Office of Science and Engineering

Silver Spring, MD, United States

Office of Science and Engineering

Silver Spring, MD, United States
SEARCH FILTERS
Time filter
Source Type

Balsam J.,Office of Science and Engineering | Balsam J.,University of Maryland University College | Rasooly R.,U.S. Department of Agriculture | Bruck H.A.,University of Maryland University College | And 2 more authors.
Biosensors and Bioelectronics | Year: 2014

The low sensitivity of Mobile Health (mHealth) optical detectors, such as those found on mobile phones, is a limiting factor for many mHealth clinical applications. To improve sensitivity, we have combined two approaches for optical signal amplification: (1) a computational approach based on an image stacking algorithm to decrease the image noise and enhance weak signals, and (2) an optical signal amplifier utilizing a capillary tube array. These approaches were used in a detection system which includes multi-wavelength LEDs capable of exciting many fluorophores in multiple wavelengths, a mobile phone or a webcam as a detector, and capillary tube array configured with 36 capillary tubes for signal enhancement.The capillary array enables a ~100× increase in signal sensitivity for fluorescein, reducing the limit of detection (LOD) for mobile phones and webcams from 1000. nM to 10. nM. Computational image stacking enables another ~10× increase in signal sensitivity, further reducing the LOD for webcam from 10 nM to 1 nM.To demonstrate the feasibility of the device for the detection of disease-related biomarkers, adenovirus DNA labeled with SYBR green or fluorescein was analyzed by both our capillary array and a commercial plate reader. The LOD for the capillary array was 5 ug/mL, and that of the plate reader was 1 ug/mL. Similar results were obtained using DNA stained with fluorescein.The combination of the two signal amplification approaches enables a ~1000× increase in LOD for the webcam platform. This brings it into the range of a conventional plate reader while using a smaller sample volume (10 ul) than the plate reader requires (100 ul). This suggests that such a device could be suitable for biosensing applications where up to 10 fold smaller sample sizes are needed.The simple optical configuration for mHealth described in this paper employing the combined capillary and image processing signal amplification is capable of measuring weak fluorescent signals without the need of dedicated laboratories. It has the potential to be used to increase sensitivity of other optically based mHealth technologies, and may increase mHealth's clinical utility, especially for telemedicine and for resource-poor settings and global health applications. © 2013 .


Balsam J.,Office of Science and Engineering | Balsam J.,University of Maryland University College | Bruck H.A.,University of Maryland University College | Rasooly A.,Office of Science and Engineering | Rasooly A.,U.S. National Cancer Institute
Methods | Year: 2013

To overcome the limited sensitivity of phone cameras for mobile health (mHealth) fluorescent detection, we have previously developed a capillary array which enables a ~100× increase in detection sensitivity. However, for an effective detection platform, the optical configuration must allow for uniform measurement sensitivity between channels when using such a capillary array sensor. This is a challenge due to the parallax inherent in imaging long parallel capillary tubes with typical lens configurations.To enable effective detection, we have developed an orthographic projection. system in this work which forms parallel light projection images from the capillaries using an object-space telecentric lens configuration. This optical configuration results in a significantly higher degree of uniformity in measurement between channels, as well as a significantly reduced focal distance, which enables a more compact sensor.A plano-convex lens (f= 150. mm) was shown to produce a uniform orthographic projection. when properly combined with the phone camera's built in lens (f= 4. mm), enabling measurements of long capillaries (125. mm) to be made from a distance of 160. mm. The number of parallel measurements which can be made is determined by the size of the secondary lens. Based on these results, a more compact configuration with shorter 32. mm capillaries and a plano-convex lens with a shorter focal length (f= 10. mm) was constructed.This optical system was used to measure serial dilutions of fluorescein with a limit of detection (LOD) of 10. nM, similar to the LOD of a commercial plate reader. However, many plate readers based on standard 96 well plate requires sample volumes of 100. μl for measurement, while the capillary array requires a sample volume of less than 10. μl.This optical configuration allows for a device to make use of the ~100× increase in fluorescent detection sensitivity produced by capillary amplification while maintaining a compact size and capability to analyze extremely small sample volumes. Such a device based on a phone or other optical mHealth technology will have the sensitivity of a conventional plate reader but have greater mHealth clinical utility, especially for telemedicine and for resource-poor settings and global health applications. © 2013 .


