Xiangzhi Song

A highly sulfite-selective ratiometric fluorescent probe based on ESIPT

The levulinate ester of 2-(benzothiazol-2-yl)phenol, 1, has been developed as a ratiometric fluorescent probe for identifying and quantitating sulfite anions. The mechanism of action is based on the sulfite-triggered intramolecular cleavage of the levulinate moiety to give 1 which, when excited with 310 nm light, decays to its ground state via an excited state intramolecular proton transfer (ESIPT) mediated pathway. We show that the intensity of the ESIPT fluorescent signal relative to that of 1 is proportional to sulfite concentration. This new probe shows good selectivity and high sensitivity for sulfite over other typically encountered anions (F−, Cl−, Br−, I−, HPO42−, SO42−, NO3−, AcO−, ClO4−, N3−, HCO3−) when measured in CH3CN/H2O (50 : 50, v/v) solution.

Selective, Highly Sensitive Fluorescent Probe for the Detection of Sulfur Dioxide Derivatives in Aqueous and Biological Environments

On the basis of a unique nucleophilic addition reaction, a novel water-soluble broadly emitting (500-700 nm) fluorescent Probe 1 was developed for the rapid detection of SO2 derivatives in aqueous media. The positively-charged benzopyrylium moiety in Probe 1 provides both excellent water solubility, making this probe applicable in 100% aqueous environments, and the ability to function as a fluorescence quencher of the coumarin moiety. Probe 1 generates a nearly instantaneous strong fluorescence signal in response to SO2 derivatives having an 8.3 nM detection limit for bisufite. The resulting Probe 1-sulfite adduct emits in the green/red spectral region (λ(max) = 585 nm) with a large Stokes shift (139 nm). The probe exhibits excellent selectivity toward SO2 derivatives over other potential interfering agents including reactive sulfur-containing species. Importantly, we demonstrate that Probe 1 can be used for the real-time sensing and bioimaging of SO2 derivatives in living cells.

Broadly Applicable Strategy for the Fluorescence Based Detection and Differentiation of Glutathione and Cysteine/Homocysteine: Demonstration in Vitro and in Vivo

Glutathione (GSH), cysteine (Cys), and homocysteine (Hcy) are small biomolecular thiols that are present in all cells and extracellular fluids of healthy mammals. It is well-known that each plays a separate, critically important role in human physiology and that abnormal levels of each are predictive of a variety of different disease states. Although a number of fluorescence-based methods have been developed that can detect biomolecules that contain sulfhydryl moieties, few are able to differentiate between GSH and Cys/Hcy. In this report, we demonstrate a broadly applicable approach for the design of fluorescent probes that can achieve this goal. The strategy we employ is to conjugate a fluorescence-quenching 7-nitro-2,1,3-benzoxadiazole (NBD) moiety to a selected fluorophore (Dye) through a sulfhydryl-labile ether linkage to afford nonfluorescent NBD-O-Dye. In the presence of GSH or Cys/Hcy, the ether bond is cleaved with the concomitant generation of both a nonfluorescent NBD-S-R derivative and a fluorescent dye having a characteristic intense emission band (B1). In the special case of Cys/Hcy, the NBD-S-Cys/Hcy cleavage product can undergo a further, rapid, intramolecular Smiles rearrangement to form a new, highly fluorescent NBD-N-Cys/Hcy compound (band B2); because of geometrical constraints, the GSH derived NBD-S-GSH derivative cannot undergo a Smiles rearrangement. Thus, the presence of a single B1 or double B1 + B2 signature can be used to detect and differentiate GSH from Cys/Hcy, respectively. We demonstrate the broad applicability of our approach by including in our studies members of the Flavone, Bodipy, and Coumarin dye families. Particularly, single excitation wavelength could be applied for the probe NBD-OF in the detection of GSH over Cys/Hcy in both aqueous solution and living cells.

A red fluorescent probe for thiols based on 3-hydroxyflavone and its application in living cell imaging

A novel red (λmaxem = 632 nm) fluorescent probe based on 3-hydroxyflavone was designed and synthesized for thiol recognition with high sensitivity and excellent selectivity. Application of the probe for selective detection of intracellular thiols has been successfully demonstrated.

