Volatile Organic Compounds Sensor Research Articles

Bacterial cellulose/polyethylene glycol composite aerogel with incorporated graphene and metal oxides for VOCs detection

It is important to monitor and detect volatile organic compounds (VOCs) for environmental protection, occupational safety and human health. Portable and compact VOC sensing devices with a fast response are needed for real-time monitoring and simple analysis. Using solvent exchange and freeze-drying techniques, an ultralight 3D bacterial cellulose (BC) aerogel is prepared and modified by polyethylene glycol with the functionalization of graphene and metal oxides to detect VOC gases. Unlike commercially available flat VOC sensors, the 3D structure of our VOC sensor with high permeability of BC composite provides superior sensing characteristics for acetone, formaldehyde and ethanol in a wider range of scenarios. The portable BC composite sensor exhibits remarkable sensitivity and selectivity toward VOCs detection. The BC composite with TiO2 has a response time of about 20 s to 1 ppm acetone and can detect as low as 1.43 ppm at room temperature. In addition, BC composites with ZnO are suitable for detecting formaldehyde in indoor air.

A Photovoltaic Self-Powered Volatile Organic Compounds Sensor Based on Asymmetric Geometry 2D MoS2 Diodes

Transition metal dichalcogenides have gained considerable interest for vapour sensing applications due to their large surface-to-volume ratio and high sensitivity. Herein, we demonstrate a new self-powered volatile organic compounds (VOC) sensor based on asymmetric geometry multi-layer molybdenum disulfide (MoS2) diode. The asymmetric contact geometry of the MoS2 diode induces an internal built-in electric field resulting in self-powering via a photovoltaic response. While illuminated by UV-light, the sensor exhibited a high responsivity of ∼60% with a relatively fast response time of ∼10 sec to 200 ppm of acetone, without an external bias voltage. The MoS2 VOC diode sensor is a promising candidate for self-powered, fast, portable, and highly sensitive VOC sensor applications.

Room Temperature Sensing of Volatile Organic Compounds Using Hybrid Layered SnO Mesoflowers and Laser-Induced Graphitic Carbon Devices.

In this work, we demonstrate chemiresistive volatile organic compound (VOC) sensors prepared by drop-cast assembly of layered tin monoxide mesoflowers (SnO-MFs) on additively produced laser-induced graphene-like carbon (LIG). The SnO-MFs were synthesized below 100 °C at ambient pressure and offer a low fabrication energy alternative route to typical furnace-prepared metal-oxide materials. The additive dropcast assembly of room-temperature operating metal oxide active material allows the substitution of LIG for metal current collectors and glass for alumina, reducing the environmental footprint of the sensor. The sensors can detect methanol (150-4000 ppm) at room temperature and humidity (∼18 °C, ∼55% RH), with response and recovery times (150 ppm methanol) of t 90,resp ≈ 50 ± 10 s and t 90,rec ≈ 5 ± 0.5 s, respectively. The sensors demonstrated a limit of detection (170 ± 40 ppm) below 8 h worker safety exposure levels (200 ppm) and stable DC resistance responses ΔR/R = 9 ± 2% to 710 ppm of methanol for over 21 days in ambient laboratory conditions, n = 4. First-principles density functional theory simulations were used to elucidate the interactions of VOC species on the SnO surfaces. LIG-SnO hybrid sensors thus present a resource-efficient route to develop chemiresistive sensors for low-power applications, although with cross-selectivity to other alcohol species.

Operation Temperature Effects on a Microwave Gas Sensor with and without Sensitive Material.

