A facile fluorescent sensor based on nitrogen-doped carbon dots derived from Listeria monocytogenes for highly selective and visual detection of iodide and pH.

Sensitive and visual analysis of iodide (I-) and pH is significant in environmental and food applications. Herein, we present a facile fluorescent sensor for highly selective and visual detection of I- and pH based on nitrogen-doped carbon dots derived from Listeria monocytogenes (NCDs-LM). The NCDs-LM-based fluorescent sensor showed a good linear relationship to I- concentrations, and the detection limit was calculated as 20 nmol L-1. The developed sensor was successfully applied to the detection of I- in drinking water and milk samples. Meanwhile, the as-synthesized NCDs-LM sensor can be used to detect pH, achieving a wide linear pH range. Furthermore, fluorescent test papers based on NCDs-LM were designed for semi-quantitative detection of I- and pH via the naked-eye colorimetric assay. The present work indicates that the NCDs-LM-based fluorescent sensor has high potential for use in environmental monitoring and food analysis.

A portable smartphone-assisted ratiometric fluorescence sensor for intelligent and visual detection of malachite green.

Developing intelligent, sensitive, and visual methods for rapidly detecting veterinary drug residues is essential for ensuring food quality and safety. A portable smartphone-assisted ratiometric fluorescent sensor was successfully designed using fluorescent Al-MOF nanosheet and rhodamine B (RhB) as fluorescent probes to adjust to the requirement of malachite green (MG) detection. The developed ratiometric fluorescent sensor allowed sensitive and selective detection of MG with good linear relationships in a wide range of 0.5-200 µg/mL. The Quantitative linearrange is 5.3 µg/mL to 200 µg/mL. The limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 1.6 µg/mL and 5.3 µg/mL respectively. The practicability of the proposed method was verified using high performance liquid chromatography (HPLC) in spiked fish tissues with satisfying recoveries and RSD. Moreover, portable smartphone-assisted fluorescent test papers were fabricated for the intelligent detection of MG. This integration of smartphones and fluorescent test papers was economical and saved time, providing an alternative strategy for the qualitative discernment and semi-quantitative analysis of MG on-site.

Application of silanized melamine sponges in matrix purification for rapid multi-residue analysis of veterinary drugs in eggs by UPLC-MS/MS.

Fast and convenient matrix purification is an important prerequisite for high-throughput analysis of drug multiresidues in food. In this study, a silanized melamine sponge was prepared and first applied in the rapid determination of multiclass veterinary drugs in eggs by ultrahigh-performance liquid chromatography-tandem mass spectrometry. Within five seconds, fast, convenient and efficient matrix separation could be achieved through simple soaking and squeezing. Compared to other matrix adsorbents, the developed material demonstrated equivalent or better purification performance. Good validation results were obtained in terms of drug recoveries (61.5%~97.0%, relative standard deviation (RSD) ≤ 10.8%), and linearities (R2 ≥ 0.999), as well as low limits of quantitation (0.3 ~ 10.9 µg·kg-1) and detection (0.1 ~ 3.8 µg·kg-1). By analyzing 52 egg samples, high concentrations of ofloxacin, trimethoprim, metronidazole, and dimetridazole were found at 542.9, 121.2, 66.1 and 58.0 µg·kg-1, respectively. The silanized melamine sponge has shown its great potential for rapid analysis of multiclass residues in food safety.

Inner-filter effect induced fluorescent sensor based on fusiform Al-MOF nanosheets for sensitive and visual detection of nitrofuran in milk.

Developing highly sensitive and visual methods for rapid detection of antibiotics is significant to ensure food quality and safety. To meet the requirement of nitrofuran antibiotics detection, luminescent fusiform Al(III)-containing metal-organic frameworks (Al-MOF) nanosheets were successfully synthesized by one-step hydrothermal method. And then, the nanosheet served as a fluorescent probe to detect nitrofuran via the inner-filter effect mechanism. The developed sensor allowed sensitive and selective detection of nitrofuran with good linear relationships. And, the detection limit (LOD) values were estimated to be 0.53, 0.838 and 0.583 µM for nitrofurazone, nitrofurantoin and furazolidone detection, respectively. The practical application of the proposed system was verified by HPLC in spiked milk samples with satisfying recoveries ranging from 88.14 to 126.21% and low relative standard deviations of 2.85 ~ 8.13%. Moreover, we designed fluorescent test papers for semi-quantitative detection of nitrofuran via naked-eye colorimetric assay. The established method provides an alternative strategy for semiquantitative detection of nitrofuran.

3D microfluidic tumor models for biomimetic engineering of glioma niche and detection of cell morphology, migration and phenotype change.

In this work, an integrated 3-dimensional microfluidic device was developed for simulation of the immune microenvironment of glioma niche through the co-culture of three kinds of related cells. Glioma cells, endothelial cells and macrophages were co-cultured together in the microfluidic device, spatially separated by the design of a coffer structure and the use of hydrogel. This platform enabled separate monitoring of the morphology change and migration of cells, as well as molecular interactions between different kinds of cells. Tumor cells were found to exhibit EMT like shape change to become thinner, and sensitive perception and taxis toward macrophages. The influence of tumor cells and the microenvironment, macrophages would be re-educated and the phenotype could be changed from M1 (tumor-suppressive) to M2 (tumor-supportive), which could be validated through cytokines analysis. This 3D microfluidic tumor model provides a powerful tool for studying the biological properties of glioma niche.

