Layer-by-layer assembly of mesoporous silica nanoparticle films for gas adsorption in exhaled breath analysis

Abstract

Exhaled breath analysis is a non-intrusive, point-of-care monitoring technique capable of detection and diagnosis of respiratory diseases, offering rapid response and recovery rates. Detection of volatile organic compounds (VOCs) in the exhaled breath vapor can serve as biomarkers for diagnosis of early onset of lung diseases such as chronic obstructive pulmonary disease (COPD), asthma etc. We aim to functionalize thin film coatings that are optically transparent in the mid-infrared region of interest (2.5 – 3.8 µm) for enhancing gas adsorption of VOCs on an optical sensor that provides on-chip sensing and real-time measurement of VOC concentration. Mesoporous silica nanoparticles exhibit various properties that are desirable for gas adsorption such as tunable particle size, tunable pore size and morphology, accessible pore walls for surface functionalization, high degree of ordering and high surface to volume ratios. In this study, we propose a controlled deposition mechanism by employing layer-by-layer (LbL) deposition method to assemble alternating multilayers of electronegative mesoporous silica nanoparticles and electropositive branched polyethylenimine (BPEI) on primed silicon wafers. By optimizing and controlling the thickness and homogeneity of the assembled multilayers, we are afforded greater degree of control over the sensitivity and selectivity of the gas sensor we aim to build using these thin films, which is portable, easy-to-use and provides real-time, point-of-care diagnosis for monitoring of respiratory diseases.