Special Issue "Paper Microfluidics: Fundamental Studies and Applications"

A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (28 February 2017).

Special Issue Editors

Prof. Dr. Frank A. Gomez
E-Mail Website
Guest Editor
Department of Chemistry and Biochemistry, California State University, Los Angeles, 5151 State University Drive, Los Angeles, CA 90032-8202, USA
Interests: microfluidics; paper-based devices; lab-on-a-chip; biosensors; microfludic fuel cells and batteries; chemometrics
Prof. Carlos D. Garcia
E-Mail Website
Guest Editor
Department of Chemistry, Clemson University, Clemson, SC 29634, USA
Interests: paper microfluidics; electrochemistry; surface science

Special Issue Information

Dear Colleagues,

Paper microfluidics is increasingly being used in a variety of scientific disciplines to examine a paucity of chemical and biological interactions. Microfluidic paper-based analytical devices (mPADs) have emerged as viable multiplexable platform with the potential to transcend existing techniques in resource-limited settings. Recently, great strides have been made by incorporating paper microfluidics technologies into microelectromechanical systems (MEMS) or “lab-on-a chip” (LOC) technologies in the pharmaceutical, defense, biotechnology, bioterrorism, and point-of-care (POC) diagnostic device industries. mPADs can be easily fabricated by patterning hydrophobic materials in hydrophilic paper. Paper has a number of advantages as a microfluidics platform due to its low cost and ability to wick aqueous fluids without the use of active pumping. Paper is also thin, lightweight, easy to stack, store, and transport, compatible with biological samples, and available in many forms with a wide range of properties. This Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel methodological developments in paper microfluidics and their applications in a myriad of disciplines.

Prof. Frank A. Gomez
Prof. Carlos D. Garcia
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Paper microfluidics,
  • microfluidic techniques,
  • point-of-care (POC) diagnostic devices,
  • lab-on-a-chip, assays

Published Papers (7 papers)