A red emitting fluorescent probe for instantaneous sensing of thiophenol in both aqueous medium and living cells with a large Stokes shift

A novel red emitting fluorescent probe for the detection of thiophenol in aqueous medium has been developed. This probe displays an instantaneous response (within seconds) and reaches a plateau within 2 min. It also exhibits a 129 nm Stokes shift and a low detection limit (8.2 nM, based on S/N = 3) in detecting thiophenol. Furthermore, the practical utility of this probe for the selective detection of thiophenol has been successfully demonstrated in both real water samples and living cells.

Leg-tracking and automated behavioural classification in Drosophila

Much remains unknown about how the nervous system of an animal generates behaviour, and even less is known about the evolution of behaviour. How does evolution alter existing behaviours or invent novel ones? Progress in computational techniques and equipment will allow these broad, complex questions to be explored in great detail. Here we present a method for tracking each leg of a fruit fly behaving spontaneously upon a trackball, in real time. Legs were tracked with infrared-fluorescent dyes invisible to the fly, and compatible with two-photon microscopy and controlled visual stimuli. We developed machine-learning classifiers to identify instances of numerous behavioural features (for example, walking, turning and grooming), thus producing the highest-resolution ethological profiles for individual flies.

Ratiometric Fluorescent Probe for Lysosomal pH Measurement and Imaging in Living Cells Using Single-Wavelength Excitation

A novel lysosome-targeting ratiometric fluorescent probe (CQ-Lyso) based on the chromenoquinoline chromorphore has been developed for the selective and sensitive detection of intracellular pH in living cells. In acidic media, the protonation of the quinoline ring of CQ-Lyso induces an enhanced intramolecular charge transfer (ICT) process, which results in large red-shifts in both the absorption (104 nm) and emission (53 nm) spectra which forms the basis of a new ratiometric fluorescence pH sensor. This probe efficiently stains lysosomes with high Pearsons colocalization coefficients using LysoTrackerDeep Red (0.97) and LysoTrackerBlue DND-22 (0.95) as references. Importantly, we show that CQ-Lyso quantitatively measures and images lysosomal pH values in a ratiometric manner using single-wavelength excitation.

A colorimetric and ratiometric fluorescent probe for Cu2+ with a large red shift and its imaging in living cells

The ester derived from picolinic acid and 4-hydroxynaphthalimide has been developed as a colorimetric and ratiometric fluorescent probe for the detection of Cu2+. Upon exposure to Cu2+ in a buffered solution, the probe displays a large red shift both in its absorption (110 nm) and emission (143 nm) spectra. This novel probe has a high sensitivity and an excellent selectivity for Cu2+ ions over competing metal ions (K+, Na+, Zn2+, Ni2+, Mn2+, Mg2+, Ca2+, Hg2+, Cd2+, Pb2+, Fe2+, Co2+, Ba2+, Ag+ and Fe3+). Most importantly, this new picolinate probe can successfully detect Cu2+ in living cells.

A phthalimide-based fluorescent probe for thiol detection with a large Stokes shift

A phthalimide-based dye, probe 1, was developed as a novel fluorescent probe for thiol detection with excellent selectivity and high sensitivity based on the combination of photo induced electron transfer (PET) and excited state intramolecular proton transfer (ESIPT) mechanisms. The probe can detect thiols quantitatively and selectively with a large Stokes shift (161 nm) and the detection limit (S/N = 3) is as low as 0.8 nM. Furthermore, this probe was successfully used for imaging thiols in living SH-SY5Y cells.

A real-time colorimetric and ratiometric fluorescent probe for rapid detection of SO2 derivatives in living cells based on a near-infrared benzopyrylium dye

A benzopyrylium-based dye, Probe 1, was developed as a near-infrared fluorescent probe for the detection of SO2 derivatives (sulfite/bisulfite) in pure aqueous solution. In the presence of sulfite/bisulfite, the solution of Probe 1 displayed significant changes in its absorption (from 650 nm to 420 nm) and emission (from 690 nm to 489 nm) spectra. Probe 1 exhibits excellent selectivity and high sensitivity toward sulfite/bisulfite and the detection limit (S/N = 3) for bisulfite is as low as 10.4 nM. Specifically, Probe 1 shows a fast response time (within 10 s) toward sulfite/bisulfite, which makes it capable for real-time sensing or imaging both in vitro and in vivo assays. Probe 2, an analogue of Probe 1, as a turn-on fluorescent probe was also developed and displayed similar properties for the detection of sulfite/bisulfite. The demonstration of Probe 1 as a ratiometric fluorescent probe and Probe 2 as a turn-on fluorescent probe for the detection of SO2 derivatives was achieved in living HeLa cells and A431 cells, respectively.