Influence of Gold/Silver Ratio in Ablative Nanoparticles on Their Interaction with Aptamers and Functionality of the Obtained Conjugates

Nano-bio-conjugates, featuring noble metal gold–silver alloy nanoparticles, represent a versatile tool in diagnostics and therapeutics due to their plasmonic and antimicrobial properties tunable by the particle’s gold molar fraction. However, little is known about how the binding of thiolated biomolecules to noble metal nanoparticles is influenced by the fraction of gold and silver atoms on the nanoparticle’s surface and to which extend this would affect the functionality of the conjugated biomolecules. In this work, we generated gold–silver alloy nanoparticles with average diameters of 7–8 nm using the modern, surfactant-free laser ablation in liquids (LAL) synthesis approach. We conjugated them with thiolated miniStrep aptamer ligands at well-controlled aptamer-to-nanoparticle surface area ratios with maxima between 12 and 27 pmol aptamer/cm2 particle surface area. The results revealed a clear correlation between surface coverage and the nanoparticles’ nominal gold/silver ratio, with maximum coverage reached for gold-rich alloys and a pronounced maximum for silver-rich alloys. However, the conjugates’ functionality, evaluated by binding of streptavidin, was surprisingly robust and hardly affected by the nominal composition. However, 1.5 times higher surface coverage was needed to obtain maximum functionality in the silver-rich conjugates. Based on these results, it may be concluded that the nominal composition of gold–silver alloy nano-bioconjugates is freely tunable without a pronounced impact on the attached ligands’ functionality, a finding highly relevant for the flexible design of nano-bio-conjugates for future biomedical applications. This study’s results may facilitate the design of alloy nano-bio-conjugates for future applications in therapeutics and diagnostics.