An absorption detection approach for multiplexed capillary electrophoresis using a linear photodiode array

A novel absorption detection method for highly multiplexed capillary electrophoresis is presented for zone electrophoresis and for micellar electrokinetic chromatography. The approach involves the use of a linear photodiode array on which a capillary array is imaged by a camera lens. Either a tungsten lamp or a mercury lamp can be used as the light source such that all common wavelengths for absorption detection are accessible by simply interchanging narrow-band filters. Each capillary spans several diodes in the photodiode array for absorption measurements. Over 100 densely packed capillaries can be monitored by a single photodiode array element with 1024 diodes. The detection limit for rhodamine 6G for each capillary in the multiplexed array is ～1.8 × 10(-)(8) M injected (S/N = 2). The cross-talk between adjacent capillaries is less than 0.2%. Simultaneous analysis of 96 samples is demonstrated.     

Intrinsic fiber-optic ultrasonic sensor array using multiplexed two-wave mixing interferometry

An intrinsic multiplexed laser interferometer is presented that allows for the simultaneous detection of acoustic waves by an array of fiber-optic sensors. The phase-modulated signals from each sensor are demodulated by use of an adaptive two-wave mixing setup. The light from each sensing fiber in the array is mixed with a reference beam in a single photorefractive crystal (PRC), and the output beams from the PRC are imaged onto separate photodetectors to create a multiplexed two-wave mixing (MTWM) system. The sensing fibers are embedded in graphite-epoxy composite panels, and detection of both acoustic emission and ultrasonic signals in these materials is demonstrated. The intrinsic MTWM system is an effective tool for the simultaneous demodulation of signals from a large fiber sensor array. Also, the adaptive nature of the MTWM setup obviates the need for active stabilization against ambient noise.     

A capillary array gel electrophoresis system using multiple laser focusing for DNA sequencing

A very simple and highly sensitive capillary array gel electrophoresis system is constructed to analyze DNA fragments. On-column detection of DNA migration in a large number of gel-filled capillaries is carried out using side-entry laser irradiation and with a CCD camera, although it has been considered impossible because the irradiation laser is scattered strongly at the surfaces of the first few capillaries. By optimizing optical conditions, the laser beam can be focused repeatedly to irradiate all the capillaries held on a plate by working each capillary as a cylindrical convex lens. DNA sequencing samples migrating in 24 capillaries can simultaneously be analyzed with the system.     

Development of a microfluidic platform with an optical imaging microarray capable of attomolar target DNA detection

In this paper, DNA hybridization in a microfluidic manifold is performed using fluorescence detection on a fiber-optic microarray. The microfluidic device integrates optics, sample transport, and fluidic interconnects on a single platform. A high-density optical imaging fiber array containing oligonucleotide-labeled microspheres was developed. DNA hybridization was observed at concentrations as low as 10 aM with response times of less than 15 min at a flow rate of 1 microL/min using 50 microL of target DNA samples. The fast response times coupled with the low sample volumes and the use of a high-density, fiber-optic microarray format make this method highly advantageous. This paper describes the initial development, optimization, and integration of the microfluidic platform with imaging fiber arrays.     

Design and processing of high-density single-mode fiber arrays for imaging and parallel interferometer applications

The design and fabrication procedures for implementing a high-density (16-microm center spacing) single-mode fiber (SMF) array are described. The specific application for this array is a parallel optical coherence tomography system for endoscopic imaging. We obtained fiber elements by etching standard single-mode SMF-28 fibers to a diameter of 14-15 microm. We equalized 1-m lengths of fiber to within 1 mm by using a fiber interferometer setup, and we describe a method for packaging arrays with as many as 100 fibers.     

Interferometer for optical coherence tomography

We describe a new interferometer setup for optical coherence tomography (OCT). The interferometer is based on a fiber arrangement similar to Young's two-pinhole interference experiment with spatial coherent and temporal incoherent light. Depth gating is achieved detection of the interference signal on a linear CCD array. Therefore no reference optical delay scanning is needed. The interference signal, the modulation of the signal, the axial resolution, and the depth range are derived theoretically and compared with experiments. The dynamic range of the setup is compared with OCT sensors in the time domain. To our knowledge, the first images of porcine brain and heart tissue and human skin are presented.     