Microwave gas sensors have garnered attention for their high sensitivity and selectivity in the detection of volatile organic compounds (VOCs). However, traditional gas sensors generally rely on sensitive materials that degrade over time and are easily affected by the environment, compromising their stability and accuracy. This study proposes a microwave VOC gas sensor based on the condensation effect. The sensor adopts a novel design without sensitive materials, utilizing the condensation effect to detect acetone gas. The sensor system consists of a microwave sensor and a temperature control device. As the sensor temperature is lowered below the boiling point of acetone, the condensation of acetone gas on the sensor surface is achieved, enabling accurate detection of acetone gas. Experimental results indicate that the accumulated amount of acetone on the sensor surface is positively correlated with its response, with the maximum response of 3000 ppm acetone gas reaching 0.34 dB. Additionally, this study investigated the detection mechanism of the sensor after adding the sensitive material MXene and compared the performance of the sensor at different temperatures (-10 °C, 0 °C, and 60 °C). The results show that at -10 °C the sensor mainly captures acetone through physical adsorption, while at 25 and 60 °C, it primarily responds through chemical adsorption, with a maximum response of 0.29 dB. The VOC sensor based on the condensation effect without sensitive materials not only achieves the same sensitivity as traditional microwave sensors but also demonstrates stronger stability and anti-interference capabilities.

Copper Phthalocyanine for Designing a Highly Selective and Disposable Electrochemical Volatile Organic Compound (VOC) Sensor

Formic acid (FA) is one of the very important organic acids that has been widely used in various industries. The highly corrosive FA can have severe adverse effects on the surrounding environment. Here, we developed an electrochemical sensor that utilizes the material properties of multi‐walled carbon nanotubes (MWCNTs), and copper phthalocyanine (CuPc) for the real‐time detection of FA gas. The response of FA has been compared with the responses of 9 common volatile organic compounds (VOCs). The chronoamperometry (CA) results revealed a high selectivity towards FA by showing an increase in the sensor current by about 25%, in contrast to the decrease of the current in response to the other VOCs. The sensitivity of the CuPc device to FA was calculated to be 38.85 mAM‐1. Material characterization (SEM, EDX, FTIR, Raman, and UV‐vis) also strongly suggests a protonation mechanism caused by the carboxylic acid group, which enhances the electrical conductivity.

Transition-Metal Nanoparticles (Fe, Co, or Ni) Encapsulated in N-Doped Carbon as Catalysts for the Oxygen Reduction Reaction and as Gas Sensors of Volatile Organic Compounds

Transition-Metal Nanoparticles (Fe, Co, or Ni) Encapsulated in N-Doped Carbon as Catalysts for the Oxygen Reduction Reaction and as Gas Sensors of Volatile Organic Compounds

Metal-organic framework modified open-cavity optical fiber Fabry-Pérot interferometer for volatile organic compound detection

Detection of volatile organic compounds (VOCs) is crucial in industrial production, environmental monitoring, and public safety. VOCs sensors need to be intrinsically safe, given the flammability and toxicity of common VOCs. Fiber optic sensors offer a passive and flexible solution for VOCs detection, attracting significant attention from researchers. In this study, ZIF-8, a subset of metal-organic frameworks, is applied to a side-polished silicon wafer, forming an open-cavity optical fiber Fabry-Pérot interferometer (FPI) with a fiber patch cable and a 3D-printed structural part. The sensing performance for prevalent VOCs, including methylbenzene, methanol, and ethanol, is experimentally explored, exhibiting sensitivities of 0.118 p.m./ppm, 0.177 p.m./ppm, and 0.412 p.m./ppm, respectively. Sensitivity differences are analyzed and demonstrated at the molecular level. The proposed technologies offer advantages such as easy fabrication, intrinsic safety, small size, and good selectivity, providing an alternative for VOCs detection in industrial production.

Fabrication of a peptide–AuNP–TiO2 nanocomposite and its application as a VOC sensor

