Kehua Xu

A New Nanobiosensor for Glucose with High Sensitivity and Selectivity in Serum Based on Fluorescence Resonance Energy Transfer (FRET) between CdTe Quantum Dots and Au Nanoparticles

A novel assembled nanobiosensor QDs-ConA-beta-CDs-AuNPs was designed for the direct determination of glucose in serum with high sensitivity and selectivity. The sensing approach is based on fluorescence resonance energy transfer (FRET) between CdTe quantum dots (QDs) as an energy donor and gold nanoparticles (AuNPs) as an energy acceptor. The specific combination of concanavalin A (ConA)-conjugated QDs and thiolated beta-cyclodextrins (beta-SH-CDs)-modified AuNPs assembles a hyperefficient FRET nanobiosensor. In the presence of glucose, the AuNPs-beta-CDs segment of the nanobiosensor is displaced by glucose which competes with beta-CDs on the binding sites of ConA, resulting in the fluorescence recovery of the quenched QDs. Experimental results show that the increase in fluorescence intensity is proportional to the concentration of glucose within the range of 0.10-50 muM under the optimized experimental conditions. In addition, the nanobiosensor has high sensitivity with a detection limit as low as 50 nM, and has excellent selectivity for glucose over other sugars and most biological species present in serum. The nanobiosensor was applied directly to determine glucose in normal adult human serum, and the recovery and precision of the method were satisfactory. The unique combination of high sensitivity and good selectivity of this biosensor indicates its potential for the clinical determination of glucose directly and simply in serum, and provides the possibility to detect low levels of glucose in single cells or bacterial cultures. Moreover, the designed nanobiosensor achieves direct detection in biological samples, suggesting the use of nanobiotechnology-based assembled sensors for direct analytical applications in vivo or in vitro.

A near-infrared reversible fluorescent probe for real-time imaging of redox status changes in vivo

Alterations of cellular redox status are closely associated with physiological and pathological processes. Glutathione (GSH) and H2O2 should be the most representative redox couple in living cells. However, up to now, there is no way to reversibly detect GSH/H2O2. In this report, a near-infrared (NIR) fluorescent probe (Cy-O-Eb) for monitoring the changes of GSH/H2O2 levels in vivo was developed based on switching on–off a five-membered ring involved in ebselen. This probe could reversibly respond to GSH and H2O2 with high selectivity, sensitivity and mitochondrial targeting. It was successfully used to monitor the changes of redox status during apoptosis and the H2O2 changes at the wound margin in zebrafish larvae. Thus, the probe would provide an ideal tool for monitoring redox status changes and studying molecular events involved in redox regulation.

A highly sensitive near-infrared fluorescent probe for cysteine and homocysteine in living cells

A near-infrared fluorescent probe (Cy-O-CHO) for the detection of endogenous Cys/Hcy in living cells was designed and synthesized. Cy-O-CHO exhibited high sensitivity and good selectivity to Cys/Hcy under physiological conditions with a detection limit of 7.9 nM for Cys.

A fast-response, highly sensitive and specific organoselenium fluorescent probe for thiols and its application in bioimaging

A novel organoselenium fluorescent probe (Rh-Se-2), which features a high signal-to-noise ratio (up to 170-fold), fast response (5 min) and excellent immunity to interferences, was designed, synthesized and applied to bioimaging.

Effect of gold nanoparticles on glutathione depletion-induced hydrogen peroxide generation and apoptosis in HL7702 cells

Gold nanoparticles (AuNPs) have shown promising biological and military applications due to their unique electronic and optical properties. However, little is known about their cytotoxicity when they come into contact with a biological system. The primary objective of this study is to determine the sequence of apoptotic signaling events that occur after modulation of the cellular redox state in HL7702 cells (human liver cell line), with emphasis on the role of the interaction of AuNPs with glutathione (GSH). After incubation with 8nm AuNPs at 50nM, there was an early decline in cytosolic GSH, which initiated mitochondrial transmembrane potential (ΔΨm) depolarization and apoptosis. Mitochondrial GSH depletion was observed at approximately 48h, after which mitochondrial hydrogen peroxide (H(2)O(2)) production increased significantly and apoptosis was further exacerbated. Bax translocation, cytochrome c release and downstream caspase 3 were first detected at 24h, notably after 48h, corresponding with increasing H(2)O(2) level. These data suggest that HL7702 cells are depleted of intracellular GSH as a result that 8nm AuNPs possess strong Au-S bonding interactions with GSH. A decrease in GSH alone can act as a potent early activator of apoptotic signaling. Increased H(2)O(2) production following mitochondrial GSH depletion represents a crucial event, which commits HL7702 cells to apoptosis through mitochondrial pathway.

High selectivity imaging of nitroreductase using a near-infrared fluorescence probe in hypoxic tumor

A highly selective and sensitive near-infrared (NIR) fluorescence probe (Cy-NO2) for imaging nitroreductase was developed and was successfully applied to investigating the relationship between epithelial-mesenchymal transitions (EMTs) in tumour progression and intracellular hypoxic level.