High-density fiber-optic DNA random microsphere array

A high-density fiber-optic DNA microarray sensor was developed to monitor multiple DNA sequences in parallel. Microarrays were prepared by randomly distributing DNA probe-functionalized 3.1-microm-diameter microspheres in an array of wells etched in a 500-microm-diameter optical imaging fiber. Registration of the microspheres was performed using an optical encoding scheme and a custom-built imaging system. Hybridization was visualized using fluorescent-labeled DNA targets with a detection limit of 10 fM. Hybridization times of seconds are required for nanomolar target concentrations, and analysis is performed in minutes.     

光纤式转镜高速相机同步转速传感器研究

设计了一款光纤转镜式高速相机同步转速传感器;运用单片机(MCU)和复杂可编程逻辑器件(CPLD)结合的方式,提出了一种高精度数字测量方法。MCU与CPLD通过串行外设接口(SPI)通信,MCU向CPLD传输相应的火花基数延时和脉冲宽度;探测信号经过放大、整形后传送到CPLD进行滤波、计数处理,CPLD将测量数据经串口发送给计算机进行实时显示,同时输出同步控制信号。测试数据表明:时间测量相对误差小于±0.2%;成像系统像漂移合成误差约为4.5 mm,像漂移时间约为3 μs,满足实验使用要求。     

Label-free parallel screening of combinatorial triazine libraries using reflectometric interference spectroscopy

The parallel reflectometric interference spectroscopy is presented as a label-free optical detection method. A new setup was adapted to accommodate sample carriers in a 96-well microplate. It allows for the first time simultaneous plate imaging by a CCD camera for the parallel detection of specific biomolecular interaction in the microplate wells at heterogeneous phase using direct optical monitoring. The detection of binding events with time resolution enables a highly parallel functional biomolecular interaction analysis (BIA). The combination of this new screening setup with combinatorial solid-phase synthesis is performed in the wells of glass-bottom microplates to accomplish the synthesis and the screening platform within one device. As a model system for a solid-phase substance library, synthesis of a triazine library and the subsequent BIA with four different antibodies were carried out. The presented setup enables a time resolution of 18 s with a total screening time of less than 35 min including baseline adjustment, BIA, and regeneration of the screening device for 96 samples in parallel. The binding studies reveal a fast classification of the different monoclonal and polyclonal antibodies and enable the detection of triazines with high binding affinity. The presented prototype is the first parallelized optical label-free detection system for biomolecular interaction analysis that is suitable for a high-throughput screening based on the 96-well microplate format.     

Two-dimensional single-shot tomography using a virtually imaged phased array and a spatial phase modulator

A virtually imaged phased array (VIPA) installed optical interferometer has been expanded to the two-dimensional (2D) tomography from the previous one-dimensional single-shot imaging technique with keeping the resolution and the measurement range. A single-shot measurement has been realized by a spatial phase modulator installed in the optical interferometer and tracing the delay time to pixel numbers on a 2D charge-coupled device (CCD) image sensor. The flexibility of the sample position was experimentally confirmed to be >25 mm, in relation to the VIPA coherency, for which the number of the interference order was confirmed to be 35. As a demonstration, a surface profile of stacked gauge blocks was observed. The repeatability of the surface position was 5?μm for the surface profilometry. In addition, a multilayer structure was observed using a glass plate. The experimental resolution was 53?μm when the amplified spontaneous emission light generated by the optical fiber amplifier was used for the light source. The single-shot measurement was confirmed by the 2D-CCD at a frame rate of 30 frames per second (FPS), and it provided evidence that the 2D scanless profilometry was successfully achieved using the VIPA optical device.     

High-speed fuel tracer fluorescence and OH radical chemiluminescence imaging in a spark-ignition direct-injection engine

An innovative technique has been demonstrated to achieve crank-angle-resolved planar laser-induced fluorescence (PLIF) of fuel followed by OH* chemiluminescence imaging in a firing direct-injected spark-ignition engine. This study used two standard KrF excimer lasers to excite toluene for tracking fuel distribution. The intensified camera system was operated at single crank-angle resolution at 2000 revolutions per minute (RPM) for 500 consecutive cycles. Through this work, it has been demonstrated that toluene and OH* can be imaged through the same optical setup while similar signal levels are obtained from both species, even at these high rates. The technique is useful for studying correlations between fuel distribution and subsequent ignition and flame propagation without the limitations of phase-averaging imaging approaches. This technique is illustrated for the effect of exhaust gas recirculation on combustion and will be useful for studies of misfire causes. Finally, a few general observations are presented as to the effect of preignition fuel distribution on subsequent combustion.     