Development of a modified quick, easy, cheap, effective, rugged, and safe method based on melamine sponge for multi-residue analysis of veterinary drugs in milks by ultra-performance liquid chromatography tandem mass spectrometry.

The purpose of this study was to develop a modified QuEChERS method based on melamine sponge for rapid determination of multi-class veterinary drugs in milks by UPLC-MS/MS. Through simple infiltration and extrusion, fast and convenient matrix purification could be achieved within several seconds, and there was no need of extra phase separation operations. Good linearity with correlation coefficient (R2) ≥0.999 was obtained for all drugs in the range of 2~500 µg·kg-1. The obtained matrix effects were within ±20% for all monitored drugs. The recoveries of all monitored drugs ranged from 60.7% to 116.0% at three spiked levels (50, 100, and 200 µg·kg-1), with relative standard deviations less than 7.4%. Comparatively low LODs and LOQs were obtained in the ranges of 0.1~3.8 µg·kg-1 and 0.2~6.3 µg·kg-1, respectively. Compared with conventional purification adsorbents, melamine sponge yielded an equal or higher purification performance with matrix removal rate as high as 52.5% and acceptable recoveries in range of 60%-120% for all monitored drugs. The satisfactory results have demonstrated the good potential of melamine sponge in matrix purification for rapid determination of multiclass residues in food safety.

An ultrasensitive chemiluminescence immunoassay for fumonisin B1 detection in cereals based on gold-coated magnetic nanoparticles.

BACKGROUND: In the present study, a novel highly sensitive magnetic enzyme chemiluminescence immunoassay (MECLIA) was developed to detect fumonisin B1 (FB1 ) in cereal samples. The gold-coated magnetic nanoparticles (Fe3 O4 @Au, GoldMag) were used as solid phase carrier to develop a competitive CLIA for detecting FB1 , in which FB1 in samples would compete with FB1 -ovalbumin coated on the surface of Fe3 O4 @Au nanoparticles for binding with FB1 antibodies. Successively, horseradish peroxidase labeled goat anti-rabbit IgG (HRP-IgG) was conjugated with FB1 antibodies on the microplate. In substrate solution containing luminol and H2 O2 , HRP-IgG catalyzed luminol oxidation by H2 O2 , generating a high chemiluminescence signal. The FB1 immune GoldMag particles were characterized by Fourier transform infrared spectroscopy, scanning electron microscope and zeta potential analysis, etc. RESULTS: The concentrations and the reaction times of these immunoreagents were optimized to improve the performances of this method. The established method could detect as low as 0.027 ng mL-1 FB1 from 0.05 ng mL-1 to 25 ng mL-1 , demonstrating little cross-reaction (less than 2.4%) with other structurally related compounds. The average intrassay relative SD (RSD) (n = 6) was 3.4% and the average interassay RSD (n = 6) was 5.4%. This method was successfully applied for the determination of FB1 in corn and wheat and gave recoveries of between 98-110% and 91-105%, respectively. CONCLUSION: The results of the present study suggest that the MECLIA approach has potential application for high-throughput fumonisin screening in cereals. © 2018 Society of Chemical Industry.

Evaluation of drug combination for glioblastoma based on an intestine-liver metabolic model on microchip.

An intestine-liver-glioblastoma biomimetic system was developed to evaluate the drug combination therapy for glioblastoma. A hollow fiber (HF) was embedded into the upper layer of the microfluidic chip for culturing Caco-2 cells to mimic drug delivery as an artificial intestine. HepG2 cells cultured in the bottom chamber of the chip acted as an artificial liver for metabolizing the drugs. The dual-drug combination to glioblastoma U251 cells was evaluated based on the intestine-liver metabolic model. The drugs, irinotecan (CPT-11), temozolomide (TMZ) and cyclophosphamide (CP), were used to dynamically stimulate the cells by continuous infusion into the intestine unit. After intestine absorption and liver metabolism, the prodrugs were transformed to active metabolites, which induced glioblastoma cells apoptosis. The anticancer activity of the CPT-11 and TMZ combination is significantly enhanced compared to that of the single drug treatments. Combination index (CI) values of the combination groups, CPT-11 and TMZ, CPT-11 and CP, and TMZ and CP, at half maximal inhibitory concentration were 0.137, 0.288, and 0.482, respectively. The results indicated that the CPT-11 and TMZ combination was superior to the CPT-11 and CP group as well as the TMZ and CP group towards the U251 cells. The metabolism mechanism of CPT-11 and TMZ was further studied by coupling with mass spectrometric analysis. The biomimetic model enables the performance of long-term cell co-culture, drug delivery, metabolism and real-time analysis of drug effects, promising systematic in vitro mimicking of physiological and pharmacological processes.

