Complex Formation\nof Gold Nanoparticles with Collagen\nin Aqueous Media Studied by X‑ray Scattering and Absorption\nSpectroscopy

Small-angle X-ray scattering and UV–vis absorption\nmeasurements\nwere performed on mixed solutions of gold nanoparticles (AuNPs) and\natelocollagen (AC), triple-helical collagen without telopeptide, in\nacetate buffer at pH 4 under different temperature conditions, i.e.,\npreparation temperature <i>T</i><sub>prep</sub> and measurement\ntemperature <i>T</i><sub>meas</sub>. Due to the significantly\nhigher electron density of gold than that of AC, the structure factor <i>S</i>(<i>q</i>) of AuNPs is readily estimated from\nthe scattering intensities of AuNP-only and mixed solutions. The resulting <i>S</i>(<i>q</i>) profile for the mixed solution indicated\nsignificant attractive interactions, especially for the smaller AuNPs.\nTherefore, the sticky sphere model was applied to analyze <i>S</i>(<i>q</i>) to determine the interaction parameters\nat different <i>T</i><sub>prep</sub> and <i>T</i><sub>meas</sub>. The attractive interactions between AuNPs were higher\nat higher <i>T</i><sub>prep</sub>, suggesting that single-chain\nAC tends to make the interactions between AuNPs more attractive than\nthose for triple-helical AC. Complex formation was also detected by\nthe aggregation-induced surface plasmon absorption shift. More densely\npacked AuNPs were detected from the absorption spectra for higher\nAuNP content at which the ζ potential disappeared, while a split\nabsorption band was also found, indicating that not all AuNPs can\nform a complex with AC at ζ = 0.