Jingjing Deng

Real-time ratiometric fluorescent assay for alkaline phosphatase activity with stimulus responsive infinite coordination polymer nanoparticles.

This study demonstrates a novel ratiometric fluorescent method for real-time alkaline phosphatase (ALP) activity assay with stimulus responsive infinite coordination polymer (ICP) nanoparticles as the probe. The ICP nanoparticles used in this study are composed of two components; one is the supramolecular ICP network formed with guanine monophosphate (GMP) as the ligand and Tb(3+) as the central metal ion, and the other is a fluorescent dye, i.e., 7-amino-4-methyl coumarin (coumarin) encapsulated into the ICP network. Upon being excited at 315 nm, the ICP network itself emits green fluorescence at 552 nm. Coumarin dye encapsulated in the ICP network emits weak fluorescence at 450 nm upon excitation at the same wavelength (315 nm), and this fluorescence emission becomes strong when the encapsulated dye is released from the network into the solution phase. Hence, we develop a ratiometric fluorescent assay based on the ALP-induced destruction of the supramolecular ICP network and the release of coumarin. This mechanism can be used for real-time ratiometric fluorescent monitoring of ALP activity by continuously measuring the ratio of fluorescent intensity at the wavelength of 552 nm (F552) to that at 450 nm (F450) (F552/F450) in the time-dependent fluorescent spectra of the coumarin@Tb-GMP suspension containing ALP with different activities. Under the experimental conditions employed here, the F552/F450 value is linear with the ALP activity within a range from 0.025 U/mL to 0.2 U/mL. The detection limit is down to 0.010 U/mL (S/N = 3). Moreover, the assay developed here is employed for ALP inhibitor evaluation. This study offers a simple yet sensitive method for real-time ALP activity assay.

Competitive Coordination of Cu2+ between Cysteine and Pyrophosphate Ion: Toward Sensitive and Selective Sensing of Pyrophosphate Ion in Synovial Fluid of Arthritis Patients

Direct selective and sensitive sensing of pyrophosphate ion (PPi) in synovial fluid of arthritis patients is of great importance because of its crucial roles in the diagnosis and therapy of arthritic diseases. In this study, we demonstrate a sensitive and selective method for PPi sensing in synovial fluid of arthritis patients with gold nanoparticles (Au-NPs) as the signal readout based on the competitive coordination chemistry of Cu(2+) between cysteine and PPi. Initially, Au-NPs stabilized with cysteine are red in color and exhibit absorption at 519 nm in the UV-vis spectrum. The addition of an aqueous solution of Cu(2+) to the Au-NPs dispersion containing cysteine causes the aggregation of Au-NPs, resulting in the wine red-to-blue color change and the appearance of a new absorption at 650 nm in the UV-vis spectrum of the Au-NPs dispersion. The subsequent addition of PPi to the Au-NPs aggregation well solubilizes the aggregated Au-NPs with the changes in both the color and the UV-vis spectrum of the Au-NPs dispersion. These changes are ascribed to the higher coordination reactivity between Cu(2+) and PPi than that between Cu(2+) and cysteine. On the basis of this, the concentration of PPi can be visualized with the naked eyes through the blue-to-wine red color change of the Au-NPs dispersion and quantitatively determined by UV-vis spectroscopy. Under the optimized conditions, the ratio of the absorbance at 650 nm (A(650)) to that at 519 nm (A(519)) shows a linear relationship with PPi concentration within a concentration range from 130 nM to 1.3 mM. The method demonstrated here is highly sensitive, free from the interference from other species in the synovial fluid, and is thus particularly useful for fast and simple clinic diagnosis of arthritic diseases.

Folic acid-functionalized fluorescent gold nanoclusters with polymers as linkers for cancer cell imaging

A novel nano-conjugate containing ultrasmall water-soluble AuNCs protected by ovalbumin as the fluorescent part, folic acid as the targeting ligand and a homopolymer N-acryloxysuccinimide as the linker has been investigated. Moreover, specific staining of HeLa cells by the nano-conjugate has been demonstrated.

Aspartic acid-promoted highly selective and sensitive colorimetric sensing of cysteine in rat brain.

