# Quantifying the Antioxidant Capacity of Inorganic Nanoparticles: Challenges and Analytical Solutions

## TL;DR

This paper addresses the challenges of measuring antioxidant activity in inorganic nanoparticles and proposes solutions for accurate quantification.

## Contribution

The study introduces optimized assay strategies to correct nanoparticle-specific interferences in antioxidant quantification.

## Key findings

- Silver, ceria, and iron oxide nanoparticles showed higher antioxidant capacities than Trolox.
- Gold nanoparticles exhibited negligible antioxidant activity.
- Optimized methods enable reproducible comparisons of nanoparticle antioxidants.

## Abstract

Antioxidant properties of inorganic nanoparticles in aqueous media are attracting growing interest due to their high surface reactivity. Materials such as cerium oxide, iron oxide, silver, and gold exhibit distinct radical-scavenging behaviors at the nanoscale, but reliable quantification remains challenging. Conventional assays developed for molecular antioxidants cannot be directly applied because probes such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) require methanol–water mixtures and are unstable in aqueous nanoparticle suspensions, while other assays are affected by nanoparticle-induced absorption or fluorescence changes. Here we demonstrate strategies to correct these interferences by independently measuring nanoparticle optical properties after oxidation and customizing assay conditions to account for the dilute, per-particle concentrations of nanomaterials. Using a high-throughput 96-well format, four adapted assays revealed that silver, ceria, and iron oxide nanoparticles possess substantially higher antioxidant capacities than Trolox, while gold showed negligible activity. This optimized approach enables reproducible comparison of nanoparticle antioxidants and provides a platform for tailoring nanostructures with enhanced radical-scavenging properties.