Design and application of a paper-based optoelectronic nose for the on-site discrimination of essential oils using a chemometric web app

Abstract

Essential oils are appreciated worldwide for their pleasant aroma, in addition to their therapeutic, pharmacological, and cosmetic functions. For these reasons, adulteration is a common practice that decreases product quality causing economic and health issues. In this study, we present for the first time the application of a simple, inexpensive and disposable paper-based optoelectronic nose (i.e. colorimetric sensor array) to (i) discriminate sixteen different types of essential oils and (ii) detect adulterated samples. The colorimetric array was prepared by adding 1.5 μL of 9 chemo-responsive dyes with different chemical properties to each circular spot of the paper-based device. 1 mL of each essential oil was transferred to a flask and bubbled with synthetic air at an airflow of 200 mL min⁻¹. Then, the optoelectronic nose was exposed to the airstream containing the volatiles from the sample for 5 minutes. Digital images from before and after exposure were obtained using a smartphone and the RGB values were extracted using appropriate software. The color changes provided a unique color map fingerprint for each essential oil. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) were successfully employed using a customized smartphone app, showing suitable discrimination of all studied essential oils as well as among adulterated and non-adulterated samples. The proof-of-concept showed the potential of the optoelectronic nose approach for the discrimination of different essential oils and the identification of adulterated samples, providing a valuable tool for quality control procedures.