Xinyue Zhu

Near-infrared and naked-eye fluorescence probe for direct and highly selective detection of cysteine and its application in living cells.

The near-infrared (NIR) fluorescence sensor for rapid, selective, and sensitive detection of cystenine (Cys) is of great importance in both biological and environmental sciences. Herein, we report a specific probe with turn-on fluorescence property, visible color change with naked-eye, and large wavelength shift on UV spectra for highly selective detection of Cys over homocysteine (Hcy) and glutathione (GSH) in both HEPES buffer (10 mM, pH 7.4) and diluted human serum. The probe based on the conjugate addition-cyclization reaction has a low limit of detection to Cys (0.16 μM as NIR fluorescence sensor and 0.13 μM as UV sensor). Kinetic study indicated that the probe has a very rapid response to Cys, owing to the much higher pseudo-first-order reaction constant with Cys (299 M(-1) s(-1)) than with Hcy (1.29 M(-1) s(-1)) or GSH (0.53 M(-1) s(-1)). Upon addition of Cys to a solution of the probe, the color changed from purple to cyan, with the maximum wavelength shifting from 582 to 674 nm in the UV spectrum and a fluorescence emission at 697 nm appearing. It has been successfully applied for determination of Cys in diluted serum and bioimaging of Cys in living cells with low cell toxicity.

Imaging of Fluoride Ion in Living Cells and Tissues with a Two-Photon Ratiometric Fluorescence Probe

A reaction-based two-photon (TP) ratiometric fluorescence probe Z2 has been developed and successfully applied to detect and image fluoride ion in living cells and tissues. The Z2 probe was designed designed to utilize an ICT mechanism between n-butylnaphthalimide as a fluorophore and tert-butyldiphenylsilane (TBDPS) as a response group. Upon addition of fluoride ion, the Si-O bond in the Z2 would be cleaved, and then a stronger electron-donating group was released. The fluorescent changes at 450 and 540 nm, respectively, made it possible to achieve ratiometric fluorescence detection. The results indicated that the Z2 could ratiometrically detect and image fluoride ion in living cells and tissues in a depth of 250 μm by two-photon microscopy (TPM).

Naphthalimide derived fluorescent probes with turn-on response for Au3+ and the application for biological visualization

The 4-N,N-dimethyl-1,8-naphthalimide based fluorescent probes have been explored for selective detection of Au(3+). Both probes show a pronounced fluorescence enhancement response to Au(3+). Hydroxy is introduced as ligand of Au(3+) for Probe 1 and the newly designed Probe 2 contains an alkyne moiety to recognize Au(3+) through an irreversible C≡C bond hydrolysis reaction. Probe 1 exhibits higher performance such as faster response, lower detection limit of 0.050μM and the better responsive effect in 99.5% water system compared with most of probes published. The Probe 2 displays high stability to pH, suitable water solubility, wider linear range (0-100μM) to Au(3+), and live-cells imaging with low cytotoxicity.

A new fluorescence turn-on probe for biothiols based on photoinduced electron transfer and its application in living cells

A new biothiol-selective fluorescent probe 1 based on photoinduced electron transfer (PET) mechanism was designed and synthesized. The UV-Vis absorption and fluorescent emission properties of probe 1 towards various analytes were studied in detail. The probe exhibited a large stokes shift (~200nm) after reacted with biothiols and could selectively detect cysteine (Cys) in dimethyl sulfoxide (DMSO)/H2O solution (9:1, v/v, 10mM phosphate buffer saline, pH3.5) over glutathione (GSH), homocysteine (Hcy) and other analytes with a detection limit of 0.117μM. In addition, probe 1 responded well to GSH, Hcy and Cys in the same above solution with pH5.5 and got the detection limits of 0.151μM, 0.128μM and 0.037μM, respectively. Probe 1 was of very low cytotoxicity and successfully applied for imaging of thiols in living cells.

A two-photon off-on fluorescence probe for imaging thiols in live cells and tissues

A two-photon (TP) fluorescence imaging probe (Z1) was designed to detect biothiols through a photoinduced electron transfer pathway utilizing N-butyl-naphthalimide as the fluorophore and 2,4-dinitrobenzene-sulfonyl as the responsive group, which were linked together by piperazine. The synthesized Z1 displayed high selectivity to biothiols, significant fluorescence off-on properties, and a marked two-photon absorption cross section (δ = 110 GM). Moreover, Z1 showed good biocompatibility and insensitivity toward changes in the biologically relevant pH range (7.2-8.4), which enabled the utilization of Z1 to monitor biothiol levels not only in live cells but also in tissues at depths of 50-250 μm.

