Time-dependent luminescence loss for individual upconversion nanoparticles upon dilution in aqueous solution

Area of Science:

• Nanotechnology
• Biophysics
• Optical Microscopy

Background:

• Single-particle luminescence microscopy offers unique insights into biological systems.
• Upconversion nanoparticles (UCNPs) are valuable for microscopy due to stable, autofluorescence-free emission.
• Previous ensemble studies indicated UCNP instability in aqueous solutions.

Purpose of the Study:

• To investigate the luminescence behavior of individual UCNPs in aqueous environments.
• To quantify luminescence loss and spectral changes at the single-particle level.
• To explore methods for enhancing UCNP stability in aqueous conditions.

Main Methods:

• Quantitative wide-field microscopy was used to monitor individual UCNPs.
• Luminescence intensity and spectral response were analyzed over time.
• The effect of sodium fluoride on UCNP stability was evaluated.

Main Results:

• Individual UCNPs exhibited rapid luminescence decay and spectral shifts in water.
• Significant heterogeneity in luminescence and band intensity ratios was observed.
• Luminescence loss was unpredictable and not correlated with initial particle properties.
• Millimolar sodium fluoride addition significantly reduced dissolution and heterogeneity.

Conclusions:

• UCNP luminescence is unstable at the individual particle level in aqueous media.
• Particle dissolution leads to unpredictable performance and heterogeneity in single-particle experiments.
• Sodium fluoride addition is a viable strategy to improve UCNP stability for aqueous microscopy.