A FRET-based supramolecular nanoprobe with switch on red fluorescence to detect SO2 derivatives in living cells

Abstract

SO₂, an important gasotransmitter, plays significant roles in human physiological activities. The reported probes for the detection of SO₂ derivatives are mostly based on the quenching or blue-shift of fluorescence, leading to interference from the background signal. Herein, we develop a novel FRET-based nanoprobe that shows turn-on fluorescence at 615 nm in the presence of SO₃²⁻/HSO₃⁻. The nanoprobe consists of N,O,B-chelated dipyrromethene (BDP) as the energy donor, and hemicyanine derivatives of HEM-CO-Ph with a responsive site to SO₃²⁻/HSO₃⁻ as the energy acceptor. Initially, the fluorescence of BDP is quenched by HEM-CO-Ph due to the efficient FRET process. In the presence of sulfites, the nucleophilic addition interrupts the conjugation of HEM-CO-Ph and results in a 200 nm blue-shift of the absorption, leading to the suppression of the FRET process and recovery of the red fluorescence of BDP. The nanoprobe shows fast response to SO₃²⁻/HSO₃⁻ with high selectivity, great biocompatibility and cellular uptake. It is the first supramolecular nanoprobe for the detection of SO₃²⁻/HSO₃⁻ by using intermolecular energy transfer, ingeniously turning the nanoprobe from “OFF” state to “ON” state. The nanoprobe is applied to monitor exogenous and endogenous SO₂ derivatives in the mitochondria of living cells.