Fabrication of eco-friendly hydrogel strips for the simultaneous quantification of heavy metal ions in aqueous environment

Abstract

A biocompatible optosensor that can be used for detection of toxic heavy metal ions such as, Cd2+ and Hg2+ through naked eye is presented here. The sensor consists of biodegradable PEGDA (Poly(ethylene glycol) diacrylate) hydrogel incorporated with plant origin fluorescent pigments as main components. Curcumin and anthocyanin, naturally occurring fluorophores are obtained from turmeric and red cabbage respectively in a facile and green route. The transparent-swelling attuned hydrogel containing optimized quantities of plant pigments yield white emission (Commission Internationale de l'Eclairage, CIE: 0.307, 0.342) on blue excitation. The white emitting optosensor makes visible colour changes to heavy metal ions (HMIs) viz., Hg2+ (green) and Cd2+ (blue). In addition, the adoption of a multivariate method, Multivariate Curve Resolution – Alternating Least Square (MCR-ALS), enhances the possibility of concurrent and precise quantification of both HMI in fresh water at ppb level. We have shown that the designed optosensor has very good analytical fidelity, as root mean square error prediction is less than 0.03. The ease of fabrication (<30 min), availability of ingredients, cost effective nature (₹ 30 or $ 0.4), possibility of adaptive dimension of gel (strip or button), biodegrading nature of hydrogel, compatibility to fiber optic spectrometer, etc. Make the optosensor a cost effective and also an eco-friendly analytical tool.