Peptides, due to their diverse and controllable properties, are used as both liquid and gas phase recognition elements for both biological and chemical targets. While it is well understood how binding of a peptide to a biomolecule can be converted into a sensing event, there is not the same mechanistic level of understanding with regard to how peptides modulate the selectivity of semiconductor/conductor-based gas sensors. Notably, a rational, mechanistic study has not yet been performed to correlate peptide properties to the sensor response for volatile organic compounds (VOCs) as a function of chemical properties. Here, we have designed a peptide that has (1) two amino acid residues that bind the sensor surface, (2) two flexible linkers (GG) that eliminate steric strain, and (3) a five amino-acid repeat that can bind the analyte of interest either by formation of a binding pocket (such as from peptides selected by phage display) or by forming a semiselective adsorption layer. The nine peptide sequences containing both a six amino acid constant sequence (WGGWGG) and a five amino acid variable sequence (XXXXX) were synthesized, and their impact on the selectivity and sensitivity of carbon nanotube (CNT) gas sensors was explored. The response of each sensor to the following VOCs with diverse chemical properties: isopropyl alcohol (polar protic), acetone (polar aprotic), isoprene (nonpolar, linear hydrocarbon), and toluene (nonpolar aromatic), was then recorded and analyzed. This study revealed multiple key factors that influence the response of peptides on CNTs to select VOCs. First, the stability of the CNT-peptide aqueous dispersion correlated to the aromaphilicity of the side chain, strongly suggesting that the side chains of peptides are interfacing with the CNT, and not the peptide backbone. Second, the sensing response profile cannot solely be explained by peptides adsorbing to the gas molecules with similar polarities/dielectrics and may instead be due to analyte displacement of the peptide side chain on the CNT surface as measured by changes in the peptide bond orientation using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). These two observations create a new paradigm to explain how peptides confer selectivity to semiconductor-/conductor-based gas sensors and can provide insights into future design and implementation of peptide-coated solid state sensors for gas targets.

Common adhesives contain harmful chemicals, posing risks to humans and the environment. Basil seeds, an underutilized resource, can offer a solution. We extracted mucilage from basil seeds and found that altering the basil seed mucilage (BSM) to water ratio allowed us to control the adhesive strength. As the concentration of BSM increased and the water evaporated, adhesive strength improved. BSM can serve as both an adhesive and pressure-sensitive adhesive. This research showcases BSM's impressive strength and stability, making it a promising eco-friendly industrial adhesive option from plant-based sources, revolutionizing the adhesive industry.

Biorecognition element (BRE)-based carbon nanotube (CNT) chemiresistors have tremendous potential to serve as highly sensitive, selective, and power-efficient volatile organic compound (VOC) sensors. While many research groups have studied BRE-functionalized CNTs in material science and device development, little attention has been paid to optimizing CNT density to improve chemiresistor performance. To probe the effect of CNT density on VOC detection, we present the chemiresistor-based sensing results from two peptide-based CNT devices counting more than 60 different individual measurements. We find that a lower CNT density shows a significantly higher noise level and device-to-device variation while exhibiting mildly better sensitivity. Further investigation with SEM images suggests that moderately high CNT density with a stable connection of the nanotube network is desirable to achieve the best signal-to-noise ratio. Our results show an essential design guideline for tuning the nanotube density to provide sensitive and stable chemiresistors.

Carbon nanotube (CNT) chemiresistors have emerged as miniaturized platforms for wearable volatile organic compound (VOC) sensors. As a promising biorecognition element (BRE), a short peptide can functionalize CNT to be sensitive and selective to target VOCs. However, unveiling the VOC‐optimized peptide‐CNT pair for gas‐phase sensing remains unclear. Here, a novel multimodal molecular toolset for designing, building, and probing suitable BRE‐CNT sensors using machine learning, molecular dynamics, and near‐edge X‐ray absorption fine structure spectroscopy is presented. This computational and experimental suite predicts the peptide conformation on the CNT surface and probes how the peptide–CNT interfaces affect the VOC sensing. Then, peptide‐functionalized CNT chemiresistors are tested against various VOCs to confirm the efficacy of the toolkit. The results show that the vertically oriented peptide on the CNT surface hinders VOC access to the peptide–CNT interface, resulting in a significantly lower sensor signal than the CNT chemiresistor with the horizontally oriented peptide. The interactive computational and experimental results strongly indicate that a peptide conformation plays an important role in VOC sensing sensitivity.

