Self-assembly of thiolated cyanine aggregates on Au(111) and Au nanoparticle surfaces

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 wavelengths. This enhances the potentiality of use of these nanoinks for photothermal anticounterfait printouts, making more difficult to reproduce the correct ΔT vs λirradiation output.

Gold nanorod/molybdenum sulfide core-shell nanostructures synthesized by a photo-induced reduction process

Coupling of plasmonic nanostructures and semiconductors gives promising hybrid nanostructures that can be used in different applications such as photosensing and energy conversion. In this report, we describe an approach for fabricating a new hybrid material by coupling a gold nanorod (Au NR) core and amorphous molybdenum sulfide (MoS_x) shell. The Au NR/MoS_x core-shell structure is achieved by exploiting the hot electrons generated in the plasmonic excitation of Au NRs to drive the reduction of [MoS₄]^2-, which is pre-adsorbed on the Au NR surface, producing a thin MoS_x layer. This approach allows us to control the thickness of the MoS_x coating layer on the Au NR surface. The resultant Au NR/MoS_x hybrid is characterized by absorption spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy elemental mapping, x-ray diffraction and x-ray photoelectron spectroscopy.

Organo-soluble porphyrin mixed monolayer-protected gold nanorods with intercalated fullerenes

Organo-soluble porphyrin mixed monolayer-protected gold nanorods were synthesized and characterized. The resulting gold nanorods encapsulated by both porphyrin thiol and alkyl thiol on their entire surface with strong covalent Au-S linkages were very stable in organic solvents without aggregation or decomposition and exhibited unique optical properties different from their corresponding spherical ones. Alkyl thiol acts as a stabilizer not only to fill up the potential space on gold nanorod surface between bulky porphyrin molecules but also to provide space for further insertion of C(60) molecules forming a stable C(60)-porphyrin-gold nanorod hybrid nanostructure.