Fiber-optic multi-sensor array for detection of low concentration volatile organic compounds

An Overview of Artificial Olfaction Systems with a Focus on Surface Plasmon Resonance for the Analysis of Volatile Organic Compounds

The last three decades have witnessed an increasing demand for novel analytical tools for the analysis of gases including odorants and volatile organic compounds (VOCs) in various domains. Traditional techniques such as gas chromatography coupled with mass spectrometry, although very efficient, present several drawbacks. Such a context has incited the research and industrial communities to work on the development of alternative technologies such as artificial olfaction systems, including gas sensors, olfactory biosensors and electronic noses (eNs). A wide variety of these systems have been designed using chemiresistive, electrochemical, acoustic or optical transducers. Among optical transduction systems, surface plasmon resonance (SPR) has been extensively studied thanks to its attractive features (high sensitivity, label free, real-time measurements). In this paper, we present an overview of the advances in the development of artificial olfaction systems with a focus on their development based on propagating SPR with different coupling configurations, including prism coupler, wave guide, and grating.

Trends in the Design of Intensity-Based Optical Fiber Biosensors (2010-2020)

There exists an increasing interest in monitoring low concentrations of biochemical species, as they allow the early-stage detection of illnesses or the monitoring of the environment quality. Thus, both companies and research groups are focused on the development of accurate, fast and highly sensitive biosensors. Optical fiber sensors have been widely employed for these purposes because they provide several advantages for their use in point-of-care and real-time applications. In particular, this review is focused on optical fiber biosensors based on luminescence and absorption. Apart from the key parameters that determine the performance of a sensor (limit of detection, sensibility, cross-sensibility, etc.), other features are analyzed, such as the optical fiber dimensions, the sensing set ups and the fiber functionalization. The aim of this review is to have a comprehensive insight of the different aspects that must be taken into account when working with this kind of sensors.

Geometrical, vibrational and physical properties of polyvinyl chloride nanocomposites: Molecular modeling approach

B3LYP/6-31G([Formula: see text], [Formula: see text]) quantum mechanical calculations were conducted to study polyvinyl chloride (PVC) and PVC with metal oxides (ZnO and CuO). Accordingly, model molecules for PVC; PVC/[Formula: see text]ZnO; PVC/[Formula: see text]CuO and PVC/[Formula: see text]ZnO/[Formula: see text]CuO, where [Formula: see text] and [Formula: see text], 2 and 3, were proposed. The calculated results of total dipole moment (TDM), HOMO–LUMO energy band gap, and molecular electrostatic potentials (ESPs) indicated that the conductivity of PVC is increased and its surface became more reactive due to interaction with metal oxides. The effect of hydration on PVC was also studied at the same level of theory in order to assess the effect of up to 23 water molecules on PVC. The TDM value of PVC is increased but HOMO/LUMO band gap energy value is decreased because of hydration. Moreover, the results of calculated ESP indicated that the reactivity in the presence of water molecules increased, which could indicate possible degradation of PVC. Additionally, some geometrical parameters were studied. Furthermore, the scaled infrared spectrum (IR) for PVC was also calculated at B3LYP/6-31G ([Formula: see text], [Formula: see text]) and indicated that there are two bands at 2990[Formula: see text]cm[Formula: see text] and 2975[Formula: see text]cm[Formula: see text] in comparison with Fourier transform infrared spectrum (FTIR).

Pd-Catalyzed Reaction-Producing Intermediate S on a Pd/In2O3 Surface: A Key To Achieve the Enhanced CS2-Sensing Performances

