Functional properties of betalains: binding of Hg2+ and Cu2+ ions, sensor capabilities, and antimicrobial activity

Abstract In this study, betalain extracts were obtained from prickly pear (PPE), dragon fruit (DFE), and red beet (RBE). The total betalain content of the extracts was determined to be 335.5 mg/L for PPE, 372.38 mg/L for DFE, and 466.21 mg/L for RBE, respectively. Fluorescence titrations with metal cations revealed PPE’s highest intensity at 280 nm excitation, with DFE and RBE also responding, though less so. The fluorescence intensity for all extracts decreased significantly upon adding Hg2+ and Cu2+, indicating strong binding. PPE and DFE showed higher sensitivity and affinity for these ions than RBE. Absorption at 350 nm increased notably, along with visible color changes enabling potential ‘naked-eye’ detection. These extracts demonstrated high selectivity for Hg2+ and Cu2+, even with competing cations. Antibacterial tests showed significant inhibition against gram-positive and gram-negative bacteria. These findings, the extracts’ strong spectral responses and anti-interference properties support their use as selective, sensitive sensors for environmental monitoring and analytical applications. Due to their inherent fluorescence properties, betalains have significant potential as biosensors.