A 3D printed Do-It-Yourself miniaturized device with a sensor responsive at six different wavelengths for reflectance measurements on paper-based supports

A low-cost portable analytical device, suitable for performing reflectance measurements on paper supports is proposed. It consists of a simple module consisting of a matrix of six types of photodiodes (six channels) with maximum sensitivity at six different wavelengths in the visible region. The device was used in combination with paper-based analytical devices (PADs) suitably prepared by 3D printing using polycaprolactone, i.e. a biodegradable and biocompatible polymer. These PADs were used both as substrates for the imbibition of colored solutions and of reagents for colorimetric reactions. The constructive and electronic aspects are described and the instrumental noise, as well as the performance of this device were carefully evaluated in terms of repeatability and reproducibility by using three different food dyes and a colorimetric assay for the determination of nitrites with the Griess reagent. The development of this device also included the management of output signals that, once converted from raw signals into reflectance values, have been elaborated by the Kubelka-Munk theory. Finally, the application to real samples consisting of commercial aqueous solutions of Tartrazine yellow (E102), Ponceau red 4R (E124) and Patent blue V (E131), usually adopted for the coloration and/or decoration of homemade cakes and sugarcoated almonds, gave results in good agreement with values obtained by absorbance measurements performed by a benchtop spectrophotometer. This type of comparison pointed out that also the nitrite detection performed by reflectance measurements on synthetic samples allowed more than reliable results to be obtained.