Yafeng Guan

Visible-light-sensitized highly luminescent europium nanoparticles: preparation and application for time-gated luminescence bioimaging

Time-gated luminescence bioimaging based on microsecond-lifetime luminescent biolabels can provide complete background-free conditions for detecting target cells in an autofluorescence biosample matrix. However, a major drawback of the current lanthanide biolabels is the requirement for UV excitation (<370 nm), which leads to damage to many biological systems and greatly affects the improvement of time-gated luminescence instruments. Herein we describe luminescent europium nanoparticles that have an excitation peak around 406 nm with high quantum yield (∼66%) and fine monodispersity in aqueous solutions. The nanoparticles were prepared by copolymerization of a visible-light-sensitized Eu3+ complex 4,4′-bis(1″,1″,1″,2″,2″,3″,3″-heptafluoro-4″,6″-hexanedion-6″-yl)chlorosulfo-o-terphenyl-Eu3+-2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine conjugated with 3-aminopropyl(triethoxy)silane, free 3-aminopropyl(triethoxy)silane and tetraethyl orthosilicate in a water-in-oil reverse microemulsion. Characterization by transmission electron microscopy and luminescence spectroscopy indicates that the nanoparticles are monodisperse, spherical and uniform in size, <50 nm in diameter, and show strong visible-light-sensitized luminescence with a large quantum yield and a long luminescence lifetime. The new nanoparticles were successfully applied to distinguish an environmental pathogen, Giardia lamblia, within a concentrate of environmental water sample using a time-gated luminescence microscope with pulsed visible light excitation. The method resulted in highly specific and sensitive imaging for Giardia lamblia. These results suggest a broad range of potential bioimaging applications where both long time microscopy observation and high signal-to-background ratio are required for samples containing high concentrations of autofluorescence background.

BODIPY-Based Fluorometric Sensor for the Simultaneous Determination of Cys, Hcy, and GSH in Human Serum

Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) are interconnected and play essential roles for regulating the redox balance of biological processes. However, finding a simple and effective method for the simultaneous determination for these three biothiols in biological systems is always a challenge. In this work, we report a method for the simultaneous quantitative determination of three biothiols in a mixture using a monochlorinated boron dipyrromethene (BODIPY)-based fluorometric sensor. At a specified period of time, after reacting with excess sensor, Hcy and GSH form predominantly sulfur-substituted BODIPY, while Cys generates sulfur-amino-diBODIPY due to a fast substitution-rearrangement-substitution reaction. A significant difference in polarities of these respective major products simplifies their separation by TLC, thus leading to the simultaneous determination of Cys, Hcy, and GSH readily. The sensor was successfully applied for the simultaneous quantitative detection of three biothiols in human serum, and the results were in good agreement with those obtained via high performance liquid chromatography (HPLC).

Cu2O nanorods modified by reduced graphene oxide for NH3 sensing at room temperature

In this work, Cu2O nanorods modified by reduced graphene oxide (rGO) were produced via a two-step synthesis method. CuO rods were firstly prepared in graphene oxide (GO) solution using cetyltrimethyl ammonium bromide (CTAB) as a soft template by the microwave-assisted hydrothermal method, accompanied with the reduction of GO. The complexes were subsequently annealed and Cu2O nanorods/rGO composites were obtained. The as-prepared composites were evaluated using various characterization methods, and were utilized as sensing materials. The room-temperature NH3 sensing properties of a sensor based on the Cu2O nanorods/rGO composites were systematically investigated. The sensor exhibited an excellent sensitivity and linear response toward NH3 at room temperature. Furthermore, the sensor could be easily recovered to its initial state in a short time after exposure to fresh air. The sensor also showed excellent repeatability and selectivity to NH3. The remarkably enhanced NH3-sensing performances could be attributed to the improved conductivity, catalytic activity for the oxygen reduction reaction and increased gas adsorption in the unique hybrid composites. Such composites showed great potential for manufacturing a new generation of low-power and portable ammonia sensors.

Luminescent europium nanoparticles with a wide excitation range from UV to visible light for biolabeling and time-gated luminescence bioimaging

Silica-encapsulated highly luminescent europium nanoparticles with a wide excitation range from UV to visible light (200-450 nm) have been prepared and used for streptavidin labeling and time-gated luminescence imaging of an environmental pathogen, Giardia lamblia.

Eggshell membrane as a multimodal solid state platform for generating fluorescent metal nanoclusters

Eggshell membrane (ESM) has been employed as a unique and especially efficient synthetic platform capable of generating fluorescent silver and gold nanoclusters via various chemical routes. Potential applications of the metal/ESM adducts include recyclable catalysts, sensing paper, surface enhanced Raman scattering interface, fluorescent surface patterning and anti-counterfeiting.

