Shujuan Zhuo

Fluorescent graphene quantum dot nanoprobes for the sensitive and selective detection of mercury ions.

Graphene quantum dots were prepared by ultrasonic route and served as a highly selective water-soluble probe for sensing of Hg(2+). The fluorescence emission spectrum of graphene quantum dots was at about 430nm. In the presence of Hg(2+), the fluorescence of the quantum dots significantly quenched. And the fluorescence intensity gradually decreased with the increasing concentration of Hg(2+). The change of fluorescence intensity is directly proportional to the concentration of Hg(2+). Under optimum conditions, the linear range for the detection of Hg(2+) was 8.0×10(-7) to 9×10(-6)M with a detection limit of 1.0×10(-7)M. In addition, the preliminary mechanism of fluorescence quenching was discussed in the paper. The constructed sensor with high sensitivity and selectivity, simple, rapid properties makes it valuable for further application.

Carbon dots based turn-on fluorescent probes for oxytetracycline hydrochloride sensing

In this paper, we have presented a facile, economic and green one-step hydrothermal synthesis route using tannic acid as carbon source to prepare water-soluble fluorescent carbon dots (CDs). The as-prepared CDs contain distinctive catechol groups on their surfaces, which have a special response toward Fe3+ ions. So the fluorescence emission of CDs gradually decreased with increasing Fe3+ ions. Such fluorescence responses can be used for well quantifying Fe3+ ions in the range of 0–5 μM with the detection limit of 24.4 nM. Most importantly, quenched fluorescence of CDs–Fe3+ could be recovered with the addition of oxytetracycline hydrochloride based on a competition mechanism, which provides a turn-on sensing strategy for oxytetracycline hydrochloride assay. The proposed sensing system has been successfully used for the assay of oxytetracycline hydrochloride in milk samples, indicating the practical potential.

Determination of nucleic acids with tetra-(N-hexadecylpyridiniumyl) porphyrin sensitized by cetyltrimethylammonium bromide (CTMAB) using a Rayleigh light-scattering technique

Using a common spectrofluorometer to measure the intensity of Rayleigh light-scattering (RLS), a method for determination of nucleic acids has been developed. At pH 10.24 and ionic strength 0.01 mol l-1 (NaCl), the Rayleigh light-scattering of the tetra-(N-hexadecylpyridiniumyl) porphyrin (TC16PyP) is greatly enhanced by nucleic acids in the presence of cetyltrimethylammonium bromide (CTMAB), with the scattering peak located at 311.8 nm. The enhanced RLS intensity is in proportion to the concentration of calf thymus DNA (ctDNA) in the range 0.2-6.0 microg ml-1 and to that of fish sperm DNA (fsDNA) in the range 0.05-3.0microg ml-1. The limits of detection are 0.016 microg ml-1 for calf thymus DNA and 0.023 microg ml-1 for fish sperm DNA when the concentration of TPP was chosen 2.0 x 10(-6) mol l-1. Four synthetic samples were determined satisfactorily.

High-throughput and rapid fluorescent visualization sensor of urinary citrate by CdTe quantum dots.

In this paper, we have presented a novel CdTe quantum dots (QDs) based fluorescent sensor for visual and turn-on sensing of citrate in human urine samples. The europium ion (Eu(3+)) can lead to the fluorescence quenching of thioglycollic acid (TGA) modified CdTe QDs due to photoinduced electron transfer accompanied by the change of emission color from yellow to orange. Next, addition of citrate breaks the preformed assembly because citrate can replace the CdTe QDs, based on the fact that the Eu(3+) ion displays higher affinity with citrate than the CdTe QDs. Thus the photoinduced electron transfer is switched off, and the fluorescence emission of CdTe QDs is rapidly (within 5min) recovered, simultaneously, the orange emission color restores to yellow. Such proposed strategy may conveniently discriminate the patient of renal stone from normal person by naked eyes. In addition to visualization detection, the fluorescence responses can be used for well quantifying citrate in the range of 0.67-133μM. So, the present, simple, low-cost and visualized citrate fluorescence sensor has great potential in the applications for earlier screening in clinical detection.