AbstractWe fabricated a volatile organic compound (VOC) sensor with a peptide–Au nanoparticle (AuNP)–TiO2 nanocomposite in which AuNPs were linked with TiO2-coated conductive peptide nanowires. The conductive peptide nanowires were formed between the AuNPs via self-assembly through the complexation of amphiphilic peptides, LESEHEKLKSKHKSKLKEHESEL, and Co(II). Furthermore, TiO2 mineralization on the surface of the peptide nanowires yielded mixed crystals of rutile and anatase, which exhibited highly effective photolytic activity. In particular, the obtained TiO2 exhibited three times greater photodecomposition activity in the unsintered state toward organic matter than did commercially available TiO2. Next, we constructed a VOC sensor by immobilizing peptide–AuNP–TiO2 nanocomposites on a comb electrode. The electrochemical properties of the nanocomposite changed drastically under light irradiation in the presence of VOCs, indicating transport of the VOC-decomposition-generated photoexcited electrons of TiO2 to AuNPs through conductive peptide nanowires, which prevented electron–hole recombination. The obtained sensor exhibited a sensing range of 2–100 ppm for dichloromethane, which was used as a representative VOC. Therefore, nanocomposites made of AuNPs linked with conductive TiO2 nanotubes may be highly effective for TiO2-driven VOC decomposition. Moreover, we believe that this nanocomposite has high sensitivity for sensing VOCs.

Enhanced Colorimetric Detection of Volatile Organic Compounds Using a Dye-Incorporated Photonic Crystal-Based Sensor Array.

Chemoresponsive dyes offer the potential to selectively detect volatile organic compounds (VOCs) unique to certain disease states. Among different VOC sensing techniques, colorimetric sensing offers the advantage of facile recognition. However, it is often challenging to discern the color changes by the naked eye. Here, highly sensitive colorimetric VOC sensor arrays from dye-incorporated colloidal photonic crystals (dye-cPhCs) are reported. cPhCs are scalably fabricated on a 4-inch wafer by spin-coating of silica nanoparticles (NPs) dispersed in a photo-cross-linkable monomer, where the gradient shear flow along the film thickness creates densely-packed square arrays of NPs in the top layers, whereas the bulk is quasi-amorphous with larger periodicities. The broadened reflection peak allows for augmented dye absorption originating from the overlap between the photonic bandgap edge of the cPhC and the dye absorption peak, leading to a more noticeable color change upon exposure to VOCs. The sensor array generates distinct color difference maps for acetaldehyde, acetone, and acetic acid, respectively, without any data amplification. The limit of detection for acetaldehyde, acetone, and acetic acid is 1, 0.1, and 0.02ppm, respectively. Moreover, VOC can be diagonalized by visually intuitive pattern recognition, and principal component analysis at reduced dimensionality is demonstrated.

High-performance and flexible sodium ion-based electrochemical devices toward self-powered wearable volatile organic compounds sensing system

Self-powered wearable electronic systems are considered the ideal solution to realize ubiquitous Internet-of-Things (IoT), personalized healthcare, and point-to-care diagnosis. Here, we demonstrate the integration of a high-performance and ultra-stable sodium ion-based micro-supercapacitor (MSC) and a high-sensitive sensor for self-powered wearable Volatile Organic Compounds (VOC) sensing systems. It is found that a sodium-based solid electrolyte exhibited high ionic conductivity, reaching 2.4 mS cm−1 at 70 °C. Further, the inclusion of TiO2 NPs additive in the solid electrolyte can reduce the crystallinity and expand the electrode/electrolyte interface, which increases about 2.25 times in the capacitance of sodium ion-based MSC. PDMS-encapsulated MSC showed ultra-stability of capacitance retention (approximately 98.8 %) after 50,000 cycles while also achieving a high flexibility of 1000 cycles with a minimal capacitance change. As a proof-of-concept of a self-powered wearable sensor, it is demonstrated that an integrated polymer electrolyte-based VOC sensor powered by a charged-MSC can continuously operate for more than 4000 s (over 1.1 h) in the ethanol/nitrogen gas chamber. Therefore, we believe that our integration of sodium ion-based electrochemical storage and VOC sensor capabilities will pave a way to revolutionize the approach of wearable electronic applications toward self-powered systems.

The O-Defective g-ZnO Sensor for VOC Gases: The Adsorption-Desorption, Electronic, and Sensitivity Properties.

