Quantum Dots in an Amphiphilic Polyethyleneimine Derivative Platform for Ratiometric and Reversible Nitric Oxide Sensing

Abstract

Nitric oxide (NO) plays a key role in a variety of biological processes. In order to analyze NO generation and distribution in vivo, a reliable in vivo NO sensing fluorescent probe is still in pursuit. Quantum dots (QDs) have high the extinction coefficient, broad absorption range, high photostability, and resistance against photobleaching that cannot be paralleled by organic fluorophores. Cationic amphiphilic polyethyleneimine derivatives (amPEIs) successfully encapsulated dozens of Fe (III) complexes of a tetra-amido macrocyclic ligand and two kinds of QDs (one emits at around 720 nm and the other at around 440 nm). QDs-Fe complex-amPEI based NO probe demonstrated accurate and reversible sensing of NO by the ratiometric photoluminescence signals by switching the environment between the nitrogen and nitric oxide conditions for more than 5 cycles. In NO saturated solution, quenching of 720 nm emitting QD PL was observed because Fe complex could absorb part of QD PL upon the binding NO to metal center. As NO was released from the Fe complex, the 720 nm QD emission was recovered. In contrast, 440 nm emitting QD acted as an internal standard. The Fe complex showed similar absorption profile at 440 nm regardless of the binding or leaving of NO, and the 440 nm QD emission intensity was independent of the NO concentration. These results showed our QDbased nitric oxide sensing platform technology can apply to real-time monitor NO in cells and in vivo models.