Au(I)-BSA nanocomposites with assembling-induced excitation-dependent multicolor emission for dynamic cell imaging

Excitation wavelength dependent (Ex-De) luminescent materials have attracted intense attention due to their great potential in multicolor bioimaging, dynamic anti-counterfeiting, and light emitting devices. However, it remains a formidable challenge to construct an Ex-De luminescent biomaterial with green starting materials, excellent biocompatibility, good water solubility, and multiple color emission for dynamic cell imaging. In this work, nanocomposites based on the facile self-assembly strategy of bovine serum albumin (BSA) and Au(I)-complex are rationally designed and synthesized to simultaneously present Ex-De fluorescence (429–516 nm) and decent phosphorescence (∼615 nm) in a dilute aqueous solution. Combinatory analyses of spectroscopic and microscopic results reveal that the luminescent mechanism of Au(I)-BSA nanocomposites is cluster-induced Ex-De fluorescence and metal-to-ligand charge transition (MLCT) based phosphorescence. Importantly, based on the excellent biocompatibility, water-solubility and color-tunable emission over the entire visible region (360–800 nm), the Au(I)-BSA nanocomposites are successfully used for cell imaging with multiple and switchable colors on demand. What is more, the solid tablets of Au(I)-BSA nanoparticles showed pressure-responsive luminescence and decent room temperature phosphorescence. This work provides an assembling-induced emission strategy for the design of water-soluble, non-cytotoxic, and color-tunable luminescent biomaterials based on the composite of protein and Au nanoparticles.