Peter Kauffman

Controlled reagent transport in disposable 2D paper networks.

Recent reports have demonstrated the multi-analyte detection capability of paper networks with multiple outlets per inlet. In this report, we focus on the capabilities of 2D paper networks with multiple inlets per outlet and demonstrate the controlled transport of reagents within paper devices. Specifically, we demonstrate methods of controlling fluid transport using the geometry of the network and dissolvable barriers. Finally, we discuss the implications for higher sensitivity detection using this type of 2D paper network.

Microfluidics without pumps: reinventing the T-sensor and H-filter in paper networks.

Conventional microfluidic devices typically require highly precise pumps or pneumatic control systems, which add considerable cost and the requirement for power. These restrictions have limited the adoption of microfluidic technologies for point-of-care applications. Paper networks provide an extremely low-cost and pumpless alternative to conventional microfluidic devices by generating fluid transport through capillarity. We revisit well-known microfluidic devices for hydrodynamic focusing, sized-based extraction of molecules from complex mixtures, micromixing, and dilution, and demonstrate that paper-based devices can replace their expensive conventional microfluidic counterparts.

Dissolvable fluidic time delays for programming multi-step assays in instrument-free paper diagnostics

Lateral flow tests (LFTs) are an ingenious format for rapid and easy-to-use diagnostics, but they are fundamentally limited to assay chemistries that can be reduced to a single chemical step. In contrast, most laboratory diagnostic assays rely on multiple timed steps carried out by a human or a machine. Here, we use dissolvable sugar applied to paper to create programmable flow delays and present a paper network topology that uses these time delays to program automated multi-step fluidic protocols. Solutions of sucrose at different concentrations (10-70% of saturation) were added to paper strips and dried to create fluidic time delays spanning minutes to nearly an hour. A simple folding card format employing sugar delays was shown to automate a four-step fluidic process initiated by a single user activation step (folding the card); this device was used to perform a signal-amplified sandwich immunoassay for a diagnostic biomarker for malaria. The cards are capable of automating multi-step assay protocols normally used in laboratories, but in a rapid, low-cost, and easy-to-use format.

Visualization and measurement of flow in two-dimensional paper networks.

The two-dimensional paper network (2DPN) is a versatile new microfluidic format for performing complex chemical processes. For chemical detection, for example, 2DPNs have the potential to exceed the capabilities and performance of existing paper-based lateral flow devices at a comparable cost and ease of use. To design such 2DPNs, it is necessary to predict 2D flow patterns and velocities within them, but because of the scattering of the paper matrix, conventional particle imaging velocimetry is not practical. In this note, we demonstrate two methods for visualization of flow in 2DPNs that are inexpensive, easy to implement, and quantifiable.

Development of a seawater battery for deep-water applications

Dissolved-oxygen seawater batteries rely on the corrosion of a reactive metal anode and the reduction of oxygen at an inert cathode to generate a potential of about 1 V when immersed in seawater. Because oxygen is not very soluble in seawater, such batteries are characterized by small cathodic current densities and are therefore most suitable for long-term low-power applications. A number of batteries have been built recently using sophisticated electrodes. The objective of this study was to evaluate the feasibility of building a seawater battery using cheap readily-available materials. The results show that magnesium anodes outperform aluminum. Although the cathodic current densities achieved in this study are markedly lower than reported previously, cathodes composed of copper (or stainless-steel) mesh perform reasonably well and facilitate the design of compact batteries with an open structure and large cathodic areas. Deep- and shallow water tests show that a battery occupying 1 m3 could produce 5 W for a year or more in oxygen-saturated waters and 1–2 W in the oxygen-starved waters of the North Pacific seafloor. The energy density of such a battery including the flotation necessary for optimal performance and recovery is estimated to be 150–400 Wh kg−1.

Progress toward multiplexed sample-to-result detection in low resource settings using microfluidic immunoassay cards

In many low resource settings multiple diseases are endemic. There is a need for appropriate multi-analyte diagnostics capable of differentiating between diseases that cause similar clinical symptoms. The work presented here was part of a larger effort to develop a microfluidic point-of-care system, the DxBox, for sample-to-result differential diagnosis of infections that present with high rapid-onset fever. Here we describe a platform that detects disease-specific antigens and IgM antibodies. The disposable microfluidic cards are based on a flow-through membrane immunoassay carried out on porous nitrocellulose, which provides rapid diffusion for short assay times and a high surface area for visual detection of colored assay spots. Fluid motion and on-card valves were driven by a pneumatic system and we present designs for using pneumatic control to carry out assay functions. Pneumatic actuation, while having the potential advantage of inexpensive and robust hardware, introduced bubbles that interfered with fluidic control and affected assay results. The cards performed all sample preparation steps including plasma filtration from whole blood, sample and reagent aliquoting for the two parallel assays, sample dilution, and IgG removal for the IgM assays. We demonstrated the system for detection of the malarial pfHRPII antigen (spiked) and IgM antibodies to Salmonella Typhi LPS (patient plasma samples). All reagents were stored on card in dry form; only the sample and buffer were required to run the tests. Here we detail the development of this platform and discuss its strengths and weaknesses.

