A microfluidic paper-based sensor for iodine monitoring as a public health indicator

Abstract

In this work, a new microfluidic paper-based analytical device (µPAD) was developed for on-site iodide quantification. As iodine is an essential micronutrient for humans, due to its fundamental role in producing the thyroid hormones, it is a key parameter to assess health condition. Iodine deficiency (ID) has contributed to continued underdevelopment for millions of people, making it the single most important and preventable cause of brain damage. In case of not fulfilling the iodine requirements for the human body, the synthesis of thyroid hormones is impaired, causing several iodine deficiency disorders. Consequently, iodine intake needs to be monitored to prevent ID. The paper-based sensor was based on the reaction of 3,3’,5,5’-tetramethylbenzidine (TMB) with H2O2, in which iodide is a catalyst. This reaction results in the oxidation of TMB, which goes from colourless to its oxidized blue colour. The design of the µPAD consisted of two layer of filter paper discs, the top layer (Whatman 4 paper) embedded in a mixture of acetic acid and hydrogen peroxide and the bottom later (Whatman 1 paper) impregnated with TMB. The µPAD was scanned at 25 minutes and analysed in ImageJ software, where the intensity of the formed colour product was converted to absorbance values. After optimization, a limit of detection of 0.89 mg/L (7.0 µM) and a limit of quantification of 2.8 mg/L (22 µM) were attained. Different types of samples were targeted, such as urine, salt and dietary supplements, corresponding to the intake and outtake of iodide. However, the salt samples presented some interferences from chloride, and the urine samples proved to have a significantly lower iodide content than the current limits of detection of the developed method. Lastly, this method was validated by comparing the obtained results for dietary supplements with potentiometric method and no significant differences between both methods were found. The µPAD was successfully developed, as it allowed for a rapid response for analysing iodide in different samples and still being a low-cost approach, since the consumables for each device cost approximately 0.12 €. The developed device allows for an economic, simpler and faster determination of iodide, which until now required complicated and time-consuming methods, adding the advantage of not needing to pre-treatment the samples to be used.

Date of Award	11 Dec 2023
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Raquel Mesquita (Supervisor) & António O. S. S. Rangel (Co-Supervisor)