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