A Bioinspired Adhesive-Integrated-Agent Strategy for Constructing Robust Gas-Sensing Arrays

A visible-light regulated luminescent switch based on a spiropyran-derived Pt(II) complex for advanced anti-counterfeiting materials

A dual optical switch regulated by visible light has been developed through an integrated strategy, including luminescent Pt(II) and photochromic spiropyran (SP) as a triplet-sensitizer and photo-regulator building block, respectively. An efficient Förster resonance energy transfer (FRET) process is achieved, along with apparent and emissive color changes under visible light irradiation and temperature stimuli, which was utilized to develop advanced anti-counterfeiting materials.

Highly Adaptive Kirigami-Metastructure Adhesive with Vertically Self-Aligning Octopus-like 3D Suction Cups for Efficient Wet Adhesion to Complexly Curved Surfaces

An essential requirement for biomedical devices is the capability of conformal adaptability on diverse irregular 3D (three-dimensional) nonflat surfaces in the human body that may be covered with liquids such as mucus or sweat. However, the development of reversible adhesive interface materials for biodevices that function on complex biological surfaces is challenging due to the wet, slippery, smooth, and curved surface properties. Herein, we present an ultra-adaptive bioadhesive for irregular 3D oral cavities covered with saliva by integrating a kirigami-metastructure and vertically self-aligning suction cups. The flared suction cup, inspired by octopus tentacles, allows adhesion to moist surfaces. Additionally, the kirigami-based auxetic metastructure with a negative Poisson's ratio relieves the stress caused by tensile strain, thereby mitigating the stress caused by curved surfaces and enabling conformal contact with the surface. As a result, the adhesive strength of the proposed auxetic adhesive is twice that of adhesives with a flat backbone on highly curved porcine palates. For potential application, the proposed auxetic adhesive is mounted on a denture and performs successfully in human subject feasibility evaluations. An integrated design of these two structures may provide functionality and potential for biomedical applications.

Machine Learning-Assisted Janus Colorimetric Face Mask for Breath Ammonia Analysis

Artificial olfactory systems have been widely used in medical fields such as in the analysis of volatile organic compounds (VOCs) in human exhaled breath. However, there is still an urgent demand for a portable, accurate breath VOC analysis system for the healthcare industry. In this work, we proposed a Janus colorimetric face mask (JCFM) for the comfortable evaluation of breath ammonia levels by combining the machine learning K-nearest neighbor (K-NN) algorithm. Such a Janus fabric is designed for the unidirectional penetration of exhaled moisture, which can reduce stickiness and ensure facial dryness and comfort. Four different pH indicators on the colorimetric array serve as recognition elements that cross-react with ammonia, capturing the optical fingerprint information on breath ammonia by mimicking the sophisticated olfactory structure of mammals. The Euclidean distance (ED) is used to quantitatively describe the ammonia concentration between 1 ppm and 10 ppm, indicating that there is a linear relationship between the ammonia concentration and the ED response (R2 = 0.988). The K-NN algorithm based on RGB response features aids in the analysis of the target ammonia level and achieves a prediction accuracy of 96%. This study integrates colorimetry, Janus design, and machine learning to present a wearable and portable sensing system for breath ammonia analysis.

Conductive Polyaniline-Based Microwire Arrays for SO2 Gas Detection

Polyaniline-based conductive polymers are promising electrochemical sensor materials due to their unique physical and chemical properties, such as good gas absorption, low dielectric loss, and chemical and thermal stabilities. The sensing performance is highly dependent on the structure and dimensions of the polyaniline-based conductive polymers. Although in situ oxidative polymerization combined with the self-assembly process has become one of the main processes for the preparation of flexible polyaniline-based gas sensors, how to prepare polyaniline materials into uniformly arranged microwire arrays is still an urgent problem. In this paper, an in-depth study was conducted on the preparation of polyaniline microwire arrays by combining a wettability interface dewetting process and a liquid-film-induced capillary bridges method. The factors influencing the preparation of polyaniline microwire arrays, including solution concentration, template width, evaporation temperature, and evaporation time, were investigated in detail. The wire formation rates were recorded from the results of SEM images. 100% microwires formation rate can be obtained by using a 1.0 mg mL-1 concentration of polyaniline solution and a 10 μm silicon template at an evaporation temperature of 80 °C for 18 h. The prepared microwire arrays can realize sulfur dioxide sensing at room temperature with a response speed of about 20 s and can detect sulfur dioxide gas as low as 1 ppm. Thus, the liquid-film-induced capillary bridge method shows a new possibility to prepare gas sensor devices for insoluble polymers.

Exploitation of Schottky-Junction-based Sensors for Specifically Detecting ppt-Concentration Gases

Gas species and concentrations of human-exhaled breath correlate with health, wherein disease markers contain volatile organic compounds (VOCs) of concentrations in parts per billion. It is expected that a gas-sensing strategy possesses a gas specificity and detection limit in the parts per trillion (ppt) range; however, it is still a challenge. This investigation has exploited the Schottky junction of gas sensors for detecting the reactance signal of ppt VOC, aiming for a specific and rapid detection toward disease marker acetone. In this new sensing paradigm, formed by the engineered energy band between metal-semiconductor contact, the Schottky junction is accessed to specific modulation of different adsorbate dopings and the corresponding reactance signal is measured. Regarding the detection toward ppt concentration of acetone, this sensing paradigm possesses rapid (∼100 s) and room-temperature response, molecular specificity, and 34 ppt of detection limit. The proposed detection paradigm is demonstrated to show a high feasibility toward detection of disease marker acetone.