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_<i>n</i>(SR)_<i>m</i> NCs. Au₂₅(MPC)₁₈ and Au₄(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 Au₄(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 Au₄(MPC)₄ NCs