Rational engineering of chromic material as near-infrared ratiometric fluorescent nanosensor for H2S monitoring in real food samples

Food pollution has aroused increasing public health concerns and poses a huge medical and financial burden today. Here, we report a facile one-pot synthesis of hydrogen sulfide (H2S)-responsive near-infrared (NIR) ratiometric fluorescent nanoprobe NIR775/Cy7Cl@HyNPs by encapsulating H2S-sensitive organic chromic cyanine dye Cy7Cl and H2S-inert fluorophore NIR775 into an amphiphilic phospholipid polymer. Because of the confinement effect of phospholipid layer, the loaded NIR775 and Cy7Cl could be brought in close proximity for fluorescence resonance energy transfer (FRET) to occur, leading to single emission of Cy7Cl at similar to 810 nm inside nanoprobe NIR775/Cy7Cl@HyNPs. However, with the introduction of H2S, the FRET process from NIR775 to Cy7Cl is disrupted due to the stimuli-responsive chromic behavior as a result of H2S-triggered nucleophilic, leading to restoring of the fluorescence emission of NIR775 at similar to 778 nm companied by a remarkable fluorescence decrease of Cy7Cl at similar to 810 nm, thereby enabling nanoprobe NIR775/Cy7Cl@HyNPs to show a NIR ratiometric response toward H2S. As expected, the nanoprobe NIR775/Cy7Cl@HyNPs exhibits a prominent practicability to precisely report the levels of H2S in actual food mediums with a wide linear range of 0.0367-120.0 mu M, a satisfactory limit detection of 11.0 nM, as well as an excellent specificity over other sulfur-containing substances (e.g. biothiols). This study emphasizes the promise for utilizing switchable chromic materials to develop a new category of NIR ratiometric fluorescent nanosensors facilitating accurate and reliable measurement in actual food and agriculture-related systems without any pretreatments, which is of great significance for safeguarding food safety and human health.