Jian-Zhang Pan

A low-cost light-emitting diode induced fluorescence detector for capillary electrophoresis based on an orthogonal optical arrangement.

In this work, a simple and low-cost miniaturized light-emitting diode induced fluorescence (LED-IF) detector based on an orthogonal optical arrangement for capillary electrophoresis (CE) was developed, using a blue concave light-emitting diode (LED) as excitation source and a photodiode as photodetector. A lens obtained from a waste DVD-ROM was used to focus the LED light beam into an approximately 80 microm spot. Fluorescence was collected with an ocular obtained from a pen microscope at 45 degrees angle, and passed through a band-pass filter to a photodiode detector. The performance of the LED-IF detector was demonstrated in CE separations using sodium fluorescein and fluorescein isothiocyanate (FITC)-labeled amino acids as model samples. The limit of detection for sodium fluorescein was 0.92 microM with a signal-to-noise ratio (S/N) of 3. The total cost of the LED-IF detector was less than

A handheld laser-induced fluorescence detector for multiple applications.

50.

Fabrication of low-melting-point alloy microelectrode and monolithic spray tip for integration of glass chip with electrospray ionization mass spectrometry.

In this paper, we present a compact handheld laser-induced fluorescence (LIF) detector based on a 450 nm laser diode and quasi-confocal optical configuration with a total size of 9.1 × 6.2 × 4.1 cm(3). Since there are few reports on the use of 450 nm laser diode in LIF detection, especially in miniaturized LIF detector, we systematically investigated various optical arrangements suitable for the requirements of 450 nm laser diode and system miniaturization, including focusing lens, filter combination, and pinhole, as well as Raman effect of water at 450 nm excitation wavelength. As the result, the handheld LIF detector integrates the light source (450 nm laser diode), optical circuit module (including a 450 nm band-pass filter, a dichroic mirror, a collimating lens, a 525 nm band-pass filter, and a 1.0mm aperture), optical detector (miniaturized photomultiplier tube), as well as electronic module (including signal recording, processing and displaying units). This detector is capable of working independently with a cost of ca.

Microdroplet chain array for cell migration assays

2000 for the whole instrument. The detection limit of the instrument for sodium fluorescein solution is 0.42 nM (S/N=3). The broad applicability of the present system was demonstrated in capillary electrophoresis separation of fluorescein isothiocyanate (FITC) labeled amino acids and in flow cytometry of tumor cells as an on-line LIF detector, as well as in droplet array chip analysis as a LIF scanner. We expect such a compact LIF detector could be applied in flow analysis systems as an on-line detector, and in field analysis and biosensor analysis as a portable universal LIF detector.

High-speed separation of proteins by sodium dodecyl sulfate-capillary gel electrophoresis with partial translational spontaneous sample injection

In this paper, a glass microchip-based emitter with a low-melting-point alloy (LMA) microelectrode and a monolithic tip for electrospray ionization mass spectrometry (ESI-MS) was described. So far, the fabrication of metal microelectrode achieving direct electrical contact in the microchannel of glass chip is still a challenge. A novel fabrication approach for LMA microelectrode in the glass chip was developed to achieve direct electrode-solution electrical contact in the microchannel. An electrode channel and a sample channel were firstly fabricated on a glass chip with a micropore connecting the two channels. The melted LMA was filled into the electrode channel under a pressure of ca. 100kPa, forming a stable and nicely fitted interface at the micropore between the sample and the electrode channels due to surface tension effect. The melted LMA filled in the electrode channel was then allowed to solidify at room temperature. The channel geometries including the distance between the sample and the electrode channels on the mask and the turning angle of the electrode channel were optimized for fabricating the LMA electrode. In this work, an improved fabrication approach for monolithic emitter tip based on pyramid-shaped tip configuration and stepped grinding method was also developed to fabricate well-defined sharp tips with a smallest tip end size of ca. 15microm x 50microm. Two types of emitter tip end including puncher-shaped tip and fork-shaped tip were produced. The emitter with the fork-shaped tip showed better working stability (4.4% RSD, TIC) at nanoliter-scale flow rate of 50nL/min. The fabrication approaches for the LMA microelectrode and emitter tip are simple and robust, and could be carried out in most of routine laboratories without the need of complicated and expensive instruments. The performance of the emitter was evaluated in the analysis of reserpine, angiotensin II and myoglobin. A continuous experiment over 6h demonstrated good stability of the present system in long-term analysis.

