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Chen JL, Njoku DI, Tang C, Gao Y, Chen J, Peng YK, Sun H, Mao G, Pan M, Tam NFY. Advances in Microfluidic Paper-Based Analytical Devices (µPADs): Design, Fabrication, and Applications. SMALL METHODS 2024:e2400155. [PMID: 38781604 DOI: 10.1002/smtd.202400155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 05/01/2024] [Indexed: 05/25/2024]
Abstract
Microfluidic Paper-based Analytical Devices (µPADs) have emerged as a new class of microfluidic systems, offering numerous advantages over traditional microfluidic chips. These advantages include simplicity, cost-effectiveness, stability, storability, disposability, and portability. As a result, various designs for different types of assays are developed and investigated. In recent years, µPADs are combined with conventional detection methods to enable rapid on-site detection, providing results comparable to expensive and sophisticated large-scale testing methods that require more time and skilled personnel. The application of µPAD techniques is extensive in environmental quality control/analysis, clinical diagnosis, and food safety testing, paving the way for on-site real-time diagnosis as a promising future development. This review focuses on the recent research advancements in the design, fabrication, material selection, and detection methods of µPADs. It provides a comprehensive understanding of their principles of operation, applications, and future development prospects.
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Affiliation(s)
- Jian Lin Chen
- Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Good Shepherd Street, Ho Man Tin, Kowloon, Hong Kong SAR, P. R. China
- State Key Laboratory of Marine Pollution, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, P. R. China
- Shenzhen Research Institute of City University of Hong Kong, Shenzhen, 518057, P. R. China
| | - Demian Ifeanyi Njoku
- Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Good Shepherd Street, Ho Man Tin, Kowloon, Hong Kong SAR, P. R. China
| | - Cui Tang
- Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Good Shepherd Street, Ho Man Tin, Kowloon, Hong Kong SAR, P. R. China
| | - Yaru Gao
- Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Good Shepherd Street, Ho Man Tin, Kowloon, Hong Kong SAR, P. R. China
| | - Jiayu Chen
- Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Good Shepherd Street, Ho Man Tin, Kowloon, Hong Kong SAR, P. R. China
| | - Yung-Kang Peng
- Shenzhen Research Institute of City University of Hong Kong, Shenzhen, 518057, P. R. China
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, P. R. China
| | - Hongyan Sun
- Shenzhen Research Institute of City University of Hong Kong, Shenzhen, 518057, P. R. China
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, P. R. China
| | - Guozhu Mao
- School of Environmental Science and Engineering, Tianjin University, Tianjin, 300350, P. R. China
| | - Min Pan
- Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Good Shepherd Street, Ho Man Tin, Kowloon, Hong Kong SAR, P. R. China
| | - Nora Fung-Yee Tam
- Department of Applied Science, School of Science and Technology, Hong Kong Metropolitan University, Good Shepherd Street, Ho Man Tin, Kowloon, Hong Kong SAR, P. R. China
- State Key Laboratory of Marine Pollution, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, P. R. China
- Shenzhen Research Institute of City University of Hong Kong, Shenzhen, 518057, P. R. China
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, P. R. China
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Malik S, Singh J, Saini K, Chaudhary V, Umar A, Ibrahim AA, Akbar S, Baskoutas S. Paper-based sensors: affordable, versatile, and emerging analyte detection platforms. ANALYTICAL METHODS : ADVANCING METHODS AND APPLICATIONS 2024; 16:2777-2809. [PMID: 38639474 DOI: 10.1039/d3ay02258g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
Paper-based sensors, often referred to as paper-based analytical devices (PADs), stand as a transformative technology in the field of analytical chemistry. They offer an affordable, versatile, and accessible solution for diverse analyte detection. These sensors harness the unique properties of paper substrates to provide a cost-effective and adaptable platform for rapid analyte detection, spanning chemical species, biomolecules, and pathogens. This review highlights the key attributes that make paper-based sensors an attractive choice for analyte detection. PADs demonstrate their versatility by accommodating a wide range of analytes, from ions and gases to proteins, nucleic acids, and more, with customizable designs for specific applications. Their user-friendly operation and minimal infrastructure requirements suit point-of-care diagnostics, environmental monitoring, food safety, and more. This review also explores various fabrication methods such as inkjet printing, wax printing, screen printing, dip coating, and photolithography. Incorporating nanomaterials and biorecognition elements promises even more sophisticated and sensitive applications.