Performances of endoscopic holography with a multicore optical fiber

A holographic setup that involves the use of a multicore optical fiber as an in situ recording medium has been developed. The hologram is transmitted to a CCD camera for electronic processing, and the image is reconstructed numerically, providing more flexibility to the holographic process. The performances of this imaging system have been evaluated in terms of the resolution limit and robustness relative to noise. The experimental cutoff frequency has been measured experimentally over a range of observation distances (4-10 mm) and presents a very good agreement with the predictions made by simulation. The system features a resolution of 5-μm objects for a 4-mm observation distance. The different sources of noise have been analyzed, and their influence on resolution has been proved to be nonrelevant.     

Capillary electrophoresis absorption detection using fiber-loop ring-down spectroscopy

The application of phase-shift, fiber-loop, ring-down spectroscopy (PS-FLRDS) as an on-line detector for capillary electrophoresis (CE) of biomolecules is demonstrated. CE was conducted using a custom-designed capillary/fiber interface coupled to an absorption detector, which is based on the ring-down of an optical signal in a closed fiber waveguide loop. The ring-down times were obtained by measuring the phase difference between intensity modulated light entering and exiting the fiber loop. The incorporation of a microlens to enhance transmission through the sample gap led to an improvement of the sensitivity by up to 80% compared to the square-cut fiber and a reduction in the detection limit. The performance of the PS-FLRDS absorption technique as an online detector was characterized by flow injection through a capillary. Good repeatability and linear response were obtained, and the detection limit using the lensed fiber/capillary interface system was determined to be alpha(min) = 1.6 cm(-1) for an absorption path of approximately 30 microm. PS-FLRDS coupled to CE was also applied to the analysis of human serum albumin (HSA) by using a NIR dye as a noncovalent label. The excess free dye and the dye/protein complex were resolved. The labeling coefficient was determined to be approximately 6, and good repeatability of peak areas (RSD = 8.7%) was obtained for the analysis of HSA. Furthermore, an excellent linear response (R2 > 0.99) was obtained between the peak areas and concentrations of HSA. The detection limit of labeled HSA was determined to be 1.67 microM.     

Generic camera model and its calibration for computational integral imaging and 3D reconstruction

Integral imaging (II) is an important 3D imaging technology. To reconstruct 3D information of the viewed objects, modeling and calibrating the optical pickup process of II are necessary. This work focuses on the modeling and calibration of an II system consisting of a lenslet array, an imaging lens, and a charge-coupled device camera. Most existing work on such systems assumes a pinhole array model (PAM). In this work, we explore a generic camera model that accommodates more generality. This model is an empirical model based on measurements, and we constructed a setup for its calibration. Experimental results show a significant difference between the generic camera model and the PAM. Images of planar patterns and 3D objects were computationally reconstructed with the generic camera model. Compared with the images reconstructed using the PAM, the images present higher fidelity and preserve more high spatial frequency components. To the best of our knowledge, this is the first attempt in applying a generic camera model to an II system.     

Use of scanned detection in optical position encoders

The use of scanning detection in optical noncontact position sensing is proposed, and a prototype is implemented, using optical scanning of pseudorandom binary sequences printed in bar-code format. Light from a vibrating fiber tip is imaged onto the printed code using a GRIN (graded index) lens, and the reflected light detected via the same lens, resulting in a single scanner module. Improved flexibility and signal processing possibilities are obtained compared to conventional diode array optical code readers. Performance limitations of scanning position encoders are analyzed and discussed. Suggestions for implementation using microoptoelectromechanical systems are presented.     

Real-time fluorescence imaging of isotachophoretic preconcentration for capillary electrophoresis

Real-time studies of the dynamic processes that take place during isotachophoresis (ITP) were performed. The experimental arrangement utilized was a real-time fluorescence imaging system based on a dye laser at 488 nm, pumped by a XeCl excimer laser. Fluorescence emitted from the migrating sample molecules was recorded by an image-intensified, thermoelectrically cooled CCD camera. The camera signals were processed by a computer and displayed on a screen in real time, allowing the ITP concentration to be monitored continuously. Real-time analysis provided additional information concerning ITP hardly obtainable using conventional detection systems or by theoretical calculations. Such experimental data can be evaluated and be compared with theoretical calculations. Information obtained by this detection technique is useful if ITP is to be used, for example as an on-line preconcentration technique in combination with capillary zone electrophoresis.     

