Ratiometric Fluorescence Probes For Reversible Detection Of Hydrogen Polysulfides Based On Upconversion Nanoparticles

As a gas signal molecule,hydrogen sulfide（H₂S）has various biological effects such as dilating blood vessels,inhibiting the proliferation of vascular smooth muscle,and resisting oxidative stress.Hydrogen polysulfides（H₂S_n）can be obtained from the oxidation of endogenous H₂S,which together maintain the redox balance of life.However,most of the current fluorescent probes for H₂S_ndetection are based on irreversible mechanisms,which are difficult to monitor the dynamic changes of H₂S_n.While living organisms in an aerobic environment need to maintain a relatively stable redox state,and the reversible changes in cellular redox can provide effective physiological information.Hence,construction of reversibly responsive fluorescent probes for detection of H₂S_ncontent changes in real time has received more and more attention.At present,most of the reversible probes for H₂S_ndetection are small molecule probes,which are prone to photobleaching and is not conducive to long-term in vivo imaging.In addition,the excitation wavelength of small molecules is in the ultraviolet or visible region,which is able to cause serious autofluorescence interferes from the sample and photodamage to the biosample because of the high energy of the excitation light.Upconversion nanoparticles（UCNPs）,as a kind of anti-Stokes luminescent material,have superior photostability and chemical stability,and are suitable for long-term imaging.At the same time,due to the low-energy near-infrared light excitation,it has the ability to provide deep tissue penetration.Based on this,we utilized UCNPs as the energy donor and a small molecular dye with reversible H₂S_nrecognition function as the energy receptor to construct the fluorescence resonance energy transfer（FRET）system.H₂S_ncan regulate the energy transfer efficiency between the energy donor and the receptor,realizing the long-term reversible monitoring of H₂S_n.The main research contents are as follows:UCNPs were used as energy donors and silicon-rhodamine SiR1 was used as energy acceptors,both of which were assembled by coating with the amphiphilic polymer DSPE-PEG to construct the upconversion fluorescent nanoprobe SiR1-UCNPs.Since the absorption spectrum of SiR1 overlapped well with the emission spectrum of UCNPs,the upconversion emission of UCNPs can be quenched by SiR1 through FRET process.After the reaction with H₂S_n,the conjugated structure of SiR1 was destroyed to result in the weakened absorption of SiR1 and the inhibition of FRET process,recovering the quenched upconversion luminescence（UCL）.After adding the sulfhydryl scavenger（NMM）into the system,the absorption of SiR1 was gradually increased and the UCL was quenched again.Because of multi-wavelength emission of UCNPs,a reference signal was introduced to construct a ratiometric signal,which can avoid the interferences from variations of the biological environment and instrument,uneven distribution of probes,and so on.The probe has excellent stability and biocompatibility,and enables successfully to apply for tracking the fluctuations of H₂S_nlevel in mouse hindlimb,arthrosis,liver,and brain.