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Affiliation(s)
- Sumit Malik
- Department of Chemistry, Maharishi Markandeshwar (Deemed to be University), Mullana, Ambala, 133203, Haryana, India.
| | - Joginder Singh
- Department of Chemistry, Maharishi Markandeshwar (Deemed to be University), Mullana, Ambala, 133203, Haryana, India.
| | - Kajal Saini
- Department of Chemistry, Maharishi Markandeshwar (Deemed to be University), Mullana, Ambala, 133203, Haryana, India.
| | - Vivek Chaudhary
- Department of Chemistry, Maharishi Markandeshwar (Deemed to be University), Mullana, Ambala, 133203, Haryana, India.
| | - Ahmad Umar
- Department of Chemistry, Faculty of Science and Arts, Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, Najran-11001, Kingdom of Saudi Arabia.
- Department of Materials Science and Engineering, The Ohio State University, Columbus 43210, OH, USA
- STEM Pioneers Training Lab, Najran University, Najran 11001, Kingdom of Saudi Arabia
| | - Ahmed A Ibrahim
- Department of Chemistry, Faculty of Science and Arts, Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, Najran-11001, Kingdom of Saudi Arabia.
- STEM Pioneers Training Lab, Najran University, Najran 11001, Kingdom of Saudi Arabia
| | - Sheikh Akbar
- Department of Materials Science and Engineering, The Ohio State University, Columbus 43210, OH, USA
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Soman SS, Samad SA, Venugopalan P, Kumawat N, Kumar S. Microfluidic paper analytic device (μPAD) technology for food safety applications. BIOMICROFLUIDICS 2024; 18:031501. [PMID: 38706979 PMCID: PMC11068414 DOI: 10.1063/5.0192295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Accepted: 04/15/2024] [Indexed: 05/07/2024]
Abstract
Foodborne pathogens, food adulterants, allergens, and toxic chemicals in food can cause major health hazards to humans and animals. Stringent quality control measures at all stages of food processing are required to ensure food safety. There is, therefore, a global need for affordable, reliable, and rapid tests that can be conducted at different process steps and processing sites, spanning the range from the sourcing of food to the end-product acquired by the consumer. Current laboratory-based food quality control tests are well established, but many are not suitable for rapid on-site investigations and are costly. Microfluidic paper analytical devices (μPADs) are a fast-growing field in medical diagnostics that can fill these gaps. In this review, we describe the latest developments in the applications of microfluidic paper analytic device (μPAD) technology in the food safety sector. State-of-the-art μPAD designs and fabrication methods, microfluidic assay principles, and various types of μPAD devices with food-specific applications are discussed. We have identified the prominent research and development trends and future directions for maximizing the value of microfluidic technology in the food sector and have highlighted key areas for improvement. We conclude that the μPAD technology is promising in food safety applications by using novel materials and improved methods to enhance the sensitivity and specificity of the assays, with low cost.
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Affiliation(s)
- Soja Saghar Soman
- Division of Engineering, New York University Abu Dhabi, Abu Dhabi, P.O. Box 129188, UAE
| | - Shafeek Abdul Samad
- Division of Engineering, New York University Abu Dhabi, Abu Dhabi, P.O. Box 129188, UAE
| | | | - Nityanand Kumawat
- Division of Engineering, New York University Abu Dhabi, Abu Dhabi, P.O. Box 129188, UAE
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Uhlikova N, Almeida MIGS, McKelvie ID, Kolev SD. Microfluidic paper-based analytical device for the speciation of inorganic nitrogen species. Talanta 2024; 271:125671. [PMID: 38306810 DOI: 10.1016/j.talanta.2024.125671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 01/08/2024] [Accepted: 01/13/2024] [Indexed: 02/04/2024]
Abstract
A microfluidic paper-based analytical device (μPAD) utilizing gas-diffusion separation and solid-phase reduction was developed for the first time for the determination of both ammonium and nitrate, which are the dominant inorganic nitrogen species in environmental waters. The device consists of 3 filter paper layers accommodating the sample, reagent and detection zones. The reagent zone is separated from the detection zone by a semipermeable hydrophobic membrane and acts as a solid-phase reactor where nitrate is reduced to ammonia by Devarda's alloy microparticles, integrated into a μPAD for the first time. The detection zone incorporates the acid-base indicators bromothymol blue (BTB) or nitrazine yellow (NY) and changes colour in two steps. Initially the colour change is caused by ammonia generated by the reaction of ammonium and sodium hydroxide in the sample zone. This colour change is followed by a subsequent colour change as a result of the ammonia produced by the reduction of nitrate by the Devarda's alloy microparticles. The corresponding reflectance value changes are used for the quantification of the two inorganic nitrogen species in the ranges 6.5-100.0 or 2.1-15.0 mg N L-1 for ammonium and 18.2-100.0 or 4.2-15.0 mg N L-1 for nitrate when BTB or NY are used, respectively. Under optimal conditions the limits of quantification of ammonium and nitrate in the case of BTB were determined as 6.5 and 18.2 mg N L-1, respectively, while the corresponding values in the case of NY were found to be 2.1 and 4.2 mg N L-1. The newly developed μPAD was stable for 62 days when stored in a freezer and 1 day at ambient temperature. It was validated with a certified reference material and successfully applied to the determination of ammonium and nitrate in spiked environmental water samples and soil extracts.
