Catechin and curcumin nanoparticle-immobilized starch cryogels as green colorimetric sensors for on-site detection of iron

Abstract

Green colorimetric sensors based on the immobilization of catechin and curcumin nanoparticles (NPs) on macroporous starch cryogels were developed for the on-site detection of iron. Starch cryogels were synthesized from rice flour, while catechin and curcumin NPs were prepared from green tea and turmeric powder, respectively. Catechin and curcumin NPs were immobilized on starch cryogels, which turned black and red-brown, respectively, after immersion in an iron solution (pH 2) for 15 min. The digital image colorimetry (DIC) results of the NP-immobilized cryogels showed excellent linearity (R2 > 0.9997), low detection limit (0.48 ± 0.01 mg L−1), and excellent accuracy for the detection of iron. The intraday precision (n = 12) ranged from 1.35 to 3.20 %RSD, while the interday precision (n = 5) ranged from 0.75 to 2.98 %RSD. The sensors can be stored for at least three months in a desiccator with −0.52% changes in performance. The concentrations of iron in water samples quantified by the developed sensors and the DIC method (0.56–1.35 mg L−1) were not significantly different to those obtained from flame atomic absorption spectrophotometry (0.30–1.29 mg−1) at a 95% confidence level.