A fluorescence digital image-based method using a 3D-printed platform and a UV-LED chamber made of polyacid lactic for quinine quantification in beverages

Abstract

A digital image-based (DIB) method for fluorometric detection was developed using an ultraviolet (UV) chamber and a spot test platform made with a 3D printer. A smartphone was used as the detector to quantify quinine in commercial tonic beverage samples. The free OpenSCAD CAD program and a Prusa i3 3D printer were used for the construction of the chamber and the spot test platform. The platform was made of polyacid lactic (PLA), where each one of the 25-wells has a maximum volume of 280 µL. The 3D-printed UV chamber was irradiated by four high brightness UV light emitting diodes (LED) with a maximum emission wavelength at 370 nm, which is required for the excitation of quinine molecules. The fluorescence signals based on the Red (R), Green (G) and Blue (B) data were simultaneously obtained from each well of the 3D-platform using the open source ImageJ software and its Readplate plugin. The B channel presented higher fluorescence intensity (FI) and was described by following analytical curve: FIB = (58.03 ± 2.75) × [QN] − (2.90 ± 3.89), with r2 = 0.991 for the linear range from 1.54 × 10−6 to 1.39 × 10−5 mol L−1. The limits of detection and quantification were 6.9 × 10−8 and 2.3 × 10−7 mol L−1, respectively. The relative standard deviation ranged from 0.25% to 1.52%. The fluorescence DIB method was in close agreement with the fluorometric method used as reference at a 95% confidence level. In addition, an analytical frequency of 10 analysis min−1, a low chemical consumption, high portability, and low-cost of acquisition and maintenance are the main features of the proposed method. Thus, the methodology developed here can be widely used in food process control as a much more economical and accessible analytical tool.