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Affiliation(s)
- Natalie Uhlikova
- School of Chemistry, The University of Melbourne, Victoria 3010, Australia
| | - M Inês G S Almeida
- School of Chemistry, The University of Melbourne, Victoria 3010, Australia
| | - Ian D McKelvie
- School of Chemistry, The University of Melbourne, Victoria 3010, Australia
| | - Spas D Kolev
- School of Chemistry, The University of Melbourne, Victoria 3010, Australia; Department of Chemical Engineering, The University of Melbourne, Victoria 3010, Australia; Sofia University "St. Kl. Ohridski", Faculty of Chemistry and Pharmacy, 1 James Bourchier Blvd., Sofia 1164, Bulgaria.
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Jantra J, Arsawiset S, Teepoo S, Keeratirawee K. Rapid colorimetric assay based on the oxidation of 2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid-diammonium salt for nitrite detection in meat products. JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH. PART. B, PESTICIDES, FOOD CONTAMINANTS, AND AGRICULTURAL WASTES 2024; 59:72-80. [PMID: 38146233 DOI: 10.1080/03601234.2023.2297639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2023]
Abstract
This work developed a rapid colorimetric method for nitrite detection in meat products. The detection was based on the reaction of nitrite with 60 mM HCl to produce radicals which further oxidized ABTS (50 µM) to form a water-soluble blue-green product (ABTS•+). The absorbance was measured at a maximum absorption wavelength of 412.5 nm. Parameters such as concentration of HCl, concentration of ABTS and reaction time were evaluated. The absorbance was linearly proportional to the concentration of nitrite (0.1-20 µM) with the limit of detection of 0.34 µM. The proposed method was a time-saving assay since it required only 2 min to complete one measurement. There was no effect of the interference produced by other ions. The assay was robust with 2.5%RSD (n = 50). In meat product samples, high accuracy was observed with the recoveries between 100 ± 2.2% and 105 ± 3.7%. The amount of nitrite in meat products detected by the ABTS method was found in the range of 5.41 - 7.62 mg/kg. The conventional Griess method was applied to determine nitrite in the same meat products. There was no statistically significant difference between the two methods (P = 0.05).
