More efficient asthma treatments could be possible thanks to a laser “trap” that examines how drug particles expelled from inhalers behave as they enter the respiratory tract.

Researchers from the University of Cambridge and the University of Birmingham developed the new method, in which they trapped individual solid particles of salbutamol sulfate (commonly used in asthma inhalers) between two focused laser beams. The team also used Raman spectroscopy to study the particles’ composition and ability to dissolve.

The work was conducted using the OCTOPUS (Optics Clustered to OutPut Unique Solutions) laser imaging system at the Science and Technology Facilities Council (STFC) Central Laser Facility.

The behavior of the drug particles was tested at different temperatures and levels of humidity. By discharging the inhaler into the laser trap, without changing the drug’s physical or chemical properties, the researchers were able to capture in air those microscopic particles, which are typically 2 µm to 5 µm in diameter.

They recorded the size, shape and chemical signature to show evidence of any water adsorption. This happened within a matter of seconds, a period that the researchers said closely replicates the time, relative humidity and trajectory of the particles in the lung.

“Our tests show how water is absorbed by following changes in chemical bond vibrations,” said Dr. Andy Ward of the Central Laser Facility, noting that such tests are typically performed on a glass slide.

Any moisture that clings to the particles as they travel is likely to increase their size, which could affect the site of particle deposition within the lung. Depending on where the drug is deposited, the treatment could be less effective or even produce negative side effects.

“You can observe the size and shape of drug particles using a microscope, but you don’t get any chemical information about what exactly is happening to the particles if they float in air,” said Cambridge researcher Dr. Markus Kalberer. “Using techniques borrowed from atmospheric chemistry, we are now able to gather that chemical information, and observe the change in the particles as they transition from solid to liquid, as they would in the human body.”

The work was funded by STFC, the Natural Environment Research Council and the European Research Council. The research was published in Chemical Communications (doi: 10.1039/C4CC05803H). 

For more information, visit www.cam.ac.uk.