Preparation of temperature sensitive molecularly imprinted polymer coatings on nickel foam for determination of ofloxacin in Yellow River water by solid-phase microextraction

Nickel foam was firstly used as a solid phase microextraction support to prepare temperature sensitive molecularly imprinted polymers using ofloxacin molecules as the template. The fluorescence intensity could be observed by the naked eye under ultraviolet light after ofloxacin adsorption onto the new materials, which was positively proportional to the adsorbance. After adsorption had occurred, the significantly different fluorescence intensities distinguished the molecularly imprinted polymers from the corresponding non-molecularly imprinted polymers. A detailed evaluation was made by different characterization methods and various adsorption experiments. Finally, the molecularly imprinted polymer on nickel foam was used as an adsorbent in solid phase microextraction, coupled with high performance liquid chromatography, to detect ofloxacin, norfloxacin and enrofloxacin in Yellow River water, obtaining recoveries of 93.2 to 108.3% and limits of quantification of 0.014 to 0.020 μg mL−1.

A near-infrared fluorescent probe based on chloroacetate modified naphthofluorescein for selectively detecting cysteine/homocysteine and its application in living cells

We have prepared a near-infrared (NIR) turn-on fluorescent probe (NFC) based on chloroacetate modified naphthofluorescein for specific detection of cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) and other amino acids (AAs) with the detection limits of 0.30 μM and 0.42 μM, respectively. The fluorescence intensity of the naphthofluorescein (NF) chromophore is modulated by an internal charge transfer (ICT) process. The probe NFC is readily available and weakly fluorescent, but of observably enhanced fluorescence after reacting with Cys or Hcy. We assumed and then demonstrated that the fluorescence off-on process involves a conjugate nucleophilic substitution/cyclization sequence. Furthermore, the probe has been successfully applied for detecting the total content of Cys and Hcy in human plasma and imaging in living cells with low toxicity.

Highly Selective Fluorescent Probe Based on Hydroxylation of Phenylboronic Acid Pinacol Ester for Detection of Tyrosinase in Cells

The detection of tyrosinase, a biomarker for melanoma, is of great significance. Herein, a fluorescent tyrosinase probe, with resorufin as the fluorophore and m-tolylboronic acid pinacol ester as the receptor, is proposed. The response relies on the tyrosinase-catalyzed hydroxylation of phenylboronic acid pinacol ester at an adjacent position followed by 1,6-rearrangement elimination to release resorufin. This probe well quantifies tyrosinase in the range from 1 to 100 U mL-1 with a detection limit of 0.5 U mL-1. Importantly, the probe exhibits high selectivity for tyrosinase over other biological substances including reactive oxygen species. In addition, it is successfully applied to the imaging of tyrosinase in cells. This probe provides a novel platform for selective detection of tyrosinase in biosystems.

A simple ratiometric fluorescent sensor for fructose based on complexation of 10-hydroxybenzo[h]quinoline with boronic acid

A simple ratiometric fluorescent sensor for fructose was presented. It consisted of 10-hydroxybenzo[h]quinoline (HBQ) which showed emission at 572nm and 3-pyridylboronic acid (PDBA) whose complex with HBQ gave emission at 500nm. The reaction of fructose with PDBA inhibited the complexation of HBQ with PDBA, resulting in the change of dual-emission intensity ratio. The sensor well quantified fructose in the range of 0.015-2.5mM with detection limit of 0.005mM. Besides, this sensor exhibited excellent selectivity and was successfully applied to fructose detection in food. This work provides a simple ratiometric sensing platform for sensitive and selective detection of fructose.

Sensitive naked eye detection and quantification assay for nitrite by a fluorescence probe in various water resources

An uncontrolled increase of nitrite concentration in groundwater, rivers and lakes is a growing threat to public health and environment. It is important to monitor the nitrite levels in water and clinical diagnosis. Herein, we developed a switch-off fluorescence probe (PyI) for the sensitive detection of nitrite ions in the aqueous media. This probe selectively recognizes nitrite ions through a distinct visual color change from colorless to pink with a detection limit of 0.1 μM. This method has been successfully applied to the determination of nitrites in tap water, lake water and Yellow River water with recoveries in the range of 94.8%-105.4%.