Inhaled medications are commonplace for administering bronchodilators, anticholinergics, and corticosteroids. While they have a defined legitimate use, they are also used in sporting events as performance-enhancing drugs. These performance enhancers can be acquired via both legal (i.e., at a pharmacy through over-the-counter medications or through a prescription) and illicit (i.e., black market and foreign pharmacies) means, thus making monitoring procurement impossible. While urine tests can detect these pharmacological agents hours after they have been inhaled, there is a significant lag time before they are observed in urine. Direct detection of these inhaled agents is complicated and requires a multiplexed approach due to the sheer number of inhaled pharmacological agents. Therefore, detection of propellants, which carry the drug into the lungs, provides a simpler path forward toward detection of broad pharmacological agents. In this paper, we demonstrate the first use of terahertz spectroscopy (THz) to detect inhaled medications in human subjects. Notably, we were able to detect and quantitate the propellant, HFA-134a, in breath up to 30 min after using an asthma inhaler, enabling the use of a point-of-care device to monitor exhaled breath for the presence of propellants. We also demonstrate via simulations that the same approach can be leveraged to detect and identify next-generation propellants, specifically HFA-152a. As a result, we provide evidence that a single point-of-care THz sensor can detect when individuals have used pressure-mediated dose inhalers (pMDIs) without further modification of the hardware.

Human health and performance monitoring (HHPM) is imperative to provide information necessary for protecting, sustaining, evaluating, and improving personnel in various occupational sectors, such as industry, academy, sports, recreation, and military. While various commercially wearable sensors are on the market with their capability of "quantitative assessments" on human health, physical, and psychological states, their sensing is mostly based on physical traits, and thus lacks precision in HHPM. Minimally or noninvasive biomarkers detectable from the human body, such as body fluid (e.g., sweat, tear, urine, and interstitial fluid), exhaled breath, and skin surface, can provide abundant additional information to the HHPM. Detecting these biomarkers with novel or existing sensor technologies is emerging as critical human monitoring research. This review provides a broad perspective on the state of the art biosensor technologies for HHPM, including the list of biomarkers and their physiochemical/physical characteristics, fundamental sensing principles, and high-performance sensing transducers. Further, this paper expands to the additional scope on the key technical challenges in applying the current HHPM system to the real field.

This paper presents a novel carbon nanotube (CNT) sensor, where the micro-trench was designed to enhance the sensing performance. Device designs for suspending CNTs have provided enhanced sensing performance due to the higher surface area of the CNTs. However, previously reported sensors for the suspended CNTs were primarily involved in complicating the fabrication and delicate process of CNT transfer, resulting in a low device yield rate. We designed a micro-trench structure between gold electrodes using conventional photolithography. In addition, we adopted post-assembly of the CNTs based on dielectrophoresis, enabling single-step chemiresistor fabrication while protecting the CNTs from further damage or contamination. The CNT sensor with the micro-trench exhibited improved sensitivity and signal-to-noise ratio in detecting isopropyl alcohol (IPA) by 33 % and 125 %, respectively, compared to the non-trenched device. In addition, the present CNT sensor detected IPA as low as 0.3 ppm.

This paper presents a microfluidic thermal flowmeter for monitoring injection pumps, which is essential to ensure proper patient treatment and reduce medication errors that can lead to severe injury or death. The standard gravimetric method for flow-rate monitoring requires a great deal of preparation and laboratory equipment and is impractical in clinics. Therefore, an alternative to the standard method suitable for remote, small-scale, and frequent infusion-pump monitoring is in great demand. Here, we propose a miniaturized thermal flowmeter consisting of a silicon substrate, a platinum heater layer on a silicon dioxide thin-membrane, and a polymer microchannel to provide accurate flow-rate measurement. The present thermal flowmeter is fabricated by the micromachining and micromolding process and exhibits sensitivity, linearity, and uncertainty of 0.722 mW/(g/h), 98.7%, and (2.36 ± 0.80)%, respectively, in the flow-rate range of 0.5–2.5 g/h when the flowmeter is operated in the constant temperature mode with the channel width of 0.5 mm. The measurement range of flow rate can be easily adjusted by changing the cross-sectional microchannel dimension. The present miniaturized thermal flowmeter shows a high potential for infusion-pump calibration in clinical settings.

