Single particle fluorescence: a simple experimental approach to evaluate coincidence effects

Area of Science:

• Environmental Science
• Analytical Chemistry
• Physics

Background:

• Real-time characterization of individual aerosol particles is vital for environmental monitoring.
• Laser-induced fluorescence and mass spectrometry are established methods for particle analysis.
• Accurately addressing single particles is a key challenge in these techniques.

Purpose of the Study:

• To develop and experimentally verify a simple approach for confirming single aerosol particle detection.
• To validate the method using dual-color fluorescence measurements.
• To establish optimal particle concentrations for minimizing coincidence effects.

Main Methods:

• Aerosolizing dye-doped particles using a medical nebulizer and aerodynamic lenses.
• Focusing particles into a laser beam within a vacuum chamber.
• Simultaneously measuring fluorescence signals in two spectral regions using independent detectors.
• Analyzing coincidence effects and pulse height distributions.

Main Results:

• Dual-color fluorescence signals were observed, allowing for direct detection of coincidence events.
• The probability of multi-particle interactions was found to be dependent on particle flux.
• A particle concentration below 1.2x10^5 particles/mL was required to achieve less than 10% two-particle coincidence.
• Experimental results aligned with a Poisson statistics-based mathematical model.

Conclusions:

• The described method effectively verifies single aerosol particle addressing.
• The approach is adaptable for direct air sampling with prior particle number density measurement.
• This technique enhances the reliability of real-time aerosol particle characterization.