Use of Selenium to Detect Mercury in Water and Cells: An Enhancement of the Sensitivity and Specificity of a Seleno Fluorescent Probe

Seleno fluorescent probe: An organoselenium fluorescent probe (FSe-1) for mercury was designed based on the irreversible deselenation mechanism. FSe-1 exhibits an ultrahigh selectivity and sensitivity for Hg(2+) detection only for reactive selenium atom sites, due the strong affinity between Se and Hg. Furthermore, the new probe has been successfully used for imaging mercury ions in RAW 264.7 cells (a mouse macrophage cell line; see figure).Inspired by the antitoxic function of selenium towards heavy-metal ions, we designed an organoselenium fluorescent probe (FSe-1) for mercury. The reaction of FSe-1 and Hg(2+) is an irreversible deselenation mechanism based on the selenophilic character of mercury. FSe-1 exhibits an ultrahigh selectivity and sensitivity for Hg(2+) detection only for reactive selenium atom sites due to the strong affinity between Se and Hg. The experimental results proved that FSe-1 was selective for Hg(2+) ions over other relevant metal ions and bioanalytes, and also showed an enhancement in sensitivity of up to 1.0 nM, which is lower than the current Environmental Protection Agency standard for drinking water. Furthermore, the new probe has been successfully applied to the imaging of mercury ions in RAW 264.7 cells (a mouse macrophage cell line) with high sensitivity and selectivity.

Bifunctional combined Au-Fe2O3 nanoparticles for induction of cancer cell-specific apoptosis and real-time imaging

We demonstrate bifunctional combined Au-Fe(2)O(3) nanoparticles (NPs) for selectively induction of apoptosis in cancer cells and real-time imaging. The as-prepared Au-Fe(2)O(3) NPs combine the merits of both Au and γ-Fe(2)O(3) NPs, maintaining excellent fluorescence quenching property and catalytic activity. Conjugated with α(Ⅴ)β(3) integrin-targeting peptide (RGD) and fluorescein isothiocyanate (FITC)-labeled capsase-3 recognition sequence (DEVD) on the Au surface, the resulting RGD/FITC-DEVD-Au-Fe(2)O(3) NPs bind preferentially to integrin α(Ⅴ)β(3)-rich human liver cancer cells (HepG2), sequentially initiate catalytic formation of hydroxyl radicals (·OH) and enable the real-time monitoring of·OH-induced caspase-3-dependent apoptosis in these cancer cells. Furthermore, the catalytic activity of RGD/FITC-DEVD-Au-Fe(2)O(3) NPs is much higher than that of individual γ-Fe(2)O(3) NPs due to the polarization effect at the Au-Fe(2)O(3) interface. Such bifunctional Au-Fe(2)O(3) NPs exhibit simultaneous targeting, therapeutic and imaging functions and are therefore promising for future therapeutic applications in cancer.

A selective near-infrared fluorescent probe for singlet oxygen in living cells

A selective near-infrared fluorescent probe (His-Cy), which features a fast response to (1)O(2) with high sensitivity and selectivity, was designed, synthesized and applied to bioimaging.

Simultaneous Determination of Superoxide and Hydrogen Peroxide in Macrophage RAW 264.7 Cell Extracts by Microchip Electrophoresis with Laser-Induced Fluorescence Detection

A method for the first time to simultaneously determine superoxide and hydrogen peroxide in macrophage RAW 264.7 cell extracts by microchip electrophoresis with laser-induced fluorescence detection (MCE-LIF) was developed. 2-Chloro-1,3-dibenzothiazolinecyclohexene (DBZTC) and bis(p-methylbenzenesulfonyl) dichlorofluorescein (FS), two probes that can be specifically derivatized by superoxide and hydrogen peroxide, respectively, were synthesized and used. Parameters influencing the derivatization and on-chip separation were optimized. With the use of a HEPES (20 mM, pH 7.4) running buffer, a 50 mm long separation channel, and a separation voltage of 1800 V, baseline separation was achieved within 48 s for the two derivatization products, DBZTC-oxide (DBO) and 2,7-dichlorofluorescein (DCF). The linearity ranges of the method were 0.08-5.0 and 0.02-5.0 microM with detection limits (signal-to-noise ratio = 3) of 10 nM (1.36 amol) and 5.6 nM (0.76 amol) for superoxide and hydrogen peroxide, respectively. The relative standard deviations (RSDs) of migration time and peak area were less than 2.0% and 5.0%, respectively. The recoveries of the cell extract samples spiked with 1.0 microM standard solutions were 96.1% and 93.0% for superoxide and hydrogen peroxide, respectively. With the use of this method, superoxide and hydrogen peroxide in phorbol myristate acetate (PMA)-stimulated macrophage RAW 264.7 cell extracts were found to be 0.78 and 1.14 microM, respectively. The method has paved a way for simultaneously determining two or more reactive oxygen species (ROS) in a biological system with high resolution.