He-Fang Wang

Surface molecular imprinting on Mn-doped ZnS quantum dots for room-temperature phosphorescence optosensing of pentachlorophenol in water.

A new type of molecularly imprinted polymer (MIP)-based room-temperature phosphorescence (RTP) optosensor was developed by anchoring the MIP layer on the surface of Mn-doped ZnS quantum dots (QDs) via a surface molecular imprinting process. The synergetic combination of the RTP property of the Mn-doped ZnS QDs and the merits of the surface imprinting polymers not only improves the RTP selectivity of the Mn-doped ZnS QDs but also makes the MIP-based RTP optosensor also applicable to selective detecting of those nonphosphorescent analytes without the need for any inducers and derivatization. The new MIP-based RTP sensing protocol was applied to detect trace pentachlorophenol (PCP) in water samples without the interference of autofluorescence and scattering light of matrixes. The detection limit for PCP was 86 nM, and the precision for five replicate detections of 0.4 microM PCP was 2.8% (relative standard deviation). The recovery of spiked PCP in river water samples ranged from 93% to 106%.

In Situ Hydrothermal Growth of Metal−Organic Framework 199 Films on Stainless Steel Fibers for Solid-Phase Microextraction of Gaseous Benzene Homologues

Metal-organic frameworks (MOFs) have received great attention due to their fascinating structures and intriguing potential applications in various fields. Herein, we report the first example of the utilization of MOFs for solid-phase microextraction (SPME). MOF-199 with unique pores and open metal sites (Lewis acid sites) was employed as the coating for SPME fiber to extract volatile and harmful benzene homologues. The SPME fiber was fabricated by in situ hydrothermal growth of thin MOF-199 films on etched stainless steel wire. The MOF-199-coated fiber not only offered large enhancement factors from 19,613 (benzene) to 110,860 (p-xylene), but also exhibited wide linearity with 3 orders of magnitude for the tested benzene homologues. The limits of detection for the benzene homologues were 8.3-23.3 ng L(-1). The relative standard deviation (RSD) for six replicate extractions using one SPME fiber ranged from 2.0% to 7.7%. The fiber-to-fiber reproducibility for three parallel prepared fibers was 3.5%-9.4% (RSD). Indoor air samples were analyzed for the benzene homologues using the SPME with the MOF-199-coated fiber in combination with gas chromatography-flame ionization detection. The recoveries for the spiked benzene homologues in the collected indoor air samples were in the range of 87%-106%. The high affinity of the MOF-199-coated fiber to benzene homologues resulted from the combined effects of the large surface area and the unique porous structure of the MOF-199, the pi-pi interactions of the aromatic rings of the analytes with the framework 1,3,5-benzenetricarboxylic acid molecules, and the pi-complexation of the electron-rich analytes to the Lewis acid sites in the pores of MOF-199.

Conjugation of glucose oxidase onto Mn-doped ZnS quantum dots for phosphorescent sensing of glucose in biological fluids.

Integrating various enzymes with nanomaterials provides various nanohybrids with new possibilities in biosensor applications. Furthermore, the enzymatic activity and stability are also improved due to the large surface area of nanomaterials. Here we report the conjugation of glucose oxidase (GOD) onto phosphorescent Mn-doped ZnS quantum dots (QDs) using 1-ethyl-3-(3-dimethylaminopropy)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as coupling reagents for glucose biosensing based on the effective quenching of the room temperature phosphorescence (RTP) of Mn-doped ZnS QDs by the H(2)O(2) generated from GOD-catalyzed oxidation of glucose. The obtained bioconjugate not only provided improved enzymatic performance with Michaelis-Menten constant of 0.70 mM but also favored biological applications because the phosphorescent detection mode avoided the interference from autofluorescence and scattering light from the biological matrix. In addition, the GOD-conjugated Mn-doped ZnS QDs showed better thermal stability in the temperature range of 20-80 degrees C. The GOD-Mn-doped ZnS QDs based RTP sensor for glucose gave a detection limit of 3 microM and two linear ranges from 10 microM to 0.1 mM and from 0.1 to 1 mM. The developed biosensor was successfully applied to the determination of glucose in real serum samples without the need for any complicated sample pretreatments.

Metal–Organic-Framework-Based Tandem Molecular Sieves as a Dual Platform for Selective Microextraction and High-Resolution Gas Chromatographic Separation of n-Alkanes in Complex Matrixes

