Fully Inkjet-Printed Paper-Based Potentiometric Ion-Sensing Devices

A fully inkjet-printed disposable and low cost paper-based device for potentiometric Na⁺- or K⁺-ion sensing has been developed. A printed ionophore-based all-solid-state ion selective electrode on a graphene/poly­(3,4-ethylenedioxythiophene) polystyrenesulfonate (G/PEDOT:PSS) nanocomposite solid contact and a printed all-solid state reference electrode consisting of a pseudosilver/silver chloride electrode coated by a lipophilic salt-incorporating poly­(vinyl chloride) membrane overprinted with potassium chloride have been combined on a microfluidically patterned paper substrate. Devices are built on standard filter paper using off-the-shelf materials. Ion sensing has been achieved within 180 s by simple addition of 20 μL of sample solution without electrode preconditioning. The limits of detection were 32 and 101 μM for Na⁺ and K⁺, respectively. The individual single-use sensing devices showed near Nernstian response of 62.5 ± 2.1 mV/decade (Na⁺) and 62.9 ± 1.1 mV/decade (K⁺) with excellent standard potential (<i>E</i>⁰) reproducibilities of 455.7 ± 5.1 mV (Na⁺) and 433.9 ± 2.8 mV (K⁺). The current work demonstrates the promising possibility of obtaining low-cost and disposable paper-based potentiometric sensing devices potentially manufacturable at large scales with industrial inkjet printing technology

Screen-Printed Electroluminescent Lamp Modified with Graphene Oxide as a Sensing Device

A screen-printed electroluminescent display with different sensing capabilities is presented. The sensing principle is based on the direct relationship between the light intensity of the lamp and the conductivity of the external layers. The proposed device is able to detect the ionic concentration of any conductive species. Using both top and bottom emission architectures, for the first time, a humidity sensor based on electroluminescent display functionalized by a graphene oxide nanocomposite is introduced. In this regard, just by coupling the display to a smartphone camera sensor, its potential was expanded for automatically monitoring human respiration in real time. Besides, the research includes a responsive display in which the light is spatially turned on in response to pencil drawing or any other conductive media. The above mentioned features together with the easiness of manufacturing and cost-effectiveness of this electroluminescent display can open up great opportunities to exploit it in sensing applications and point-of-care diagnosis

Screen-Printed Electroluminescent Lamp Modified with Graphene Oxide as a Sensing Device

A screen-printed electroluminescent display with different sensing capabilities is presented. The sensing principle is based on the direct relationship between the light intensity of the lamp and the conductivity of the external layers. The proposed device is able to detect the ionic concentration of any conductive species. Using both top and bottom emission architectures, for the first time, a humidity sensor based on electroluminescent display functionalized by a graphene oxide nanocomposite is introduced. In this regard, just by coupling the display to a smartphone camera sensor, its potential was expanded for automatically monitoring human respiration in real time. Besides, the research includes a responsive display in which the light is spatially turned on in response to pencil drawing or any other conductive media. The above mentioned features together with the easiness of manufacturing and cost-effectiveness of this electroluminescent display can open up great opportunities to exploit it in sensing applications and point-of-care diagnosis

Boron Doped Diamond Paste Electrodes for Microfluidic Paper-Based Analytical Devices

Boron doped diamond (BDD) electrodes have exemplary electrochemical properties; however, widespread use of high-quality BDD has previously been limited by material cost and availability. In the present article, we report the use of a BDD paste electrode (BDDPE) coupled with microfluidic paper-based analytical devices (μPADs) to create a low-cost, high-performance electrochemical sensor. The BDDPEs are easy to prepare from a mixture of BDD powder and mineral oil and can be easily stencil-printed into a variety of electrode geometries. We demonstrate the utility and applicability of BDDPEs through measurements of biological species (norepinephrine and serotonin) and heavy metals (Pb and Cd) using μPADs. Compared to traditional carbon paste electrodes (CPE), BDDPEs exhibit a wider potential window, lower capacitive current, and are able to circumvent the fouling of serotonin. These results demonstrate the capability of BDDPEs as point-of-care sensors when coupled with μPADs

Multilayer Paper-Based Device for Colorimetric and Electrochemical Quantification of Metals

The release of metals and metal-containing compounds into the environment is a growing concern in developed and developing countries, as human exposure to metals is associated with adverse health effects in virtually every organ system. Unfortunately, quantifying metals in the environment is expensive; analysis costs using certified laboratories typically exceed $100/sample, making the routine analysis of toxic metals cost-prohibitive for applications such as occupational exposure or environmental protection. Here, we report on a simple, inexpensive technology with the potential to render toxic metals detection accessible for both the developing and developed world that combines colorimetric and electrochemical microfluidic paper-based analytical devices (mPAD) in a three-dimensional configuration. Unlike previous mPADs designed for measuring metals, the device reported here separates colorimetric detection on one layer from electrochemical detection on a different layer. Separate detection layers allows different chemistries to be applied to a single sample on the same device. To demonstrate the effectiveness of this approach, colorimetric detection is shown for Ni, Fe, Cu, and Cr and electrochemical detection for Pb and Cd. Detection limits as low as 0.12 μg (Cr) were achieved on the colorimetric layer while detection limits as low as 0.25 ng (Cd and Pb) were achieved on the electrochemical layer. Selectivity for the target analytes was demonstrated for common interferences. As an example of the device utility, particulate metals collected on air sampling filters were analyzed. Levels measured with the mPAD matched known values for the certified reference samples of collected particulate matter

