Transparent, flexible, and eco-friendly starch-based films for reversible optoelectronic noses for food spoilage monitoring in smart packaging.

A reversible optoelectronic nose is presented consisting of ten acid-base indicators incorporated into a starch-based film, covering a wide pH range. The starch substrate is odorless, biocompatible, flexible, and exhibits high tensile resistance. This optical artificial olfaction system was used to detect the early stages of food decomposition by exposing it to the volatile compounds produced during the spoialge process of three food products (beef, chicken, and pork). A smartphone was used to capture the color changes caused by intermolecular interactions between each dye and the emitted volatiles over time. Digital images were processed to generate a differential color map, which uses the observed color shifts to create a unique signature for each food product. To effectively discriminate among different samples and exposure times, we employed chemometric tools, including hierarchical cluster analysis (HCA) and principal component analysis (PCA). This approach detects food deterioration in a practical, cost-effective, and user-friendly manner, making it suitable for smart packaging. Additionally, the use of starch-based films in the food industry is preferable due to their biocompatibility and biodegradability characteristics.

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

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.

µOPTO: A microfluidic paper-based optoelectronic tongue as presumptive tests for the discrimination of alkaloid drugs for forensic purposes.

Natural and synthetic alkaloids are widely used for several applications, ranging from clinical purposes to criminal activities. Presumptive color tests are considered a leading tool to reveal on-scene substance identification via rapid chemical reactions that result in visual color changes. Colorimetric tests are popular due to their inherent simplicity, low cost, promptitude and portability; however, in many cases the results of such tests may not be predictable, partly because of the interference from similar species. In this proof-of-concept study, we present a paper-based microfluidic optoelectronic tongue - the so-called µOPTO - comprised of 6 indicators in lieu of one specific test and capable of discriminating 8 different alkaloid drugs (i.e. scopolamine, atropine, cocaine, morphine, ephedrine, caffeine, dipyrone and alprazolam) used for recreational, criminal and medical purposes. The wax printing method was employed to fabricate the microfluidic analytical device with six circular spots for reagent accommodation connected to a centered spot to enable simultaneous reactions with one sample injection. Digital images were obtained using an ordinary flatbed scanner, and the RGB information from before and after sample exposure was extracted using appropriate software. The color changes related to each spot were used to build differential maps with a unique fingerprint for each drug. The chemometric tools (i.e. PCA and HCA) showed suitable discrimination of all studied alkaloids in different quantities. To demonstrate a practical application, different alcoholic beverages spiked with scopolamine - a famous substance that causes drug abuse - were analyzed using the optoelectronic tongue. The results showed that small quantities of the drug were identified in different beverages, demonstrating that our device has the potential to be used in situ to prevent ingestion of contaminated samples.

Chemical QR Code: A simple and disposable paper-based optoelectronic nose for the identification of olive oil odor.

Olive oil is an appreciated food product with high nutritional value, besides being an essential component in many culture diets. In this study, we present for the first time the application of a simple and non-invasive paper-based optoelectronic nose designed in a QR code configuration to evaluate the odor of olive oils. The chemical QR code was fabricated by the addition of 12 dyes, which provided high dimensional data resulting from the interaction between the volatile compounds and the colorimetric array. The color changes were employed to build differential maps with a unique fingerprint (i) to discriminate between olive oil and other edible oil samples; (ii) to quantify nonanaldehyde as an oxidation marker; and (iii) to identify oxidized oils through principal component analysis (PCA) and hierarchical component analysis (HCA). By developing suitable mobile apps, we anticipate the employment of the chemical QR code for portable, low-cost, and in-situ evaluation of food product quality.