Yang M.,University of Maryland Baltimore County | Yang M.,University of Jinan | Sun S.,University of Maryland Baltimore County | Kostov Y.,University of Maryland Baltimore County | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2011

There is a well-recognized need for low cost biodetection technologies for resource-poor settings with minimal medical infrastructure. Lab-on-a-chip (LOC) technology has the ability to perform biological assays in such settings. The aim of this work is to develop a low cost, high-throughput detection system for the analysis of 96 samples simultaneously outside the laboratory setting. To achieve this aim, several biosensing elements were combined: a syringe operated ELISA lab-on-a-chip (ELISA-LOC) which integrates fluid delivery system into a miniature 96-well plate; a simplified non-enzymatic reporter and detection approach using a gold nanoparticle-antibody conjugate as a secondary antibody and silver enhancement of the visual signal; and carbon nanotubes (CNT) to increase primary antibody immobilization and improve assay sensitivity. Combined, these elements obviate the need for an ELISA washer, electrical power for operation and a sophisticated detector. We demonstrate the use of the device for detection of Staphylococcal enterotoxin B, a major foodborne toxin using three modes of detection, visual detection, CCD camera and document scanner. With visual detection or using a document scanner to measure the signal, the limit of detection (LOD) was 0.5 ng/ml. In addition to visual detection, for precise quantitation of signal using densitometry and a CCD camera, the LOD was 0.1 ng/ml for the CCD analysis and 0.5 ng/ml for the document scanner. The observed sensitivity is in the same range as laboratory-based ELISA testing. The point of care device can analyze 96 samples simultaneously, permitting high throughput diagnostics in the field and in resource poor areas without ready access to laboratory facilities or electricity. © 2011 Published by Elsevier B.V.


Balsam J.,University of Maryland College Park | Ossandon M.,U.S. National Cancer Institute | Kostov Y.,University of Maryland Baltimore County | Bruck H.A.,University of Maryland College Park | And 3 more authors.
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2011

In this paper, we describe a simple charge-coupled device (CCD) based lensless fluorometer with sensitivity in the range of current ELISA plate readers. In our lensfree fluorometer, a multi-wavelength LED light source was used for fluorophore excitation. To collimate the light, we developed a simple optical Söller collimator based on a "stack of pinholes" (a stack of black PMMA with array of pinholes machined with laser) enabling the light to be collimated from the LED through the filters and the assay's microfluidics directly onto the CCD without a lens. The elimination of the lens that is used in almost all other current CCD based detection systems has four major advantages: (1) It simplifies the device design and fabrication while reducing cost. (2) It reduces the distance between the sample and the measuring device (without a lens the distance needed to focus the image on the CCD is reduced and the fluorometer can be more compact). (3) It couples the CCD and the detected surface by using an optical Söller Collimator which allows the use of filters for fluorescence detection. (4) It also uncouples the CCD and the microfluidics to enable the use of interchangeable fluidics while protecting the delicate CCD. The lensless CCD-based fluorometer is capable of detecting 16 samples simultaneously, and was used for in vitro detection of botulinum neurotoxin serotype A (BoNT-A) activity with a FRET assay that measures cleavage of a fluorophore-tagged peptide substrate specific for BoNT-A (SNAP-25) by the toxin light chain (LcA). The limit of detection (LOD) of our lensless fluorometer is 1.25 nM, which is similar to the LOD of a modern ELISA plate reader. Combined with microfluidics, this simple low cost point-of-care (POC) medical diagnostic system may be useful for the performance of many other complex medical diagnostic assays without a laboratory and thus potentially enhancing the accessibility and the quality of health care delivery in underserved populations. © 2011 The Royal Society of Chemistry.