Direct selective determination of cysteine in the cerebral system is of great importance because of the crucial roles of cysteine in physiological and pathological processes. In this study, we report a sensitive and selective colorimetric assay for cysteine in the rat brain with gold nanoparticles (Au-NPs) as the signal readout. Initially, Au-NPs synthesized with citrate as the stabilizer are red in color and exhibit absorption at 520 nm. The addition of an aqueous solution (20 μL) of cysteine or aspartic acid alone to a 200 μL Au-NP dispersion causes no aggregation, while the addition of an aqueous solution of cysteine into a Au-NP dispersion containing aspartic acid (1.8 mM) causes the aggregation of Au-NPs and thus results in the color change of the colloid from wine red to blue. These changes are ascribed to the ion pair interaction between aspartic acid and cysteine on the interface between Au-NPs and solution. The concentration of cysteine can be visualized with the naked eye and determined by UV-vis spectroscopy. The signal output shows a linear relationship for cysteine within the concentration range from 0.166 to 1.67 μM with a detection limit of 100 nM. The assay demonstrated here is highly selective and is free from the interference of other natural amino acids and other thiol-containing species as well as the species commonly existing in the brain such as lactate, ascorbic acid, and glucose. The basal dialysate level of cysteine in the microdialysate from the striatum of adult male Sprague-Dawley rats is determined to be around 9.6 ± 2.1 μM. The method demonstrated here is facile but reliable and durable and is envisaged to be applicable to understanding the chemical essence involved in physiological and pathological events associated with cysteine.

Real-time colorimetric assay of inorganic pyrophosphatase activity based on reversibly competitive coordination of Cu2+ between cysteine and pyrophosphate ion.

In this study we demonstrate a new colorimetric method for real-time pyrophosphatase (PPase) activity assay based on reversible tuning of the dispersion/aggregation states of gold nanoparticles (Au-NPs) by controlling the coordination of Cu(2+) between cysteine and pyrophosphate ion (PPi) with PPase. The addition of Cu(2+) to the cysteine-stabilized Au-NP dispersion results in the aggregation of Au-NPs, while the further addition of PPi to this aggregation turns the aggregated Au-NPs into their dispersed state because of the higher coordination reactivity between Cu(2+) and PPi than that between Cu(2+) and cysteine. The subsequent addition of PPase to the PPi-triggered dispersed Au-NPs restores the aggregation state of Au-NPs because PPase catalyzes the hydrolysis of PPi into orthophosphate and thus consumes PPi in the reaction system. In this study, we utilize this reversibility of the change between the aggregation/dispersion states of Au-NPs for real-time colorimetric monitoring of PPase activity by continuously measuring the ratio of absorbance at the wavelength of 650 nm (A650) to that at 522 nm (A522) in the time-dependent UV-vis spectra of Au-NP dispersions containing different activities of PPase. To calculate the kinetics of the PPase-catalyzed hydrolysis of PPi, the A650/A522 values are converted into PPi concentrations to obtain the time-dependent changes of PPi concentrations in the dispersions containing different activities of PPase. The initial reaction rates (v0) are thus achieved from the time-dependent logarithm of PPi concentrations with the presence of different PPase activities. Under the experimental conditions employed here, the v0 values are linear with the PPase activity within a range from 0.025 to 0.4 U with a detection limit down to 0.010 U (S/N = 3). Moreover, the colorimetric method developed here is also employed for PPase inhibitor evaluation. This study offers a simple yet effective method for real-time PPase activity assay.

Visualization and quantification of neurochemicals with gold nanoparticles: opportunities and challenges.

Gold nanoparticle (Au-NP)-based colorimetric assays offer new opportunitites for the visualization and quantification of neurochemicals involved in physiological and pathological processes due to their high sensitivity, designability, and low technical demands. In this Research News, we systematically review the advances on the development of Au-NP-based colorimetric methods for visualization and quantification of neurochemicals and their potential applications for effectively monitoring neurochemicals in the central nervous system. By integration of the favourable surface chemistry with the high extinction coefficient of Au-NPs, some new principles and methods could be developed for the quantification of neurochemicals involved in brain functions. New strategies to design the surface chemistry of Au-NPs, along with the key challenges yet to be addressed to achieve online visualization and quantification of neurochemicals in the central nervous system, are illustrated and discussed. The questions opened here should inspire future investigations and lead to discoveries that continue the development of the effective analytical protocols based on Au-NPs for neurochemical visualization and quantification.

Quantum dot-DNA aptamer conjugates coupled with capillary electrophoresis: A universal strategy for ratiometric detection of organophosphorus pesticides.

Based on the highly sensitivity and stable-fluorescence of water-soluble CdTe/CdS core-shell quantum dots (QDs) with broad-specificity DNA aptamers, a novel ratiometric detection strategy was proposed for the sensitive detection of organophosphorus pesticides by capillary electrophoresis with laser-induced fluorescence (CE-LIF). The as-prepared QDs were first conjugated with the amino-modified oligonucleotide (AMO) by amidation reaction, which is partial complementary to the DNA aptamer of organophosphorus pesticides. Then QD-labeled AMO (QD-AMO) was incubated with the DNA aptamer to form QD-AMO-aptamer duplex. When the target organophosphorus pesticides were added, they could specifically bind the DNA aptamer, leading to the cleavage of QD-AMO-aptamer duplex, accompany with the release of QD-AMO. As a result, the ratio of peak height between QD-AMO and QD-AMO-aptamer duplex changed in the detection process of CE-LIF. This strategy was subsequently applied for the detection of phorate, profenofos, isocarbophos, and omethoate with the detection limits of 0.20, 0.10, 0.17, and 0.23μM, respectively. This is the first report about using QDs as the signal indicators for organophosphorus pesticides detection based on broad-specificity DNA aptamers by CE-LIF, thus contributing to extend the scope of application of QDs in different fields. The proposed method has great potential to be a universal strategy for rapid detection of aptamer-specific small molecule targets by simply changing the types of aptamer sequences.

