Flavonoid-incorporated starch and poly(vinyl alcohol) film: Sensitive and selective colorimetric sensor for copper identification and quantification in beverages and environmental samples

Abstract

Colorimetric sensors based on an eco-friendly sensor molecule immobilized into a polymer matrix have broad applications for detecting trace elements. However, their potential for quantitative analysis of these elements remains little explored. Here, we incorporated rutin or quercetin into films based on starch, poly(vinyl alcohol), and glycerol to detect and quantify Cu2+ in different matrices. The films were characterized by colorimetric assays, thickness, and solubility analyses, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and mechanical assays. Incorporating the flavonoids in the film decreased its solubility, tensile strength, and modulus of elasticity, while increased its cross-sectional surface irregularity. XRD and DSC results indicated an increase in film crystallinity in the presence of rutin or quercetin. FTIR analyses showed a more effective incorporation of quercetin than rutin in the polymeric matrix, which was confirmed by flavonoid release studies from the film. The film containing quercetin exhibited selectivity in identifying copper in liquid matrices, changing its color from light yellow to dark yellow. An analytical method to quantify Cu2+ was developed, presenting a linear response range of 0.20–1.20 mg L−1, with detection and quantification limits of 0.060 and 0.20 mg L−1, respectively, very lower than other methods based on polymeric matrices containing natural dyes. The method was successfully applied for Cu2+ determination in cachaça and tap water samples, achieving high accuracy (96–104% of recovery) and precision (relative standard deviation < 6.7%). Our findings represent an advancement in the field of sensors based on natural dyes, demonstrating that such sensors can achieve high sensitivity without the need for complex sample preparation methods.