Balsam J.,University of Maryland College Park | Ossandon M.,U.S. National Cancer Institute | Bruck H.A.,Office of Science and Engineering | Rasooly A.,Office of Science and Engineering | Rasooly A.,U.S. National Cancer Institute
Analyst | Year: 2012

To address the needs of medical diagnostics in resource-poor settings, it is necessary to develop low cost, simple and portable Point of Care detectors for integrated medical diagnostics. Previously, we have described a simple lensless fluorometer with sensitivity in the range of current ELISA plate readers. The key to the lensfree fluorometer is the uniform spatial distribution of light, which we achieved using a simple optical collimator based on a "stack of pinholes" (a stack of black PMMA plates with arrays of pinholes machined via laser) enabling the light to be collimated from the LED light source through the necessary wavelength filters and the assay's microfluidics directly onto the CCD without a lens. In this paper, we describe the optical principle for designing these Söller collimators for lensfree CCD-based fluorometry. The illuminating surface was modeled as a collection of differential areas emitting uniformly and spherically, and the intensity contribution of each emitting area was summed over the detector surface. To compute the final light intensity distribution from such a differential model we derived an integral equation to sum the individual intensity contributions from the two-dimensional emitting surface. The equation is for a single-hole collimator. Light intensity measurements were taken by placing a collimator with a particular aspect ratio (the ratio of hole length to diameter (L/d)) over the CCD image sensor and capturing an image. The resulting image is the 2D light intensity profile generated by the collimator. As the aspect ratio is increased the slope of the light intensity profile increases, corresponding to an increased degree of collimation. To test the model, the measured maximum and mean light intensities were compared with the theoretical predictions generated from the model. There was an agreement between the variation of the mean (R 2 = 0.990) and maximum (R2 = 0.938) values of light intensities with aspect ratios based modeling. These profile measurements suggest an excellent agreement with the theoretical predictions. The integral equation presented here can be used to perfect the design of the optical Söller collimator. These results may lead to the development of more effective Söller collimators for lensfree CCD-based fluorometry for use in simple low cost lensfree optical detectors with the potential to enhance the accessibility and the quality of health care for underserved populations. © 2012 The Royal Society of Chemistry.


Sun S.,Office of Science and Engineering | Sun S.,University of Maryland Baltimore County | Yang M.,University of Maryland Baltimore County | Yang M.,University of Jinan | And 3 more authors.
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2010

A miniature 96 sample ELISA-lab-on-a-chip (ELISA-LOC) was designed, fabricated, and tested for immunological detection of Staphylococcal Enterotoxin B (SEB). The chip integrates a simple microfluidics system into a miniature ninety-six sample plate, allowing the user to carry out an immunological assay without a laboratory. Assay reagents are delivered into the assay plate without the need for separate devices commonly used in immunoassays. The ELISA-LOC was constructed using Laminated Object Manufacturing (LOM) technology to assemble six layers with an acrylic (poly(methyl methacrylate) (PMMA)) core and five polycarbonate layers micromachined by a CO2 laser. The ELISA-LOC has three main functional elements: reagent loading fluidics, assay and detection wells, and reagent removal fluidics, a simple "surface tension" valve used to control the flow. To enhance assay sensitivity and to perform the assay without a lab, ELISA-LOC detection combines several biosensing elements: (1) carbon nanotube (CNT) technology to enhance primary antibody immobilization, (2) sensitive ECL (electrochemiluminescence) detection, and (3) a charge-coupled device (CCD) detector for measuring the light signal generated by ECL. Using a sandwich ELISA assay, the system detected SEB at concentrations as low as 0.1 ng ml-1, which is similar to the reported sensitivity of conventional ELISA. The fluidics system can be operated by a syringe and does not require power for operation. This simple point-of-care (POC) system is useful for carrying out various immunological assays and other complex medical assays without a laboratory. © 2010 The Royal Society of Chemistry.


