Piezoresistive membrane surface stress sensors for characterization of breath samples of head and neck cancer patients

For many diseases, where a particular organ is affected, chemical by-products are found in the patient’s exhaled breath. Breath analysis is often done using gas chromatography and mass spectrometry, but interpretation of results is difficult and time-consuming. We performed characterization of patients’ exhaled breath samples by an electronic nose technique based on an array of nanomechanical membrane sensors. Each membrane is coated with a different polymer layer. By pumping the exhaled breath into a measurement chamber, volatile organic compounds present in patients’ breath diffuse into the polymer layers and deform the membranes by changes in surface stress. The bending of the membranes is measured via four piezoresistive bridges at the fixation points of the membrane. The resistance changes in the Wheatstone bridge are converted in an electronic circuit to voltages and are recorded. The sensor deflection pattern allows to characterize the condition of the patient. In a clinical study, we investigated breath samples from head & neck cancer patients and healthy persons. Evaluation using principal component analysis (PCA) allowed clear distinction between the two groups. As head & neck cancer can be completely removed by surgery, the breath of cured patients was investigated after surgery again and the results were very similar to those of the healthy control group indicating that surgery was successful.