Additive-Free Synthesis of In2O3 Cubes Embedded into Graphene Sheets and Their Enhanced NO2 Sensing Performance at Room Temperature

In this report, we developed an additive-free synthesis of In2O3 cubes embedded into graphene networks with InN nanowires (InN-NWs) and graphene oxide (GO) as precursors by a facile one-step microwave-assisted hydrothermal method. In absence of GO, the InN-NWs maintained their chemical composition and original morphology upon the same treatment. At varying mass ratios of InN-NWs and GO, the different morphologies and distributions of In2O3 could be obtained on graphene sheets. The uniform distribution, which is usually considered favorable for enhanced sensing performance, was observed in In2O3 cubes/reduced graphene oxide (rGO) composites. The room-temperature NO2 sensing properties of the In2O3 cubes/rGO composites-based sensor were systematically investigated. The results revealed that the sensor exhibited a significant response to NO2 gas with a concentration lower to 1 ppm, and an excellent selectivity, even though the concentrations of interferential gases were 1000 times that of NO2. The enhanced NO2 sensing performances were attributed to the synergistic effect of uniformly distributed In2O3 cubes and graphene sheets in the unique hybrid architectures without the interfering of extra additives.

Detection of Glutathione in Vitro and in Cells by the Controlled Self-Assembly of Nanorings

Taking advantage of a reduction-controlled biocompatible condensation reaction and self-assembly, we have developed a new method for the determination of glutathione (GSH) concentration in vitro and in HepG2 human liver cancer cells. Upon reduction by GSH under physiological conditions (pH 7.4 in buffer), the small molecule CBT-Cys(SEt) condenses and self-assembles into nanorings, increasing the UV absorbance at 380 nm (with significant linear correlation in the 0-87 μM GSH range and a limit of detection of 1 μM). This method is also selective to GSH rather than cysteine in biological samples. Through the use of added internal standards, we successfully determined the concentration of GSH in HepG2 cells to be 14.96 μM (2.99 fmol/cell). To better understand the mechanism of nanoring self-assembly, the condensation product of CBT-Cys(SEt) formed using different concentrations of GSH and different reaction times were characterized by transmission electron microscopy (TEM).

Enhancement of sensitivity of paper-based sensor array for the identification of heavy-metal ions

Paper-based microfluidic devices have been widely investigated in recent years. Among various detection techniques, colorimetric method plays a very important role in paper-based microfluidic devices. The limitation, however, is also clear: they generally require highly sensitive indicators. In this work, we have developed a novel enrichment-based paper test for the discrimination of heavy-metal ions. Comparing to regular paper-based microfluidic devices, enrichment-based technique showed largely improved sensitivity. Combining with eight pyridylazo compounds and array technologies-based pattern-recognition, we have obtained the discrimination capability of eight different heavy-metal ions at same concentration as low as 50 μM using our enrichment-based pyridylazo compounds array paper. Identification of the heavy-metal ions was readily achieved using a standard chemometric approach. This method can be, of course, used for other analytes as well.

The calibration of cellphone camera-based colorimetric sensor array and its application in the determination of glucose in urine

In this work, a novel approach that can calibrate the colors obtained with a cellphone camera was proposed for the colorimetric sensor array. The variations of ambient light conditions, imaging positions and even cellphone brands could all be compensated via taking the black and white backgrounds of the sensor array as references, thereby yielding accurate measurements. The proposed calibration approach was successfully applied to the detection of glucose in urine by a colorimetric sensor array. Snapshots of the glucose sensor array by a cellphone camera were calibrated by the proposed compensation method and the urine samples at different glucose concentrations were well discriminated with no confusion after a hierarchical clustering analysis.

Comprehensive two‐dimensional liquid chromatography (NPLC×RPLC) with vacuum‐evaporation interface

A comprehensive two-dimensional liquid chromatographic system incorporating a vacuum-evaporation interface was developed. Normal-phase liquid chromatography with a CN microcolumn was used as the first dimension (1(st)-D), and reversed-phase liquid chromatography with a C(18) monolithic column was used as the second dimension (2(nd)-D). An electronically controlled dual-position, ten-port valve with two identical storage loops served as the interface and the analysis time in the 2(nd)-D was 1.5 min. The solvent in the loops of the interface was evaporated at 25 degrees C under vacuum conditions, leaving the analytes on the inner wall of the loops. The mobile phase of the 2(nd)-D dissolved the analytes in the loop and injected them onto the second column, allowing an on-line solvent exchange of the fractions from the 1(st)-D to the 2(nd)-D. The chromatographic resolution of analytes on the two dimensions was evaluated. Sample loss due to evaporation in the interface was investigated with standard samples having different boiling points. The usefulness of the comprehensive 2-DLC system was demonstrated in the analysis of a traditional Chinese medicine Radix salviae miltiorrhiza bage extract.