Project description:Paper-based microfluidic devices are an attractive platform for developing low-cost, point-of-care diagnostic tools. As paper-based devices' detection chemistries become more complex, more complicated devices are required, often entailing the sequential delivery of different liquids or reagents to reaction zones. Most research into flow control has been focused on introducing delays. However, delaying the flow can be problematic due to increased evaporation leading to sample loss. We report the use of a CO2 laser to uniformly etch the surface of the paper to modify wicking speeds in paper-based microfluidic devices. This technique can produce both wicking speed increases of up to 1.1× faster and decreases of up to 0.9× slower. Wicking speeds can be further enhanced by etching both sides of the paper, resulting in wicking 1.3× faster than unetched channels. Channels with lengthwise laser-etched grooves were also compared to uniformly etched channels, with the most heavily grooved channels wicking 1.9× faster than the fastest double-sided etched channels. Furthermore, sealing both sides of the channel in packing tape results in the most heavily etched channels, single-sided, double-sided, and grooved, wicking over 13× faster than unetched channels. By selectively etching individual channels, different combinations of sequential fluid delivery can be obtained without altering any channel geometry. Laser etching is a simple process that can be integrated into the patterning of the device and requires no additional materials or chemicals, enabling greater flow control for paper-based microfluidic devices.
Project description:We describe the design and characteristics of a paper-based analytical device for analyte concentration enrichment. The device, called a hybrid paper-based analytical device (hyPAD), uses faradaic electrochemistry to create an ion depletion zone (IDZ), and hence a local electric field, within a nitrocellulose flow channel. Charged analytes are concentrated near the IDZ when their electrophoretic and electroosmotic velocities balance. This process is called faradaic ion concentration polarization. The hyPAD is simple to construct and uses only low-cost materials. The hyPAD can be tuned for optimal performance by adjusting the applied voltage or changing the electrode design. Moreover, the throughput of hyPAD is 2 orders of magnitude higher than that of conventional, micron-scale microfluidic devices. The hyPAD is able to concentrate a range of analytes, including small molecules, DNA, proteins, and nanoparticles, in the range of 200-500-fold within 5 min.
Project description:Most laboratory assays take advantage of multi-step protocols to achieve high performance, but conventional paper-based tests (e.g., lateral flow tests) are generally limited to assays that can be carried out in a single fluidic step. We have developed two-dimensional paper networks (2DPNs) that use materials from lateral flow tests but reconfigure them to enable programming of multi-step reagent delivery sequences. The 2DPN uses multiple converging fluid inlets to control the arrival time of each fluid to a detection zone or reaction zone, and it requires a method to disconnect each fluid source in a corresponding timed sequence. Here, we present a method that allows programmed disconnection of fluid sources required for multi-step delivery. A 2DPN with legs of different lengths is inserted into a shared buffer well, and the dropping fluid surface disconnects each leg at in a programmable sequence. This approach could enable multi-step laboratory assays to be converted into simple point-of-care devices that have high performance yet remain easy to use.
Project description:Current procedures for the assessment of chronic wound infection are time-consuming and require complex instruments and trained personnel. The incidence of chronic wounds worldwide, and the associated economic burden, urge for simple and cheap point-of-care testing (PoCT) devices for fast on-site diagnosis to enable appropriate early treatment. The enzyme myeloperoxidase (MPO), whose activity in infected wounds is about ten times higher than in non-infected wounds, appears to be a suitable biomarker for wound infection diagnosis. Herein, we develop a single-component foldable paper-based device for the detection of MPO in wound fluids. The analyte detection is achieved in two steps: (i) selective immunocapture of MPO, and (ii) reaction of a specific dye with the captured MPO, yielding a purple color with increasing intensity as a function of the MPO activity in infected wounds in the range of 20-85 U/mL. Ex vivo experiments with wound fluids validated the analytic efficiency of the paper-based device, and the results strongly correlate with a spectrophotometric assay.
Project description:Failure to utilize valving and automation techniques has restricted the complexity of fluidic operations that can be performed in paper microfluidic devices. We developed a toolkit of paper microfluidic valves and methods for automatic valve actuation using movable paper strips and fluid-triggered expanding elements. To the best of our knowledge, this is the first functional demonstration of this valving strategy in paper microfluidics. After introduction of fluids on devices, valves can actuate automatically after a) a certain period of time, or b) the passage of a certain volume of fluid. Timing of valve actuation can be tuned with greater than 8.5% accuracy by changing lengths of timing wicks, and we present timed on-valves, off-valves, and diversion (channel-switching) valves. The actuators require ~30 ?l fluid to actuate and the time required to switch from one state to another ranges from ~5 s for short to ~50 s for longer wicks. For volume-metered actuation, the size of a metering pad can be adjusted to tune actuation volume, and we present two methods - both methods can achieve greater than 9% accuracy. Finally, we demonstrate the use of these valves in a device that conducts a multi-step assay for the detection of the malaria protein PfHRP2. Although slightly more complex than devices that do not have moving parts, this valving and automation toolkit considerably expands the capabilities of paper microfluidic devices. Components of this toolkit can be used to conduct arbitrarily complex, multi-step fluidic operations on paper-based devices, as demonstrated in the malaria assay device.