Mitochondria Targeted Nanoscale Zeolitic Imidazole Framework-90 for ATP Imaging in Live Cells

Zeolitic imidazole frameworks (ZIFs) are an emerging class of functional porous materials with promising biomedical applications such as molecular sensing and intracellular drug delivery. We report herein the first example of using nanoscale ZIFs (i.e., ZIF-90), self-assembled from Zn2+ and imidazole-2-carboxyaldehyde, to target subcellular mitochondria and image dynamics of mitochondrial ATP in live cells. Encapsulation of fluorescent Rhodamine B (RhB) into ZIF-90 suppresses the emission of RhB, while the competitive coordination between ATP and the metal node of ZIF-90 dissembles ZIFs, resulting in the release of RhB for ATP sensing. With this method, we are able to image mitochondrial ATP in live cells and study the ATP level fluctuation in cellular glycolysis and apoptosis processes. The strategy reported here could be further extended to tune nanoscale ZIFs inside live cells for targeted delivery of therapeutics to subcellular organelles for advanced biomedical applications.

Colorimetric and Fluorescent Dual Mode Sensing of Alcoholic Strength in Spirit Samples with Stimuli-Responsive Infinite Coordination Polymers

This study demonstrates a new strategy for colorimetric and fluorescent dual mode sensing of alcoholic strength (AS) in spirit samples based on stimuli-responsive infinite coordination polymers (ICPs). The ICP supramolecular network is prepared with 1,4-bis(imidazol-1-ylmethyl)benzene (bix) as the ligand and Zn(2+) as the central metal ion in ethanol, in which rhodamine B (RhB) is encapsulated through self-adaptive chemistry. In pure ethanol solvent, the as-formed RhB/Zn(bix) is well dispersed and quite stable. However, the addition of water into the ethanol dispersion of RhB/Zn(bix) destroys Zn(bix) network structure, resulting in the release of RhB from ICP into the solvent. As a consequence, the solvent displays the color of released RhB and, at the meantime, turns on the fluorescence of RhB, which constitutes a new mechanism for colorimetric and fluorescent dual mode sensing of AS in commercial spirit samples. With the method developed here, we could distinguish the AS of different commercial spirit samples by the naked eye within a wide linear range from 20 to 100% vol and by monitoring the increase of fluorescent intensity of the released RhB. This study not only offers a new method for on-spot visible detection of AS in commercial spirit samples, but also provides a strategy for designing dual mode sensing mechanisms for different analytical purposes based on novel stimuli-responsive materials.

Stimulus Response of Au-NPs@GMP-Tb Core-Shell Nanoparticles: Toward Colorimetric and Fluorescent Dual-Mode Sensing of Alkaline Phosphatase Activity in Algal Blooms of a Freshwater Lake.

In this study, we demonstrate a colorimetric and fluorescent dual-mode method for alkaline phosphatase activity (APA) sensing in freshwater lake with stimuli-responsive gold nanoparticles@terbium-guanosine monophosphate (Au-NPs@GMP-Tb) core-shell nanoparticles. Initially, the core-shell nanoparticles were fabricated based on Au-NPs decorated with a fluorescent GMP-Tb shell. Upon being excited at 290 nm, the as-formed Au-NPs@GMP-Tb core-shell nanoparticles emit green fluorescence, and the decorated GMP-Tb shell causes the aggregation of Au-NPs. However, the addition of ALP destroys GMP-Tb shell, resulting in the release of Au-NPs from the shell into the solvent. As a consequence, the aggregated Au-NPs solubilizes with the changes in the UV-vis spectrum of the dispersion, and in the meantime, the fluorescence of GMP-Tb shell turns off, which constitutes a new mechanism for colorimetric and fluorescent dual-mode sensing of APA. With the method developed here, we could monitor the dynamic change of APA during an algal bloom of a freshwater lake, both by the naked eye and further confirmed by fluorometric determination. This study not only offers a new method for on-site visible detection of APA but also provides a strategy for dual-mode sensing mechanisms by the rational design of the excellent optical properties of Au-NPs and the adaptive inclusion properties of the luminescent infinite coordination polymers.