Atomically thin two-dimensional (2D) materials are ideal gas sensing materials with ultrahigh sensitivity due to the high surface-to-volume ratio, low electronic noise, and tunable Fermi level alignment. However, obtaining selectivity to a target analyte in the presence of other confounding gases in the environment remains an issue preventing selective gas sensing using 2D materials. In the present work, we fabricate a selective nitrogen dioxide (NO2) sensor using WSe2 by adding a simple oil layer as a filter. For this proof of concept study, we used polydimethylsiloxane (PDMS) due to its dipole moment being similar to NO2 (similar to 0.3 D). This PDMS layer helps selectively detect NO2 and filter out both more polar gases, such as ammonia (NH3) and hydrogen sulfide (H2S), as well as nonpolar gases, such as carbon monoxide (CO), that are likely to be present in the background environment. Not only did we obtain a selective response for single components but also we observed an improved sensing response (around 200%) when NO2 is mixed with other gases compared to the intrinsic WSe2 device without modification. The obtained results were found to be reproducible and reversible. The charge transfer effect of different gases to WSe2 devices was characterized by an atomic force microscope (AFM) through phase imaging techniques.

This paper presents a study on peptide-functionalized carbon nanotube (CNT) chemiresistors, where the effect of CNT density is investigated to optimize their gas sensing performances. While previous CNT density studies mostly focused on sensor performance and its reliability testing from a handful of devices, we systemically control CNT density and investigate more than 30 devices in terms of sensitivity, noise, and signal-to-noise ratio (SNR). The results exhibit that the higher CNT resistance results in 1) higher sensitivity, 2) higher noise, and 3) lower SNR. These results indicate that careful control of CNT density is crucial for optimizing CNT-based gas sensors.

Human performance monitoring and health protection requires precise monitoring of chemical and biochemical biomarkers. The biomarker detection in physiologically relevant media, such as sweat, saliva, and exhaled breath faces significant challenges ranging from chemical interference to environmental extremity. This presentation will provide an in-depth look on the factors governing in the biomarker sensor development. Specific attention will be given to the bio recognition element (BRE) design, biotic-abiotic interface, surface BRE packing density, and the electronic/electrochemical detection mode to mitigate the challenges in the biomarker sensor development. We will conclude this paper by opening up the discussion on the path towards ultrasensitive and selective electronic/electrochemical biomarker sensor development and its effective operation-relevant test and evaluation.

Simultaneous measurement of skin physiological and physical properties are important for the diagnosis of skin diseases and monitoring of human performance, since it provides more comprehensive understanding on the skin conditions. Current skin analysis devices, however, require each of probes and unique protocols for the measurement of individual skin properties, resulting in inconvenience and increase of measurement uncertainty. This paper presents a pen-type skin analyzing device capable tomeasure three key skin properties at the same time: transepidermal water loss (TEWL), skin conductance, and skin hardness. It uses a single truncated hollow cone (THC) probe integrated with a humidity sensor, paired electrodes, and a load cell for the multimodal assessment of the skin properties. The present device measured TEWL with a sensitivity of 0.0068 (%/s)/(g/m2/h) and a linearity of 99.63%, conductance with a sensitivity of 1.02 µS/µS and a linearity of 99.36%, and hardness with a sensitivity of 0.98 Shore 00/Shore 00 and a linearity of 99.85%, within the appropriate ranges for the human skin. The present pen-type device has a high potential for the skin health diagnosis as well as the human performance monitoring applications.

This paper presents peptide-functionalized carbon nanotube (CNT) field-effect transistors (FETs) aimed to discriminate four different volatile organic compounds (VOCs) (isopropyl alcohol, acetone, isoprene, and toluene) found in breath. Previous CNT FETs for VOC detection have shown detection of explosives or food quality indicators. Sensing human breath gases related to an individual's health and/or performance, however, has not yet been explored by using peptide-based CNT FETs. In addition, previous CNT FETs have required complicated immobilization techniques, such as design of fusion peptides (combination of known peptides with linker residuals), or special chemical treatments for the CNT functionalization. The present, novel CNT FETs are functionalized with 12-mer peptides identified using phage display. The identified peptides have an affinity to CNTs, making them easy to be functionalized without additional conjugate linkers or surface modifications. From VOCs exposure test results, the present CNT FETs, utilizing the specific peptides, successfully showed not only discrimination of the four different breath-related VOCs, but also the advantageous characteristics of being easily functionalized. The proposed CNT FETs have potentials for wearable breath monitoring applications such as personal health diagnosis and real-time human performance assessments.