Ring-Oven-Assisted In Situ Synthesis of Metal-Organic Frameworks on the Lab-On-Paper Device for Chemiluminescence Detection of Nitrite in Whole Blood.

In situ synthesis of metal-organic frameworks (MOFs) on flexible materials for the fabrication of functional platforms and micro-devices is challenging. The time-/precursor-consuming procedure and uncontrollable assembly are stumbling blocks for constructing this platform. Herein, a novel in situ MOF synthesis method on paper substrates by use of the ring-oven-assisted technique was reported. Utilizing the ring-oven's heating and washing function, MOFs can be synthesized in 30 min on the designated position of paper chips with extremely low-volume precursors. The principle of this method was explained by steam condensation deposition. The MOFs' growth procedure was theoretically calculated by crystal sizes and the results conformed to the Christian equation. As different MOFs (Cu-MOF-74, Cu-BTB, Cu-BTC) can be synthesized successfully on paper-based chips, the ring-oven-assisted in situ synthesis method has great generality. Then, the prepared Cu-MOF-74 loading paper-based chip was applied to the chemiluminescence (CL) detection of nitrite (NO2-), based on the catalysis effect of Cu-MOF-74 on the NO2--H2O2 CL system. Also, by the delicate design of the paper-based chip, NO2- can be detected with the detection limit (DL) of 0.5 nM in whole blood samples without sample pretreatment. This work establishes a distinctive method for the in situ synthesis of MOFs and the application of MOFs on paper-based CL chips.

Tetrakis(4-pyridylphenyl)ethylene-based Zinc Metal-Organic Framework with Aggregation-Induced Chemiluminescence Emission on a Paper Platform for Formaldehyde Detection in Breath.

Volatile formaldehyde (FA) in exhaled breath (EB) is considered as a biomarker for lung cancer (LC). On-the-spot selective and sensitive detection of gaseous FA is rather important for LC screening and diagnosis. Herein, a tetrakis(4-pyridylphenyl)ethylene (Py-TPE)-based zinc metal-organic framework (MOF) with excellent aggregation-induced emission (AIE) property was utilized for absorption and selective detection of FA in EB. The porous Zn-Py-TPE served as a gaseous confinement cavity for the adsorption of FA in EB. Interestingly, Zn-Py-TPE was aggregated on paper, and then aggregation-induced chemiluminescence (CL) emission can be triggered by only adding bis(2,4,6-trichlorophenyl)oxalate (TCPO). Though without H2O2, the CL of Zn-Py-TPE-TCPO was enhanced greatly by FA. FA promoted the aggregation of Zn-Py-TPE on paper by forming halogen bonding between FA and Zn-Py-TPE, which contributed to the better selectivity. FA can also stimulate the production of more singlet oxygen (1O2) in the Zn-Py-TPE-TCPO CL system. Hence, FA could be detected via the proposed Zn-Py-TPE-TCPO system with a quantification linear range of 1.0-100.0 ppb and detection limit of 0.3 ppb. This portable, low-cost, and sensitive paper-based platform can achieve trace FA detection in EB and is expected to provide an on-the-spot screening platform for lung cancer.

Aggregation-induced chemiluminescence system for sensitive detection of mercury ions.

As mercury ions (Hg2+) are emanated to surroundings in the course of various natural events and human activities, an accurate sensing of Hg2+ is essential for human health and environmental protection. Herein, a new aggregation-induced chemiluminescence (CL) sensor for fast, sensitive, and selective detection of Hg2+ is developed, based on the CL enhancement of bis(2,4,6-trichlorophenyl)oxalate (TCPO)-H2O2 system by thiolate-protected gold complexes (Au(I)-thiolate complexes) in the aggregated state. Because Hg2+ has a strong interaction with hydrosulfuryl (-SH) groups in Au(I)-thiolate complexes, the aggregation is disrupted and the CL is quenched. The decrease of CL intensity is proportional to Hg2+ contents with a linear range of 0.005-10 µg mL-1 and the limit of detection (LOD) is 3 ng mL-1. To the best of our knowledge, this is the first AIE CL sensor for Hg2+ detection. The study opens up attractive perspectives for developing simple and rapid aggregation-induced CL methods in monitoring heavy metals.

Fe(III) bipyridyl or phenanthroline complexes with oxidase-like activity for sensitive colorimetric detection of glutathione.

In this study, three types of Fe(III) bipyridyl or phenanthroline (Fe(III)-L3 ) complex could directly catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to induce blue chromogenic changes without H2 O2 . Fe(III)-L3 complex could induce a colour change in TMB directly after a short incubation time. Due to the high oxidase-like activity of the Fe(III)-L3 complexes, superoxide anion radicals (O2 •- ) were formed in solution. Intermediates radical involving oxo-iron species were then produced that oxidized TMB to its oxidation products (oxTMB), which had an absorbance maximum at 652 nm. Glutathione (GSH) could inhibit the oxidation reaction of the Fe(III)-L3 complex-TMB system, a rapidly colorimetric method was established for the specific detection of GSH that had a detection limit of 0.1 µM. Furthermore, Fe(III)-L3 complexes could catalyze TMB to oxTMB directly without H2 O2 . This fast and simple colorimetric method may open a new avenue for application in the point-of-care diagnosis field using the TMB chromogenic system.

