Functional-Group-Dependent Formation of Bioactive Fluorescent-Plasmonic Nanohybrids

We detail the assembly, driven by metal-affinity coordination, of fluorescent-plasmonic hybrid constructs that are also biologically active. The hybrid constructs are prepared by first assembling polymer-encapsulated luminescent quantum dots that present amine-, carboxy-, and lipoic acid-terminated groups (QD-FG) and plasmonic gold nanoparticles capped with rather low density of lipoic acid-appended zwitterion ligands (AuNP-LA-ZW). The dual QD-AuNP constructs were then coupled to polyhistidine-appended maltose binding proteins, yielding the final trifunctional assemblies. The coordination of amine-, carboxy-, and lipoic acid-terminated QDs with AuNP-LA-ZW was characterized using steady-state and time-resolved fluorescence quenching measurements. We measured rather different coordination affinities between the functional groups on the QDs and the AuNP surfaces. This assembly mode still allowed the partially exposed AuNPs in the inorganic/polymer hybrid to bind to polyhistidine-appended proteins. This protein assembly was confirmed using amylose affinity chromatography, which also confirmed the structural integrity of the hybrid and biological activity of the bound protein. Owing to the high colloidal stability of the surface-modified QDs and AuNP-LA-ZW, combined with flexible functionalization, we anticipate that this strategy could facilitate the integration of hybrid inorganic/polymer constructs with specific photophysical properties into biological systems.