Expanding Toolbox of Imageable Protein-Gold Hybrid Materials

As a new class of bio-abiotic hybrid materials, a series of highly fluorescent self-assembled protein-gold hybrid materials (PGHMs) with different emission wavelengths (blue (B), green (G), yellow (Y), and red (R) colored under UV irradiation) are synthesized by using various combinations of proteins and free amino acids as stabilizer and reducing agents. The synthesis process was controllable by modulating the pH of the reaction solutions. The synthesized PGHMs (PGHM-Blue (PGHM-B), PGHM-Green (PGHM-G), PGHM-Yellow (PGHM-Y), and PGHM-Red (PGHM-R)) exhibited distinct fluorescent properties and showed low cytotoxicity as justified by a bacteria-based test system. The sizes of PGHMs are approximately 100 nm with gold core diameters 0.8–1.8 nm as shown by SEM and TEM images. The assembly of PGHMs was dynamic and occurred through a free radical associated cross-linking process. This general strategy expanded the toolbox of protein-gold hybrid materials. The photostable bio-abiotic hybrid fluorescent nanomaterials can be an alternative to conventional fluorescent probes such as organic dyes and quantum dots for bioimaging studies.