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This Special Issue based on 15 articles/reviews focusses on low-cost sensor technology, gas sensors, chemical sensors, advanced active materials, sensing nanomaterials, sensor nodes, hardware innovation, data communication, system integration, sensor testing, functional characterization, sensor modeling, processing and correction algorithms, new sensing solutions, advanced proof of concepts, and chemical detection applications. Proper calibration techniques of chemical sensors have been explored, both in the laboratory and in field applications. Sensing solutions have been applied in the context of biochemical detection and gas monitoring.

The gas sensitivity of the W defect in WS2 (VW/WS2) to five toxic gases—HCHO, CH4, CH3HO, CH3OH, and CH3CH3—has been examined in this article. These five gases were adsorbed on the VW/WS2 surface, and the band, density of state (DOS), charge density difference (CDD), work function (W), current–voltage (I–V) characteristic, and sensitivity of adsorption systems were determined. Interestingly, for HCHO-VW/WS2, the energy level contribution of HCHO is closer to the Fermi level, the charge transfer (B) is the largest (0.104 e), the increase in W is more obvious than other adsorption systems, the slope of the I–V characteristic changes more obviously, and the calculated sensitivity is the highest. To sum up, VW/WS2 is more sensitive to HCHO. In conclusion, VW/WS2 has a great deal of promise for producing HCHO chemical sensors due to its high sensitivity and selectivity for HCHO, which can aid in the precise and efficient detection of toxic gases.

Dendrimers are a special type of ball-shaped hyperbranched polymers consisting of branched monomers organized stepwise around a multifunctional core. They possess many reactive functions, and they are easily accessible as they are located on the surface of the dendrimers. By modifying their terminal functions, it is possible to change the specificities of dendrimers to give them the desired properties. Dendrimers have been used as catalysts, in diverse fields of nanomedicine, and for the elaboration or modification of materials. The internal structure of dendrimers should be carefully chosen depending on the sought-after properties. Poly(phosphorhydrazone) (PPH) dendrimers possess a relatively rigid and hydrophobic internal structure and an easily functionalized surface, which make them appealing in the field of materials. Indeed, they can be used as a matrix, as glue for stabilizing multilayers, or as multifunctional tools. This review describes the use of PPH dendrimers and dendrons (dendritic wedges) for elaborating sensitive chemical, electrochemical, and biological sensors.

Driven by technological advances from Industry 4.0, Healthcare 4.0 synthesizes medical sensors, artificial intelligence (AI), big data, the Internet of things (IoT), machine learning, and augmented reality (AR) to transform the healthcare sector. Healthcare 4.0 creates a smart health network by connecting patients, medical devices, hospitals, clinics, medical suppliers, and other healthcare-related components. Body chemical sensor and biosensor networks (BSNs) provide the necessary platform for Healthcare 4.0 to collect various medical data from patients. BSN is the foundation of Healthcare 4.0 in raw data detection and information collecting. This paper proposes a BSN architecture with chemical sensors and biosensors to detect and communicate physiological measurements of human bodies. These measurement data help healthcare professionals to monitor patient vital signs and other medical conditions. The collected data facilitates disease diagnosis and injury detection at an early stage. Our work further formulates the problem of sensor deployment in BSNs as a mathematical model. This model includes parameter and constraint sets to describe patient body characteristics, BSN sensor features, as well as biomedical readout requirements. The proposed model’s performance is evaluated by multiple sets of simulations on different parts of the human body. Simulations are designed to represent typical BSN applications in Healthcare 4.0. Simulation results demonstrate the impact of various biofactors and measurement time on sensor selections and readout performance.

The paper presents principle of operation and design of the most popular chemical sensors for measurement of volatile organic compounds (VOCs) in outdoor and indoor air. It describes the sensors for evaluation of explosion risk including pellistors and IR-absorption sensors as well as the sensors for detection of toxic compounds such as electrochemical (amperometric), photoionization and semiconductor with solid electrolyte ones. Commercially available sensors for detection of VOCs and their metrological parameters—measurement range, limit of detection, measurement resolution, sensitivity and response time—were presented. Moreover, development trends and prospects of improvement of the metrological parameters of these sensors were highlighted.

A heptagonal cladding (HC) with the rotated-hexacore (RH) in photonic crystal fiber (H-PCF) has been made for the field of chemical sensing in the terahertz (THz) area. There are five layers of circular air holes (CAH) in the heptagonal cladding region and two layers of rotated-hexa of CAH in the area of the core that have been second hand to enterprise this PCF. This suggested H-PCF, a full-vectorial finite element method (FEM) and perfectly matched layers (PML) boundary condition has been utilized based on a software instrument. After simulation results, the proposed sensor displays the relative sensitivity (RS) 68.48%, 69.20%, 66.78% and the confinement losses (CL) are 2.13 × 10 −09  dB/m, 1.92 × 10 −09  dB/m and 2.70 × 10 −06  dB/m for focused analytics Ethanol ( n  = 1.354), Benzene ( n  = 1.366) and Water ( n  = 1.330) independently at 1 THz frequency regime. We have also discussed total power fraction, effective mode index, and effective area elaborately here. However, our proposed H-PCF is suitable for the user such as in chemical sensors as well as in many diverse industrial and medical areas.