Adsorption-desorption performance, electronic properties, and sensitivity of O-defective g-ZnO (ODZO) gas sensors for volatile organic compounds (VOCs) are calculated using density functional theory and nonequilibrium Green's formalism. The VOCs are CH2O, CH4, C2H4O, CH4O, and C2H6. The intrinsic g-ZnO (IZO) and ODZO exhibit strong adsorption capabilities for C2H4O and CH4O. The IZO (0.118 e) and ODZO (0.059 e), which act as electron donors, exhibit the highest charge transfer to CH2O, indicating a strong interaction. The VOCs adsorption on the IZO and ODZO systems maintain nonmagnetic semiconductor characteristics. Additionally, the introduction of an O-defect causes the adsorption energy and charge transfer amount of ODZO to show an overall decrease, indicating better desorption ability. Notably, the sensitivity results show that the ODZO gas sensors exhibit high sensitivity to CH2O (39.3%), C2H4O (29.0%), and CH4O (19.6%) at a voltage of 2.6 V, consistent with the adsorption-desorption performance and electronic properties.

Innovative Wearable Sweat Sensor Array for Real-Time Volatile Organic Compound Detection in Noninvasive Diabetes Monitoring.

Wearable sweat sensors are reshaping healthcare monitoring, providing real-time data on hydration and electrolyte levels with user-friendly, noninvasive devices. This paper introduces a highly portable two-channel microfluidic device for simultaneous sweat sampling and the real-time detection of volatile organic compound (VOC) biomarkers. This innovative wearable microfluidic system is tailored for monitoring diabetes through the continuous and noninvasive tracking of acetone and ammonia VOCs, and it seamlessly integrates with smartphones for easy data management. The core of this system lies in the utilization of carbon polymer dots (CPDs) and carbon dots (CDs) derived from monomers such as catechol, resorcinol, o-phenylenediamine, urea, and citric acid. These dots are seamlessly integrated into hydrogels made from gelatin and poly(vinyl alcohol), resulting in an advanced solid-state fluorometric sensor coating on a cellulose paper substrate. These sensors exhibit exceptional performance, offering linear detection ranges of 0.05-0.15 ppm for acetone and 0.25-0.37 ppm for ammonia, with notably low detection limits of 0.01 and 0.08 ppm, respectively. Rigorous optimization of operational parameters, encompassing the temperature, sample volume, and assay time, has been undertaken to maximize device performance. Furthermore, these sensors demonstrate impressive selectivity, effectively discerning between biologically similar substances and other potential compounds commonly present in sweat. As this field matures, the prospect of cost-effective, continuous, personalized health monitoring through wearable VOC sensors holds significant potential for overcoming barriers to comprehensive medical care in underserved regions. This highlights the transformative capacity of wearable VOC sweat sensing in ensuring equitable access to advanced healthcare diagnostics, particularly in remote or geographically isolated areas.

Computational study of pure and Lithium decorated bismuthene for detection of VOCs

To meet the crucial need for VOC detection, we propose a nanosensor based on bismuthene, employing density functional theory calculations. This nano-sensor aims to detect specific volatile organic compounds (VOCs) present in human breath, including acetone (C3H6O), ethanol (C2H6O), methanol (CH3OH), formaldehyde (CH2O), and toluene (C7H8), which serve as potential biomarkers for identifying physiological disorders. Additionally, we investigate how carbon dioxide (CO2) and water vapor (H2O), common in exhaled breath, interact with bismuthene as likely interfering species. Notably, toluene exhibited higher adsorption energy with pure and Li-decorated bismuthene. The favorable adsorption and desorption performance of bismuthene with molecules such as formaldehyde, methanol, and acetone at near-ambient temperatures suggest its suitability as a VOCs sensor with simple operational conditions. The density of states, charge analysis, adsorption properties, sensitivity, conductivity, selectivity, and recovery time have been calculated and discussed. Our results highlight Bismuthene’s potential as an efficient nano-sensor for detecting VOCs associated with pulmonary malignancies.

Facile Preparation of TiO2NTs/Au@MOF Nanocomposites for High-Sensitivity SERS Sensing of Gaseous VOC.

