Aijun Tong

Abasic Site-Containing DNAzyme and Aptamer for Label-Free Fluorescent Detection of Pb2+ and Adenosine with High Sensitivity, Selectivity, and Tunable Dynamic Range

An abasic site called dSpacer has been introduced into duplex regions of the 8-17 DNAzyme and adenosine aptamer for label-free fluorescent detection of Pb(2+) and adenosine, respectively. The dSpacer can bind an extrinsic fluorescent compound, 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND), and quench its fluorescence. Addition of Pb(2+) enables the DNAzyme to cleave its substrate and release ATMND from DNA duplex, recovering the fluorescence of ATMND. Similarly, the presence of adenosine induces structural switching of the aptamer, resulting in the release of ATMND from the DNA duplex and a subsequent fluorescence enhancement. Under optimized conditions, this label-free method exhibits detection limits of 4 nM for Pb(2+) and 3.4 muM for adenosine, which are even lower than those of the corresponding labeled-DNAzyme and aptamer sensors. These low detection limits have been obtained without compromising any of the selectivity of the sensors. Finally, the dynamic range of the adenosine sensor has been tuned by varying the number of hybridized base-pairs in the aptamer duplex. The method demonstrated here can be applied for label-free detection and quantification of a broad range of analytes using other DNAzymes and aptamers.

Salicylaldehyde Azines as Fluorophores of Aggregation-Induced Emission Enhancement Characteristics

A series of salicylaldehyde azine derivatives were found to exhibit interesting aggregation-induced emission enhancement (AIEE) characteristics. In good solvent, all these compounds displayed very weak fluorescence, while strong emission was observed when they were placed in poor solvent. Moreover, the AIEE color of these compounds varied from green to red depending on the substituents on azines. Their in situ formation also promises potential applications in fluorescence sensing of hydrazine.

Highly sensitive and selective optical chemosensor for determination of Cu2+ in aqueous solution

A highly selective and sensitive rhodamine-based colorimetric chemosensor (1) for quantification of divalent copper in aqueous solution has been investigated in this work. It was designed using salicylaldehyde hydrazone and rhodamine 6G as copper-chelating and signal-reporting groups, respectively. In environmentally friendly media (50%(v/v) water/ethanol and 10mM NaAc-HAc neutral buffer (pH 7.0)), the sensor exhibited selective absorbance enhancement to Cu(2+) over other metal ions at 529 nm, with a dynamic working range of 0.05-5.00 microM and a detection limit of 10nM Cu(2+), respectively. To achieve fluorometric determination of Cu(2+), the Cu(2+)-induced absorbance enhancement of 1 was efficiently converted to fluorescence quenching by fluorescence inner filter effects using rhodamine B (RB) as a fluorophore. The selectivity and sensitivity of fluorescence analysis were similar to those of absorptiometric measurement. Both absorptiometric and fluorometric methods were successfully applied to the detection of Cu(2+) in three water samples.

Reversible Photochromic System Based on Rhodamine B Salicylaldehyde Hydrazone Metal Complex

Photochromic molecules are widely applied in chemistry, physics, biology, and materials science. Although a few photochromic systems have been developed before, their applications are still limited by complicated synthesis, low fatigue resistance, or incomplete light conversion. Rhodamine is a class of dyes with excellent optical properties including long-wavelength absorption, large absorption coefficient, and high photostability in its ring-open form. It is an ideal chromophore for the development of new photochromic systems. However, known photochromic rhodamine derivatives, such as amides, exhibit only millisecond lifetimes in their colored ring-open forms, making their application very limited and difficult. In this work, rhodamine B salicylaldehyde hydrazone metal complex was found to undergo intramolecular ring-open reactions upon UV irradiation, which led to a distinct color and fluorescence change both in solution and in solid matrix. The complex showed good fatigue resistance for the reversible photochromism and long lifetime for the ring-open state. Interestingly, the thermal bleaching rate was tunable by using different metal ions, temperatures, solvents, and chemical substitutions. It was proposed that UV light promoted isomerization of the rhodamine B derivative from enol-form to keto-form, which induced ring-opening of the rhodamine spirolactam in the complex to generate color. The photochromic system was successfully applied for photoprinting and UV strength measurement in the solid state. As compared to other reported photochromic molecules, the system in this study has its advantages of facile synthesis and tunable thermal bleaching rate, and also provides new insights into the development of photochromic materials based on metal complex and spirolactam-containing dyes.

