# A turn-on AIE sensor for nanomolar detection of perrhenate in aqueous media

## TL;DR

A new fluorescent sensor detects perrhenate in water with high sensitivity and speed, potentially useful for monitoring radioactive contamination.

## Contribution

A novel 'light-switch' Ru(ii) complex is developed for nanomolar detection of ReO4− in pure aqueous media.

## Key findings

- The Ru(ii) complex shows rapid and sensitive detection of ReO4− with a limit of quantification of 1.5 nM.
- Aggregation of the complex is driven by electrostatic and hydrogen bonding interactions with ReO4−.
- The sensor responds to ReO4− within 1 second and has a limit of detection of 3.4 nM for the optimal complex Ru3.

## Abstract

The “light-switch” Ru(ii) polypyridine complexes have been developed as a novel fluorescent sensor for rapid and sensitive detection of ReO4− anions in pure aqueous media. When counterions (Cl−) in aqueous solution are specifically exchanged by ReO4− anions, the “light-switch” Ru(ii) polypyridine complexes exhibit a significant fluorescence emission enhancement, accompanied by the formation of nanoaggregates. This aggregation is driven by weak interactions with electrostatic attraction, anion⋯π, C–H⋯anion hydrogen bonding and π–π stacking interactions between ReO4− anions and “light-switch” Ru(ii) polypyridine complexes, which is confirmed by single crystal structure analysis, density functional theory (DFT) and Energy decomposition analysis (EDA). The anion exchange-induced aggregation effect of the Ru(ii) polypyridine complexes demonstrate a potent “light-switch” strategy, capable of rapid response to ReO4− within 1 s and a limit of quantification of 1.5 nM, below the WHO guideline value for its radioactive analogue 99TcO4− (1.6 nM), demonstrating potential for monitoring pertechnetate contamination. This work opens a new way for future research based on “light-switch” Ru(ii) polypyridine complexes as turn-on fluorescent sensing probes for ReO4−/99TcO4− anions detection in aqueous media.

The optimal complex, Ru3, achieves high sensitivity and selective in a “turn-on” luminescent response to ReO4− in pure aqueous medium, with LOD of 3.4 nM.