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Research

Open AccessArticle
Characterization of Reagent Pencils for Deposition of Reagents onto Paper-Based Microfluidic Devices
Micromachines 2017, 8(8), 242; https://doi.org/10.3390/mi8080242 - 05 Aug 2017
Cited by 2
Abstract
Reagent pencils allow for solvent-free deposition of reagents onto paper-based microfluidic devices. The pencils are portable, easy to use, extend the shelf-life of reagents, and offer a platform for customizing diagnostic devices at the point of care. In this work, reagent pencils were [...] Read more.
Reagent pencils allow for solvent-free deposition of reagents onto paper-based microfluidic devices. The pencils are portable, easy to use, extend the shelf-life of reagents, and offer a platform for customizing diagnostic devices at the point of care. In this work, reagent pencils were characterized by measuring the wear resistance of pencil cores made from polyethylene glycols (PEGs) with different molecular weights and incorporating various concentrations of three different reagents using a standard pin abrasion test, as well as by measuring the efficiency of reagent delivery from the pencils to the test zones of paper-based microfluidic devices using absorption spectroscopy and digital image colorimetry. The molecular weight of the PEG, concentration of the reagent, and the molecular weight of the reagent were all found to have an inverse correlation with the wear of the pencil cores, but the amount of reagent delivered to the test zone of a device correlated most strongly with the concentration of the reagent in the pencil core. Up to 49% of the total reagent deposited on a device with a pencil was released into the test zone, compared to 58% for reagents deposited from a solution. The results suggest that reagent pencils can be prepared for a variety of reagents using PEGs with molecular weights in the range of 2000 to 6000 g/mol. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle
An Inexpensive Paper-Based Aluminum-Air Battery
Micromachines 2017, 8(7), 222; https://doi.org/10.3390/mi8070222 - 17 Jul 2017
Cited by 9
Abstract
Paper-based batteries are an alternative to traditional batteries due to their low cost, portability, and simplicity to operate. In the present work, we demonstrate an improved and inexpensive paper-based aluminum-air battery employing KOH as the electrolyte with sufficient energy to power small devices. [...] Read more.
Paper-based batteries are an alternative to traditional batteries due to their low cost, portability, and simplicity to operate. In the present work, we demonstrate an improved and inexpensive paper-based aluminum-air battery employing KOH as the electrolyte with sufficient energy to power small devices. The dimensions of the device, electrode size, and electrolyte concentration were optimized with respect to amperage and reproducibility. The maximum amperage of 17.4 mA and maximum power of 3.0 mW was achieved with a 9 cm2 battery with anode and cathode electrode areas of 5.1 cm2 and 3.75 cm2 respectively, using 1.5 M potassium hydroxide (KOH). In a series configuration, the batteries generate sufficient energy to power light-emitting diodes (LEDs), a flashlight, a glucometer, and a pregnancy test. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle
Monitoring Acid–Base Titrations on Wax Printed Paper Microzones Using a Smartphone
Micromachines 2017, 8(5), 139; https://doi.org/10.3390/mi8050139 - 02 May 2017
Cited by 7
Abstract
This study describes the use of a smartphone for monitoring acid–base titrations on wax printed paper microzones. An array of twelve microzones of 5 mm diameter each was wax printed on filter paper. The analytical performance of the proposed devices was explored with [...] Read more.
This study describes the use of a smartphone for monitoring acid–base titrations on wax printed paper microzones. An array of twelve microzones of 5 mm diameter each was wax printed on filter paper. The analytical performance of the proposed devices was explored with acid–base titrations examples, where jaboticaba peel extract was used as a natural pH indicator. The color intensity was captured using a smartphone and analyzed through a free App named Photometrix®. Before titrations, color intensity versus pH was calibrated to be used as a reference in titrations as (i) strong acid versus strong base; (ii) strong base versus strong acid; and (iii) weak acid versus strong base. In all examples, images were obtained after the addition of each aliquot of titrant solutions. The obtained titration curves showed the same behavior as the conventional titration curves. After evaluating the feasibility of the proposed methodology, the concentration level of acetic acid was obtained in three vinegar samples. Although the obtained values ranged from 5% to 8% compared to the concentrations on the conventional method, the proposed methodology presented high analytical reliability. The calculated concentrations of acetic acid in three samples ranged from 3.87% to 3.93%, and the proposed methodology did not significantly differ from classic acid–base titration at a confidence level of 95%. The acid–base titration on paper-based devices is outstanding, since any titration can be completed within 5 min using 20 µL volumes. Besides, the use of a smartphone to capture images followed by analysis in a free app offers simplicity to all users. The proposed methodology arises as a new strand to be exploited in the diffusion of the analytical chemistry education field as well as an alternative for quantitative analysis with extremely simplified instrumentation. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle
Paper-Based Analytical Device for Zinc Ion Quantification in Water Samples with Power-Free Analyte Concentration
Micromachines 2017, 8(4), 127; https://doi.org/10.3390/mi8040127 - 18 Apr 2017
Cited by 14
Abstract
Insufficient sensitivity is a general issue of colorimetric paper-based analytical devices (PADs) for trace analyte detection, such as metal ions, in environmental water. This paper demonstrates the colorimetric detection of zinc ions (Zn2+) on a paper-based analytical device with an integrated [...] Read more.
Insufficient sensitivity is a general issue of colorimetric paper-based analytical devices (PADs) for trace analyte detection, such as metal ions, in environmental water. This paper demonstrates the colorimetric detection of zinc ions (Zn2+) on a paper-based analytical device with an integrated analyte concentration system. Concentration of Zn2+ ions from an enlarged sample volume (1 mL) has been achieved with the aid of a colorimetric Zn2+ indicator (Zincon) electrostatically immobilized onto a filter paper substrate in combination with highly water-absorbent materials. Analyte concentration as well as sample pretreatment, including pH adjustment and interferent masking, has been elaborated. The resulting device enables colorimetric quantification of Zn2+ in environmental water samples (tap water, river water) from a single sample application. The achieved detection limit of 0.53 μM is a significant improvement over that of a commercial colorimetric Zn2+ test paper (9.7 μM), demonstrating the efficiency of the developed analyte concentration system not requiring any equipment. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle
Paper-Based Colorimetric Biosensor for Tear Glucose Measurements
Micromachines 2017, 8(4), 104; https://doi.org/10.3390/mi8040104 - 29 Mar 2017
Cited by 25
Abstract
This paper describes a paper-based colorimetric biosensor for measuring glucose concentration levels in human tear samples. Colorimetric biosensors were wax printed on paper platforms and modified with chitosan previously prepared in acetic acid. The proposed device was explored to measure the glucose levels [...] Read more.
This paper describes a paper-based colorimetric biosensor for measuring glucose concentration levels in human tear samples. Colorimetric biosensors were wax printed on paper platforms and modified with chitosan previously prepared in acetic acid. The proposed device was explored to measure the glucose levels in human tear samples using 3,3′,5,5′-tetramethylbenzydine (TMB) as the chromogenic reagent. The paper-based colorimetric biosensor exhibited a linear behavior for the glucose concentration range between 0.1 and 1.0 mM. The achieved analytical sensitivity and limit of detection (LOD) were 84 AU/mM and 50 µM, respectively. Moreover, the device provided analytical reliability and no statistical difference when compared to the data recorded with a commercial glucometer. The proof-of-concept of our device was successfully demonstrated by measuring the glucose levels in six tear samples from nondiabetic subjects. In general, the results showed that the colorimetric biosensor has noticeable potential to be used as a powerful tool for tear glucose monitoring, since this fluid offers lower potential interferences, non-invasive sample collection and is pain-free. Furthermore, the proposed device could facilitate the treatment of diabetic patients who need constant control of glucose levels and cannot tolerate multiple finger sticks per day. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessFeature PaperArticle
Experimental Analysis of Fabrication Parameters in the Development of Microfluidic Paper-Based Analytical Devices (µPADs)
Micromachines 2017, 8(4), 99; https://doi.org/10.3390/mi8040099 - 25 Mar 2017
Cited by 3
Abstract
Microfluidic paper-based analytical devices (µPADs) have emerged as viable multiplexable platforms with the potential to transcend existing analytical techniques in resource-limited settings. µPADs are fabricated by patterning hydrophobic materials on hydrophilic paper. Reproducibility in fabrication is essential in a myriad of applications and [...] Read more.
Microfluidic paper-based analytical devices (µPADs) have emerged as viable multiplexable platforms with the potential to transcend existing analytical techniques in resource-limited settings. µPADs are fabricated by patterning hydrophobic materials on hydrophilic paper. Reproducibility in fabrication is essential in a myriad of applications and particularly, in the development of point-of-care (POC) diagnostic devices that utilize paper-based platforms. A critical step in fabrication involves the wax heating process that determines the channel dimensions and the depth at which hydrophobic wax material permeates paper to create barriers. In this paper, we assess µPAD viability by examining two fabrication parameters that affect wax ink spreading and permeation using a commercial heat press: temperature and time of heating. Analysis of the µPADs revealed that functional chips could be fabricated at temperatures between 143 and 215 °C and time of heating between 50 and 135 s, while non-functioning chips were obtained at temperatures between 76 and 140 °C and time of heating between 5 and 45 s. Wax ink spread and permeated paper consistently between 143 and 215 °C. Also shown is a simple three dimensional (3D) microfluidic channel fabricated in a single sheet of cellulose paper utilizing the fabrication conditions described herein. This work demonstrates that controlling the extent of wax printing in the fabrication process of a µPAD can yield versatile and interesting devices for use in both resource-rich and -limited settings. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle
Paper-Based Microfluidic Device with a Gold Nanosensor to Detect Arsenic Contamination of Groundwater in Bangladesh
Micromachines 2017, 8(3), 71; https://doi.org/10.3390/mi8030071 - 01 Mar 2017
Cited by 7
Abstract
In this paper, we present a microfluidic paper-based analytical device (μPAD) with a gold nanosensor functionalized with α-lipoic acid and thioguanine (Au–TA–TG) to detect whether the arsenic level of groundwater from hand tubewells in Bangladesh is above or below the World Health Organization [...] Read more.
In this paper, we present a microfluidic paper-based analytical device (μPAD) with a gold nanosensor functionalized with α-lipoic acid and thioguanine (Au–TA–TG) to detect whether the arsenic level of groundwater from hand tubewells in Bangladesh is above or below the World Health Organization (WHO) guideline level of 10 μg/L. We analyzed the naturally occurring metals present in Bangladesh groundwater and assessed the interference with the gold nanosensor. A method was developed to prevent interference from alkaline metals found in Bangladesh groundwater (Ca, Mg, K and Na) by increasing the pH level on the μPADs to 12.1. Most of the heavy metals present in the groundwater (Ni, Mn, Cd, Pb, and Fe II) did not interfere with the μPAD arsenic tests; however, Fe III was found to interfere, which was also prevented by increasing the pH level on the μPADs to 12.1. The μPAD arsenic tests were tested with 24 groundwater samples collected from hand tubewells in three different districts in Bangladesh: Shirajganj, Manikganj, and Munshiganj, and the predictions for whether the arsenic levels were above or below the WHO guideline level agreed with the results obtained from laboratory testing. The μPAD arsenic test is the first paper-based test validated using Bangladesh groundwater samples and capable of detecting whether the arsenic level in groundwater is above or below the WHO guideline level of 10 μg/L, which is a step towards enabling the villagers who collect and consume the groundwater to test their own sources and make decisions about where to obtain the safest water. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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