Prevalence of Balantidium coli infection in sows in Hunan province, subtropical China.

Balantidium coli is a cosmopolitan parasitic-opportunistic pathogen that can be found throughout the world. However, little information is available about prevalence of B. coli in pigs in China. In the present study, the prevalence of B. coli in pigs was investigated in Hunan province, subtropical China, between January 2012 and August 2014. A total of 3925 diarrheic fecal samples from nine representative administrative regions in Hunan province, subtropical China, were examined for the presence of B. coli cysts and/or trophozoites using microscopy after sedimentation with water. The overall prevalence of B. coli in pigs was 36.9 % (1450/3925). The present survey revealed high circulation of B. coli in pigs in Hunan province, subtropical China, which poses potential threats to human health. The results of the present investigation have important implications for the control of B. coli infections in pigs in Hunan province, subtropical China. To our knowledge, this is the first comprehensive report of B. coli prevalence in sows in Hunan province, subtropical China.

A metal-organic framework loaded paper-based chemiluminescence sensor for trace acetone detection in exhaled breath.

Trace acetone determination in breath can be regarded as a noninvasive method for diagnosis of diabetes. Here, a paper-based CL gas sensor combined with UiO-66 as the preconcentrator was established for sensitive detection of trace acetone in exhaled breath. UiO-66 with excellent adsorption performance and unique water stability was used for the adsorption and enrichment of acetone gas under high humidity conditions in exhaled breath. As acetone can remarkably increase the chemiluminescence (CL) of the 2,4-dinitrophenylhydrazine (DNPH)-potassium permanganate (KMnO4) system, a sensitive CL device based on a paper substrate for trace acetone detection was established and the detection limit was 0.03 ppm. The fabricated method was used to assess the content of trace acetone in exhaled breath with satisfactory recoveries of 90-110%. It is expected to realize the noninvasive determination of acetone for diabetic patients in exhaled breath.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing.

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (µPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with µPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on µPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of µPads for POCT were discussed.

Paper-based Chemiluminescence Device with Co-Fe Nanocubes for Sensitive Detection of Caffeic Acid.

In this work, a new chemiluminescence (CL) system of Co-Fe prussian blue analogs nanocubes (Co-Fe PBA NCs) that can catalyze luminol to produce strong CL in the absence of H2O2 was established. Co-Fe PBA NCs have the property of oxidase-like activity, and it can catalyze the generation of active oxygen radicals in a dissolved oxygen system. Since caffeic acid (CA) can remove reactive oxygen species in the system, a sensitive detection method for CA on a paper-based chip was developed. Under the optimal conditions, this method showed a good linear response to CA in the range of 10 - 800 ng mL-1 with a limit of 3 ng mL-1. The proposed method had been used for the determination of CA in tea samples. The results may open a new avenue for the catalytic property on luminol CL system without extra oxidants.

Long-Lasting Luminol Chemiluminescence Emission with 1,10-Phenanthroline-2,9-dicarboxylic Acid Copper(II) Complex on Paper.

As most of the known systems are flashtype, long-lasting chemiluminescence (CL) emissions are extremely needed for the application of cold light sources, accurate CL quantitative analysis, and biological mapping. In this work, the flashtype system of luminol was altered to a long lasting CL system just because of the paper substrate. The Cu(II)-based organic complex was loaded on the paper surface, which can trigger luminol-H2O2 to produce a long lasting CL emission for over 30 min. By using 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) as the ligand, a hexacoordinated Cu(II)-based organic complex was synthesized by the simple freeze-drying method. It is interesting that the complex morphology can be controlled by adding different amounts of water in the synthesizing procedure. The complex with a certain size can be definitely trapped in the pores of the cellulose. Then, slow diffusion, which can be attributed to the long lasting CL emission, was produced. With the high catalytic activity of the complex, reactive oxygen species from H2O2 was generated and was responsible for the high CL intensity. By using the paper substrate, the flash-type luminol system can be easily transferred to the long-duration CL system without any extra reagent. This long-lasting emission system was used for hydrogen sulfide detection by the CL imaging method. This paper-based sensor has great potential for CL imaging in the clinical field in the future.

Copper-based metal-organic xerogels on paper for chemiluminescence detection of dopamine.

In this work, copper(ii)-containing metal-organic xerogels (Cu-MOXs), which were composed of copper as the central ion and 2,2'-bipyridine-6,6'-dicarboxylic acid as the ligand, were quickly synthesized by a mild facile strategy. The Cu-MOXs exhibited superior catalytic performance for the luminol-H2O2 chemiluminescence (CL) system. The possible mechanism was studied via CL spectra, UV-Vis absorption and electron paramagnetic resonance (ESR). Since dopamine (DA) can inhibit the reaction of this system, a sensitive paper-based CL device for the detection of DA was established. Under the optimal experimental conditions, the linear range of this method was 40-200 nM with a detection limit of 10 nM. The proposed method was used for the determination of DA in urine samples.