Project description:Microfluidic discs have been employed in a variety of applications for chemical analyses and biological diagnostics. These platforms offer a sophisticated fluidic toolbox, necessary to perform processes that involve sample preparation, purification, analysis, and detection. However, one of the weaknesses of such systems is the uni-directional movement of fluid from the disc center to its periphery due to the uni-directionality of the propelling centrifugal force. Here we demonstrate a mechanism for fluid movement from the periphery of a hydrophobic disc toward its center that does not rely on the energy supplied by any peripheral equipment. This method utilizes a ventless fluidic network that connects a column of working fluid to a sample fluid. As the working fluid is pushed by the centrifugal force to move toward the periphery of the disc, the sample fluid is pulled up toward the center of the disc analogous to a physical pulley where two weights are connected by a rope passed through a block. The ventless network is analogous to the rope in the pulley. As the working fluid descends, it creates a negative pressure that pulls the sample fluid up. The sample and working fluids do not come into direct contact and it allows the freedom to select a working fluid with physical properties markedly different from those of the sample. This article provides a demonstration of the "micro-pulley" on a disc, discusses underlying physical phenomena, provides design guidelines for fabrication of micro-pulleys on discs, and outlines a vision for future micro-pulley applications.
Project description: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.
Project description:In recent years, the use of prescribed and non-prescribed drugs has increased. Therefore, advances in new technologies and sensors for detecting molecules in natural environments are required. In this work, a 3D-printed polylactic acid stencil is used to fabricate paper-based analytical devices (ePADs). Herein, we report the use of carbon-based lab-manufactured conductive ink for the fabrication of sensors towards the detection of chloroquine and escitalopram. For each batch, eight ePADs were successfully fabricated. Firstly, the fabricated sensors were evaluated morphologically by scanning electron microscopy and electrochemically by cyclic voltammetry and electrochemical impedance spectroscopy experiments. The sensors displayed a well-defined voltammetric profile in the presence of the redox couple, when compared to a commercial carbon screen-printed electrode. Differential pulse voltammetry conducted the detection of chloroquine and escitalopram with detection limits of 4.0 and 0.5 µmol L-1, respectively. The ePADs fabricated using the 3D stencil are here presented as alternatives for the fabrication of electrochemical analytical devices.Supplementary informationThe online version contains supplementary material available at 10.1007/s10008-021-05075-w.
Project description:With increasing use of publicly available gene expression data sets, the quality of the expression data is a critical issue for downstream analysis, gene signature development, and cross-validation of data sets. Thus, identifying reliable expression measurements by leveraging multiple mRNA expression platforms is an important analytical task. In this study, we propose a statistical framework for selecting reliable measurements between platforms by modeling the correlations of mRNA expression levels using a beta-mixture model. The model-based selection provides an effective and objective way to separate good probes from probes with low quality, thereby improving the efficiency and accuracy of the analysis. The proposed method can be used to compare two microarray technologies or microarray and RNA sequencing measurements. We tested the approach in two matched profiling data sets, using microarray gene expression measurements from the same samples profiled on both Affymetrix and Illumina platforms. We also applied the algorithm to mRNA expression data to compare Affymetrix microarray data with RNA sequencing measurements. The algorithm successfully identified probes/genes with reliable measurements. Removing the unreliable measurements resulted in significant improvements for gene signature development and functional annotations.
Project description:We have developed a self-blotting TEM grid for use with a novel instrument for vitrifying samples for cryo-electron microscopy (cryoEM). Nanowires are grown on the copper surface of the grid using a simple chemical reaction and the opposite smooth side is used to adhere to a holey sample substrate support, for example carbon or gold. When small volumes of sample are applied to the nanowire grids the wires effectively act as blotting paper to rapidly wick away the liquid, leaving behind a thin film. In this technical note, we present a detailed description of how we make these grids using a variety of substrates fenestrated with either lacey or regularly spaced holes. We explain how we characterize the quality of the grids and we describe their behavior under a variety of conditions.