Sensitive and selective fluorescence determination of trace hydrazine in aqueous solution utilizing 5-chlorosalicylaldehyde

A facile fluorescent method for the determination of hydrazine in aqueous solution with excellent sensitivity was developed. 5-chlorosalicylaldehyde (CS), a readily commercially available compound, was applied as the derivatization reagent in this work. Under the addition of CS to hydrazine aqueous solution (ethanol/water/acetic acid=30/66/4), an intense fluorescence enhancement was observed at 570 nm with a large stokes shift of approximately 170 nm. Upon the optimal condition, the fluorescence intensity linearly increased with the concentration of hydrazine in the range of 0.2 and 9.3 microM with a correlation coefficient of R2=0.9995 (n=10) and a detection limit of 0.08 microM. The R.S.D. was 2.0% (n=5). Determination of hydrazine in river and drinking water samples was successfully performed. Hydrazine vapor sensing by the proposed method was also reported.

A new fluorescent probe of rhodamine B derivative for the detection of copper ion.

A new fluorescent probe, rhodamine B hydrazide oxalamide (RBHO), which shows very weak fluorescence, was synthesized, and its fluorescence could be substantially enhanced by the addition of copper ion. The probe shows a high selectivity and sensitivity to copper ion by forming a 1:1 complex in acetonitrile, and the chelating is reversible. Limit of detection for copper ion in acetonitrile was found to be 3.7x10(-8)mol L(-1). It was also found that copper ion could catalyze the hydrolysis of the probe in 50% (v/v) buffered (10mM Tris-HCl, pH 7.0) water/acetonitrile giving a highly fluorescent product, and the fluorescence detection of copper ion was developed in this neutral buffered media with a detection limit of 6.4x10(-7)mol L(-1). Determination of copper ion in water and synthetic samples in the presence of different interfering metal ions was successfully carried out with the new probe RBHO.

Label-free catalytic and molecular beacon containing an abasic site for sensitive fluorescent detection of small inorganic and organic molecules.

In this work, two methods with complementary features, catalytic and molecular beacon (CAMB) and label-free fluorescent sensors using an abasic site, have been combined into new label-free CAMB sensors that possess advantages of each method. The label-free method using a dSpacer-containing molecular beacon makes CAMB more cost-effective and less interfering with the catalytic activity, while CAMB allows the label-free method to use true catalytic turnovers for signal amplifications, resulting in a new label-free CAMB sensor for Pb(2+) ion, with a detection limit of 3.8 nM while maintaining the same selectivity. Furthermore, by using CAMB to overcome the label-free methods limitation of requiring excess enzyme strands, a new label-free CAMB sensor using aptazyme is also designed to detect adenosine down to 1.4 μM, with excellent selectivity over other nucleosides.

A new coumarin-based fluorescence turn-on chemodosimeter for Cu2+ in water.

A highly selective and sensitive coumarin-based chemodosimeter 1 for Cu(2+) in water is reported in this work. 1 was designed and facilely synthesized by a one-step reaction with coumarin as a fluorophore and 2-picolinic acid as the binding moiety, which showed very week fluorescence in buffer solution, and its fluorescence was considerably enhanced by the addition of Cu(2+) at room temperature in 5 min. Mechanism study suggested that Cu(2+) promoted the hydrolysis of 1 via the catalytic sensing cycle, generating a highly fluorescent product 7-hydroxycoumarin with fluorescence signal greatly amplified. The probe exhibited remarkably selective fluorescence enhancement to Cu(2+) over other metal ions at 454 nm, with a detection limit of 35 nM Cu(2+). Under optimal condition, 1 was successfully used for the determination of Cu(2+) in fetal equine serum and two water samples.

The study of the partitioning mechanism of methyl orange in an aqueous two-phase system.

An aqueous two-phase system of dodecyl triethylammonium bromide (C(12)NE, cationic surfactant) and sodium dodecyl sulfate (SDS, anionic surfactant) mixture is proposed for the extraction of some dyes and porphyrin compounds. Transparent two phase-systems are formed when the surfactant concentrations and C(12)NE/SDS ratios are in certain regions. In this study, the aqueous two phase-systems were prepared by mixing 0.1 mol l(-1) C(12)NE and SDS with a molar ratio of 1.7:1.0. The results showed that negatively charged chlorophyll (sodium copper chlorophyllin) and positively charged dye (methyl violet) were efficiently extracted into the upper phase. The negatively charged methyl orange (pH>7) was moved into the upper phase mostly while amphoteric methyl orange (pH<3) was distributed in the two phases uniformly. Except for hydrophobic force, charge interaction between solute and surfactant also play an important role in the extraction process.

A facile, sensitive and selective fluorescent probe for heparin based on aggregation-induced emission

A facile, rapidly responsive fluorescence turn-on probe for heparin with high selectivity and sensitivity was reported in this paper. The probe could aggregate on the negatively charged heparin template through electrostatic interactions and then display intense fluorescence due to its aggregation-induced emission (AIE) characteristics. Under optimal condition, the probe showed high selectivity to heparin over chondroitin sulfate(ChS), hyaluronic acid (HA), dextran (DeX) and other substances, with a linear range of 0.2-14 μg/mL, and a detection limit of 57.6 ng/mL. In diluted serum, it also showed good performance.