Abstract:
When the body temperature rises above 40.6 °C,
heat stress in the cells causes mitochondrial damage. This damage
can lead to apoptosis, multiple organ failure, and even death. The
dysregulation of SO2 levels in the mitochondria is linked to this
heat stress, and its detection may act as an early indicator of heat
stroke. Graphene quantum dots (GQDs), a common class of zerodimensional
carbon-based fluorescent nanomaterials, have shown
immense potential as sensory probes, and it is a prospective
candidate for monitoring SO2 levels in living cells. Herein, we
report a combination of a donor−two acceptor (D2A) red-emissive
di-picolinium salt (PPy-Br) and hydroxy-functionalized graphene
quantum dots (GQDs-OH) as the fluorescence resonance energy
transfer (FRET)-based ratiometric sensor for bisulfite ions
detection in aqueous media. The dye-GQD nanoconjugate displays excellent photostability and good aqueous dispersibility
allowing the monitoring of SO2 levels in living cells during heat stress. The PPy-Br:GQD nanoconjugate is indifferent to a large
number of cations, anions, or biologically relevant species and displays a detection limit of 36 nM for the solution phase detection of
bisulfite. PPy-Br is biocompatible with human cell lines and endocytoses into the cells to ensure monitoring of SO2 levels in the
mitochondrial milieu. PPy-Br-treated human breast cancer cells displayed a gradual decrease in fluorescence at temperatures above
40 °C, indicating an increase in SO2 levels in heat-stressed cells. The PPy-Br:GQDs sensing conjugate is efficient in the real-time
monitoring of intracellular SO2 levels and demonstrates enough prospects for further explorations as a diagnostic kit for heat stroke
monitoring.
