Biomedical subjects

Paul Yager

Publications and source records attributed to Paul Yager.

12 recordsLinked to original sources

PubMed2006

Compact, high performance surface plasmon resonance imaging system.

We report the construction and characterization of a new compact surface plasmon resonance imaging instrument. Surface plasmon resonance imaging is a versatile technique for detection, quantification and visualization of biomolecular binding events which have spatial structure. The imager uses a folded light path, wide-field optics and a tilted detector to implement a high performance optical system in a volume 7 in. x 4 in. x 2 in. A bright diode light source and an image detector with fast frame rate and integrated digital signal processor enable real-time averaging of multiple images for improved signal-to-noise ratio. Operating angle of the imager is adjusted by linear translation of the light source. Imager performance is illustrated using resolution test targets, refractive index test solutions, and competition assays for the antiepileptic drug phenytoin. Microfluidic flowcells are used to enable simultaneous assay of three sample streams. Noise level of refractive index measurements was found to decrease proportional to the square root of the number of pixels averaged, reaching approximately 5 x 10(-7) refractive index units root-mean-square for 160 x 120 pixels image regions imaged for 1s. The simple, compact construction and high performance of the imager will allow the device to be readily applied to a wide range of applications.

Diagnostic Imaging↗

PubMed2006

Lateral spread of an amplification signal using an enzymatic system on a conductive surface.

In this letter, we report a novel signal amplification phenomenon that rapidly and dramatically increases both the magnitude and the lateral extent of the original signal. This phenomenon utilizes an enzyme immobilized on a conductive surface to generate amplified signals at locations remote from the original site of enzyme activity. The result is demonstrated on a microfluidic platform using the established precipitating enzyme-substrate system of horseradish peroxidase (HRP) and 3,3',5,5'-tetramethylbenzidine (TMB) on a surface plasmon resonance (SPR) imaging system.

Electric Conductivity↗

PubMed2006

Microfluidic diagnostic technologies for global public health.

The developing world does not have access to many of the best medical diagnostic technologies; they were designed for air-conditioned laboratories, refrigerated storage of chemicals, a constant supply of calibrators and reagents, stable electrical power, highly trained personnel and rapid transportation of samples. Microfluidic systems allow miniaturization and integration of complex functions, which could move sophisticated diagnostic tools out of the developed-world laboratory. These systems must be inexpensive, but also accurate, reliable, rugged and well suited to the medical and social contexts of the developing world.

Developing Countries↗

PubMed2006

Recirculating flow accelerates DNA microarray hybridization in a microfluidic device.

A recirculating microfluidic device fabricated by laminating Mylar and glass was developed for the analysis of hybridization of oligonucleotides to DNA microarrays. The device is part of a system that provides controlled hybridization to DNA probes immobilized in a microarray of polyacrylamide gel pads using recirculation and temperature control. The system was used to obtain real-time kinetics of DNA hybridization and more accurate melting profiles of target-probe duplexes than possible using a static hybridization format. Recirculation shortened the time of perfect match target-probe hybridization from 6 hours to 2 hours and shifted the Td by 1.54 degrees C, relative to static conditions. The experimental results were consistent with a three-dimensional simulation of hybridization using a recirculating buffer system.

Buffers↗

PubMed2005

Diffusion based analysis in a sheath flow microchannel: the sheath flow T-sensor.

This paper describes a microfluidic channel that allows for diffusion-based analysis of adsorbing species without passivation of the channel surfaces. The sheath flow configuration was used to measure the diffusion coefficient of fluorescently labeled species from their spatial distribution within the microchannel by analyzing the derivative of the intensity profile at the interface between two distinct core fluids. Measurements for both a small molecule (rhodamine B) and an intermediate-sized protein (wheat germ agglutinin) were made, demonstrating the utility of the sheath flow T-sensor.

Diffusion↗

PubMed2005

Cross-talk problem on a fluorescence multi-channel microfluidic chip system.

Development of a compact fluorescence-based detection system for use in a micro-analytical system, such as a point-of-care diagnostic system, often requires a multi-channel microfluidic chip system. Since the materials used for microfluidic chips usually are transparent in the visible region and have a refractive indices higher than that of air or the surrounding environment, the fluorescence emission and scattered excitation light can propagate through the chip. We observed that such propagation can cause cross-talk between adjacent channels, and may become the major source of noise in the system and/or photo bleach the fluorescent samples in the adjacent channels, particularly for the small distances between the channels found in microfluidic chips, usually in order of several micro m. We monitored this cross-talk using fluorescein as a fluorescent sample and Mylar sheeting as a microfluidic chip material. We then discuss how this cross-talk can be avoided using a simple, inexpensive and effective method.

Artifacts↗

PubMed2004

Suppression of non-specific adsorption using sheath flow.

The use of a confining sheath fluid within a microfluidic channel in order prevent non-specific adsorption of analytes to the walls of microchannels is demonstrated. A sheath-flow channel fabricated using laser cutting of Mylar films is developed. Numerical simulations of convective and diffusive mass transport within the channel are presented. The device is characterized experimentally using epifluorescence microscopy. It is demonstrated that the device is capable of preventing the adsorption of Rhodamine B to the walls of the channel for a period that would allow for adsorption-free T-sensor measurements to be made within the core of the flow channel. Generalized scaling rules based on the diffusion coefficient, sheath thickness and affinity of the potential adsorbant for the surface material are discussed. The controlled adsorption of the protein bovine serum albumin (BSA) to a gold surface is also demonstrated using SPR microscopy.

