Purification of Au/Au Core/Satellite Supraparticles by Asymmetric Flow Field Flow Fractionation for SERS Nanotag-based Applications

Over the last decades, nanoparticles have been increasingly used in biomedical applications, such as immunolabelling, requiring high control over size and shape. Nanoparticle synthesis often lacks the required reaction control which necessitates additional purification steps. For this purpose, asymmetric flow field flow fractionation (AFFF) is a powerful tool to purify particles and characterize them online. Here, we systematically studied the usability of AFFF for the purification of a colloid primarily containing self-assembled Au/Au core/satellite particles (C/S particles). In this case, purification of C/S particles from unbound monomeric AuNP satellites, which were added in excess during synthesis, is needed. We successfully demonstrated the effective separation of monomeric SERS-inactive AuNP satellites from the highly SERS-active C/S particles. While centrifugation is a commonly used and easy bench-top method, separation with AFFF offers an improved resolution and recovery. A linearly decreasing crossflow profile enabled us to achieve a separation with sufficient resolution and good recovery. Purified C/S colloids exhibit an increase in SERS activity of 25%, improving their usability for SERS-based applications by avoiding false-negative results.