Design and development of a microfluific paper-based analytical device ( μPAD) for magnesium determination in saliva

Of all the cations in the body, magnesium is the second most important intracellular cation and the fourth most prevalent. Disorders involving magnesium are categorized into two groups: hypomagnesemia (magnesium deficiency) and hypermagnesemia. In this way, the determination of magnesium has aroused great interest, because it helps in the clinical context and epidemiological research. Therefore, the objective of this work was to develop a microfluidic paper-based analytical device (µPAD) for the quantification of magnesium in saliva samples. In this case, the µPAD is based on the colorimetric reaction between magnesium and eriochrome cyanine to form an intense orange/reddish dye. After the reaction, it is necessary to use a flatbed scanner to obtain a high-resolution image of the detection zone for determination the intensity of the orange/reddish colour within each detection zone measured with Image J software. Under the optimum conditions, the proposed µPAD method was characterized by a linear calibration range for magnesium concentration 0.082 – 0.247 mmol/L. The detection and quantification limits were 0.062 mM and 0.081 mM, respectively. The reagents, eriochrome cyanine, NH4Cl and NH4OH consumption were 0.043 mg, 1.62 mg and 13.0 mg per calibration curve and the sample consumption was 120 µl per each determination.