Metal-organic frameworks (MOFs) were employed to design tandem molecular sieves as a dual platform for selective solid-phase microextraction (SPME) and high-resolution gas chromatographic (GC) separation of target analytes in complex matrixes. An elegant combination of a ZIF-8-coated fiber for SPME with a ZIF-8-coated capillary for GC allows selective extraction and separation of n-alkanes from complex matrixes such as petroleum-based fuel and biological fluids. The proposed tandem ZIF-8 molecular sieves not only offered good enhancement factors from 235 (hexane) to 1212 (nonane), but also exhibited wide linearity with 3 orders of magnitude for the tested linear alkanes. The limits of detection for the linear alkanes ranged from 0.46 ng L(-1) (nonane) to 1.06 ng L(-1)(hexane). The relative standard deviations of retention time, peak area, peak height, and half peak width for five replicate determinations of the tested n-alkanes at 30 ng L(-1) were 0.02-0.26%, 1.9-8.6%, 1.4-6.0%, and 1.3-7.2%, respectively. The developed tandem ZIF-8 molecular sieves were further used for the determination of linear alkanes in petroleum-based fuel and human serum. The large diversity in structure and pore size allows various combinations of MOFs for designing an MOF-based tandem molecular sieve platform to achieve different selectivities in extraction and chromatographic separation and to solve headache problems in complex real sample analysis.

Exploring Mn-doped ZnS quantum dots for the room-temperature phosphorescence detection of enoxacin in biological fluids.

While most research works focus on the development of quantum dots (QDs)-based fluorescence sensors, much less attention is paid to the phosphorescence properties of QDs and their potential for phosphorescence detection. In this work, the phosphorescence property of Mn-doped ZnS QDs is explored to develop a novel room-temperature phosphorescence (RTP) method for the facile, rapid, cost-effective, sensitive, and selective detection of enoxacin in biological fluids. The Mn-doped ZnS QDs-based RTP method reported here does not need the use of deoxidants and other inducers and allows the detection of enoxacin in biological fluids without interference from autofluorescence and the scattering light of the matrix. The Mn-doped ZnS QDs offer excellent selectivity for detecting enoxacin in the presence of the main relevant metal ions in biological fluids, biomolecules, and other kinds of antibiotics. Quenching of the phosphorescence emission due to the addition of enoxacin at 1.0 microM is unaffected by 5000-fold excesses of Na (+) and 10000-fold excesses of K (+), Mg (2+), and Ca (2+). Amino acids such as tryptophan, histidine, and l-cysteine at 1000-fold concentration of enoxacin do not affect the detection of enoxacin. Glucose does not affect the detection at 10000-fold concentration of enoxacin. Typical coadministers (mainly other types of antibiotics) such as ceftezole, cefoperazone, oxacillin, and kalii dehydrographolidi succinas are permitted at 50-, 10-, 100-, and 50-fold excesses, respectively, without interference with the detection of enoxacin. The precision for 11 replicate detections of 0.4 microM enoxacin is 1.8% (RSD). The detection limit for enoxacin is 58.6 nM. The recovery of spiked enoxacin in human urine and serum samples ranges from 94 to 104%. The developed Mn-doped ZnS QDs-based RTP method is employed to monitor the time-dependent concentration of enoxacin in urine from a healthy volunteer after the oral medication of enoxacin. The investigation provides evidence that doped QDs are promising for RTP detection in further applications.

Fluorescence Resonance Energy Transfer Inhibition Assay for α-Fetoprotein Excreted during Cancer Cell Growth Using Functionalized Persistent Luminescence Nanoparticles

Persistent-luminescence nanoparticles (PLNPs) are promising as a new generation of photoluminescent probes for detection of biomolecules and bioimaging. Here we report a fluorescence resonance energy transfer (FRET) inhibition assay for α-fetoprotein (AFP) excreted during cancer cell growth using water-soluble functionalized PLNPs based on Eu2+- and Dy3+-doped Ca1.86Mg0.14ZnSi2O7. Polyethyleneimine-coated PLNPs were conjugated with AFP-antibody-coated gold nanoparticles as a sensitive and specific persistent photoluminescence probe for detection of AFP in serum samples and imaging of AFP excreted during cancer cell growth. Such PLNPs do not contain toxic heavy metals. Their long-lasting afterglow nature allows detection and imaging without external illumination, thereby eliminating the autofluorescence and scattering light from biological matrixes encountered under in situ excitation.

Discrimination of Saccharides with a Fluorescent Molecular Imprinting Sensor Array Based on Phenylboronic Acid Functionalized Mesoporous Silica

A fluorescent indicator-displacement molecular imprinting sensor array based on phenylboronic acid functionalized mesoporous silica was developed for discriminating saccharides. D-Fructose imprinted material (FruIM), D-xylose imprinted material (XylIM) together with a control blank nonimprinted material (NIM) were synthesized as the elements of the imprinting sensor array. Spectrofluorimetric titrations of the three materials with eight selected saccharides were carried out, and Stern-Volmer quenching constants (K(SV)) of NIM, FruIM, and XylIM with the eight selected saccharides were obtained to investigate the interaction of the materials with saccharides. The present approach couples molecular imprinting technique to indicator-displacement strategy with the use of one conventional saccharide receptor (phenylboronic acid) and one commercially available fluorescent dye (Alizarin Red S., ARS) as the indicator, and allows identifying two template saccharides (D-fructose and D-xylose) plus eight nontemplate saccharides (D-arabinose, D-glucose, D-galactose, D-mannose, L-sorbose, D-ribose, L-rhamnose and sucrose). The principal component analysis (PCA) plot shows a clear discrimination of the 10 tested saccharides at 100 mM and the first principal component possesses 94.8% of the variation. Besides, the developed saccharide imprinted sensor array is successfully applied to discriminating three brands of orange juice beverage.

