An integrated electrochemical platform empowered by paper for fast nickel detection in cosmetics

Nickel is one of the most common allergens found in cosmetics: a high exposure to nickel can cause serious effects on human health, as contact dermatitis or eczema. Considering the spread of this type of allergy among the population and the predominant use of cosmetic products, use portable and easy-to-use devices, which allow a quick and accurate assessment of nickel above the permitted limits, could represent a valid and alternative tool for the protection of human health. In this study, we developed a hybrid paper-polyester printed strip for fast, simple, and low-cost determination of nickel at concentrations consistent with the allowable limits in cosmetics, exploiting the differential pulse adsorptive stripping voltammetry in the presence of dimethylglyoxime as Nicomplexing agent. We report a novel configuration to produce an integrated fully-printed electrochemical device, in which the screen-printed electrode, printed on polyester, is successfully combined with a wax-printed filter paper disk in order to allow the investigation in treatment of complex matrices such as cosmetics ones. In addition, the use of filter paper allows to store all the reagents necessary for carrying out the determination. The method developed has allowed to work with small amount of sample (microliters level), obtaining a detection limit equal to 2 µM in standard solution and 5 µM in the two chosen matrices, namely cream and a synthetic gel. In order to evaluate the applicability, the device was also tested for the analysis of two commercial products, obtaining satisfactory results in terms of sensitivity and repeatability. The accuracy has been also evaluated by inductively coupled plasma-mass spectrometry (ICP-MS) measurements, with high correlation between the two approaches