Rapid on-site colorimetric detection of arsenic(V) by NH-MIL-88(Fe) nanozymes-based ultraviolet-visible spectroscopic and smartphone-assisted sensing platforms.

BACKGROUND

Because arsenate (As(V)) is a highly toxic pollutant, timely on-site monitoring of its concentration is crucial for mitigating potential environmental and health hazards. Traditional on-site detection methods for As(V) often face limitations of long response time and low sensitivity. Nanozymes are nanomaterials that exhibit enzyme-like catalytic activity. Nanozyme-based colorimetric detection can amplify signals and improve detection sensitivity by catalytically converting a minimal substrate quantity into a substantial amount. However, current nanozymes-based As(V) detection methods still suffer from prolonged response time and the lack of convenient detection tools.

RESULTS

We develop a rapid and sensitive strategy for on-site colorimetric As(V) detection using a metal-organic framework (MOF) nanozyme, NH-MIL-88(Fe). NH-MIL-88(Fe) featured abundant Fe unsaturated metal centers (UMCs) and ordered porous structure, exhibiting excellent peroxidase-like activity, rapid As(V) adsorption, and high water dispersity. Fe UMCs efficiently catalyzed the oxidization of colorless tetramethylbenzidine (TMB) to blue oxTMB in the presence of HO. As(V) selectively inhibited this activity, reducing Ultraviolet-visible (UV-vis) absorption at 650 nm and fading the solution color. Mechanistically, As(V) interacted with Fe UMCs through As-O-Fe bonds, impeding Fe reduction and Fe catalytic ability, reducing •OH production. Under optimized conditions, As(V) was detected within 15 min, with detection limits of 2.78 μg L via UV-vis and 13.56 μg L via smartphone-assisted platform, covering a linear range of 5.00-600.00 μg L. Additionally, NH-MIL-88(Fe) was incorporated into an agarose hydrogel to create a portable composite for smartphone-based colorimetric analysis As(V).

SIGNIFICANCE AND NOVELTY

This study addresses the existing issues of nanozyme-based As(V) sensors, elucidates the molecular mechanism by which As(V) affects NH-MIL-88(Fe) nanozymes activity, and confirms the precision and accuracy of the established method in spiked river samples. Our rapid, sensitive, and facile approach offers a practical and efficient solution for on-site As(V) detection, facilitating swift intelligent risk identification and effective pollution prevention and remediation.