Yang M.,University of Maryland, Baltimore | Yang M.,University of Jinan | Sun S.,University of Maryland, Baltimore | Kostov Y.,University of Maryland, Baltimore | And 2 more authors.
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2010

We describe a new eight channel Lab-On-a-Chip (LOC) for a Carbon Nanotube (CNT) based immunoassay with optical detection of Staphylococcal Enterotoxin B (SEB) for food safety applications. In this work, we combined four biosensing elements: (1) CNT technology for primary antibody immobilization, (2) Enhanced Chemiluminescence (ECL) for light signal generation, (3) a cooled charge-coupled device (CCD) for detection and (4) polymer lamination technology for developing a point of care immunological assay for SEB detection. Our concept for developing versatile LOCs, which can be used for many different applications, is to use a modular design with interchangeable recognition elements (e.g. various antibodies) to determine the specificity. Polymer lamination technology was used for the fabrication of a six layer, syringe operated LOC capable of analyzing eight samples simultaneously. An anti-SEB antibody-nanotube mixture was immobilized onto a polycarbonate strip, to serve as an interchangeable ligand surface that was then bonded onto the LOC. SEB samples are loaded into the device and detected by an ELISA assay using Horse Radish Peroxidase (HRP) conjugated anti-SEB IgG as a secondary antibody and ECL, with detection by a previously described portable cooled CCD detector. Eight samples of SEB in buffer or soy milk were assayed simultaneously with a limit of detection of 0.1 ng mL-1. CNT immobilization of the antibody increased the sensitivity of detection six fold. Use of a simple interchangeable immunological surface allows this LOC to be adapted to any immunoassay by simply replacing the ligand surface. A syringe was used to move fluids for this assay so no power is needed to operate the device. Our versatile portable point-of-care CCD detector combined with the LOC immunoassay method described here can be used to reduce the exposure of users to toxins and other biohazards when working outside the lab, as well as to simplify and increase sensitivity for many other types of immunological diagnostics and detection assays. © 2010 The Royal Society of Chemistry.


Bruck H.A.,University of Maryland College Park | Yang M.,Central South University | Kostov Y.,University of Maryland Baltimore County | Rasooly A.,Office of Science and Engineering | Rasooly A.,U.S. National Cancer Institute
Methods | Year: 2013

A new approach to label free biosensing has been developed based on the principle of "electrical percolation". In electrical percolation, long-range electrical connectivity is formed in randomly oriented and distributed systems of discrete elements. By applying this principle to biological interactions, it is possible to measure biological components both directly and electronically. The main element for electrical percolation biosensor is the biological semiconductor (BSC) which is a multi-layer 3-D carbon nanotube-antibody network. In the BSC, molecular interactions, such as binding of antigens to the antibodies, disrupt the network continuity causing increased resistance of the network. BSCs can be fabricated by immobilizing conducting elements, such as pre-functionalized single-walled carbon nanotubes (SWNTs)-antibody complex, directly onto a substrate, such as a Poly(methyl methacrylate) (PMMA) surface (also known as plexi-glass or Acrylic).BSCs have been demonstrated for direct (label-free) electronic measurements of antibody-antigen binding using SWNTs. If the concentration of the SWNT network is slightly above the electrical percolation threshold, then binding of a specific antigen to the pre-functionalized SWNT dramatically increases the electrical resistance due to changes in the tunneling between the SWNTs. Using anti-staphylococcal enterotoxin B (SEB) IgG as a "gate" and SEB as an "actuator", it was demonstrated that the BSC was able to detect SEB at concentrations of 1. ng/ml. Based on this concept, an automated configuration for BSCs is described here that enables real time continuous detection. The new BSC configuration may permit assembly of multiple sensors on the same chip to create "biological central processing units (CPUs)" with multiple biological elements, capable of processing and sorting out information on multiple analytes simultaneously. © 2013 .


