Laser-plotter manufactured colorimetric four-leaf clover-like MIP/PAD for maleic hydrazide detection

A laser-based approach to manufacture a colorimetric Paper Analytical Device (PAD) integrating Molecularly Imprinted Polymer (MIP) for maleic hydrazide (MH), is proposed. The device has a four-leaf clover-like shape (4L-MIP/PAD) and was desing to integrate the MH complete analysis; MH is an anthropic plant growth regulator widely spread/found in vegetables. The 4L-MIP/PAD has been shaped with a CO2-laser plotter and integrates a CO2- laser-activated fiberglass layer functionalized with UV in-situ synthesized MIP. The 4L-MIP/PAD graphical sketch is reported in Scheme 1; the PAD houses the MIP at the center, while each foldable leaf allows the implementation of a specific analysis step. 4L-MIP/PAD based MH analysis procedure: a drop of the sample extract (40 μL) is deposited on the MIP, (1) the sample is removed by paper capillarity folding the 'absorption-leaf', the MIP washing is performed depositing a water drop on the MIP, (2) the washing-phase was removed folding the 'washing leaf’. Eventually, the analyte is eluted depositing a drop of an alkaline solution on the MIP, (3) then the folding of the colorimetric left allows the colorimetric reaction; the latter relise, on the on-paper adsorbed Folin-Ciocâlteu reagent. The 4L-MIP/PAD-based complete MH analysis requires 30 min, and the colorimetric signal acquisition needs just a smartphone camera. 4L-MIP/PAD-based ensures the MH determination between 10 to 100 ppm (RSD≤13%, n=3), showing a LOD of 3.3 ppm. These figures of merits allow cover the admitted residual law limits for root and tuber vegetables (maximum residue level: 50 ppm for potatoes, 30 ppm for carrots, and 15 ppm for garlic and onions). The 4L-MIP/PAD selectivity was tested against different kinds of pesticides and several food matrix components (vitamins, amino acids, organic acids); despite the non-selective of the Folin-Ciocâlteu reagent, the 4L-MIP/PAD exhibits a high selectivity toward MH. Tests on the device stability and the application in food samples are actually on course.