Qinglong Qiao

Aziridinyl Fluorophores Demonstrate Bright Fluorescence and Superior Photostability by Effectively Inhibiting Twisted Intramolecular Charge Transfer

Replacing conventional dialkylamino substituents with a three-membered aziridine ring in naphthalimide leads to significantly enhanced brightness and photostability by effectively suppressing twisted intramolecular charge transfer formation. This replacement is generalizable in other chemical families of fluorophores, such as coumarin, phthalimide, and nitrobenzoxadiazole dyes. In highly polar fluorophores, we show that aziridinyl dyes even outperform their azetidinyl analogues in aqueous solution. We also proposed one simple mechanism that can explain the vulnerability of quantum yield to hydrogen bond interactions in protonic solvents in various fluorophore families. Such knowledge is a critical step toward developing high-performance fluorophores for advanced fluorescence imaging.

A turn-on fluorescent probe for imaging lysosomal hydrogen sulfide in living cells

Hydrogen sulfide (H2S) is an endothelial gasotransmitter which has been extensively studied recently in various physiological processes. H2S can induce lysosomal membrane destabilization leading to an autophagic event of precipitation apoptosis coupled with calpain activation, thus ensuring cellular demise. In this study, we developed a lysosome-targetable fluorescent probe for the recognition of H2S with considerable fluorescence enhancement. Through introducing a lysosome-targetable group 4-(2-aminoethyl)-morpholine into the H2S probe N-imide termus of 4-azide-1,8-naphthalimide, the new compound Lyso-AFP can recognize H2S in lysosomes. This probe emerges as a more biocompatible analysis tool with low poison by-product than reported H2S fluorescent probes.

A turn-on fluorescent probe for hydrogen sulfide and its application in living cells

Hydrogen sulfide (H2S) is an important endogenous signalling molecule in cellular physiology and pathology. Accordingly, sensitive, selective and reliable methods for H2S detection are in high demand. Fluorescence-based methods thus have received great attentions in recent years. Herein we describe the design, synthesis and application of a probe for H2S detection based on the reduction of azide to amine. This probe is highly sensitive and selective toward H2S over biothiols and other biologically relevant species. Finally, the probe was successfully applied for H2S fluorescent imaging in living cells.

A ratiometric fluorescent probe for fluoride ion based on naphthoimidazolium receptor

Three imidazolium derivatives 3–5 were designed and synthesized, in which naphthaimidazolium group acted as both fluorophore and anion receptor. Compound 3 exhibited high selectivity for F− in CH3CN solution over all the other anions and acted as a ratiometric fluorescent probe for F− with an enhanced blue-shift in emission. However, the fluorescence of compound 4 and 5 displayed a quenched blue-shift in emission with fluoride ion and could be quenched by some other tested anions, where the degree of quenching depended on the characteristic of the anions. More importantly, only compound 3 could detect F− in DMSO–water (95 : 5, v/v) aqueous solution ratiometrically. Based on the analysis of the results of 1H-NMR and 19F-NMR, it was deduced that compound 3 bound with F− mainly by the force of hydrogen bonding, while compound 4 and 5 coordinated with F− through electrostatic interaction.

A wash-free SNAP-tag fluorogenic probe based on the additive effects of quencher release and environmental sensitivity

A 1,8-naphthalimide-derived fluorogenic probe was reported to label SNAP-tag fusion proteins in living cells. The probe can rapidly label a SNAP-tag and exhibit a fluorescence increase of 36-fold due to the additive effects of environment sensitivity of fluorophores and inhibition of photo-induced electron transfer from O6-benzylguanine to the fluorophore. The labeling of intracellular proteins has been successfully achieved without a wash-out procedure.

Ground-state conformers enable bright single-fluorophore ratiometric thermometers with positive temperature coefficients

Fluorescence thermometry based on organic dyes affords high spatial and temporal resolution with a simple system design and low cost, for measuring temperatures in microenvironments. Many fluorescent thermometers consist of two types of fluorophores with distinct temperature responses, and the ratios of their fluorescence intensities afford accurate temperature information. Yet, the reliability of these ratiometric thermometers is vulnerable to photobleaching induced system variations. In this paper, we have proposed and demonstrated a new strategy, to achieve ratiometric temperature measurements from 15 °C to 75 °C, based on ground-state conformational isomers of a single type of dye. These ground-state conformers emit bright fluorescence, in contrast to excited-state conformational changes that generally quench emissions. Moreover, thermal equilibrium of these conformers and their distinct spectra lead to ratiometric temperature readings that are not affected by photobleaching. We expect that our design strategy has significant implications for developing fluorescence thermometry with outstanding reliability.