Ratiometric optical sensing of chloride ions with organic fluorophore-gold nanoparticle hybrids: A systematic study of design parameters and surface charge effects

摘要

Colloidal nanoparticles are often stabilized by high surface charges. These create an electrical potential that may strongly affect the concentration of dissolved ions, which presents a formidable problem for the use of nanoparticles in ion-sensing applications. This effect is investigated systematically with organic fluorophore-gold nanoparticle hybrids, which have a chloride-sensitive fluorophore attached at varying distances from their surface. The distance-dependent fluorescence response is quantitatively assessed using fluorescence spectroscopy. The readout in ion sensing with charged nanoparticles (NPs) is greatly affected by the surface charge. This effect is demonstrated systematically on organic fluorophore-gold NP hybrids in which the dye-to-surface distance is varied by a polyethylene glycol (PEG) spacer. The effect on the readout is observable by fluorescence spectroscopy. Effective distances are measured with fluorescence correlation spectroscopy and calculated with semiempirical models.