Fast Responsive Optically Functionalized Mesoporous Gold Nanostructures
for pH Sensing

Two different routes turkivish and sol-gel methods are used to synthesize sodium citrate and polyethylene glycol<br/>functionalized gold nanostructures. Field emission scanning electronmicroscope (FESEM) analysis confirms<br/>spherical-shaped gold nanoparticles (AuNPs) and self-assembled Au nanodendritic (AuNDs) structures. Highresolution<br/>transmission electron microscopy (HRTEM) confirmed the spherical and dendritic morphology with<br/>particle sizes 9 nm of AuNPs and 3 nm of AuNDs, respectively. An atomic force microscope (AFM) shows average<br/>surface roughness (Ra) ~2.5 nm of AuNPs which is reduced to 1.5 nm in AuNDs. The AuNPs and AuNDs show<br/>heterogeneous chemical bonding and thermal stability at high temperatures. Brunauer-Emmett-Teller-based<br/>surface area is calculated at around 18 m2/g for AuNPs and 54 m2/g for AuNDs. The creosol red immobilized<br/>AuNPs (CR-AuNPs) and AuNDs (CR-AuNDs) sol demonstrate pka around 8.9 and 9.2 at 575 nm, respectively. The<br/>CR-AuNDs sol exhibit a time reaction 0.5 s which is relatively high than CR-AuNPs ~0.6 s. Both Au-structures<br/>show non-leachable behavior.