Smartphone-Enabled Colorimetric Trinitrotoluene Detection Using Amine-Trapped Polydimethylsiloxane Membranes

A smartphone-enabled platform for easy and portably colorimetric analysis of 2,4,6-trinitro­toluene (TNT) using amine-trapped PDMS is designed and implemented. The amine-trapped polydimethyl­siloxane (PDMS) is simply prepared by immersing the cured PDMS in aminosilane solutions forming an amine-containing polymer. After contacting with TNT-containing solutions, the colorless PDMS showed a rapid colorimetric change which can be easily identified by the naked eye. The amine-trapped PDMS was carefully optimized to achieve visible detection of TNT at concentrations as low as 1 μM. Using an integrated camera in the smartphone, pictures of colored PDMS membranes can be analyzed by a home-developed mobile application. Thus, the TNT amount can be precisely quantified. Direct TNT detection in real samples (e.g., drinking, tap, and lake waters) is demonstrated as well. The smartphone-enabled colorimetric method using amine-trapped PDMS membranes realizes a convenient and efficient approach toward a portable system for field TNT detections

Cellphone-Enabled Microwell-Based Microbead Aggregation Assay for Portable Biomarker Detection

Quantitative biomarker detection methods featured with rapidity, high accuracy, and label-free are demonstrated for the development of point-of-care (POC) technologies or “beside” diagnostics. Microbead aggregation via protein-specific linkage provides an effective approach for selective capture of biomarkers from the samples, and can directly readout the presence and amount of the targets. However, sensors or microfluidic analyzers that can accurately quantify the microbead aggregation are scared. In this work, we demonstrate a microwell-based microbeads analyzing system, by which online manipulations of microbeads including trapping, arraying, and rotations can be realized, providing a series of microfluidic approaches to layout the aggregated microbeads for further convenient characterizations. Prostate specific antigen is detected using the proposed system, demonstrating the limit of detection as low as 0.125 ng/mL (3.67 pM). A two-step reaction kinetics model is proposed for the first time to explain the dynamic process of microbeads aggregation. The developed microbeads aggregation analysis system has the advantages of label-free detection, high throughput, and low cost, showing great potential for portable biomarker detection

Nanoelectronic Platform for Ultrasensitive Detection of Protein Biomarkers in Serum using DNA Amplification

Silicon nanowire field effect transistors (NWFETs) are low noise, low power, ultrasensitive biosensors that are highly amenable to integration. However, using NWFETs to achieve direct protein detection in physiological buffers such as blood serum remains difficult due to Debye screening, nonspecific binding, and stringent functionalization requirements. In this work, we performed an indirect sandwich immunoassay in serum combined with exponential DNA amplification and pH measurement by ultrasensitive NWFET sensors. Measurements of model cytokine interleukin-2 concentrations from <20 fM to >200 pM were demonstrated, surpassing the conventional NWFET urease-based readout. Our approach paves way for future development of universal, highly sensitive, miniaturized, and integrated nanoelectronic devices that can be applied to a wide variety of analytes

Gradient evolution inside the microfluidic gradient generator.

<p>(<b>A</b>) A macroscopic image of the gradient generator. (<b>B–C</b>) Gradient evolution inside the microfluidic gradient generator at different pumping rates powered by mechanical pump: (<b>B</b>) Visualization of the gradient at level 2 (Lv2), 5 (Lv5), 8 (Lv8), and 10 (Lv10)), as denoted by the dashed boxes. Fluorescence images were captured within each zone 2 hours after starting the pump. Fluorescence intensity was measured in the middle of the cell migration region denoted by the red dashed lines. Yellow dashed lines denote the upper and lower boundaries of the microchannel. (<b>C</b>) Normalized fluorescence intensity of the fluorescein gradients along the cell migration channel (red dashed line in b) at different pumping rates. (<b>D</b>) Fluorescein gradient evolution across the cell migration region (Lv10) inside the microfluidic gradient generator powered by ALZET® osmotic pumps (5 µL/hr) throughout a 9-day period. Normalized by taking the fluorescent intensity at 0 µm as 1. (<b>E</b>) Shear stress within the cell migration region modeled using COMSOL. Inset at bottom: a model cell (height 1.5 µm), experiences shear stresses in the range of 0.03–0.14 dynes/cm².</p

Microfluidic platform for short-term chemotaxis assay.

<p>(<b>A</b>) Time-lapse images of MSCs migration under a PDGF-BB gradient for 24 hours. Images were taken every 15 minutes and individual color-coded cell tracks were assembled after 0, 8, 16, and 24 hours. A movie clip of the 24-hour cell migration data is available (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044995#pone.0044995.s008" target="_blank">Mov. S1</a>). (<b>B, C</b>) Migration traces of cells initially seeded in the lower PDGF-BB concentration region (cell no. 1-13) and in the higher PDGF-BB concentration region (cell no. 14-26), respectively. These cell traces (<b>B</b>) indicate that cells in the bottom half of the channel (0–50 ng/mL of PDGF-BB) exhibited directed migration, whereas (<b>C</b>) cells in the top half of the channel (50–100 ng/mL of PDGF-BB) exhibited random motion. Axes are in the units of 200 microns. (<b>D</b>) Chemotactic index, CI of MSCs in 0–50 ng/ml and 50–100 ng/ml PDGF-BB regions. Statistical significance was determined by Student's <i>t</i>-test comparing cells in the bottom and top parts of the channel (*p<0.05).</p

Microfluidic platform for long-term chemotaxis assay.

<p>(<b>A</b>) Long-term migration of MSCs (labeled with CFSE/Calcein AM) within a PDGF-BB gradient (0–100 ng/ml). The total number of cells present within the cell migration region was 105 at 0 hour and 107 at 72 hours. Limited by the visualization area of microscope, fluorescent images of adjacent areas were taken individually and spliced together. (<b>B</b>) Cell distribution within the cell migration region in the presence (0–100 ng/mL PDGF-BB) or absence (0-0 ng/mL or 100-100 ng/mL PDGF-BB) of a chemotactic gradient. Data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044995#pone-0044995-g004" target="_blank">Figure 4A</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044995#pone.0044995.s003" target="_blank">S3</a>, and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044995#pone.0044995.s005" target="_blank">S5</a> were represented as ratios of number of cells present in the upper half of the channel to that in the lower half of the channel. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044995#s2" target="_blank">Results</a> are means ± STD for n = 3. Statistical significance was determined by Student's <i>t</i>-test comparing results in the presence of a gradient from 0 and 72 hours (*p<0.05).</p