Ultrathin water layers on mannosylated gold nanoparticles

We investigated the effect of air humidity on two gold nanoparticle systems, one functionalized with an oligo(ethylene glycol) ligand, and one functionalized with a mixture of the same with a dimannoside ligand. The dimannoside ligand was chosen to mimic the surface chemistry of viral spike proteins. We characterized the particles by electron microscopy, dynamic light scattering, and infrared spectroscopy. We probed particles adsorbed on hydrophilic and hydrophobic surfaces with atomic force microscopy (AFM) and vibrational sum frequency generation (VSFG) spectroscopy, both operated under variable air humidity. For AFM, we additionally tested hydrophilic and hydrophobic tips. While VSFG indicated preferential hydration of the dimannoside and proved conformational changes in the organic ligands, AFM provided sub-nanometer changes in particle topography due to water adsorption. In general, the dimannoside nanoparticles condense ultrathin water layers upon humidity increase. In contrast, we found that the water adsorption on the oligo(ethylene glycol) particles depends little on humidity. Our insights into structural changes on glyconanoparticles and the hydration properties of glycosylated particles are of application value for biosensors and help model the transmission of airborne viruses, such as influenza.