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Infrared Lightbox and iPhone App for Improving Detection
Limit of Phosphate Detecting Dip Strips
Microfluidics laboratory at the University of Rhode Island, Kingston, RI, USA
Presented by:
Hojat Heidari-Bafroui
Co-authors:
Brenno Ribeiro, Amer Charbaji, Constantine Anagnostopoulos, Mohammad Faghri
Please cite to our works: https://doi.org/10.1016/j.measurement.2020.108607
and: https://publications.waset.org/10011330/infrared-lightbox-and-iphone-
app-for-improving-detection-limit-of-phosphate-detecting-dip-strips

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Contents:
 Introduction
 Why is monitoring phosphate important?
 Molybdenum blue method
 Paper-based device
 Cellphone-based point-of-care testing
 Scopes of this research
 Infrared lightbox and iPhone analyzer application
 Result and discussion
 Effect of reaction time
 Improvement of phosphate dip strips
 Conclusions

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Introduction
 Why is monitoring phosphate important?
 Eutrophication
Algal bloom
Fish mortality

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Introduction
 Molybdenum blue method
 Widespread colorimetric approach
 Introduced by Murphy and Riley (1962)
 phosphate first react with a reagent consisting of ammonium molybdate and potassium antimony
(III) tartrate
 consequently reduced by ascorbic acid to form the phospho-antimonyl molybdenum blue (PAMB)
S. Islam et al. (2016)

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Introduction
 Paper-based devices
 Inexpensive, disposable and convenient analytical devices
 Jayawardane et al. (2012) proposed a 3-D microfluidic paper-based analytical device (𝜇PAD)
Jayawardane et al. (2012) Jayawardane et al. (2014)

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Q. Fu et al. (2019) : Organophosphate
pesticides (OPs) A. Shahvar et al. (2020) :
water content in ethanol
Z. Xu et al. (2020) :
Heavy metal ions
Introduction
 Use of smartphones for rapid point-of-care testing

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A. Shahvar et al. (2019) :
sulfite in food samples
N. Moonrungsee
et al. (2015) : phosphorus in
soil
M. Xiao et al. (2020) : Heavy metal ions
Introduction
 Lightboxes with light emitting diodes (LED) to provide consistent visible light intensity conditions

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Introduction
 The objectives of this research:
 to produce an inexpensive, portable infrared lightbox
 using an infrared camera to take advantage of the peak absorbance of the molybdenum blue
reaction.
 to develop an iOS application to measure and analyze the RGB pixel values of pictures
 to present a highly accessible worldwide system for tracking and analyzing field measurements
 to combine the above techniques into a portable reader unit for significant improvements in the
measuring capabilities of commercial paper-based phosphate devices

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Experimental
 Commercial phosphate test strips
 Indigo
• Simple paper-based dip strip
• Comparing color formed on
strip with color chart
• Low resolution
• Phosphate results: 0, 30, 75,
150, and 300 ppm

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 Commercial phosphate test strips
 Quantofix
• Requires more user
involvement and manipulation
of acidic reagents
• Comparing color formed on
strip with color chart
• Higher resolution
• Phosphate results: 0, 3, 10, 25,
50, and 100 ppm
Experimental

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700 nm
850 nm
He and Honeycutt (2005)- Absorption spectra
of the phosphomolybdenum blue complexes
Experimental
 Infrared lightbox unit
 standard technique for determining low concentrations of phosphate is spectrometric method
 maximum absorbance peak occurs in the wavelength of around 850

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Experimental
 infrared filters of cameras
No infrared filter camera (NoIR)
Raspberry Pi with NoIR camera unit

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Experimental
 Raspberry Pi: A small single-board computers developed by the Raspberry Pi Foundation
 Remotely control Raspberry Pi by cellphone

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 Infrared Lightbox wirelessly controlled by a cellphone
 Secure shell method (SSH)
 Virtual network computing (VNC)
 File transfer protocol (FTP)
Experimental

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 Colorimetric Analyzer App
 Built for iOS using Apple’s XCode IDE
 Designed as an image processing app for analyzing RGB values from photos
 Connected to a constructed online date center to track field measurements
Experimental

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Experimental
 Analytical procedure of the colorimetric analyzer
 All glassware and reusable vials washed by a phosphate free detergent and 1M HCL for 3 times
 Stock solution of phosphate (100 ppm) and diluted to 0, 0.1, 0.25, 0.50, 0.75, 1, 2.5, 5, 7.5, 10, 25,
50, and 75 ppm phosphate.
 Indigo and Quantofix test kits were run following the manufacturers’ instructions
 The images were captured in the visible light spectrum using a desktop scanner and in the
infrared zone by using the lightbox unit.
 Red intensity for the visible light and the grayscale for the infrared light

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Results and discussion
 Effect of the reaction time
Indigo test kits Quantofix test kits

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Indigo test kits Quantofix test kits
 Improvement of phosphate test strips

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Limit of detection = yBlank + 3sBlank
Limit of quantification = yBlank + 10sBlank
Table 2- Comparison of Limits of Detection (LOD) and
Limits of Quantification (LOQ) in the visible and infrared
light conditions
Table 1- Comparison of the coefficients (with 95%
confidence bounds) and the determination coefficients (R2)
for the exponential curve (y=a-b*exp(-x/c) ) fit to the visible
and infrared data

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Conclusions
 A portable and low-cost infrared lightbox was used to take advantage of maximum absorption of
molybdenum blue reaction
 An iPhone-based analyzer app
 An expensive spectrometers are not required to take advantage of the infrared spectra
 LOD decreased from 9.2 to 1.4 ppm for the Indigo strips (by a factor of 6)
 LOD decreased from 1.35 to 0.34 ppm for the Quantofix phosphate test strips (by a factor of 4)
 Capturing images by the lightbox provided accurate and repeatable results with RSD values less than
1.2%.
 The lightbox and colorimetric analyzer can be further developed to be used for other colorimetric
reactions such as Nitrate and Nitrite

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