Intra-tracheal device facilitates transport and visualization of inhaled vaccines

Viral-induced respiratory diseases, such as COVID-19 and the flu, mutate rapidly. Developing vaccines to treat them, however, is a slow, complex process. Inhaled vaccines offer a strategic approach to dealing with respiratory pathogens, activating the immune system at the trachea, the gateway to the pulmonary system.

Understanding dynamic transport processes is critical to vaccine development. Chen et al. developed a non-invasive, real-time imaging photoacoustic system to study how nano-adjuvants, substances that increase the efficacy of vaccines, absorb in the trachea.

The system utilizes indocyanine-green (ICG), a medical dye that absorbs near-infrared light and emits a photoacoustic signal. The researchers combined ICG and a nano-adjuvant to create a vaccine tag that is trackable through tissue layers.

The team then developed a real-time imaging device to track the distribution of the nano-adjuvant through the three-layered tracheal wall. The device, an intra-tracheal photoacoustic endoscopy (IT-PAE) system, sends a laser beam down a catheter in an optical fiber. The probe, small enough to be sent down a rabbit’s trachea, excites the ICG with laser light and collects the resulting sound waves. As the probe is rotated and moved up the trachea, it obtains a three-dimensional image.

By quantifying the velocity and photoacoustic intensity, the researchers could determine that the middle cartilage layer of the trachea slows the rate of drug transport.

“IT-PAE showed excellent resolution, contrast, and penetration depth, therefore enabling quantitative assessment of nano-adjuvant diffusion rates within the tracheal wall,” said author Jian Zhang.

The team plans to develop the IT-PAE into a user-friendly instrument for research institutions to use in drug development of novel vaccines. They also hope to establish the system as a diagnostic tool.

Source: “Intra-tracheal photoacoustic endoscopy for in vivo tracking of inhaled nano-adjuvants,” by Xiaowei Chen, Chaohao Liang, Fengbing He, Xue Wen, Yibo Tang, Jiarui Chen, Weizhan Luo, Kedi Xiong, and Jian Zhang, APL Photonics (2025). The article can be accessed at https://doi.org/10.1063/5.0288806 .