Design of a microfluidic paper-based device for the quantification of phenolic compounds in wine samples

In this work, the design and development of a microfluidic paper-based device (μPAD) for the quantification of total phenolic compounds (TPC) in wines is described. The developed μPAD was based upon the vertical flow concept and the colour reaction used was the known Folin-Ciocalteu reaction using gallic acid as reference phenolic compound. After studying operational parameters, namely type of paper, reagents and sample volume, a dynamic range of 5-50 mg L^-1 was obtained with a limit of detection of 1.2 mg L^-1. The described device proved to have good precision (relative standard deviation < 5%) and no significant interferences were observed from known compounds present in wines. Furthermore, the stability of the colour product and of the device itself were assessed; the μPAD was stable for 30 days (in the dark at room temperature) and it could be scanned up to 8 h after sample introduction. The developed μPAD pose as a simple method for TPC quantification and was successfully applied to several wine samples including sparkling and table wines with two different approaches: i) using gallic acid as reference compound with standard addition; and ii) using taniraisin with external calibration. The accuracy of the proposed μPAD method was assessed by comparison with the reference spectrophotometric method according to the International Organisation of Vine and Wine (OIV) recommendations.