Hulie Zeng

Chip-based enantioselective open-tubular capillary electrochromatography using bovine serum albumin-gold nanoparticle conjugates as the stationary phase

In this study, chip‐based enantioselective open‐tubular CEC (OT‐CEC) was developed employing BSA‐gold nanoparticle (GNP) conjugates as a chiral stationary phase. An immobilization procedure was realized by prederivatization of the glass microchannel with (3‐mercaptopropyl)‐trimethoxysilane to provide thiol groups, which linked the BSA‐GNP conjugates on the inner surface of the microchannels. Incorporation of GNPs into immobilization of BSA selectors greatly increased the BSA phase ratio and favored the BSA stationary phase generated sufficient EOF. Good resolutions of FITC‐labeled ephedrine and norephedrine isomers were achieved with 36 mm effective separation channel length within 250 s. The constructed OT‐CEC microdevice exhibited good repeatabilities for run‐to‐run enantioseparations and kept an enantioselective lifetime of more than 1 month. The effects of pH values and concentrations of a running buffer on the selectivity and resolution of enantioseparations were investigated.

Inkjet Nanoinjection for High-Thoughput Chemiluminescence Immunoassay on Multicapillary Glass Plate

We report a novel chemiluminescence diagnosis system for high-throughput human IgA detection by inkjet nanoinjection on a multicapillary glass plate. As proof-of-concept, microhole-based polydimethylsiloxane (PDMS) sheets were aligned on a multicapillary glass plate to form a microwell array as microreactors for enzyme-linked immunosorbent assay (ELISA). The multicapillary glass plate was utilized as a switch that controlled the holding/passing of the solution. Further, anti-IgA-labeled polystyrene (PS) microbeads was assembled into the microwell array, and an inkjet nanoinjection was specially used to distribute the sample and reagent solution for chemiluminescence ELISA, enabling high-throughput detection of human IgA. As a result, the performance of human IgA tests revealed a wider range for the calibration curve and a lower limit of detection (LOD) of 0.1 ng mL(-1) than the ELISA by a standard 96-well plate. The analysis time and reagent consumption were significantly decreased. The IgA concentrations in saliva samples were determined after 10000-fold dilution by the developed ELISA system showing comparable results by conventional immune assay with 96-wells. Thus, we believe that the inkjet nanoinjection for high-throughput chemiluminescence immunoassay on a multicapillary glass plate will be promising in disease diagnosis.

Development of an automatic multi-channel ink-jet ejection chemiluminescence system and its application to the determination of horseradish peroxidase.

In this work, an automatic multi-channel ink-jet for chemiluminescence (CL) analysis was developed. The four-channel ink-jet device was controlled by a home-made circuit. Differing from the classic flow injection CL, the whole procedure for CL analysis was automatically completed on a hydrophobic glass side. CL reaction of luminal and hydrogen peroxide for the determination of horseradish peroxidase (HRP) was selected as an application to automatic CL analysis platform. All solutions delivered by different channels were precisely ejected to the same position of the glass slide for the CL analysis. The consumption of reaction solution was reduced to nanoliter level. The whole CL analysis could be completed in less than 4min, which was benefited from the prompt solution mixing in small size of droplet. The CL intensity increased linearly with HRP concentration in the range from 0.01 to 0.5μgmL(-1). The limit of detection (LOD) (S/N=3) was 0.005μgmL(-1). Finally, the automatic CL system could also be used for the detection of HRP in HRP-protein conjugates, which showed its practical application in immunoassay.

Accurate and highly reproducible picoliter injection system for capillary electrophoresis.

A novel, highly accurate sample injection system for capillary electrophoresis (CE) was developed based on an inkjet microchip capable of reproducing exact introduction volumes at the picoliter level. The difficulty in analyte discrimination using electrokinetic injection was also overcome using this injection method. The injection system consisted of an XY stage, an inkjet droplet ejection microchip, and a reservoir with a plug-in septum. To evaluate the precision of the system, a mixture of NBD-labeled amino acids consisting of Gly, L-Phe, L-Asp, and L-Ser was separated, and the performance was compared with that of traditional hydrodynamic and electrokinetic injection methods. The results demonstrated that the introduced volume highly relied on the number of droplets with low relative standard derivation (RSD) and good linear correction coefficient in the proposed injection method. In addition, a urine sample was analyzed via CE coupled with the inkjet injection system for the detection of the amino acid taurine. The concentration of urinary taurine was determined to be 2.42 ± 0.08 μM (confidence level, 95%; RSD, 1.05%; n = 4) with a recovery of 98.92-109.54% (n = 3). These results demonstrate the inkjet injection system we developed has the potential to revolutionize capillary electrophoretic separation in practical and commercial applications that require an automated accurate injection system.

