Xiang-Qun Guo

Development of a novel rhodamine-type fluorescent probe to determine peroxynitrite

A novel method for the determination of peroxynitrite using rhodamine B hydrazide as a fluorogenic probe is described. The method is based on the oxidation of rhodamine B hydrazide, a colorless, non-fluorescent substance, by peroxynitrite to give rhodamine B-like fluorescence emission. The fluorescence increase is linearly related to the concentration of peroxynitrite in the range of 7.5x10(-8)-3.0x10(-6) mol l(-1) with a detection limit of 2.4x10(-8) mol l(-1) (3sigma). The optimal conditions for the detection of peroxynitrite were evaluated and the possible detection mechanism was also discussed in this paper.

Facile one-pot synthesis of near-infrared luminescent gold nanoparticles for sensing copper (II)

Novel near-infrared luminescent gold nanoparticles (NIRL-AuNPs) were synthesized by a simple, rapid and one-pot procedure. The driving force for the formation of these NIRL-AuNPs was attributed to the heat-assisted reduction of a gold(I)-thiol complex. These gold nanoparticles were characterized by TEM, DLS, FT-IR and XPS. Luminescence studies indicated that these NIRL-AuNPs exhibited strong emission with peak maximum at 810 nm, microsecond-range photoluminescence lifetime, large Stokes shifts (>400 nm) and stabilities towards photobleaching and chemical oxidation. The sensing application for Cu(2+) ions of these NIRL-AuNPs was demonstrated. These as-synthesized gold nanoparticles will provide a new NIRL nanomaterial for in vitro and in vivo applications.

Electron transfer quenching by nitroxide radicals of the fluorescence of carbon dots

Blue fluorescent carbon dots (CDs) were synthesized by a microwave assisted one-step procedure without surface passivation. The intermolecular interactions between the CDs and nitroxide radicals in aqueous and aprotic solution were investigated. The fluorescence of the CDs was found to be efficiently quenched by the paramagnetic nitroxide radical. A SOMO (singly occupied molecular orbital) facilitated electron transfer was proposed to account for the quenching of the fluorescence of the CDs in the CD@TEMPO conjugate, formed via electrostatic interactions between the negatively charged CDs and the cationic 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide free radical (4-AT). Covalently spin-labeled CDs by the paramagnetic nitroxide radical yield a weakly fluorescent spin-labeled conjugate (CD–TEMPO), which exhibits sensitive fluorescence and electron spin resonance (ESR) bimodal response towards ascorbic acid (AA) at the μM level. The fluorescence intensity of the spin-labeled CDs was also found to be sensitive to paramagnetic factors and thus establishes its promising potential for constructing a bimodal responsive sensor with off–on fluorescence and on–off ESR signaling for the detection of antioxidants and carbon-centered radicals.

Study on the interaction between rivanol and DNA and its application to DNA assay

Abstract Rivanol (RVN) binds to the double helical DNA with a high affinity, as deduced from the absorption and fluorescence spectral data. Extensive hypochromism and red shifts in the absorption spectra were observed when RVN binds to calf thymus DNA (CT DNA), which suggested the intercalation mechanism of RVN into DNA bases. Upon binding to DNA, the fluorescence from RVN was efficiently quenched by the DNA bases, with no shifts in the emission maximum. The large increases in the polarization upon binding to CT DNA supported the intercalation of RVN into the helix. Iodide quenching studies showed that the magnitude of Ksv of the free RVN was higher than that of the bound RVN. The results of competitive binding studies showed that RVN can be displaced by ethidium bromide. Thermal denaturation experiments exhibited that the quenching of the fluorescence from RVN by single strand (ssDNA) was smaller than that by double strand (dsDNA). The results of all above further studies also proved the intercalation of RVN into DNA base stack. Quenching of fluorescence from RVN by DNA can be employed for sensitive detection of DNA. The limit of detection for CT DNA was 16 ng ml−1.

Fluorescent core-shell silica nanoparticles as tunable precursors: towards encoding and multifunctional nano-probes

Core-shell silica nanoparticles comprised of a RuBpy doped silica core and a Pas-DTPA doped silica shell were synthesized and post-functionalized with an encoding fluorescence combination and multiplex imaging function.

Investigation of the anthracene–nitroxide hybrid molecule as a probe for hydroxyl radicals

A new method for the determination of hydroxyl radicals is proposed. The method is based on the use of a hybrid molecule consisting of a fluorescent chromophore, anthracene, and a nitroxide radical. In the hybrid molecule, the nitroxide quenches the fluorescence of anthracene strongly. The reaction of hydroxyl radicals with dimethyl sulfoxide generates quantitatively methyl radicals, which then combine with the nitroxide moiety of the hybrid molecules to result in an increase in the fluorescence intensity. The fluorescence increase is proportional to the concentration of hydroxyl radicals. The proposed method is capable of detecting hydroxyl radicals generated in the Fenton system. It is a simple and sensitive technique for the determination of hydroxyl radicals.

