The fate of differently functionalized gold nanorods in human serum: A response from capillary electrophoresis-inductively coupled plasma mass spectrometry

- A CE-ICP-MS method for the speciation of gold nanorods is optimized.
- Free and protein-bound nanorods are for the first time characterized in human serum.
- Surface functionalization has an impact of protein-mediated transformations.

A highly selective and sensitive method was developed to characterize intrinsic intramolecular interactions between potential theranostic agents, gold nanorods (AuNRs), and plasma proteins. The method is based on a hyphenation of capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS), which enables monitoring the speciation changes of AuNRs under physiologically compatible conditions. To improve the separation resolution between the intact nanorods and different gold-protein conjugates, the CE system was optimized by varying the type and concentration of background electrolyte, applied voltage, and sample loading. Optimization allowed also for acquiring the acceptable figures of merit such as migration time and peak area precision of 4.7-8.2% and 5.1-6.3%, respectively, detection limits in the range of 5.5-5.7 μg L−1 Au, and recoveries on the order of 91-99%. With the developed method the metal-specific profiles were recorded for differently functionalized AuNPs in combinations with individual serum proteins and in human serum. In case of carboxy-modified AuNPs, proteinization in real-serum environment occurs without albumin participation, apo-transferrin dominating the protein corona under equilibrium conditions. On the contrary, the AuNRs with surface amino-groups first form the albumin conjugate but albumin in this “soft” corona becomes slowly replaced by other, less abundant proteins, exhibiting a higher affinity toward the aminated surface.