A piezoelectric drop-on-demand generator for accurate samples in capillary electrophoresis

In this work, we propose a piezoelectric droplet generator for injection of well-defined amounts of sample in capillary electrophoresis. We demonstrate stable, precise and drop-on-demand droplet formation for various solutions, with precise control of waveform driving piezoelectric crystal inside the ink-jet head. By tuning the waveform, we can also manipulate the droplet size and delivery frequency. This injector was used in sampling for capillary electrophoresis. As a state-of-the-art application, the analysis of theobromine, caffeine and theophiline using micellar electrokinetic chromatography was developed. The volume of sample (single droplet) analyzed in this experiment was 179 pL (RSD=1.2%, n=10). The detection limits for caffeine, theobromine, and theophiline are 0.02, 0.08 and 0.06 mM L(-1), respectively. Compared with conventional methods, the combination of picoliter droplet dispenser with capillary electrophoresis allows precise and accurate sampling, as well as for reduced sample consumption, which will prove to be an efficient tool in quantitative separation and analysis.

A surface plasmon resonance sensor on a compact disk-type microfluidic device

A surface plasmon resonance (SPR) sensor on a compact disk (CD)-type microfluidic device was developed to miniaturize the elements of a complete analytical system, pump and valves. The CD-type microfluidic device was fabricated by attaching a polydimethylsiloxane disk plate that contained microchannels and reservoirs to a flat polycarbonate disk plate that contained grating films with a thin layer of Au. The optical system of the SPR sensor and the theory for its operation are based on the principle of a grating coupled-type SPR. The sample and reagent solutions in the reservoirs on the CD-type microfluidic device were sequentially introduced into the detection chamber by centrifugal force generated by the rotation of the microfluidic device. The variation of resonance wavelength was dependent on the refractive index of the sample solution. This CD-type SPR sensor was successfully used in an immunoassay of immunoglobulin A (IgA). The anti-IgA, blocking reagent, sample and washing solution in the reservoirs were sequentially introduced into the detection chamber by changing the frequency of rotation of the microfluidic device. IgA in the sample solution was adsorbed to the anti-IgA immobilized on the Au thin layer in the detection chamber and was then detected by the SPR sensor.

An integrated enzyme‐linked immunosorbent assay system with an organic light‐emitting diode and a charge‐coupled device for fluorescence detection

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.

Accurate nano-injection system for capillary gas chromatography

The first version of nano-injection device for capillary gas chromatography (cGC) based on inkjet microchip was developed. The nano-injector could accurately control the injection volume in nano-liter, even pico-liter range. Its configuration and mechanism were discussed in detail. Adopting photolithography and plasma etching technology, we firstly fabricated the inkjet microchip and stuck to a piezoelectric device to eject droplets. Then, a special feedback tube was added to make it function as a nano-injector for cGC, which was an important design to compensate pressure difference between the evaporation chamber of cGC and the sample extrusion chamber of inkjet microchip. The injected volume can be precisely controlled by the number of injected droplets. Excellent precision (RSDs were below 10.0%, n=5) was observed for the injection of ethanol at elevated pressure. Minimum injection volume was about 1.25nL at present. Additionally, good repeatability of the calibration curves for the hydrocarbons ethanolic solution (the RSDs of all components were below 5.30%, n=5) confirmed its feasibility in quantitative analysis regardless of concentration. These results suggested that it can be an accurate nano-injector for cGC.

A Compact Immunoassay Platform Based on a Multicapillary Glass Plate

A highly sensitive, rapid immunoassay performed in the multi-channels of a micro-well array consisting of a multicapillary glass plate (MCP) and a polydimethylsiloxane (PDMS) slide is described. The micro-dimensions and large surface area of the MCP permitted the diffusion distance to be decreased and the reaction efficiency to be increased. To confirm the concept of the method, human immunoglobulin A (h-IgA) was measured using both the proposed immunoassay system and the traditional 96-well plate method. The proposed method resulted in a 1/5-fold decrease of immunoassay time, and a 1/56-fold cut in reagent consumption with a 0.05 ng/mL of limit of detection (LOD) for IgA. The method was also applied to saliva samples obtained from healthy volunteers. The results correlated well to those obtained by the 96-well plate method. The method has the potential for use in disease diagnostic or on-site immunoassays.

Quantitative-nanoliter immunoassay in capillary immune microreactor adopted inkjet technology

A quantitatively controlled immunoassay at the nanoliter level based on inkjet technology was developed. The volumes of solutions/samples introduced were accurately controlled at the nanoliter level by using a four-channel inkjet microchip. Antibody/antigen recognition was performed in an amino modified capillary with a short diffusion distance. As a proof-of-concept, a sandwich immunoassay of human IgA was conducted using the developed method. The results demonstrated a low detection limit (0.03 ng mL−1) and a wide linear range (0.1–100 ng mL−1, R2 = 0.9959), comparable to currently used methods. For each capillary immunoassay, the volumes of the ejected solutions for human IgA, FITC conjugated anti-human IgA and the glycine–HCl dissociation solution were 52.15 ± 1.53 nL, 65.70 ± 2.06 nL and 37.51 ± 0.96 nL, respectively. This method, in which an inkjet functions as a novel “nanoliter pipette” in combination with a capillary for nanoliter immunoassays, has promising applications in areas of clinical diagnosis and drug screening.