Dynamic [Cl−]i measurement with chloride sensing quantum dots nanosensor in epithelial cells

Abstract

We have synthesized a chloride sensing quantum dots (QD) nanosensor, Cl-QD, for thedynamic measurements of chloride ion concentration in the millimolar range, a sensitivitythat is applicable to most physiological intracellular chloride ion concentration([Cl−]i) measurements in epithelial cells. The Cl-QD is synthesized by conjugating an anionreceptor, 1-(2-mercapto-ethyl)-3-phenyl-thiourea (MEPTU) to a water soluble CdSe/ZnSQD at an emission wavelength of 620 nm. Upon binding of chloride ions to the Cl-QD, aphoto-induced electron transfer mechanism caused the fluorescence of the QD to quench. Thisresulted in an inversely proportional relationship between the chloride ion concentrationand the fluorescence intensity of the Cl-QD. We have utilized this Cl-QD to measure[Cl−]i in T84 and CF-PAC cultured cells, with either the C1C-2 or CFTR chloride channels beingmanipulated by pharmacological chloride channel activators and inhibitors. Activations ofC1C-2 and CFTR chloride channels in T84 by the respective lubiprostone and genisteincaused predictive increases in the fluorescence of the Cl-QD, i.e., a decrease of[Cl−]i. Conversely, glibenclamide, a chloride channel inhibitor, applied to the CF-PAC cellscaused a predictable decrease in the fluorescence of Cl-QD due to the increase of[Cl−]i. These are the first data in using QD-based chloride ion sensors for dynamic measurementsof intracellular chloride ion concentrations in epithelial cells.