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Affiliation(s)
- Jongjit Jantra
- King Mongkut's Institute of Technology Ladkrabang, Prince of Chumphon Campus, Pathio, Chumphon, Thailand
| | - Supattra Arsawiset
- Department of Chemistry, Faculty of Science and Technology, Rajamangala University of Technology, Thanyaburi, Pathum Thani, Thailand
| | - Siriwan Teepoo
- Department of Chemistry, Faculty of Science and Technology, Rajamangala University of Technology, Thanyaburi, Pathum Thani, Thailand
| | - Kanchalar Keeratirawee
- King Mongkut's Institute of Technology Ladkrabang, Prince of Chumphon Campus, Pathio, Chumphon, Thailand
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Samkumpim T, Alahmad W, Tabani H, Varanusupakul P, Kraiya C. Application of oxygen scavengers in gel electromembrane extraction: A green methodology for simultaneous determination of nitrate and nitrite in sausage samples. Food Chem 2023; 422:136190. [PMID: 37137238 DOI: 10.1016/j.foodchem.2023.136190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 04/02/2023] [Accepted: 04/16/2023] [Indexed: 05/05/2023]
Abstract
The generation of oxygen from electrolysis in gel electromembrane extraction (G-EME) causes a negative error when applied to the analysis of easily oxidized species such as nitrite. Nitrite in G-EME is oxidized by oxygen to nitrate, leading to the negative error and the impossibility of simultaneous analysis. In this work, the application of oxygen scavengers to the acceptor phase of the G-EME system was attempted to minimize the oxidation effect. Several oxygen scavengers were selected and examined according to their compatibility with ion chromatography. The mixture of sulfite and bisulfite (14 mg L-1) showed the highest efficiency in preventing the oxidation of nitrite to nitrate. Under the optimized conditions, a good linear range was obtained (10-200 μg L-1; R2 > 0.998) with a detection limit of 8 µg L-1 for both nitrite and nitrate. This method was applied to the simultaneous determination of nitrite and nitrate in sausage samples.
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Affiliation(s)
- Thidarat Samkumpim
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
| | - Waleed Alahmad
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
| | - Hadi Tabani
- Department of Environmental Geology, Research Institute of Applied Sciences (ACECR), Shahid Beheshti University, Tehran, Iran
| | - Pakorn Varanusupakul
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
| | - Charoenkwan Kraiya
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand; Electrochemistry and Optical Spectroscopy Center of Excellence, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
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Wang M, Cui J, Wang Y, Yang L, Jia Z, Gao C, Zhang H. Microfluidic Paper-Based Analytical Devices for the Determination of Food Contaminants: Developments and Applications. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2022; 70:8188-8206. [PMID: 35786878 DOI: 10.1021/acs.jafc.2c02366] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Food safety is an issue that cannot be ignored at any time because of the great impact of food contaminants on people's daily life, social production, and the economy. Because of the extensive demand for high-quality food, it is necessary to develop rapid, reliable, and efficient devices for food contaminant detection. Microfluidic paper-based analytical devices (μPADs) have been applied in a variety of detection fields owing to the advantages of low-cost, ease of handling, and portability. This review systematically discusses the latest progress of μPADs, including the fundamentals of fabrication as well as applications in the detection of chemical and biological hazards in foods, hoping to provide suitable screening strategies for contaminants in foods and accelerating the technology transformation of μPADs from the lab into the field.
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Affiliation(s)
- Minglu Wang
- Shandong Provincial Key Laboratory of Animal Resistance Biology, Key Laboratory of Food Nutrition and Safety of Shandong Normal University, College of Life Science, Shandong Normal University, Jinan 250014, PR China
| | - Jiarui Cui
- Shandong Provincial Key Laboratory of Animal Resistance Biology, Key Laboratory of Food Nutrition and Safety of Shandong Normal University, College of Life Science, Shandong Normal University, Jinan 250014, PR China
| | - Ying Wang
- College of Food Science and Engineering, Shandong Agricultural University, Tai'an 271018, PR China
| | - Liu Yang
- Shandong Provincial Key Laboratory of Animal Resistance Biology, Key Laboratory of Food Nutrition and Safety of Shandong Normal University, College of Life Science, Shandong Normal University, Jinan 250014, PR China
| | - Zhenzhen Jia
- Shandong Provincial Key Laboratory of Animal Resistance Biology, Key Laboratory of Food Nutrition and Safety of Shandong Normal University, College of Life Science, Shandong Normal University, Jinan 250014, PR China
| | - Chuanjie Gao
- Shandong Province Institute for the Control of Agrochemicals, Jinan, 250131, PR China
| | - Hongyan Zhang
- Shandong Provincial Key Laboratory of Animal Resistance Biology, Key Laboratory of Food Nutrition and Safety of Shandong Normal University, College of Life Science, Shandong Normal University, Jinan 250014, PR China
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Suvanasuthi R, Chimnaronk S, Promptmas C. 3D printed hydrophobic barriers in a paper-based biosensor for point-of-care detection of dengue virus serotypes. Talanta 2022; 237:122962. [PMID: 34736687 DOI: 10.1016/j.talanta.2021.122962] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Revised: 10/06/2021] [Accepted: 10/09/2021] [Indexed: 11/24/2022]
Abstract
Paper-based biosensor is one of the most commonly used platforms for point-of-care testing (POCT). Among these platforms, microfluidic paper-based analytical devices (μPADs) have the most versatile designs due to the different hydrophobic barrier patterns and layers of the devices. In addition, μPADs can also be used in combination with other biosensor platforms to improve the performance of the device. Simple and convenient methods for fabricating low-cost and design-adjustable hydrophobic barriers on paper are one of the most challenging aspects for creating μPADs. This work demonstrated a simple technique for using the common polylactic acid (PLA) filament and wax filament to create hydrophobic barriers on paper for μPADs using a commercialized 3D printer. As a proof of concept, the papers with 3D printed PLA barrier were used in combination with a fluidic chip in a prototype biosensor, in which the barrier paper housed four cell-free reactions and the fluidic chip achieved sample delivery to the reactions in the device. Our designed prototype was capable of discriminating dengue virus serotypes based on small nucleotide sequence differences. The proposed combination of 3D-printed barrier paper and fluidic chip provides a versatile platform for rapid prototyping of POCT with possible compatibility with various detection systems.
