Thermal and Chemical Stability of Thiol Bonding on Gold Nanostars

Abstract

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.

Photothermal effect of gold nanostar patterns inkjet-printed on coated paper substrates with different permeability

“…The much higher temperature increase achieved on the printed GNS patterns under ambient conditions compared to the values previously reported for GNS in aqueous solutions [17,30] is likely due to the absence of the thermal dissipation from the bulk solvent (water) that has a high thermal capacity compared to air (see the model provided in Supporting Information File 2). …”

Gold Nanostar Substrates for Metal-Enhanced Fluorescence through the First and Second Near-Infrared Windows

“…[54][55][56] SEM imaging showed that the surfaces of substrates fabricated with S-AuNS (Figure 3a) and L-AuNS ( Figure 3d) were densely populated by particles. SAuNS were more homogeneously distributed on the surface of glass substrates compared to L-AuNS, possibly due to an increased propensity of L-AuNS to aggregate in solution before self-assembly.…”

“…32 bBSA is known to bind to both glass and Au surfaces; on glass, through non-covalent physisorption, while on Au surfaces, through coordinative interaction between gold and the bBSA thiol groups. [54][55][56] When AuNS substrates were coated with bBSA monolayers, their LSPR peak positions were red-shifted by about 6-9 nm, due to the higher refractive index of bBSA compared to air ( Figure S4, Supporting Information). Similarly, a previous report showed bBSA provides a spacing of ~4-8 nm between the dye molecules and the Au surface, while the streptavidin attached to the dyes, provides an additional separation distance of ~4 nm, resulting to a total spacing of ~12 nm.…”

Photothermal effect of gold nanostars inkjet-printed on coated paper substrate under near-infrared irradiation

“…A steep temperature increase,turning into a plateau after 15-20 s, was observed in all cases as it shown in The measured values of temperature jump, ΔT max , indicate a photo-thermal effect much more effective than that previously observed in GNS solutions and for GNS monolayers. 10,13 As a comparison, control experiments performed by irradiating the blank paper substrate at the same laser intensities showed almost negligible photothermal effect (ΔT≤0.4°C). A measurable thermal load (ΔT max > 20 o C) was obtained even from the GNS patterns printed with low concentration of inks (C GNS = 0.042 mg/mL).…”

“…within the LSPR of these GNS. 13 The increase of temperature of these GNS solutions under NIR irradiation is shown in Figure 3. The temperature increases following an exponential growth law with average growth times ≅ 120-140 s up to a plateau value.…”