Although chemiresistive gas sensors, based on metal-oxide semiconductors, have exhibited particular promise for the monitoring of air pollution, they are often limited because of poor selectivity. In that case, to overcome this issue, according to the essence of the gas-sensing process, the method of reforming the surface reaction path on the surface of the sensing materials was used. Here, we report that Pd nanoparticles supported over the In₂O₃ composites, featured with a yolk-shell structure, enable the trace detection of carbon disulfide (CS₂) gas molecules, which are immensely dangerous to humans and animals. Moreover, the prominent enhancement of the gas response and the ultraselective CS₂-sensing characteristic were acquired in comparison with pristine In₂O₃ sensors. Significantly, density functional theory calculations revealed that the Pd supported on In₂O₃ greatly facilitates the adsorption capacity to CS₂, and the intermediate S, produced by Pd-catalyzed desulfurization reaction, on the Pd/In₂O₃ surface during the sensing process is a key to achieving a high CS₂ gas response as well as ultraselectivity, which is well in agreement with the X-ray photoelectron spectroscopy analysis results. On the basis of these results, a new sensing mechanism model for the CS₂-sensing process was put forward.

Advanced Micro- and Nano-Gas Sensor Technology: A Review

Micro- and nano-sensors lie at the heart of critical innovation in fields ranging from medical to environmental sciences. In recent years, there has been a significant improvement in sensor design along with the advances in micro- and nano-fabrication technology and the use of newly designed materials, leading to the development of high-performance gas sensors. Advanced micro- and nano-fabrication technology enables miniaturization of these sensors into micro-sized gas sensor arrays while maintaining the sensing performance. These capabilities facilitate the development of miniaturized integrated gas sensor arrays that enhance both sensor sensitivity and selectivity towards various analytes. In the past, several micro- and nano-gas sensors have been proposed and investigated where each type of sensor exhibits various advantages and limitations in sensing resolution, operating power, response, and recovery time. This paper presents an overview of the recent progress made in a wide range of gas-sensing technology. The sensing functionalizing materials, the advanced micro-machining fabrication methods, as well as their constraints on the sensor design, are discussed. The sensors' working mechanisms and their structures and configurations are reviewed. Finally, the future development outlook and the potential applications made feasible by each category of the sensors are discussed.

Comparison between Different Structures of Suspended-Core Microstructured Optical Fibers for Volatiles Sensing

In this paper, different core structures of microstructured optical fibers (MOFs) for low-finesse Fabry⁻Pérot (FP) sensors are experimentally compared to get the highest sensitivity. These devices are designed for volatile organic compounds (VOCs) measurements. Indium tin oxide (ITO) thin films were deposited by sputtering on the MOFs and different optical fast Fourier transform (FFT) phase responses from the FP were measured for saturated atmospheres of ethanol. It has been demonstrated that the sensitivities of the developed sensors depend strongly on the geometry and the dimensions of the MOF-cores. The sensors show recovery times shorter than 100 s and the baselines are fully recovered after every exposure to ethanol vapors.

A Portable Array-Type Optical Fiber Sensing Instrument for Real-Time Gas Detection

A novel optical fiber array-type of sensing instrument with temperature compensation for real-time detection was developed to measure oxygen, carbon dioxide, and ammonia simultaneously. The proposed instrument is multi-sensing array integrated with real-time measurement module for portable applications. The sensing optical fibers were etched and polished before coating to increase sensitivities. The ammonia and temperature sensors were each composed of a dye-coated single-mode fiber with constructing a fiber Bragg grating and a long-period filter grating for detecting light intensity. Both carbon dioxide and oxygen sensing structures use multimode fibers where 1-hydroxy-3,6,8-pyrene trisulfonic acid trisodium salt is coated for carbon dioxide sensing and Tris(2,2′-bipyridyl) dichlororuthenium(II) hexahydrate and Tris(bipyridine)ruthenium(II) chloride are coated for oxygen sensing. Gas-induced fluorescent light intensity variation was applied to detect gas concentration. The portable gas sensing array was set up by integrating with photo-electronic measurement modules and a human-machine interface to detect gases in real time. The measured data have been processed using piecewise-linear method. The sensitivity of the oxygen sensor were 1.54%/V and 9.62%/V for concentrations less than 1.5% and for concentrations between 1.5% and 6%, respectively. The sensitivity of the carbon dioxide sensor were 8.33%/V and 9.62%/V for concentrations less than 2% and for concentrations between 2% and 5%, respectively. For the ammonia sensor, the sensitivity was 27.78%/V, while ammonia concentration was less than 2%.