Probing the Adsorption Characteristic of Metal–Organic Framework MIL-101 for Volatile Organic Compounds by Quartz Crystal Microbalance

As volatile organic compounds (VOCs) are a major group of air pollutants, development of materials for efficient adsorption and removal of VOCs is of great significance in both environmental and analytical sciences. Here we report metal-organic frameworks (MOFs) MIL-101 for the effective adsorption of VOCs at atmospheric pressure. A simple device was designed for quartz crystal microbalance (QCM), and six VOCs with various functional groups and polarities, i.e., n-hexane, toluene, methanol, butanone, dichloromethane, and n-butylamine, were chosen as targets to probe the adsorption properties of MIL-101. The developed device allows measurement of the adsorption isotherms and monitoring of the dynamic process for the adsorption of VOCs on MOFs, and also provides a useful tool for characterization of MOFs. The adsorption isotherms of the VOCs on MIL-101 followed the Dubinin-Astakhov equation with the characteristic energy from 5.70 (methanol) to 9.13 kJ mol(-1) (n-butylamine), Astakhov exponent from 0.50 (n-butylamine) to 3.03 (n-hexane), and the limiting adsorption capacity from 0.08 (n-hexane) to 12.8 (n-butylamine) mmol g(-1). MIL-101 exhibited the strongest affinity to n-butylamine, but the weakest affinity to n-hexane. The determined Astakhov exponents and the isosteric heats of adsorption revealed the energetic heterogeneity of MIL-101. MIL-101 showed the most energetically homogeneous for n-hexane, but the most energetically heterogeneous for n-butylamine. The dynamic process of adsorption monitored by the QCM system demonstrated the distribution of the sorption sites within MIL-101. The metal sites within the MIL-101 were vital in adsorption process. MIL-101 gave much higher affinity and bigger adsorption capacity to VOCs than activated carbon, offering great potential for real applications in the adsorption and removal of VOCs.

Self‐Assembly of Mn‐Doped ZnS Quantum Dots/Octa(3‐aminopropyl)octasilsequioxane Octahydrochloride Nanohybrids for Optosensing DNA

Simple plan! Nanohybrids have been built from capped Mn-doped ZnS quantum dots and octa(3-aminopropyl)octasilsequioxane octahydrochloride (OA-POSS) by means of electrostatic self-assembly for the development of a novel room-temperature phosphorescence sensor for DNA sensing in biological fluids (see graphic).

High-performance separation of fullerenes on metal-organic framework MIL-101(Cr).

The discovery of C60 and C70 has evoked a series of investigations in chemistry, physics, and materials sciences, and has stimulated the development of new separation and purification methods for fullerenes. High-performance liquid chromatography (HPLC) is the best technique of choice, and has been widely used for the separation and purification of fullerenes on various stationary phases. Metal–organic frameworks (MOFs) are an emerging class of microporous materials, and their unusual properties such as permanent nanoscale porosity, high surface area, uniform structured cavities, and the availability of in-pore functionality and outer-surface modification are advantageous for diverse applications including gas adsorption and storage, catalysis, drug delivery, sensing, and imaging. Large diversity in structure, adsorption affinity, pore size, high surface area, and pore volume next to the minimal dead volumes make MOFs suitable advanced chromatographic separation media. Recently, several MOFs, such as MOF-5, HKUST-1, MIL-47, and MIL-53 have been successfully used as the stationary phases for HPLC separation of small molecules. Potential applications of MOFs for HPLC separation of carbon nanomaterials like fullerenes should be considerable, but has not been explored so far. Herein we report the exploration of MOFs as the stationary phase for HPLC separation of fullerenes with excellent selectivity and high throughput. To demonstrate the proofof-concept, we used MIL-101(Cr) as the stationary phase for HPLC because of its high surface area, large windows (12 and 16 14.5 ), mesoporous pores (29 to 34 ), and excellent chemical and solvents stability. MIL-101(Cr) is built up from a hybrid supertetrahedral building unit, which is formed by terephthalate ligands and trimeric chromium octahedral clusters. Even though its excellent properties, MIL-101(Cr) has never been explored as HPLC stationary phase before. MIL-101(Cr) was synthesized according to F rey et al. (See the Supporting Information). The successful preparation of MIL-101(Cr) was confirmed by X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) (Figure S1–S3 in the Supporting Information). The suspension of MIL-101(Cr) in dichloromethane (CH2Cl2) was slurry-packed into a stainless steel column (5 cm long 4.6 mm i.d.) under 6000 psi for 10 min. The performance of the MIL-101(Cr) packed column was firstly demonstrated for the separation of C60 and C70. As shown in Figure 1, the MIL-101(Cr) packed column (5 cm