Simple pencil‐drawn paper‐based devices for one‐spot electrochemical detection of electroactive species in oil samples

Abstract

We propose here simple electrochemical cells assembled with electrodes pencil drawn on paper for conducting one-spot tests enabling olive oil to be easily distinguished from other vegetable oils. They consist of small circular pads of hydrophilic paper defined by hydrophobic barriers, these last printed by using custom-designed rubber stamps, where working, reference, and counterelectrodes are drawn by pencil leads. These cells were first wetted with a small volume of aqueous electrolyte, avoiding coating of the upper surface of electrodes. A controlled volume of edible oil samples was then applied on top of the moist cell. The results found proved that these devices can be adopted as effective platforms suitable for the detection of electroactive compounds present in edible oils. In fact, they allow voltammetric profiles to be recorded not only for the oxidation of water soluble species (ortho-diphenols, as well as some monophenols and polyphenols) present in olive oils, but also for electroactive hydrophobic components (e.g., α-tocopherol) present in sunflower oils, which were chosen as model of seed oils. The whole of collected findings pointed out that simple one-spot tests performed by these devices enable olive oils to be easily distinguished from other edible oils on the basis of their clearly different voltammetric profiles. A satisfactory interdevice reproducibility (±13%) was estimated by applying strictly similar extra virgin olive oil samples onto seven different cells carefully prepared by the same procedure. An operating mechanism able to account for the detection of also electroactive hydrophobic compounds present in oils is proposed.

Emerging Considerations for the Future Development of Electrochemical Paper‐Based Analytical Devices

“…The main application using the separation and microfluidic properties of paper is the quantification of small molecules such as glucose, lactate, uric acid, and ascorbic acid ,. With the development of this area, better understanding of the construction principles of these devices, different strategies for the application of nontreated samples, better electrochemical interfaces, etc., it is now possible to detect a wide variety of analytes in different matrixes such as metals, ions,, bacteria, pollutants, disease biomarkers, drugs, and food contamination . Whatman's paper is also easily modified to produce even better results: its hydrophobicity can be tuned,, it can be made omniphobic, its conductivity can be enhanced by incorporating carbon materials or soaking with conducting polymer, it can be modified by different nanomaterials, etc.…”

“…[19][20]32] With the development of this area, better understanding of the construction principles of these devices, different strategies for the application of nontreated samples, better electrochemical interfaces, etc., it is now possible to detect a wide variety of analytes in different matrixes such as metals, [34] ions, [22d,35] bacteria, [12a] pollutants, [36] disease biomarkers, [37] drugs, and food contamination. [38] Whatman's paper is also easily modified to produce even better results: its hydrophobicity can be tuned, [37,39] it can be made omniphobic, [40] its conductivity can be enhanced by incorporating carbon materials or soaking with conducting polymer, [41] it can be modified by different nanomaterials, [42] etc. However, as discussed previously, it is also necessary to evaluate whether Whatman No.…”

Determination of Ascorbic Acid in Commercial Tablets Using Pencil Drawn Electrochemical Paper-based Analytical Devices

“…Consequently, the graphite amount to be deposited on the paper surface depends on the pencil hardness. 25 Many publications have been reported in literature showing the use of pencil-drawn electrodes for direct electroanalytical measurements, 26,27 strain sensors, 28 flexible sensors 24 or even as detectors for analytical separations on microfluidic devices. 29 Two of the remarkable advantages of pencil electrodes are certainly the simplicity and the low cost.…”

Rapid determination of hydrophilic phenols in olive oil by vortex-assisted reversed-phase dispersive liquid-liquid microextraction and screen-printed carbon electrodes

“…However, the traditional Folin-Ciocalteu method, based on the colorimetric determination of total polyphenols, is still very useful to estimate the antioxidant capacity of VOO with a simple procedure and low cost [6,7]. Also, alternative electrochemical methods have been developed with the same purpose [8][9][10][11][12][13][14][15][16][17].…”