Ratiometric electrochemiluminescence sensing and intracellular imaging of ClO- via resonance energy transfer.

Abstract

Electrochemiluminescence resonance energy transfer (ECL-RET) is a versatile signal transduction strategy widely used in the fabrication of chem/biosensors. However, this technique has not yet been applied in visualized imaging analysis of intracellular species due to the insulating nature of thecell membrane. Here, we construct a ratiometric ECL-RET analytical method for hypochlorite ions (ClO-) by ECL luminophore,with a luminol derivative (L-012) as the donor and afluorescence probe (fluorescein hydrazide) as the acceptor. L-012 can emit astrong blue ECL signal and fluorescein hydrazide has negligible absorbance and fluorescence signal in the absence of ClO-. Thus, theECL-RET process is turned off at this time. In the presence of ClO-, however, the closed-loop hydrazide structure in fluorescein hydrazide is opened via specific recognition with ClO-, accompanied with intensified absorbance and fluorescence signal. Thanks to the spectral overlap between theECL spectrum of L-012 and theabsorption spectrum of fluorescein, theECL-RET effect isgradually recovered with the addition of ClO-. Furthermore, the ECL-RET system has been successfully applied to image intracellular ClO-. Although the insulating nature of thecell itself can generate ashadow ECL pattern in the cellular region, extracellular ECL emission penetrates thecell membrane and excites intracellular fluorescein generated by the reactions between fluorescein hydrazide and ClO-. The cell imaging strategy via ECL-RET circumvents the blocking of thecell membrane and enables assays of intracellular species. The importance of theECL-RET platform lies in calibrating the fluctuation from theexternal environment and improving the selectivity by using fluorescent probes. Therefore, this ratiometric ECL sensor has shown broad application prospects in the identification of targets in clinical diagnosis and environmental monitoring.