence (TPL) properties of the GNS between the pegylated GNS and [Cun(L1@GNS)](2n+) revealed that the grafted copper complex does not change them to any extent. Finally, the stability against demetallation and transmetallation of the complexes, as well as the fast kinetics of complexation of the monodispersed macrocycle and of L1@GNS, have been examined, suggesting [Cun(L1@GNS)](2n+) as a device capable of TPL optical tracking and NIR photothermal therapy and as a possible agent for PET imaging.

Self-assembled monolayers of gold nanostars: a convenient tool for near-IR photothermal biofilm eradication.

Monolayers of gold nanostars (GNS) are grafted on mercaptopropyltrimethoxysilane-coated glass slides. In the formed monolayers the localized surface plasmon resonance of GNS can be tuned in the 700-1100 nm range. Upon laser excitation of the nearIR LSPR an efficient photothermal response is observed, inducing local hyperthermia and efficient killing of Staphylococcus aureus biofilms.

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.

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.

Triton X-100 for three-plasmon gold nanostars with two photothermally active NIR (near IR) and SWIR (short-wavelength IR) channels.

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.

A molecular thermometer for nanoparticles for optical hyperthermia.

We developed an all-optical method to measure the temperature on gold (nanorods and nanostars) and magnetite nanoparticles under near-infrared and radiofrequency excitation by monitoring the excited state lifetime of Rhodamine B that lies within =/~20 nm from the nanoparticle surface. We reached high temperature sensitivity (0.029 ± 0.001 ns/°C) and low uncertainty (±0.3 °C). Gold nanostars are =/~3 and =/~100 times more efficient than gold nanorods and magnetite nanoparticles in inducing localized hyperthermia.

Synthesis of rubrolide analogues as new inhibitors of the photosynthetic electron transport chain.

Many natural products have been used as a model for the development of new drugs and agrochemicals. Following this strategy 11 rubrolide analogues, bearing electron-withdrawing and -donating groups at both benzene rings, were prepared starting from commercially available mucobromic acid. The ability of all compounds to inhibit the photosynthetic electron transport chain in the chloroplast was investigated. The rubrolide analogues were effective in interfering with the light-driven ferricyanide reduction by isolated chloroplasts. The IC(50) values of the most active derivatives are in fact only 1 order of magnitude higher than those of commercial herbicides sharing the same mode of action, such as Diuron (0.27 µM). QSAR studies indicate that the most efficient compounds are those having higher ability to accept electrons, either by a reduction process or by an electrophilic reaction mechanism. The results obtained suggest that the rubrolide analogues represent promising candidates for the development of new active principles targeting photosynthesis to be used as herbicides.

Controlled synthesis of gold nanostars by using a zwitterionic surfactant.

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.