Study of antioxidant effects on malignant glioma cells by constructing a tumor-microvascular structure on microchip.

In this work, a three-dimensional tumor-microvascular structure was simulated on a microfluidic chip for study of antioxidants effects on malignant glioma cells in vitro. The 3D hydrogel containing lumen was constructed to co-culture endothelial cells and glioma cells to mimic tumor microvascular environment. Macroporous gelatin transglutaminase (TG) hydrogel was prepared with biological and mechanical properties suitable for cells culture and nutrient refresh. To reform a vessel structure, U87 cells were dispersed in the TG-gelatin hydrogel and HUVEC cells were seeded in the lumen of hydrogel. Three typical antioxidants (α-lipoic acid, catechins and ascorbic acid) have been selected to research the antioxidant effects of glioma cells in the simulative tumor microenvironment. The results showed that the HUVEC cells formed vessel presented the transportation and penetrable functions for antioxidants from lumen to glioma cells. The antioxidants displayed higher selectivity to U87 cells than HUVEC cells and α-lipoic acid has a strong antioxidant capacity.

Quantitative determination of VEGF165 in cell culture medium by aptamer sandwich based chemiluminescence assay.

In this work, we have developed a sensitive and selective chemiluminescence (CL) assay for vascular endothelial growth factor (VEGF165) quantitative detection based on two specific VEGF165 binding aptamers (Apt). VEGF is a predominant biomarker in cancer angiogenesis, and sensitive detection method of VEGF are highly demanded for both academic study and clinical diagnosis of multiple cancers. In our experiment, VEGF165 was captured in a sandwich structure assembled by two binding aptamers, one capture aptamer was immobilized on streptavidin-coated magnetic beads (MBs) and another VEGF-binding aptamer was labeled by biotin for further phosphatase conjunction. After Apt-VEGF-Apt sandwich was formed on MBs surface, alkaline phosphatase (ALP) was modified to the second aptamer to catalyze CL reaction. By applying 4-methoxy-4-(3-phosphatephenyl)-spiro-(1,2-dioxetane-3,2-adamantane) (AMPPD) as CL substrate, strong signal intensity was achieved. VEGF165 content as low as 1ng/mL was detected in standard spiked samples by our assay, and linear range of working curve was confirmed from 1 to 20ng/mL. Then our method was successfully applied for cell culture medium analysis and on-chip hypoxic HepG2-HUVEC co-culture model study with excellent accuracy equal to ELISA Kit. Our developed assay demonstrated an outstanding performance in VEGF165 quantification and may be further extended to clinical testing of important biomarkers as well as probing microchip cell culture model.

Gold nanoparticles modified porous silicon chip for SALDI-MS determination of glutathione in cells.

The gold nanoparticles (Au NPs) modified porous silicon chip based surface assisted laser desorption/ionization mass spectrometry (SALDI-MS) was developed to capture and analyze glutathione (GSH) in cells. With silver-assisted chemical etching, Ag nanoparticles (Ag NPs) were generated and deposited on the silicon surface and the nanopores were etched on silicon substrate. Then Au NPs were in-situ synthesized on the ridges of silicon nanopores. This Ag-Au NPs modified porous silicon surface could specially capture and enrich thiol compounds through Au-S binding, and it could also function as matrix to assist ionization for SALDI-MS. The silicon chip was array patterned for high throughput SALDI-MS detection. GSH and cysteine could be distinguished without the interference from matrix signals. This approach was successfully applied to preconcentration and detection of GSH in Caco-2 cells. The GSH alterations in cells under drug stimulation were investigated. This invented silicon chip showed great potential for more efficient analysis of small thiol biomarkers in complex biological samples.

Multi-channel cell co-culture for drug development based on glass microfluidic chip-mass spectrometry coupled platform.

RATIONALE: Cell-based drug assay plays an essential role in drug development. By coupling a microfluidic chip with mass spectrometry (MS), we developed a multifunctional platform. Cell co-culture, cell apoptosis assay, fluorescence and MS detection of intracellular drug absorption could be simultaneously conducted on this platform. METHODS: Three micro-channels were fabricated through photolithography technology to conduct the cell co-culture. Cell apoptosis after drug treatment was assayed by fluorescent probes (Hoechst 33342). Intracellular Dox absorption was analyzed by confocal fluorescent microscopy. With a high voltage (~ 4.5 kV) applied onto the microfluidic chip, the ionization spray was successfully generated by dropping isopropanol onto it. By coupling with a Shimadzu LCMS-2010 A mass spectrometer, intracellular CPA absorption was detected on the microfluidic chip. RESULTS: The microfluidic chip-MS coupled platform showed high biocompatibility. Distinction of cell apoptosis between co-cultured and mono-cultured cells was detected. The results of intracellular drug absorption well explained the different cell apoptosis rate. CONCLUSIONS: Cell-based drug assay was facilely and successfully conducted on the microfluidic chip-MS coupled platform. This technology we have devised could promote MS application in the field of drug development. Copyright © 2016 John Wiley & Sons, Ltd.