Highly Sensitive Temperature Sensors Based on Fiber-Optic PWM and Capacitance Variation Using Thermochromic Sensing Membrane

In this paper, we propose a temperature/thermal sensor that contains a Rhodamine-B sensing membrane. We applied two different sensing methods, namely, fiber-optic pulse width modulation (PWM) and an interdigitated capacitor (IDC)-based temperature sensor to measure the temperature from 5 °C to 100 °C. To the best of our knowledge, the fiber-optic PWM-based temperature sensor is reported for the first time in this study. The proposed fiber-optic PWM temperature sensor has good sensing ability; its sensitivity is ~3.733 mV/°C. The designed temperature-sensing system offers stable sensing responses over a wide dynamic range, good reproducibility properties with a relative standard deviation (RSD) of ~0.021, and the capacity for a linear sensing response with a correlation coefficient of R² ≈ 0.992 over a wide sensing range. In our study, we also developed an IDC temperature sensor that is based on the capacitance variation principle as the IDC sensing element is heated. We compared the performance of the proposed temperature-sensing systems with different fiber-optic temperature sensors (which are based on the fiber-optic wavelength shift method, the long grating fiber-optic Sagnac loop, and probe type fiber-optics) in terms of sensitivity, dynamic range, and linearity. We observed that the proposed sensing systems have better sensing performance than the above-mentioned sensing system.

A High Sensitivity IDC-Electronic Tongue Using Dielectric/Sensing Membranes with Solvatochromic Dyes

In this paper, an electronic tongue/taste sensor array containing different interdigitated capacitor (IDC) sensing elements to detect different types of tastes, such as sweetness (glucose), saltiness (NaCl), sourness (HCl), bitterness (quinine-HCl), and umami (monosodium glutamate) is proposed. We present for the first time an IDC electronic tongue using sensing membranes containing solvatochromic dyes. The proposed highly sensitive (30.64 mV/decade sensitivity) IDC electronic tongue has fast response and recovery times of about 6 s and 5 s, respectively, with extremely stable responses, and is capable of linear sensing performance (R² ≈ 0.985 correlation coefficient) over the wide dynamic range of 1 µM to 1 M. The designed IDC electronic tongue offers excellent reproducibility, with a relative standard deviation (RSD) of about 0.029. The proposed device was found to have better sensing performance than potentiometric-, cascoded compatible lateral bipolar transistor (C-CLBT)-, Electronic Tongue (SA402)-, and fiber-optic-based taste sensing systems in what concerns dynamic range width, response time, sensitivity, and linearity. Finally, we applied principal component analysis (PCA) to distinguish between various kinds of taste in mixed taste compounds.

Fast, Highly-Sensitive, and Wide-Dynamic-Range Interdigitated Capacitor Glucose Biosensor Using Solvatochromic Dye-Containing Sensing Membrane

In this paper, we proposed an interdigitated capacitor (IDC)-based glucose biosensor to measure different concentrations of glucose from 1 μM to 1 M. We studied four different types of solvatochromic dyes: Auramine O, Nile red, Rhodamine B, and Reichardt's dye (R-dye). These dyes were individually incorporated into a polymer [polyvinyl chloride (PVC)] and N,N-Dimethylacetamide (DMAC) solution to make the respective dielectric/sensing materials. To the best of our knowledge, we report for the first time an IDC glucose biosensing system utilizing a solvatochromic-dye-containing sensing membrane. These four dielectric or sensing materials were individually placed into the interdigitated electrode (IDE) by spin coating to make four IDC glucose biosensing elements. The proposed IDC glucose biosensor has a high sensing ability over a wide dynamic range and its sensitivity was about 23.32 mV/decade. It also has fast response and recovery times of approximately 7 s and 5 s, respectively, excellent reproducibility with a standard deviation of approximately 0.023, highly stable sensing performance, and real-time monitoring capabilities. The proposed IDC glucose biosensor was compared with an IDC, potentiometric, FET, and fiber-optic glucose sensor with respect to response time, dynamic range width, sensitivity, and linearity. We observed that the designed IDC glucose biosensor offered excellent performance.