Sequential Flow Controllable Microfluidic Device for G‑Quadruplex DNAzyme-Based Electrochemical Detection of SARS-CoV‑2 Using a Pyrrolidinyl Peptide Nucleic Acid

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a significant health issue globally. Point-of-care (POC) testing that can offer a rapid and accurate diagnosis of SARS-CoV-2 at the early stage of infection is highly desirable to constrain this outbreak, especially in resource-limited settings. Herein, we present a G-quadruplex DNAzyme-based electrochemical assay that is integrated with a sequential flow controllable microfluidic device for the detection of SARS-CoV-2 cDNA. According to the detection principle, a pyrrolidinyl peptide nucleic acid probe is immobilized on a screen-printed graphene electrode for capturing SARS-CoV-2 DNA. The captured DNA subsequently hybridizes with another DNA probe that carries a G-quadruplex DNAzyme as the signaling unit. The G-quadruplex DNAzyme catalyzes the H2O2-mediated oxidation of hydroquinone to benzoquinone that can be detected using square-wave voltammetry to give a signal that corresponds to the target DNA concentration. The assay exhibited high selectivity for SARS-CoV-2 DNA and showed a good experimental detection limit at 30 pM. To enable automation, the DNAzyme-based assay was combined with a capillary-driven microfluidic device featuring a burst valve technology to allow sequential sample and reagent delivery as well as the DNA target hybridization and enzymatic reaction to be operated in a precisely controlled fashion. The developed microfluidic device was successfully applied for the detection of SARS-CoV-2 from nasopharyngeal swab samples. The results were in good agreement with the standard RT-PCR method and could be performed within 20 min. Thus, this platform offers desirable characteristics that make it an alternative POC tool for COVID-19 diagnosis

Sequential Flow Controllable Microfluidic Device for G‑Quadruplex DNAzyme-Based Electrochemical Detection of SARS-CoV‑2 Using a Pyrrolidinyl Peptide Nucleic Acid

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a significant health issue globally. Point-of-care (POC) testing that can offer a rapid and accurate diagnosis of SARS-CoV-2 at the early stage of infection is highly desirable to constrain this outbreak, especially in resource-limited settings. Herein, we present a G-quadruplex DNAzyme-based electrochemical assay that is integrated with a sequential flow controllable microfluidic device for the detection of SARS-CoV-2 cDNA. According to the detection principle, a pyrrolidinyl peptide nucleic acid probe is immobilized on a screen-printed graphene electrode for capturing SARS-CoV-2 DNA. The captured DNA subsequently hybridizes with another DNA probe that carries a G-quadruplex DNAzyme as the signaling unit. The G-quadruplex DNAzyme catalyzes the H2O2-mediated oxidation of hydroquinone to benzoquinone that can be detected using square-wave voltammetry to give a signal that corresponds to the target DNA concentration. The assay exhibited high selectivity for SARS-CoV-2 DNA and showed a good experimental detection limit at 30 pM. To enable automation, the DNAzyme-based assay was combined with a capillary-driven microfluidic device featuring a burst valve technology to allow sequential sample and reagent delivery as well as the DNA target hybridization and enzymatic reaction to be operated in a precisely controlled fashion. The developed microfluidic device was successfully applied for the detection of SARS-CoV-2 from nasopharyngeal swab samples. The results were in good agreement with the standard RT-PCR method and could be performed within 20 min. Thus, this platform offers desirable characteristics that make it an alternative POC tool for COVID-19 diagnosis

Microfluidic Paper-Based Analytical Device for Aerosol Oxidative Activity

Human exposure to particulate matter (PM) air pollution has been linked with respiratory, cardiovascular, and neurodegenerative diseases, in addition to various cancers. Consistent among all of these associations is the hypothesis that PM induces inflammation and oxidative stress in the affected tissue. Consequently, a variety of assays have been developed to quantify the oxidative activity of PM as a means to characterize its ability to induced oxidative stress. The vast majority of these assays rely on high-volume, fixed-location sampling methods due to limitations in assay sensitivity and detection limit. As a result, our understanding of how personal exposure contributes to the intake of oxidative air pollution is limited. To further this understanding, we present a microfluidic paper-based analytical device (μPAD) for measuring PM oxidative activity on filters collected by personal sampling. The μPAD is inexpensive to fabricate and provides fast and sensitive analysis of aerosol oxidative activity. The oxidative activity measurement is based on the dithiothreitol assay (DTT assay), uses colorimetric detection, and can be completed in the field within 30 min following sample collection. The μPAD assay was validated against the traditional DTT assay using 13 extracted aerosol samples including urban aerosols, biomass burning PM, cigarette smoke, and incense smoke. The results showed no significant differences in DTT consumption rate measured by the two methods. To demonstrate the utility of the approach, personal samples were collected to estimate human exposures to PM from indoor air, outdoor air on a clean day, and outdoor air on a wildfire-impacted day in Fort Collins, CO. Filter samples collected on the wildfire day gave the highest oxidative activity on a mass normalized basis, whereas typical ambient background air showed the lowest oxidative activity