Suyan Qiu

Electrochemical impedance spectroscopy sensor for ascorbic acid based on copper(I) catalyzed click chemistry.

Copper(I) species can be acquired from the reduction of copper(II) by ascorbic acid (AA) in situ, and which in turn quantitative catalyze the azides and alkynes cycloaddition reaction. In this study, propargyl-functionalized ferrocene (propargyl-functionalized Fc) has been modified on the electrode through reacting with azide terminal modified Au electrode via copper(I) catalyzed azides and alkynes cycloaddition (CuAAC) reaction. The electrochemical impedance spectroscopy (EIS) measurement has been applied to test the electron transfer resistance of the Au electrode before and after click reaction. The changes of the fractional surface coverage (θ) with different AA concentrations are characterized. It is found that the θ value has a linear response to the logarithm of AA concentration in the range of 5.0 pmol/L to 1.0 nmol/L with the detection limits of 2.6 pmol/L. The sensor shows a good stability and selectivity. And it has been successfully applied to the AA detection in the real samples (urine) with satisfactory results.

A fluorescent probe for detection of histidine in cellular homogenate and ovalbumin based on the strategy of clickchemistry

A sensitive and selective fluorescent probe for histidine has been designed by taking the advantages of the click chemistry reaction (copper(I)-catalyzed azides and alkynes cycloaddition) and the inhibition of copper(II)-induced ascorbate oxidation by histidine. The fluorescence intensity decreases with the increasing of histidine concentration, and the value of F₀/F shows a good linear relationship with the concentration of histidine over the range of 0.5-100 μM with a detection limit of 76 nM, which is lower than those of many other fluorescent sensors. Moreover, the sensor has high specificity for histidine compared to some potential interferents, such as other amino acids and metal ions. In addition, the proposed sensor has been applied to determine histidine in cellular homogenate and ovalbumin samples with satisfactory results. The preferable simplicity, sensitivity and specificity for the detection of histidine indicate that the proposed sensor have potential prospect in environmental and biomedical analysis.

Colorimetric and fluorometric dual-readout sensor for lysozyme

A novel, highly sensitive and selective dual-readout sensor (colorimetric and fluorometric) for the detection of lysozyme was proposed. The fluorescence of triazolylcoumarin molecules was quenched by Au nanoparticles (AuNPs) initially through the fluorescence resonance energy transfer (FRET), after the addition of lysozyme, the stronger binding of lysozyme onto the surfaces of AuNPs made triazolylcoumarin molecules remove from the AuNPs surface and led to the recovery of the fluorescence of triazolylcoumarin molecules, and accompanied by the discernable color change of the solution from red to purple. The lowest detectable concentration for lysozyme was 50 ng mL(-1) by the naked eye, and the limit of detection (LOD) was 23 ng mL(-1) by fluorescence measurements. In addition, satisfactory results for lysozyme detection in hen egg white were confirmed in the study. Moreover, the presented sensor provides a reliable option to determine lysozyme with high sensitivity and selectivity.

Determination of copper(II) in the dairy product by an electrochemical sensor based on click chemistry.

Herein, a novel sensitive electrochemical sensor for copper(II) based on Cu(I) catalyzed alkyne-azide cycloaddition reaction (CuAAC) is described. The catalyst of Cu(I) species is derived from electrochemical reduction of Cu(II) through bulk electrolysis (BE) with coulometry technique. The propargyl-functionalized ferrocene (propargyl-functionalized Fc) is covalently coupled onto the electrode surface via CuAAC reaction and forms propargyl-functionalized Fc modified gold electrode, which allows a good and stable electrochemical signal. The change of current at peak (dI), detected by differential pulse voltammetry (DPV), exhibits a linear response to the logarithm of Cu(II) concentration in the range of 1.0×10(-14)-1.0×10(-9) mol L(-1). It is also found that the proposed sensor has a good selectivity for copper(II) assay even in the presence of other common metal ions. Additionally, the proposed method has been applied to determine copper(II) in the dairy product (yoghurt) with satisfactory results.

A novel fluorescent sensor for mutational p53 DNA sequence detection based on click chemistry.

A novel fluorescent sensor for DNA sequence has been designed by taking advantages of copper nanoparticles (CuNPs) selectively formed on double stranded (ds) DNA template and Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Copper(II) is derived from CuNPs which previously formed on the dsDNA template, and then copper(II) is reduced to copper(I) by ascorbate, which in turn induced CuAAC reaction between the weak-fluorescent compound (3-azido-7-hydroxycoumarin) and propargyl alcohol to form strong fluorescence compounds (1,2,3-triazole compounds). Since CuNPs are accumulated efficiently in the major groove of dsDNA and ssDNA has no groove, it indicates that the proposed sensor owns the merits of low detection limit, high sensitivity and selectivity for mutational p53 sequence detection. Additionally, the method has been successfully applied to recognize the sequence which contains a single-base mismatch in the short human p53 gene fragment. Furthermore, it has also been applied to detect DNA sequence in complex medium (hela cellular homogenate) with satisfactory results.

Colorimetric probe for copper(II) ion detection based on cost-effective aminoquinoline derivative

A readily available aminoquinoline derivative (5-(quinolin-8-yliminol)pentanal, QYP) is used as a new cost-effective colorimetric probe for Cu2+ ion detection by forming a complex with a stoichiometry of 1 : 2. The QYP conjugated with Cu2+ ions induces a discernable color change from light yellow to red-brown in the solution, and the corresponding UV-Vis absorption shifts from 380 nm to 510 nm dramatically. The detection limit for Cu2+ ions is 2.0 μM by the naked eye, approaching other previously reported colorimetric methods, and without tedious conditions. Other possible contaminated metal ions cause no significant interference to detecting Cu2+ ions with the proposed probe. The stability constant of the complex is estimated to be 7.87 × 1010 M−2, which suggests the high stability of the conjugation of QYP with Cu2+ ions. Besides, it was successfully applied to assay Cu2+ ions in river water samples, indicating that the probe may become a great potential candidate in complex sample determination.

A colorimetric sensor for pH utilizing a quinoline derivative

A simple sensor utilizing a simple aminoquinoline derivative (5-(quinolin-8-yliminol) pentanal, QYP) has been successfully developed for the naked-eye colorimetric assay of pH. The QYP compound presents strong solvatochromism due to the solute–solvent interaction, and it is sensitive to a pH change in the solution. The color of the solution changes from orange to colorless upon increasing the pH value, which is well consistent with the corresponding UV/vis absorbance variation. UV absorbance has a direct linear relationship with the pH values in the range of 4.0 to 8.0 in phosphate-buffered saline, and the corresponding color variation could be distinguished readily by the naked eye.

Label-free fluorometric method for monitoring conformational flexibility of laccase based on a selective laccase sensor.

A facile and selective fluorescence sensor for laccase determination has been proposed depending on the interaction between 3-azidocoumarin and trametes versicolor (Tv) laccase in this paper. The azido group of 3-azidocoumarin that is electron-rich α-nitrogen can directly interact with histidines that coordinate to three copper sites through hydrogen bonds and forms a new complex, which decreases the electron-donating ability of the azido group, leading to enhance the fluorescence intensity of the sensing system. Also, other common proteins have no significant interference for the proposed laccase sensor. Additionally, the proposed fluorescence sensor is extended to demonstrate the conformational flexibility of Tv laccase by the urea denaturant. A good consistency of the results obtained with the presented laccase sensor and CD spectra is performed. Furthermore, the relationship between the catalytic activity and the unfolding percentage of the unfolded Tv laccase through the proposed laccase sensor is also elucidated well.