Sensor Array Design for Complex Sensing Tasks

Chemical detection in complex environments presents numerous challenges for successful implementation. Arrays of sensors are often implemented for complex chemical sensing tasks, but systematic understanding of how individual sensor response characteristics contribute overall detection system performance remains elusive, with generalized strategies for design and optimization of these arrays rarely reported and even less commonly adopted by practitioners. This review focuses on the literature of nonspecific sensor array design and optimization strategies as well as related work that may inform future efforts in complex sensing with arrays.

Highly Sensitive Multi-Channel IDC Sensor Array for Low Concentration Taste Detection

In this study, we designed and developed an interdigitated capacitor (IDC)-based taste sensor array to detect different taste substances. The designed taste sensing array has four IDC sensing elements. The four IDC taste sensing elements of the array are fabricated by incorporating four different types of lipids into the polymer, dioctyl phenylphosphonate (DOPP) and tetrahydrofuran (THF) to make the respective dielectric materials that are individually placed onto an interdigitated electrode (IDE) via spin coating. When the dielectric material of an IDC sensing element comes into contact with a taste substance, its dielectric properties change with the capacitance of the IDC sensing element; this, in turn, changes the voltage across the IDC, as well as the output voltage of each channel of the system. In order to assess the effectiveness of the sensing system, four taste substances, namely sourness (HCl), saltiness (NaCl), sweetness (glucose) and bitterness (quinine-HCl), were tested. The IDC taste sensor array had rapid response and recovery times of about 12.9 s and 13.39 s, respectively, with highly stable response properties. The response property of the proposed IDC taste sensor array was linear, and its correlation coefficient R2 was about 0.9958 over the dynamic range of the taste sensor array as the taste substance concentration was varied from 1 μM to 1 M. The proposed IDC taste sensor array has several other advantages, such as real-time monitoring capabilities, high sensitivity 45.78 mV/decade, good reproducibility with a standard deviation of about 0.029 and compactness, and the circuitry is based on readily available and inexpensive electronic components. The proposed IDC taste sensor array was compared with the potentiometric taste sensor with respect to sensitivity, dynamic range width, linearity and response time. We found that the proposed IDC sensor array has better performance. Finally, principal component analysis (PCA) was applied to discriminate different types of taste of the mixed taste substances.

A high sensitivity and wide dynamic range fiber-optic sensor for low-concentration VOC gas detection

In this paper, we propose a volatile organic compound (VOC) gas sensing system with high sensitivity and a wide dynamic range that is based on the principle of the heterodyne frequency modulation method. According to this method, the time period of the sensing signal shift when Nile Red containing a VOC-sensitive membrane of a fiber-optic sensing element comes into contact with a VOC. This sensing membrane produces strong, fast and reversible signals when exposed to VOC gases. The response and recovery times of the proposed sensing system were less than 35 s, and good reproducibility and accuracy were obtained.

Response characterization of a fiber optic sensor array with dye-coated planar waveguide for detection of volatile organic compounds

We have developed a multi-array side-polished optical-fiber gas sensor for the detection of volatile organic compound (VOC) gases. The side-polished optical-fiber coupled with a polymer planar waveguide (PWG) provides high sensitivity to alterations in refractive index. The PWG was fabricated by coating a solvatochromic dye with poly(vinylpyrrolidone). To confirm the effectiveness of the sensor, five different sensing membranes were fabricated by coating the side-polished optical-fiber using the solvatochromic dyes Reinhardt's dye, Nile red, 4-aminophthalimide, 4-amino-N-methylphthalimide, and 4-(dimethylamino)cinnamaldehyde, which have different polarities that cause changes in the effective refractive index of the sensing membrane owing to evanescent field coupling. The fabricated gas detection system was tested with five types of VOC gases, namely acetic acid, benzene, dimethylamine, ethanol, and toluene at concentrations of 1, 2,…,10 ppb. Second-regression and principal component analyses showed that the response properties of the proposed VOC gas sensor were linearly shifted bathochromically, and each gas showed different response characteristics.