Sniffing out cancer in the breath: detection of non-polar volatile compounds through carrier scattering in random networks of carbon nanotubes

Abstract

Exhaled breath of cancer patients contains certain nonpolar volatile organic compounds (VOCs) which are not present in the breath of a healthy person. An electronic nose composed of an array of random network (RN) of carbon nanotube (CNT) sensors could in principle detect cancer from breath, but the notoriously low sensitivity of CNT sensors to nonpolar VOCs limits their accuracy. We have achieved a marked improvement of the RN-CNT chemiresistors' response to the nonpolar VOCs found in the breath of lung cancer patients by functionalizing them with different types of nonpolymeric organic films as well as discontinuous films composed of sponge-like wires of hexaperi-hexabenzocoronene (HBC) molecules. By monitoring the changes in conductance, work function and organic film thickness during exposure we show that the enhanced sensitivity of the functionalized RN-CNTs to nonpolar cancer biomarkers stems from carrier scattering induced by swelling of the organic film. Based on these findings, we show that an array of RN-CNT sensors can discriminate between the VOCs found in the breath of patients with lung cancer and in healthy controls. Hence, controlling the carrier scattering in RN-CNTs via deliberate functionalization with suitable organic films could become an important factor in the design of sensors for nonpolar VOCs, which have hitherto been difficult to trace. The results presented here are an important step towards the development of a robust, cost effective electronic nose for sniffing out nonpolar VOCs as biomarkers for cancer in patients' breath.