Design of a disposable μPAD for on-hand quantification of urinary creatinine

Abstract

In this work, a new microfluidic paper-based analytical device (μPAD) was developed for on-hand creatinine quantification in urine samples. When compared to other conventional methods, this innovative paper device is more accessible, portable, providing low-cost analysis and applicable to non-invasive biological fluids. Furthermore, this paper approach is environmentally friendly, as it uses small amounts of reagents, results in low waste production and it is disposable by incineration. Its configuration consisted in two layers of filter paper discs of 9.5 mm of diameter, in which the top layer served as a reservoir and the bottom layer contained the reagent (alkaline picrate). This hydrophilic unit consisting of two-layer of filter paper was aligned within a laminated plastic pouch to set the hydrophobic separation, with 3 mm holes for the sample insertion. When inserted, creatinine of the standard/sample reacts with alkaline picric acid (colorimetric reaction), and the colour changes from yellow to orange/red. Under optimal conditions, the developed method allowed creatinine quantification in the dynamic range of 2.20-35.0 mg/dL, with a limit of detection (LOD) of 0.66 mg/dL and a limit of quantification (LOQ) of 2.20 mg/dL. The image was scanned after 20 minutes and was processed in ImageJ software to obtain the colour intensity developed, later converted to pseudo-absorbance. The stability of the reaction product after the sample insertion was verified until 3 hours and the device could be scanned within that time. The μPAD allows to obtain linear calibration curves up to one week when stored in vacuum and placed in the fridge at approximately 4 ºC. Finally, the method was validated by the results obtained with the developed device and a comparison method, and it was demonstrated that there were no statistically significant differences between them. As so, it was possible to conclude that this novel device was successfully developed, as it proved to be sensitive and simple, as well as affordable, as it showed a cost of approximately 0.40 € (in terms of consumables).

Date of Award	24 Nov 2022
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Raquel Mesquita (Supervisor) & António O. S. S. Rangel (Co-Supervisor)