Two low-cost optical–chemical sensors based on plastic optical fibers (POFs) and molecularly imprinted polymers (MIPs) are developed and tested for the detection of 4-chloro-2-methylphenoxyacetic acid (MCPA), a herbicide of great interest in environmental monitoring. The first sensor is based on an optical splitter composed of two modified POFs coupled with an MIP for measuring MCPA. The second type of sensor is based on a surface plasmon resonance (SPR) D-shaped POF platform combined with the same MIP receptor for MCPA. The two proposed polymer-based sensors, exploiting different optical phenomena, were tested using similar equipment, consisting of white light sources and spectrometers. The experimental results show that both MCPA sensors present high selectivity for the target analyte and similar performances in terms of detection limits (LODs) of 3 nM and detection ranges (between 3 nM and 500 nM) by exploiting the MIP’s sites with a similar affinity constant. The polymer-based sensors exhibited better performances than those achieved by the electrochemical technique combined with the same MIP presented in the literature. Then, tests performed on real samples demonstrated good recovery values (between 82% and 116%), assessing the applicability of both sensors in real-world scenarios. Moreover, the POF-MIP splitter sensor configuration can be fabricated without expensive fabrication steps, such as spinning and sputtering processes.

In this paper, we design and optimize a single-mode photonic crystal (PhC) nanobeam-grating (NBG) structure with antisymmetric quarter-elliptical walls geometry based on the computational finite element method (FEM). This structure is capable of providing a wide bandwidth spectrum for chemical sensing (ChS) operation due to the 2∆λ ≈ 110 nm wide bandgap (with a Bragg wavelength center of λ B ≈ 1550 nm) and filtering out the undesired optical modes. Due to the ChS mode intensification (fundamental mode TE 1 wavelength λ = 1550 nm) with a high quality (Q) factor Q = 3.565 × 10 3 and a very small modal volume (MVol) V mode  = 0.0012(λ res /n Si ) 3 in the cavity area as well as confinement of the evanescent wave mode (EWM) in the air grating near the cavity (where chemical analyte, ChAn, is placed) supporting a very high confinement factor (CFac), Γ ≈ 0.45, the single-mode PhC nanobeam resonator offers a very good platform for ChS operation with very low light dissipation. The proposed nanobeam photonic resonator structure can analyze a very small surface analyte, 0.01199 µm 2 of ChAn such as ethanol (C 2 H 5 OH) and water (H 2 O) with extremely high sensitivities S Ethanol ≈ 1554.22 nm/RIU and S Water ≈ 1549.49 nm/RIU, respectively. The high sensitivity S and high Q/V mode ratio, the capability of Label-Free sensing operation as well as being ultra-compact, indicate that the single-mode nanobeam structure as a passive photonic structure is a very practical candidate in the Lab-on-a-Chip (LOC) chemical sensor systems.

Fiber-type electronics is a crucial field for realizing wearable electronic devices with a wide range of sensing applications. In this paper, we begin by discussing the fabrication of fibers from conjugated polymers. We then explore the utilization of these fibers in the development of field-effect and electrochemical transistors. Finally, we investigate the diverse applications of these fiber-type transistors, encompassing chemical and physical sensors. Our paper aims to offer a comprehensive understanding of the use of conjugated polymers in fiber-type transistor-based sensors.

Laser-induced graphene (LIG) has emerged as a promising electrode material for electrochemical point-of-care diagnostics. LIG offers a large specific surface area and excellent electron transfer at low-cost in a binder-free and rapid fabrication process that lends itself well to mass production outside of the cleanroom. Various LIG micromorphologies can be generated when altering the energy input parameters, and it was investigated here which impact this has on their electroanalytical characteristics and performance. Energy input is well controlled by the laser power, scribing speed, and laser pulse density. Once the threshold of required energy input is reached a broad spectrum of conditions leads to LIG with micromorphologies ranging from delicate irregular brush structures obtained at fast, high energy input, to smoother and more wall like albeit still porous materials. Only a fraction of these LIG structures provided high conductance which is required for appropriate electroanalytical performance. Here, it was found that low, frequent energy input provided the best electroanalytical material, i.e., low levels of power and speed in combination with high spatial pulse density. For example, the sensitivity for the reduction of K 3 [Fe(CN) 6 ] was increased almost 2-fold by changing fabrication parameters from 60% power and 100% speed to 1% power and 10% speed. These general findings can be translated to any LIG fabrication process independent of devices used. The simple fabrication process of LIG electrodes, their good electroanalytical performance as demonstrated here with a variety of (bio)analytically relevant molecules including ascorbic acid, dopamine, uric acid, p-nitrophenol, and paracetamol, and possible application to biological samples make them ideal and inexpensive transducers for electrochemical (bio)sensors, with the potential to replace the screen-printed systems currently dominating in on-site sensors used. Graphical abstract