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between tetracarboxy aluminum phthalocyanine and tetra-N-hexadecylpyridiniumyl porphyrin

A new method was developed for determination of micro amounts of nucleic acids based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic tetracarboxy aluminum phthalocyanine (AlC(4)Pc) and a cationic tetra-N-hexadecylpyridiniumyl porphyrin (TC(16)PyP). The fluorescence of the AlC(4)Pc, with the maximum emission wavelength at 701nm, could be quenched by TC(16)PyP at its proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence is proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 1-200ngmL(-1) for fish sperm DNA (FS DNA) and 2-400ngmL(-1) for calf thymus DNA (CT DNA). The corresponding detection limits are 0.59ngmL(-1) for FS DNA and 0.82ngmL(-1) for CT DNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.

Luminescent phosphate sensor based on upconverting graphene quantum dots

ABSTRACT In this paper, we have presented a novel graphene quantum dots based upconversion fluorescent sensor for detection of phosphate. The upconversion fluorescence of graphene quantum dots with emission wavelength at 407 nm was quenched by rare earth ion, Eu3+ in proper concentration. The quenching constant is calculated from Stern–Volmer equation. Importantly, quenched fluorescence of graphene quantum dots-Eu3+ could be recovered with the addition of phosphate based on a competition mechanism, which provides a turn-on sensing strategy for phosphate assay. The recovered fluorescence is proportional to the concentration of phosphate. The linear range for the detection of phosphate was 1 to 12 µM with a detection limit of 100 nM. The proposed sensing system has been successfully used for the assay of phosphate in real river water samples, indicating the practical potential.

Eu(III)-induced room-temperature fast transformation of CdTe nanocrystals into nanorods.

A fast and mild synthesis method of highly crystalline CdTe nanorods (NRs) was developed by adding europium nitrate hexahydrate to an aqueous solution of CdTe nanocrystals (NCs) at room temperature within 30 min. It was suggested that strong coordination strength of Eu(III) decreases zeta potential, thereby accelerates aggregation of NCs, and favors the transformation process from NCs to NRs. The oriented attachment of aggregated particles was suggested as a major path for the formation of highly crystalline NRs under experimental conditions. The proposed extremely fast room-temperature methodology opens up novel pathways for the synthesis of one-dimensional (1D) semiconductor nanostructures with high crystallinity, which would become potential candidates for many practical applications such as photovoltaics, circuit design and fabrication of functional architectures.

Spectrophotometric Method for the Direct Determination of Anionic Surfactant Sodium Dodecyl Benzenesulfonate (SDBS) Using a Hydrophobic Near‐Infrared (NIR) Cationic Cyanine Dye Without Solvent Extraction

Abstract A new hydrophobic near‐infrared (NIR) cationic cyanine dye was synthesized and evaluated as a new reagent for the determination of anionic surfactant sodium dodecyl benzenesulfonate (SDBS). The cyanine dye with an absorption maximum at 770 nm reacted with SDBS, causing significant hypochromism. Under the optimal conditions, the decreased absorption is proportional to the concentration of SDBS over the range 2.9 × 10−7–1 × 10−5 mol/L. The detection limit was 1.9 × 10−7 mol/L. The relative standard deviation for 1.43 × 10−6 mol/L SDBS was 1.3% (n = 9). The proposed method was applied to determination of anionic surfactant in the river with 93–106% recovery levels. Preliminary research shows that the hypochromism is due to the formation of dye aggregate facilitated by SDBS.

Determination of gamma-globulin at nanogram levels by its quenching effect on the fluorescence of a red emitting conjugated polymer

In this study, a novel fluorescence sensing strategy has been proposed for γ-globulin (γ-IgG) assay, based on the measurement of quenched fluorescence signals resulting from the interaction of a water-soluble conjugated polymer, poly[2,5-di(propyloxysulfonate)-1,4-phenylene-ethynylene-9,10-anthrylene] (referred to as PPEASO3), with γ-IgG. The red fluorescence of PPEASO3 at 682 nm is greatly quenched when trace amounts of γ-IgG are added. Under optimal experimental conditions, the quenched fluorescence intensity is linear with the concentration of γ-IgG in the range 5–1000 ng mL−1 with a detection limit of 0.8 ng mL−1. The proposed method is simple and sensitive for the detection of trace amounts of γ-IgG and used to determine the content of γ-IgG in synthetic samples with satisfactory results.