Xiaoqing Xiong

Thermally activated delayed fluorescence of fluorescein derivative for time-resolved and confocal fluorescence imaging.

Compared with fluorescence imaging utilizing fluorophores whose lifetimes are in the order of nanoseconds, time-resolved fluorescence microscopy has more advantages in monitoring target fluorescence. In this work, compound DCF-MPYM, which is based on a fluorescein derivative, showed long-lived luminescence (22.11 μs in deaerated ethanol) and was used in time-resolved fluorescence imaging in living cells. Both nanosecond time-resolved transient difference absorption spectra and time-correlated single-photon counting (TCSPC) were employed to explain the long lifetime of the compound, which is rare in pure organic fluorophores without rare earth metals and heavy atoms. A mechanism of thermally activated delayed fluorescence (TADF) that considers the long wavelength fluorescence, large Stokes shift, and long-lived triplet state of DCF-MPYM was proposed. The energy gap (ΔEST) of DCF-MPYM between the singlet and triplet state was determined to be 28.36 meV by the decay rate of DF as a function of temperature. The ΔE(ST) was small enough to allow efficient intersystem crossing (ISC) and reverse ISC, leading to efficient TADF at room temperature. The straightforward synthesis of DCF-MPYM and wide availability of its starting materials contribute to the excellent potential of the compound to replace luminescent lanthanide complexes in future time-resolved imaging technologies.

Ratiometric Fluorescence Imaging of Cellular Polarity: Decrease in Mitochondrial Polarity in Cancer Cells

Mitochondrial polarity strongly influences the intracellular transportation of proteins and interactions between biomacromolecules. The first fluorescent probe capable of the ratiometric imaging of mitochondrial polarity is reported. The probe, termed BOB, has two absorption maxima (λabs = 426 and 561 nm) and two emission maxima--a strong green emission (λem = 467 nm) and a weak red emission (642 nm in methanol)--when excited at 405 nm. However, only the green emission is markedly sensitive to polarity changes, thus providing a ratiometric fluorescence response with a good linear relationship in both extensive and narrow ranges of solution polarity. BOB possesses high specificity to mitochondria (Rr =0.96) that is independent of the mitochondrial membrane potential. The mitochondrial polarity in cancer cells was found to be lower than that of normal cells by ratiometric fluorescence imaging with BOB. The difference in mitochondrial polarity might be used to distinguish cancer cells from normal cells.

Construction of Long-Wavelength Fluorescein Analogues and Their Application as Fluorescent Probes

Born to dye: Five fluorescein analogues were synthesised (see scheme). One analogue was found to emit in the NIR region with a high quantum yield, excellent photostability and good permeability. Three derivatives were found to specifically stain mitochondria and one dye responds to thiols with a strong turn-on NIR fluorescence signal and colorimetric change, in vitro and in vivo.

A New Tridentate Sulfur Receptor as a Highly Sensitive and Selective Fluorescent Sensor for Cu2+ Ions

The introduction of Lawessons reagent into a bis-rhodamine spirolactam system afforded a new fluorescent sensor for Cu(2+) ions, SRR, which contained a new tridentate sulfur ligand. SRR showed excellent specificity for Cu(2+) ions over other cations (including Cu(+), Hg(2+), and Fe(3+)), very high sensitivity (10 nM), and a rapid response time (3 min). The detection mechanism was investigated by (1)H NMR, (13)C NMR, (31)P NMR, and ESR spectroscopy, MS, and Gaussian calculations. Coordination of a Cu(2+) ion to the tridentate sulfur ligand, which promotes ring-opening of the rhodamine groups, followed by a spontaneous reduction reaction (Cu(2+) into Cu(+)), has been proposed as the sensing mechanism.

A turn-on and colorimetric metal-free long lifetime fluorescent probe and its application for time-resolved luminescent detection and bioimaging of cysteine

A turn-on and colorimetric metal-free long lifetime fluorescent probe for sensing Cys has been synthesized. Utilizing the long emission-lifetime of DCF-MPYM, the time-resolved luminescent assay of DCF-MPYM-thiol for sensing Cys was realized successfully. DCF-MPYM-thiol can realize confocal and time-resolved microscopy bioimaging for Cys in living cells.

Ratiometric fluorescent probe based on novel red-emission BODIPY for determination of bovine serum albumin

A novel red-emission boron-dipyrromethene(BODIPY) dye with a pyrrole ring was synthesized simply via one-pot reaction. The spectral properties of it were investigated under the conditions of different solvents. The results show that the as-prepared BODIPY dye is extremely sensitive to solvent polarity, and the fluorescent emission enhances with the decrease of solvent polarity. In aqueous buffer, the addition of bovine serum albumin leads to a ratiometric change in absorption spectra with an association constant of 1.16×106 L/mol. Meanwhile, the fluorescence emission increases greatly at 622 nm but changes slightly at 575 nm. The response time is very short(less than 3 min), and the changes of color can be noticed by naked eyes. Bovine serum albumin can be detected by this ratiometric fluorescence probe, but other proteins or enzymes cannot be detected by this method, which indicates that this novel dye has high selectivity towards bovine serum albumin. The reason is that bovine serum albumin has suitable hydrophobic cavities for binding with the dye. In addition, the dye molecule can penetrate cell membrane easily and make a fast fluorescent stain, which makes it a potential probe for living-cell fluorescence imaging.