An ultra-sensitive and ratiometric fluorescent probe based on the DTBET process for Hg²⁺ detection and imaging applications

In this article, we present an ultra-sensitive and ratiometric fluorescent probe (TR-Hg) for Hg²⁺ detection based on the mechanism of aggregation induced emission (AIE) and dark through-bond energy transfer (DTBET). The probe was constructed using tetraphenylethene as the dark donor and rhodamine B thiolactone as the acceptor. By exploiting the advantages of DTBET, which eliminates emission leakage from dark donors and provides nearly 100% energy transfer efficiency, TR-Hg exhibits more than a 30000-fold fluorescence ratio enhancement after reacting with Hg²⁺. TR-Hg demostrates (i) a detection limit of 43 pM, which is the lowest among the reported ratiometric Hg²⁺ probes, (ii) excellent selectivity, fast response-time (<10 s) and a wide pH application range, (iii) strong applicability for paper-based colorimetric assay, where readout can be performed by the naked eye, and (iv) fluorescent imaging of Hg²⁺ in onion epidermal tissues, indicating its potential use in living organisms.