Fe(II)-EDTA chelate-induced aromatic hydroxylation of terephthalate as a new method for the evaluation of hydroxyl radical-scavenging ability

The investigation of Fe(II)-EDTA chelate-induced aromatic hydroxylation of terephthalate in pH 7.4 phosphate buffer solution and a new method for the evaluation of hydroxyl radical-scavenging ability are reported. The method is based on attack of the hydroxyl radical on the terephthalate to produce highly fluorescent 2-hydroxyterephthalate, which is detected fluorimetrically. The formation of hydroxyl radical is believed to be the result of the reduction of molecular oxygen by Fe(II)-EDTA to form superoxide radical, which in turn dismutates to hydrogen peroxide, and then Fe(II)-EDTA catalyzes the decomposition of hydrogen peroxide to produce hydroxyl radical. The mechanism of the generation of hydroxyl radical in the proposed system was confirmed. This study established a simple and inexpensive method for the evaluation of the scavenging ability of some compounds on hydroxyl radicals.

Application of vitamin K3 as a photochemical fluorescence probe in the determination of nucleic acids

ABSTRACT An in situ photochemical fluorescence probe method for the determination of nucleic acids with vitamin k3(VK3) as the photochemical fluorescence probe was developed for the first time. It was based on the conversion of VK3 into an intensively fluorescent product on irradiating with UV radiation. The photochemical reaction is decelerated by nucleic acids. The determination can be carried out by measuring the fluorescence intensity at a fixed time. The calibration graph was linear in the range of 0– 1.5 μg/ml for CT DNA and 0–2.0μg/ml for yeast RNA, the limit of detection was 10 ng/ml for CT DNA and 26 ng/ml for yeast RNA. The kinetic behaviour of the photochemical reaction and the effects of some experimental conditions were investigated and discussed in detail. CT DNA could be determined in the presence of 40%(w/w) yeast RNA and yeast RNA was determined when the content of CT DNA in synthetic samples was below 6%(w/w).

Fluorimetric determination of hemoglobin using spiro form rhodamine B hydrazide in a micellar medium

A novel fluorimetric method for the determination of hemoglobin (Hb) using spiro form rhodamine B hydrazide (RBH) as fluorogenic reagent in the presence of sodium dodecylbenzene sulfonate (SDBS) surfactant micelles is described. The method employs the reaction of Hb with RBH, a colorless, non-fluorescent spirolactam hydrazide in SDBS micelles to generate highly fluorescent product rhodamine B and hence leads to a large increase in fluorescence intensity. The fluorescence increase is linearly related to the concentration of Hb in the range 0.2-12.0 nmol l(-1) with a detection limit of 0.086 nmol l(-1) (3sigma). The optimal conditions for the detection of Hb are evaluated and the possible detection mechanism is also discussed. The proposed method has been applied to the determination of Hb in human blood.

Water-soluble off-on spin-labeled quantum-dots conjugate.

Quantum dots (QDs) have some desirable properties that would circumvent the functional limitations encountered by conventional organic dyes in biotechnological applications. They show narrow and tunable emission bands that make multiple-color measurement possible, broad absorption spectra that allow simultaneous excitation of several particle sizes at a single wavelength, and excellent photostability that allows long-term imaging of live cells. With all these features, QDs have rapidly emerged as new fluorescent probes in a variety of applications. QDs are nanoscale crystalline particles surrounded by a layer of organic ligand molecules. Their dual inorganic–organic structural nature provides great flexibility to decorate each particle with ligands that have multiple functions and thereby offers unprecedented opportunities to expand the regime of fluorophore chemistry. A main objective of our research in this area is to exploit approaches to the synthesis of QD conjugates in the aqueous medium from readily available precursors, and to engineer the QDs with a paramagnetic tail so that they can hybridize a electron paramagnetic resonance and fluorescence (EPR-F) technique to develop a novel spin-labeled fluorescent probe. Conventional spin-labeled fluorescent probes are small organic fluorophores labeled with nitroxide radicals. In these probes, the paramagnetic nitroxide radical acts as an effective quencher of the excited singlet state of the fluorophore, and thus makes the fluorophore–nitroxide conjugate an off–on switch when the nitroxide moiety yields a diamagnetic alkoxyamine by trapping free radicals or is reduced to a diamagnetic hydroxylamine. The quenching effect of the nitroxide radical on the emission of trioctylphosphine oxide (TOPO)-capped CdSe QDs was observed in toluene solution, and the complex of TOPO-capped CdSe QDs with 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide has been proved to be sensitive to the carbon-centered free radical