Radionuclide imaging of miniaturized chemical analysis systems

We propose radionuclide imaging as a valuable tool for the study of molecular interactions in miniaturized systems for chemical analysis. Sensitive and quantitative imaging can be performed with compounds labeled with short-lived positron-emitting radionuclides, such as (11)C and (68)Ga, within selected parts of the system. Radionuclide imaging is not restricted to transparent materials since the relatively energetic positrons can penetrate high optical density materials. Experimentally, a radiotracer is introduced into the object of study, which is subsequently placed on a phosphor storage plate. After exposure, the plate is scanned with a laser and a digital, quantitative image can be reconstituted. To demonstrate the concept, three types of microstructures suited for integration in chemical analysis systems were imaged with (11)C- and (68)Ga-labeled tracers. The influence of factors such as geometry of the object and type of radionuclide on resolution and sensitivity was investigated. The resolution ranged from 0.9 to 2.7 mm (fwhm). Measuring low amounts of radioactivity in the three structures, 2-20 Bq could be detected, which corresponded to 2.3-500 amol or 2.4-110 pM tracer. The imaging approach was applied to study analyte concentration and sample dilution effects on the performance of a capillary extraction column integrated in an automated LC-ESI-MS system. The utility of the technique was further illustrated by imaging of microchannels in a zeonor plastic compact disk and in a poly(dimethylsiloxane) material for the study of nonspecific peptide adsorption.     

A compact,automated and long working distance optical tweezer system

We demonstrate a compact, automated, long working distance optical tweezer system using a novel mechanism for controlling the position of the optical trap. Our system uses a single focusing lens with a working distance of 4.5?mm and the trapping beam is steered by moving the lens with a miniature coil-magnet assembly. The sample is imaged through a 100×?microscope objective and a CCD camera captures the magnified image. A custom image processing software detects the position of the laser beam and identifies the sample objects. This information is used to generate appropriate electrical signals to drive the coils which move the focusing lens along the desired path. The system is fairly simple and power efficient due to minimal usage of optical elements in the laser path; hence our setup is simple, low-cost and requires low optical power. Computer-generated arbitrary trapping paths and time-shared trapping patterns are successfully demonstrated. Efficient trapping of micron size spheres with laser powers as low as 1.5?mW is observed.     

Ultrasonic computed tomography reconstruction of the attenuation coefficient using a linear array

The attenuation coefficient distribution and sound velocity distribution in the breast can be used to complement B-mode ultrasound imaging in the detection of breast cancer. This study investigated an approach for reconstructing the attenuation coefficient distribution in the breast using a linear array. The imaging setup was identical to that for conventional B-mode breast imaging, and the same setup has been used for reconstruction of sound velocity distributions in previous studies. In this study, we further developed a reconstruction method for the attenuation coefficient distribution. In particular, the proposed method incorporates the segmentation information from B-mode images and uses the sound velocity distribution to compensate for refraction effects. Experiments were conducted with a setup consisting of a 5-MHz, 128-channel linear array, a programmable digital array system, a phantom, and a computer. The constructed phantom contained materials mimicking the following breast tissues: glandular tissue, fat, cysts, high-attenuation tumors, and irregular tumors. Application of the proposed technique resulted in all the cysts and tumors (including high-attenuation and irregular tumors) being distinguished by thresholding the reconstructed attenuation coefficients. We have demonstrated that it is possible to use the same imaging setup to acquire data for B-mode image, sound velocity distribution, and attenuation coefficient distribution simultaneously. Moreover, the experimental data indicate its potential in improving the detection of breast cancer.     

Laser-induced fluorescence detection by liquid core waveguiding applied to DNA sequencing by capillary electrophoresis

A new laser-induced fluorescence detector for capillary electrophoresis (CE) is described. The detector is based on transverse illumination and collection of the emitted fluorescent light via total internal reflection along the separation capillary. The capillary is coated with a low refractive index fluoropolymer and serves as a liquid core waveguide (LCW). The emitted light is detected end-on with a CCD camera at the capillary exit. The observed detection limit for fluorescein is 2.7 pM (550 ymol) in the continuous-flow mode and 62 fM in the CE mode. The detector is applied to DNA sequencing. One-color G sequencing is performed with single-base resolution and signal-to-noise ratio approximately 250 for peaks around 500 bases. The signal-to-noise ratio is approximately 50 for peaks around 950 bases. Full four-color DNA sequencing is also demonstrated. The high sensitivity of the detector is suggested to partly be due to the efficient rejection of scattered laser light in the LCW. The concept should be highly suitable for capillary array detection.