Surface-enhanced Raman spectroscopy (SERS) is a promising and highly sensitive molecular fingerprint detection technology. However, the development of SERS nanocomposites that are label-free, highly sensitive, selective, stable, and reusable for gaseous volatile organic compounds (VOCs) detection remains a challenge. Here, we report a novel TiO2NTs/AuNPs@ZIF-8 nanocomposite for the ultrasensitive SERS detection of VOCs. The three-dimensional TiO2 nanotube structure with a large specific surface area provides abundant sites for the loading of Au NPs, which possess excellent local surface plasmon resonance (LSPR) effects, further leading to the formation of a large number of SERS active hotspots. The externally wrapped porous MOF structure adsorbs more gaseous VOC molecules onto the noble metal surface. Under the synergistic mechanism of physical and chemical enhancement, a better SERS enhancement effect can be achieved. By optimizing experimental conditions, the SERS detection limit for acetophenone, a common exhaled VOC, is as low as 10-11 M. And the relative standard deviation of SERS signal intensity from different points on the same nanocomposite surface is 4.7%. The acetophenone gas achieves a 1 min response and the signal reaches stability in 4 min. Under UV irradiation, the surface-adsorbed acetophenone can be completely degraded within 40 min. The experimental results demonstrate that this nanocomposite has good detection sensitivity, repeatability, selectivity, response speed, and reusability, making it a promising sensor for gaseous VOCs.

Advancements in miniaturized infrared spectroscopic-based volatile organic compound sensors: A systematic review

The global trends of urbanization and industrialization have given rise to critical environmental and air pollution issues that often receive insufficient attention. Among the myriad pollution sources, volatile organic compounds (VOCs) stand out as a primary cluster, posing a significant threat to human society. Addressing VOCs emissions requires an effective mitigation action plan, placing technological development, especially in detection, at the forefront. Photonic sensing technologies rooted in the infrared (IR) light and matter interaction mechanism offer nondestructive, fast-response, sensitive, and selective chemical measurements, making them a promising solution for VOC detection. Recent strides in nanofabrication processes have facilitated the development of miniaturized photonic devices and thus sparked growing interest in the creation of low-cost, highly selective, sensitive, and fast-response IR optical sensors for VOC detection. This review work thus serves a timely need to provide the community a comprehensive understanding of the state of the art in this field and illuminate the path forward in addressing the pressing issue of VOC pollution.

ZIF-8-Based Surface Plasmon Resonance and Fabry-Pérot Sensors for Volatile Organic Compounds.

This work explores the use of ZIF-8, a metal-organic framework (MOF) material, for its use in the optical detection of volatile organic compounds (VOCs) in Fabry-Pérot and surface plasmon resonance (SPR)-based sensors. The experiments have been carried out with ethanol (EtOH) and show response times as low as 30 s under VOC-saturated atmospheres, and the estimated limit of detection is below 4000 ppm for both sensor types. The selectivity towards other VOCs is relatively poor, although the dynamics of adsorption/desorption differ for each VOC and could be used for selectivity purposes. Furthermore, the hydrophobicity of ZIF-8 has been confirmed and the fabricated sensors are insensitive to this compound, which is a very attractive result for its practical use in gas sensing devices.

Orchestrated Octuple C−H Activation: A Bottom‐Up Topology Engineering Approach toward Stimuli‐Responsive Double‐Heptagon‐Embedded Wavy Polycyclic Heteroaromatics

AbstractCuriosity‐driven innovations on the design and synthesis of nonplanar polycyclic aromatic/heteroaromatic compounds with new molecular topologies unfold exciting opportunities for harnessing their intriguing supramolecular properties and thereby the development of novel functional organic materials. This work presents such an innovative synthetic concept of a bottom‐up molecular topology engineering through a unique orchestrated octuple C−H activation reaction, toward the rapid synthesis of a novel class of double heptagon‐incorporated nitrogen‐doped laterally‐fused polycyclic compounds with rarely reported wavy structural configuration. The profound impact of the molecular wavy structures of these compounds on their properties is manifested by weak and tunable solid‐state intermolecular interactions controlling the electronic properties of the materials, leading to reversibly switchable fluorochromism in the solid state and thin films with mechanical force and solvent vapors as external stimuli, thereby indicating their potential applicability in rewritable fluorescent optical recording media, security papers, mechanosensors, volatile organic compound (VOC) sensors etc.