Balsam J.,Office of Science and Engineering | Balsam J.,University of Maryland University College | Bruck H.A.,University of Maryland University College | Rasooly A.,Office of Science and Engineering | Rasooly A.,U.S. National Cancer Institute
Sensors and Actuators, B: Chemical | Year: 2013

Mobile health (mHealth) analytical technologies are potentially useful for carrying out modern medical diagnostics in resource-poor settings. Effective mHealth devices for underserved populations need to be simple, low cost, and portable. Although cell phone cameras have been used for biodetection, their sensitivity is a limiting factor because currently it is too low to be effective for many mHealth applications, which depend on detection of weak fluorescent signals. To improve the sensitivity of portable phones, a capillary tube array was developed to amplify fluorescence signals using their waveguide properties. An array configured with 36 capillary tubes was demonstrated to have a ∼100× increase in sensitivity, lowering the limit of detection (LOD) of mobile phones from 1000 nM to 10 nM for fluorescein. To confirm that the amplification was due to waveguide behavior, we coated the external surfaces of the capillaries with silver. The silver coating interfered with the waveguide behavior and diminished the fluorescence signal, thereby proving that the waveguide behavior was the main mechanism for enhancing optical sensitivity. The optical configuration described here is novel in several ways. First, the use of capillaries waveguide properties to improve detection of weak florescence signal is new. Second we describe here a three dimensional illumination system, while conventional angular laser waveguide illumination is spot (or line), which is functionally one-dimensional illumination, can illuminate only a single capillary or a single column (when a line generator is used) of capillaries and thus inherently limits the multiplexing capability of detection. The planar illumination demonstrated in this work enables illumination of a two dimensional capillary array (e.g., x columns and y rows of capillaries). In addition, the waveguide light propagation via the capillary wall provides a third dimension for illumination along the axis of the capillaries. Such an array can potentially be used for sensitive analysis of multiple fluorescent detection assays simultaneously. The simple phone based capillary array approach presented in this paper is capable of amplifying weak fluorescent signals thereby improving the sensitivity of optical detectors based on mobile phones. This may allow sensitive biological assays to be measured with low sensitivity detectors and may make mHealth practical for many diagnostics applications, especially in resource-poor and global health settings.


Qu F.,Central South University | Qu F.,Qufu Normal University | Zhang Y.,Central South University | Rasooly A.,Office of Science and Engineering | Yang M.,Central South University
Analytical Chemistry | Year: 2014

To increase the loading of glucose oxidase (GOx) and simplify glucose biosensor fabrication, hydrogel prepared from ferrocene (Fc) modified amino acid phenylalanine (Phe, F) was utilized for the incorporation of GOx. The synthesized hydrogel displays good biocompatibility and contains a significant number of Fc moieties, which can be considered as an ideal matrix to immobilize enzymes for the preparation of mediator-based biosensors. The hydrogel was studied by scanning electron microscopy, which indicated that it was composed of nanofibers with a diameter of around 50-100 nm and length extended to 1 mm. With the addition of GOx into the hydrogel and by directly dropping the resulting biocomposite onto the electrode surface, a glucose biosensor, that displays good performance due to improved enzyme loading and efficient electron transfer, can be simply constructed. The favorable network structure and good biocompatibility of the hydrogel could effectively avoid enzyme leakage and maintain the bioactivity of the enzymes, which resulted in good stability of the biosensor. The biosensor was utilized for the detection of glucose in blood samples with results comparable to those obtained from the hospital. The hydrogel as a functional component of an amperometric biosensor has implications for future development of biosensors and for clinical applications. © 2014 American Chemical Society.

Loading Office of Science and Engineering collaborators
Loading Office of Science and Engineering collaborators