2 research outputs found
Optical Properties of 2‑Methacryloyloxyethyl Phosphorylcholine-Protected Au<sub>4</sub> Nanoclusters and Their Fluorescence Sensing of C‑Reactive Protein
We present the solution synthesis
of thiolated 2-methacryloyloxyethyl
phosphorylcholine (MPC)-protected Au nanoclusters (NCs). This water-soluble
lipid-mimetic MPC was first used for the size focusing synthesis of
thiolate (SR)-protected Au<sub><i>n</i></sub>(SR)<sub><i>m</i></sub> NCs. Au<sub>25</sub>(MPC)<sub>18</sub> and Au<sub>4</sub>(MPC)<sub>4</sub> NCs are selectively synthesized, without
the need for electrophoretic or chromatographic isolation of size
mixed products, by including ethanol or not in the solvent. The Au<sub>4</sub>(MPC)<sub>4</sub> NCs emit at yellow wavelengths (580–600
nm) with a quantum yield (3.6%) and an average lifetime of 1.5 μs.
Also for the first time, we report C-reactive protein (CRP) sensing
using Au NCs, with a detection limit (5 nM) low enough for the clinical
diagnosis of inflammation. This is based on the quenching effect of
specific CRP–MPC interactions on the fluorescence of the Au<sub>4</sub>(MPC)<sub>4</sub> NCs
Generation of Singlet Oxygen by Photoexcited Au<sub>25</sub>(SR)<sub>18</sub> Clusters
The generation of highly reactive
singlet oxygen (<sup>1</sup>O<sub>2</sub>) is of major importance
for a variety of applications such
as photodynamic therapy (PDT) for cancer treatment, water treatment,
catalytic oxidation, and others. Herein, we demonstrate that <sup>1</sup>O<sub>2</sub> can be efficiently produced through the direct
photosensitization by Au<sub>25</sub>(SR)<sub>18</sub><sup>–</sup> clusters (H−SR = phenylethanethiol or captopril) without
using conventional organic photosensitizers under visible/near-IR
(532, 650, and 808 nm) irradiation. <sup>1</sup>O<sub>2</sub> was
successfully detected by direct observation of the characteristic <sup>1</sup>O<sub>2</sub> emission around 1276 nm as well as three different <sup>1</sup>O<sub>2</sub>-selective probes. Water-soluble Au<sub>25</sub>(captopril)<sub>18</sub><sup>–</sup> clusters were explored
for cytocompatibility and photodynamic activity toward cancer cells.
In addition, selective catalytic oxidation of organic sulfide to sulfoxide
by <sup>1</sup>O<sub>2</sub> was demonstrated on the photoexcited
Au<sub>25</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)<sub>18</sub><sup>–</sup> clusters. It is suggested that the optical gap of Au<sub>25</sub>(SR)<sub>18</sub> clusters (∼1.3 eV) being larger than the
energy of <sup>1</sup>O<sub>2</sub> (0.97 eV) allows for the efficient
energy transfer to <sup>3</sup>O<sub>2</sub>. In addition, the long
lifetime of the electronic excited states of Au<sub>25</sub>(SR)<sub>18</sub> and the well-defined O<sub>2</sub> adsorption sites are
the key factors that promote energy transfer from Au<sub>25</sub>(SR)<sub>18</sub><sup>–</sup> to molecular oxygen, thus facilitating
the formation of <sup>1</sup>O<sub>2</sub>. Finally, neutral Au<sub>25</sub>(SR)<sub>18</sub><sup>0</sup> can also produce <sup>1</sup>O<sub>2</sub> as efficiently as does the anionic Au<sub>25</sub>(SR)<sub>18</sub><sup>−</sup>