Orchestrated Octuple C-H Activation: A Bottom-Up Topology Engineering Approach toward Stimuli-Responsive Double-Heptagon-Embedded Wavy Polycyclic Heteroaromatics.

Curiosity-driven innovations on the design and synthesis of nonplanar polycyclic aromatic/heteroaromatic compounds with new molecular topologies unfold exciting opportunities for harnessing their intriguing supramolecular properties and thereby the development of novel functional organic materials. This work presents such an innovative synthetic concept of a bottom-up molecular topology engineering through a unique orchestrated octuple C-H activation reaction, toward the rapid synthesis of a novel class of double heptagon-incorporated nitrogen-doped laterally-fused polycyclic compounds with rarely reported wavy structural configuration. The profound impact of the molecular wavy structures of these compounds on their properties is manifested by weak and tunable solid-state intermolecular interactions controlling the electronic properties of the materials, leading to reversibly switchable fluorochromism in the solid state and thin films with mechanical force and solvent vapors as external stimuli, thereby indicating their potential applicability in rewritable fluorescent optical recording media, security papers, mechanosensors, volatile organic compound (VOC) sensors etc.

Early Detection of Ventilator-associated Pneumonia From Exhaled Breath in Intensive Care Unit Patients.

Evaluate associations between volatile organic compounds (VOCs) in heat and moisture exchange (HME) filters and the presence of ventilator-associated pneumonia (VAP). Clinical diagnostic criteria for VAP have poor interobserver reliability, and cultures are slow to result. Exhaled breath contains VOCs related to gram-negative bacterial proliferation, the most identified organisms in VAP. We hypothesized that exhaled VOCs on HME filters can predict nascent VAP in mechanically ventilated intensive care unit patients. Gas chromatography-mass spectrometry was used to analyze 111 HME filters from 12 intubated patients who developed VAP. Identities and relative amounts of VOCs were associated with dates of clinical suspicion and culture confirmation of VAP. Matched pairs t tests were performed to compare VOC abundances in HME filters collected within 3 days pre and postclinical suspicion of VAP (pneumonia days), versus outside of these days (non-pneumonia days). A receiver operating characteristic curve was generated to determine the diagnostic potential of VOCs. Carbon disulfide, associated with the proliferation of certain gram-negative bacteria, was found in samples collected during pneumonia days for 11 of 12 patients. Carbon disulfide levels were significantly greater ( P = 0.0163) for filters on pneumonia days. The Area Under the Curve of the Reciever Operating Characteristic curve (AUC ROC) for carbon disulfide was 0.649 (95% CI: 0.419-0.88). Carbon disulfide associated with gram-negative VAP can be identified on HME filters up to 3 days before the initial clinical suspicion, and approximately a week before culture confirmation. This suggests VOC sensors may have potential as an adjunctive method for early detection of VAP.

Engineering luminescent quantum dots through laser ablation of samarium oxide (Sm2O3): A novel approach for enhanced fiber optic gas sensing

Underexplored Sm2O3, with tunable redox and high-surface nanostructures, emerges as a promising volatile organic compounds (VOCs) sensor material for next-gen applications. This study presents the successful synthesis of novel Sm2O3 luminescent quantum dots using a unique pulsed laser ablation technique. Material characterization by FESEM, XRD, EDAX, and HRTEM confirmed the formation of cubic polycrystalline quantum dots. The optical properties were studied by UV-Vis absorption and PL spectroscopy. These quantum dots were then employed in clad-modified fiber optic gas sensors operating at room temperature. Sensor response towards various VOCs, including acetone, ethanol, methanol, and ammonia, were evaluated. Ethanol displayed remarkable sensitivity and selectivity among the other, with a response of 104 ×103 Counts/kPa at 25 °C for 500 ppm. Rapid response and recovery times of 48 and 55 seconds, respectively, further highlights the sensor’s performance. These results establish Sm2O3 quantum dots as a promising and highly effective material for ethanol sensing.