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Affiliation(s)
- Rooge Suvanasuthi
- Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, 73170, Thailand
| | - Sarin Chimnaronk
- Institute of Molecular Biosciences, Mahidol University, Nakhon Pathom, 73170, Thailand.
| | - Chamras Promptmas
- Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, 73170, Thailand.
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Ferreira FTSM, Mesquita RBR, Rangel AOSS. Design and Functionalization of a µPAD for the Enzymatic Determination of Nitrate in Urine. Molecules 2021; 26:molecules26216355. [PMID: 34770764 PMCID: PMC8588010 DOI: 10.3390/molecules26216355] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 10/18/2021] [Accepted: 10/19/2021] [Indexed: 11/16/2022] Open
Abstract
In this work, the design of a microfluidic paper-based analytical device (μPAD) for the quantification of nitrate in urine samples was described. Nitrate monitoring is highly relevant due to its association to some diseases and health conditions. The nitrate determination was achieved by combining the selectivity of the nitrate reductase enzymatic reaction with the colorimetric detection of nitrite by the well-known Griess reagent. For the optimization of the nitrate determination μPAD, several variables associated with the design and construction of the device were studied. Furthermore, the interference of the urine matrix was evaluated, and stability studies were performed, under different conditions. The developed μPAD enabled us to obtain a limit of detection of 0.04 mM, a limit of quantification of 0.14 mM and a dynamic concentration range of 0.14-1.0 mM. The designed μPAD proved to be stable for 24 h when stored at room temperature in air or vacuum atmosphere, and 60 days when stored in vacuum at -20 °C. The accuracy of the nitrate μPAD measurements was confirmed by analyzing four certified samples (prepared in synthetic urine) and performing recovery studies using urine samples.
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Charbaji A, Heidari-Bafroui H, Anagnostopoulos C, Faghri M. A New Paper-Based Microfluidic Device for Improved Detection of Nitrate in Water. SENSORS 2020; 21:s21010102. [PMID: 33375290 PMCID: PMC7794956 DOI: 10.3390/s21010102] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Revised: 12/06/2020] [Accepted: 12/23/2020] [Indexed: 12/11/2022]
Abstract
In this paper, we report a simple and inexpensive paper-based microfluidic device for detecting nitrate in water. This device incorporates two recent developments in paper-based technology suitable for nitrate detection and has an optimized microfluidic design. The first technical advancement employed is an innovative fibrous composite material made up of cotton fibers and zinc microparticles that can be incorporated in paper-based devices and results in better nitrate reduction. The second is a detection zone with an immobilized reagent that allows the passage of a larger sample volume. Different acids were tested—citric and phosphoric acids gave better results than hydrochloric acid since this acid evaporates completely without leaving any residue behind on paper. Different microfluidic designs that utilize various fluid control technologies were investigated and a design with a folding detection zone was chosen and optimized to improve the uniformity of the signal produced. The optimized design allowed the device to achieve a limit of detection and quantification of 0.53 ppm and 1.18 ppm, respectively, for nitrate in water. This accounted for more than a 40% improvement on what has been previously realized for the detection of nitrate in water using paper-based technology.
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