Adsorption↗

PubMed2003

Controlled microfluidic reconstitution of functional protein from an anhydrous storage depot.

A novel method has been developed for preserving molecules in microfluidic devices that also enables the control of the spatial and temporal concentrations of the reconstituted molecules within the devices. In this method, a storage cavity, embedded in a microchannel, is filled with a carbohydrate matrix containing, for example, a reagent. When the matrix is exposed to flowing liquid, it dissolves, resulting in the controlled reconstitution and release of the reagent from the cavity. The technique was demonstrated using two different model systems; the successful preservation and controlled release of beta-galactosidase was achieved. This method has possible applications for simple point-of-care drug delivery and immunoassays, and could be used to pattern the surfaces of microchannels. More broadly, this preservation and controlled release technique can be applied where the preservation and/or spatial and temporal control of chemical concentrations are desired.

Dimethylpolysiloxanes↗

PubMed2003

Nonlinear decrease of background fluorescence in polymer thin-films - a survey of materials and how they can complicate fluorescence detection in microTAS.

Polymers and plastics are receiving increased attention as materials for microfluidics and microTAS applications. Given the ubiquity of fluorescence detection techniques in micro-analytical systems, the fluorescence properties of polymers and plastics should not be overlooked. We survey some commonly available polymer thin-films for their fluorescence behaviour under standardized conditions to determine which materials are most suitable for high-sensitivity fluorescence detection lab chips. The initial fluorescence intensities of some of the materials surveyed were significantly higher than glass and fused silica controls, and decreased over the three hour period with complex kinetics. We then discuss how this has confounded fluorescence detection in our analytical context, and possible mechanisms for the decrease.

Membranes, Artificial↗

PubMed2003

A smart microfluidic affinity chromatography matrix composed of poly(N-isopropylacrylamide)-coated beads.

The efficient upstream processing of complex biological or environmental samples for subsequent biochemical analysis remains a challenge in many analytical systems. New microfluidic platforms that provide multidiagnostic capabilities on single chips face a similar challenge in getting specific analytes purified or contaminants removed in different fluid streams. Here, stimuli-responsive polymers have been used to construct "smart" beads that can be reversibly immobilized on microfluidic channel walls to capture and release targets. The 100-nm latex beads were surface-modified with the temperature-sensitive polymer poly(N-isopropylacrylamide) (PNIPAAm). At room temperature, a suspension of these beads flows through a microfluidic channel constructed of poly(ethylene terephthalate). However, when the temperature in the channel is raised above the lower critical solution temperature (LCST) of PNIPAAm, the beads aggregate and adhere to the walls of the channel. The adhered beads are stable for long durations on the channel walls (demonstrated up to 70 min) in the presence of flow. The beads were further modified with the affinity moiety biotin, which tightly binds streptavidin. The dual-modified beads were adhered to the channel walls and functioned as a chromatographic affinity separation matrix, capable of binding streptavidin that was flowed through the microfluidic channel. Upon the reverse thermal stimulation to below the PNIPAAm LCST, the beads and captured streptavidin were observed to quickly dissolve and elute from the channel walls. This temperature-responsive affinity chromatography matrix can thus be flowed into a column and aggregated via temperature change, followed by the controlled release of affinity-captured targets back into the microfluidic flow stream.

Acrylamides↗

PubMed2002

Cell lysis and protein extraction in a microfluidic device with detection by a fluorogenic enzyme assay.

A critical requirement for achieving a micro total analytical system for the analysis of cells and their constituent proteins is to integrate the lysis and fractionation steps on-chip. Here, an experimental microfluidic system integrating the lysis of bacterial cells and the extraction of a large intracellular enzyme, beta-galactosidase, is demonstrated. The beta-galactosidase is detected and quantified using a fluorogenic enzyme assay and a numerical model. While the focus is on the lysis of typical gram-negative bacterial cells (E. coli), the techniques described here could, in principle, be applied to a variety of different cell types.

Bacterial Proteins↗

PubMed2002

Passive electrophoresis in microchannels using liquid junction potentials.

The formation of the liquid junction potential (LJP) is a well-studied phenomenon that occurs in the presence of ionic concentration gradients. Although the LJP has been well characterized, its impact has generally been overlooked in microfluidic applications. The characteristics of flow in microfluidic channels cause this phenomenon to be particularly important, both as a source of deviation from anticipated results and as a tool capable of being harnessed to perform useful tasks. It is demonstrated that LJPs formed in microchannels can induce appreciable electrophoretic transport of charged species without the use of electrodes or an external power supply. This process is demonstrated in an H-filter (an H-shaped microfluidic channel used to bring two fluids into contact allowing extraction of diffusing species from one stream to another) by generating junction potentials between two flowing streams containing different concentrations of strong electrolytes and observing the mass transport of the charged dye fluorescein between those streams. It is shown that the LJP can be controlled to either accelerate or decelerate mass transport across a fluid interface in the absence of an interposed membrane. A preliminary mathematical description of the phenomena is offered to support the hypothesis that the observed mass transport is a result of the LJP. Possible practical microfluidic applications of electrophoretic transport without electrodes are discussed.

Diffusion↗