Molecular Surface Quantification of Multi-Functionalized Gold Nanoparticles Using UV-Vis Spectroscopy Deconvolution

: Multi-functional gold nanoparticles (AuNPs) are of great interest, owing to their vast potential for use in many areas including sensing, imaging, delivery, and medicine. A key factor in determining the biological activity of multi-functional AuNPs is the quantification of surface conjugated molecules. There has been a lack of accurate methods to determine this for multi-functionalized AuNPs. In this work, we address this limitation by using a new method based on deconvolution and Levenberg-Marquardt algorithm fitting of UV-Vis spectrum to calculate the precise concentration and number of cytochrome C (Cyt C) and Zinc Porphyrin (Zn Porph) bound to each multi-functional AuNP. Dynamic light scattering (DLS), Zeta potential measurements, and Transmission Electron Microscopy (TEM) were used to confirm the functionalization of AuNPs with Cyt C and Zn Porph. Despite the overlapping absorption bands of Cyt C and Zn Porph this method was able to reveal the accurate concentration and number of Cyt C and Zn Porph molecules attached per AuNP. Furthermore, using this method we were able to identify unconjugated molecules, suggesting the need for further purification of the sample. This guide provides a simple and effective method to quickly quantify molecules bound to AuNPs, giving users accurate and valuable information, especially for applications in drug delivery and biosensors.