Salivary calcium determination with a specially developed microfluidic paper-based device for point-of-care analysis

Abstract

The calcium monitoring in the body not only anticipates several potential diseases (osteoporosis, kidney stones or high blood pressure) but also helps to improve target therapies and follow-up the patient's health status. Calcium monitoring is essential for the diagnosis of one of the most common endocrine disorders worldwide, namely hyperparathyroidism. So, in this work, a new Point-of-care test (POC-test) using a microfluidic paper-based analytical device (μPAD) for calcium quantification in saliva samples is described. The developed μPAD was based on the colorimetric reaction between calcium and cresolphthalein complexone (CPC) which forms an intense purple colour product. The developed device enabled calcium quantification in the range of 0.27–4.50 mmol/L (11.0–180 mg/L) with a detection limit of 80 µmol/L (3.2 mg/L). The accuracy of the developed μPAD was confirmed by analysing saliva samples (#10) and comparing the results obtained with the atomic absorption spectrometry reference procedure; the relative deviation between the two sets of results was below 10 %. A correlation between salivary calcium content and calcium content in blood was established and it was possible to conclude that salivary calcium concentrations above 1.55 mmol/L is an indicator of hypercalcemia. The developed device was stable for 2 weeks when stored at room temperature in vacuum conditions.