Image caption: Protease-triggered volatile release from nanosensors. Credit: Cygny Malvar.

Breath contains hundreds to thousands of trace volatile organic compounds (VOCs), which come from environmental exposure or are produced as metabolic products in the body. With ties to metabolic processes in the body, breath VOC composition is potentially informative of health status. However, breath biomarker discovery through traditional means of VOC profiling using GC-MS has been hindered by statistical and technical challenges. Instead of relying on endogenous breath VOCs to monitor health, an alternative approach is to generate breath biomarkers de novo. This can be achieved via delivery of exogenous agents into the body that are metabolized into volatile products by disease-specific processes. Current clinical breath tests using this approach have focused application in gastrointestinal and liver diseases. In my research, I have demonstrated that we can extend this approach to engineer breath biomarkers for acquired respiratory diseases (e.g. infections) and genetic respiratory diseases (e.g. alpha-1 antitrypsin deficiency) and do so by leveraging pathology-driving protease activity.

Volatile-releasing activity based nanosensors (vABNs) are nanoparticles carrying surface-bound VOC reporter payloads. When VOCs are surface-bound, they exist in a non-volatile pro-form. When VOCs are released from the nanoparticle carrier, they recover their characteristic mass and volatility to undergo phase transition and can be detected as a gas. In my recent Nature Nanotechnology publication, I describe the development of vABNs and demonstrate that peptide substrate linkers can be used to anchor VOC reporters to nanoparticle carriers for programmed protease-triggered VOC release. I further show that when delivered into the lungs, vABNs generate a bio-orthogonal breath readout for pulmonary protease activity that can be used to monitor respiratory disease. Furthermore, this engineered breath readout can serve as a pharmacodynamic biomarker to optimize drug dosing. For the story behind the collaboration that enabled this work, check out my Behind the Paper post on the Nature Research Bioengineering Community website!

Figure 1. (a) Schematic of approach. In our initial proof-of-concept, vABNs were built to sense the activity of neutrophil elastase (NE), an inflammation-associated protease released by neutrophils to kill bacterial pathogens during infection. (b) Quantification of volatile reporters in breath from healthy controls versus mice with lung infection using mass spectrometry. Each peak represents one mouse.


L. W. Chan, M. N. Anahtar, T. H. Ong, K. E. Hern, R. R. Kunz, S. N. Bhatia. Engineering synthetic breath biomarkers for respiratory disease. Nat. Nanotechnol. 15, 792-800 (2020).

L. W. Chan. Advances in activity-based diagnostics for infectious disease and microbiome health. Curr. Opin. Biomed. In press.