A portable surface plasmon resonance sensor system for real-time monitoring of small to large analytes

Many environmental applications exist for biosensors capable of providing real-time analyses. One pressing current need is monitoring for agents of chemical- and bio-terrorism. These applications require systems that can rapidly detect small organics including nerve agents, toxic proteins, viruses, spores and whole microbes. A second area of application is monitoring for environmental pollutants. Processing of grab samples through chemical laboratories requires significant time delays in the analyses, preventing the rapid mapping and cleanup of chemical spills. The current state of development of miniaturized, integrated surface plasmon resonance (SPR) sensor elements has allowed for the development of inexpensive, portable biosensor systems capable of the simultaneous analysis of multiple analytes. Most of the detection protocols make use of antibodies immobilized on the sensor surface. The Spreeta 2000 SPR biosensor elements manufactured by Texas Instruments provide three channels for each sensor element in the system. A temperature-controlled two-element system that monitors for six analytes is currently in use, and development of an eight element sensor system capable of monitoring up to 24 different analytes will be completed in the near future. Protein toxins can be directly detected and quantified in the low picomolar range. Elimination of false positives and increased sensitivity is provided by secondary antibodies with specificity for different target epitopes, and by sensor element redundancy. Inclusion of more than a single amplification step can push the sensitivity of toxic protein detection to femtomolar levels. The same types of direct detection and amplification protocols are used to monitor for viruses and whole bacteria or spores. Special protocols are required for the detection of small molecules. Either a competition type assay where the presence of analyte inhibits the binding of antibodies to surface-immobilized analyte, or a displacement assay, where antibodies bound to analyte on the sensor surface are displaced by free analyte, can be used. The small molecule detection assays vary in sensitivity from the low micromolar range to the high picomolar.

An Experimental and Theoretical Study of the Turbulent and Laminar Convection Generated under a Horizontal Ice Sheet Floating on Warm Salty Water

Abstract In an experimental and theoretical study we model a phenomenon which occurs in the summer polar oceans; namely, the melting of flat sheets of either glacial ice or desalinated sea ice which float over sea water held at a temperature above freezing. Our laboratory results show when the solution salinity is such that the temperature of maximum density is below the freezing temperature, or for sea water salinities greater than 25‰, the heat transfer to the ice takes place in three regions. First, just beneath the ice, there is a boundary layer across which the salinity increases almost to its far-field value and the temperature increases linearly. Below this, there is an unstable convective boundary layer, which appears to be part double-diffusive, part pure thermal convection. Finally, there is a region of deep thermal convection. From comparison of a one-dimensional theoretical model of the heat transfer with the laboratory study, we find that the ice melts about twice as fast for this convective ...

Programming paper networks for point of care diagnostics

Lateral flow tests (LFTs) are well-suited for rapid point-of-care testing in low resource settings. The wicking action of the paper strip moves the sample and reagents through the device without a need for pumps, but LFTs are typically limited to tests that can be carried out in a single fluidic step. The materials from LFTs can be reconfigured to create paper networks that automatically carry out multi-step fluidic operations, while retaining the same easy-to-use format as a conventional LFT. Here, we describe basic principles of wicking and system-level behavior of paper networks by analogy to electrical circuits. We describe key design principles for a previously-developed 2D paper network (2DPN) and introduce an alternative linear paper network (Pseudo-1DPN) that takes advantage of system-level behavior to perform clean sequential fluid delivery while reducing device running time.

Disposable Autonomous Device for Swab-to-Result Diagnosis of Influenza

A prototype of a self-contained, automated, disposable device for chemically amplified protein-based detection of influenza virus from nasal swab specimens was developed and evaluated in a clinical setting. The device required only simple specimen manipulation without any dedicated instrumentation or specialized training by the operator for interpretation. The device was based on a sandwich immunoassay for influenza virus nucleoprotein; it used an enzyme-labeled antibody and a chromogenic substrate to provide an amplified visible signal, in a two-dimensional paper network format. All reagents were stored within the device. Device performance was assessed at Seattle Childrens Hospital; clinical staff collected nasal swab samples from 25 patients and then operated test devices on site to detect influenza A and B in those specimens. The total test time from device initiation to result was approximately 35 min. Device performance for influenza A detection was ∼70% accurate using in-house qRT-PCR influenza A as a gold-standard comparison. The ratio of valid to total completed device runs yielded a success rate of 92%, and the negative predictive value for both the influenza A and B assay was 81%. The ability to diagnose respiratory infections rapidly and close to the patient was well received by hospital staff, inspiring further optimization of device function.