Fluorescent aerosol labeling via probe volatilization for non-destructive physicochemical analysis of aerosols

Background

Aerosols, which are suspensions of solid or liquid particles in a gaseous medium, play significant roles in various biological, technological, and environmental systems. They are crucial in processes such as virus transmission, pulmonary drug delivery, and atmospheric phenomena like light scattering and cloud nucleation. Measuring the physicochemical properties of aerosol particles, such as pH, viscosity, and phase state, is necessary for understanding critical phenomena like respiratory virus transmission and climate change. However, such measurements are challenging due to their small particle sizes and mass densities. Fluorescent probe spectroscopy is one of the few techniques that can measure these properties in situ without destroying the sample. However, this technique typically requires premixing the fluorescent probe with the aerosol particles before generation, a method not applicable to many classes of aerosols of critical societal importance like those exhaled from humans or found in the ambient environment. This restrictive limitation necessitates the development of new methods to label aerosols post-formation to enable fluorescent-probe based analytical measurements.

Technology

The technology uses a volatilization chamber to heat fluorescent probe molecules (e.g., Nile red or Prodan), generating gas-phase probes that condense onto a controlled aerosol flow. The aerosol-probe mixture passes through the chamber under regulated relative humidity and then into a fluorescence detection flow tube for real-time analysis of physicochemical properties. Validated with polyethylene glycol aerosols, model secondary organic aerosols (toluene SOA), and artificial saliva particles, this approach introduces only trace probe amounts, preserving the native particle state. It supports flexible probe selection and tuning of signal intensity by adjusting the probe solution’s temperature, all while enabling non-destructive, in situ characterization without prior premixing.

By eliminating the need for premixing before particle generation, this method can label ambient or exhaled aerosols that traditional techniques cannot address, and it avoids complex trapping or coagulation setups restricted to larger particles. Its gas-phase partitioning strategy and kinetic control allow rapid, uniform probe deposition across submicron particles, offering insights into hygroscopicity, viscosity, and phase behavior in real-world samples. This simplicity, adaptability, and compatibility with diverse aerosol types and analytic platforms distinguish it from existing fluorescence-based aerosol measurement techniques.

Benefits

• Enables in situ fluorescent labeling of real-world aerosols (exhaled breath, ambient air) without the need for premixing
• Non‐destructive analysis that preserves original aerosol physicochemical properties by introducing only trace probe amounts
• Flexible applicability to diverse probe molecules (e.g., Nile red, Prodan) and particle systems (PEG, SOA, artificial saliva)
• Allows real‐time assessment of aerosol hygroscopicity, phase state and viscosity via humidity‐dependent fluorescence shifts
• Simpler setup than complex trapping methods, with tunable signal intensity achieved by adjusting probe‐solution temperature
• Paves the way for advanced studies in disease transmission, drug delivery and atmospheric chemistry

Applications

• Airborne pathogen detection
• Exhaled breath diagnostics
• Aerosol drug delivery testing
• Ambient air quality monitoring
• Atmospheric research instrumentation

Additional info

Fluorescent probe molecules are volatilized in a heated chamber through which aerosol flows, enabling gas-phase probes to condense onto submicron particles. Controlled RH conditioning and an aerosol flow tube with electrical mobility sizing and fluorescence detection permit real-time assessment of hygroscopicity, viscosity, and phase state. Validated on PEG, secondary organic, and artificial saliva aerosols, trace probe loading minimally perturbs original particle properties while enabling flexible, in situ labeling without premixing.