Optical Properties of 2-Methacryloyloxyethyl Phosphorylcholine-Protected Au₄ 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 n (SR) m NCs. Au 25 (MPC) 18 and Au 4 (MPC) 4 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 4 (MPC) 4 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 4 (MPC) 4 NCs.