A compact short‐capillary based high‐speed capillary electrophoresis bioanalyzer

Establishing cell migration assays in multiple different microenvironments is important in the study of tissue repair and regeneration, cancer progression, atherosclerosis, and arthritis. In this work, we developed a miniaturized and massive parallel microfluidic platform for multiple cell migration assays combining the traditional membrane-based cell migration technique and the droplet-based microfluidic technique. Nanoliter-scale droplets are flexibly assembled as building blocks based on a porous membrane to form microdroplet chains with diverse configurations for different assay modes. Multiple operations including in-droplet 2D/3D cell culture, cell co-culture and cell migration induced by a chemoattractant concentration gradient in droplet chains could be flexibly performed with reagent consumption in the nanoliter range for each assay and an assay scale-up to 81 assays in parallel in one microchip. We have applied the present platform to multiple modes of cell migration assays including the accurate cell migration assay, competitive cell migration assay, biomimetic chemotaxis assay, and multifactor cell migration assay based on the organ-on-a-chip concept, for demonstrating its versatility, applicability, and potential in cell migration-related research.

A simple fabrication method for tapered capillary tip and its applications in high-speed CE and ESI-MS

In this study, we developed a picoliter‐scale partial translational spontaneous injection approach which is suitable for high‐speed protein separation under sodium dodecyl sulfate‐capillary gel electrophoresis mode. On the basis of this approach, we built a high‐speed CE system for protein separation based on a short capillary and slotted‐vial array. The system has the advantages of simple structure, ease of building without the requirement of microfabricated devices, convenient operation, and low cost. Under the optimized conditions, picoliter‐scale sample plugs (corresponding to ∼65 μm plug length) were obtained, which ensured both the high speed and the high efficiency in protein separation. Five fluorescein isothiocyanate labeled proteins including myoglobin, egg albumin, bovine serum albumin, phosphorylase b, and myosin were separated within 60 s with an effective separation length of 1.5 cm. Theoretical plates per meter ranging from 2.58×105 to 1.28×106 (corresponding to 0.78–3.88 μm plate height) were obtained. The separation speed and separation efficiency of the present system are comparable to those of most microchip‐based capillary electrophoresis systems for protein separation. The relative standard deviations of the migration times were in the range of 0.9–1.3% (n=5). Good linear relationships between log relative molecular mass and migration time were obtained in the molecular weigh range of 17 200–500 000, which demonstrate the present system can be applied in protein relative molecular mass determination.

Automated liquid operation method for microfluidic heterogeneous immunoassay.

Here, a compact high‐speed CE bioanalyzer based on a short capillary has been developed. Multiple modules of picoliter scale sample injection, high‐speed CE separation, sample changing, LIF detection, as well as a custom designed tablet computer for data processing, instrument controlling, and result displaying were integrated in the bioanalyzer with a total size of 23 × 17 × 19 cm (length × width × height). The high‐speed CE bioanalyzer is capable of performing automated sample injection and separation for multiple samples and has been successfully applied in fast separations of amino acids, chiral amino acids, proteins and DNA fragments. For instance, baseline separation of six FITC‐labeled amino acids and ultrahigh‐speed separation of three amino acids could be achieved within 7 and 1 s, respectively. The separation speed and efficiency of the optimized high‐speed CE system are comparable to or even better than those reported in microchip‐based CE systems. We believe this bioanalyzer could provide an advanced platform for fundamental research in bioscience and clinical diagnosis, as well as in quality control for drugs, foods, and feeds.

A robust and extendable sheath flow interface with minimal dead volume for coupling CE with ESI-MS

Fabrication of capillaries with tapered tips is an important technique that is required in many analytical chemistry areas, such as ESI‐MS, CE, electrochemical analysis, and microinjection. This paper describes a simple and effective grinding‐based fabrication method for capillaries with tapered tips. A novel grinding mode utilizing the combination of rotation and precession of an elastic capillary was developed, which significantly improved the controllability to the grinding process as well as the capillary tip shape. The capillary was fabricated by fixing it in an electric drill installed perpendicularly, and grind the capillary tip rotated around its own axis as well as the drill axis on sandpapers. Compared with conventional fabrication techniques for capillary tips, the present method is easy to control the capillary tip shape in routine laboratories without the requirement of expensive equipments or poisonous reagent (e.g. hydrofluoric acid (HF) solution). Various capillaries with different tip diameters and tip taper angles could be fabricated using the present method with good controllability and reproducibility. These capillaries were applied in high‐speed CE and ESI‐MS analysis to demonstrate the feasibility and potential of this fabrication method.

A Low-Cost Palmtop High-Speed Capillary Electrophoresis Bioanalyzer with Laser Induced Fluorescence Detection

In this work, an automated liquid operation method for multistep heterogeneous immunoassay toward point of care testing (POCT) was proposed. A miniaturized peristaltic pump was developed to control the flow direction, flow time and flow rate in the microliter range according to a program. The peristaltic pump has the advantages of simple structure, small size, low cost, and easy to build and use. By coupling the peristaltic pump with an antibody-coated capillary and a reagent-preloaded cartridge, the complicated liquid handling operation for heterogeneous immunoassay, including sample metering and introduction, multistep reagent introduction and rinsing, could be triggered by an action and accomplished automatically in 12 min. The analytical performance of the present immunoassay system was demonstrated in the measurement of human IgG with fluorescence detection. A detection limit of 0.68 μg/mL IgG and a dynamic range of 2-300 μg/mL were obtained.