An infrared reflectance spectroscopic study of a pH-tunable network of nanoparticles linked by hydrogen bonding

This paper presents novel findings of the pH-tunable structural properties of a hydrogen-bonded nanoparticle network using an infrared reflectance spe ctroscopic (IRS) technique. Gold nanoparticles encapsulated with thiolates and alkylthiols terminated with carboxylic groups were utilized as building blocks and molecular linkers, respectively, for assembling the network fil m. The IRS bands associated with the reactivities of the carboxylic acid gr oups on the nanoparticles allowed us to analyze the structures during surfa ce titration of the network thin films. IRS data have revealed that the net work, linked by predominantly head-to-head hydrogen bonding, could be rever sibly tuned between the neutral protonated and the ionic deprotonated state s. This protonation/deprotonation process was also found to exhibit membran e-type properties, as supported by open-circuit potential measurement of th e membrane. These findings have important implications to designing nanopar ticle-based functional nanostructures for molecular recognition.