ISO 20814:2019

Overview

ISO 20814:2019 - Nanotechnologies - Testing the photocatalytic activity of nanoparticles for NADH oxidation - specifies an in vitro method to measure the photocatalytic activity (PCA) of nanoparticles (NPs) suspended in aqueous, physiologically relevant conditions. The standard quantifies UV-induced NADH (nicotinamide adenine dinucleotide, reduced) photo-oxidation as a proxy for nanoparticle photo-toxicity potential. The assay is multiplexed (96-well plate) and applicable to single NPs as well as NP aggregates and agglomerates.

Key topics and technical requirements

• Assay principle: Monitor decrease in NADH fluorescence before and after controlled UV exposure to determine the NADH photo-oxidation rate attributable to NPs.
• Multiplex format: Uses a 96‑well plate, UV trans‑illuminator and multi‑well fluorescence reader for simultaneous measurements at several NP concentrations.
• Calibration and corrections:
  • UV trans‑illuminator intensity calibrated by 2‑nitrobenzaldehyde (2NB) actinometry to obtain well-specific light correction factors.
  • Corrects for spontaneous NADH photo‑oxidation (without NPs) and intrinsic NP fluorescence.
• Quantitation:
  • Determine photo‑oxidation rate across a dilution series; identify the linear range of rate vs NP concentration.
  • Report NADH equivalent specific PCA (NADH photo‑oxidation rate per unit NP mass).
• Reagents and sample prep: Standard reagents include NADH (working ~250 μmol/L, verified by A339 nm ≈ 1.56 ± 0.05), phosphate buffer pH 8, 2NB, phenolphthalein, and recommended NP dispersion protocols. NP stock concentration adjusted so peak absorbance (300–800 nm) is 1.4–1.6.
• Quality and performance: Precision data (repeatability, reproducibility) and interlaboratory comparison (Annex C) are included to support method robustness.

Practical applications and users

• Nanomaterial safety assessment: Screening of TiO2, ZnO, WO3, CeO2, quantum dots, carbon nanotubes and other photosensitive NPs for potential ROS‑driven oxidative stress and photo‑toxicity.
• R&D and formulation: Researchers developing photoactive nanomaterials or coatings can compare PCA under physiological-like conditions.
• Regulatory and compliance testing: Laboratories performing hazard evaluation, ecotoxicology or consumer product safety assessments.
• Manufacturers and quality control: Routine batch screening to monitor photocatalytic behavior.

Related standards

• ISO/TS 80004‑1 and ISO/TS 80004‑2 - nanotechnology vocabulary
• ISO 20507:2014 - definition reference for PCA
• ISO 10676 and ISO 10678 - existing PCA test methods (not directly applicable to NP photo-toxicity; ISO 20814 addresses NP-specific needs)

Keywords: ISO 20814:2019, photocatalytic activity, nanoparticles, NADH oxidation, photo‑toxicity, UV actinometry, 96‑well assay, NADH equivalent specific PCA.