Precise and real-time detection of dopamine (DA) is essential for biomedical diagnostics and for understanding its role in neurological and metabolic disorders. This study presents a high-performance photonic crystal fiber-based localized surface plasmon resonance (PCF-LSPR) biosensor for refractive index-based dopamine sensing, integrating experimentally measured refractive index data with detailed numerical simulations. The proposed sensor employs a D-shaped PCF geometry to enhance the interaction between the guided core mode and localized surface plasmons supported by gold (Au), silver (Ag), and bimetallic Au-Ag nanoparticles. The refractive index of dopamine solutions was experimentally measured over the concentration range of 25-150 mM using an Abbe refractometer and directly incorporated into the numerical model to ensure realistic and application-oriented performance evaluation. Finite element method (FEM) simulations were carried out to analyze the coupling between the fundamental core-guided mode and the surface plasmon polariton (SPP) mode through confinement loss spectra. The results show that all three plasmonic configurations achieve a high wavelength sensitivity of 5000 nm/RIU with excellent linearity (R-2 = 1) and a resolution of 2 x 10(-6) RIU. While the wavelength sensitivity and resolution are identical, variations in full-width at half-maximum (FWHM), figure of merit (FOM), and amplitude sensitivity reveal the influence of plasmonic material selection. Silver nanoparticles exhibit the narrowest resonance peaks and highest FOM, whereas the bimetallic Au-Ag configuration provides an optimal balance between sensitivity, resonance stability, and chemical robustness. All configurations demonstrate a low limit of detection (LOD) of 4 x 10(-10) RIU2/nm. These findings highlight the strong potential of the proposed PCF-LSPR biosensor for real-time dopamine monitoring in biomedical and neurochemical applications.

The development of high-performance electrochemical sensors for dopamine (DA) detection remains a significant challenge, particularly in achieving high sensitivity, selectivity, and environmental sustainability. In this work, we report a green and efficient strategy for fabricating a nanostructured electrochemical sensor based on dopamine-functionalized graphene oxide (GODA) decorated with gold sononanoparticles (AuSNPs). The AuSNPs were synthesized via a rapid, ultrasonic-assisted, green method using Juniperus leaf extract as both the reducing and stabilizing agent, ensuring an eco-friendly synthesis route. The resulting GODA@AuSNPs nanocomposite was deposited onto a glassy carbon electrode (GCE) to construct a sensitive sensing platform. Structural and physicochemical characterization using UV-Vis, FTIR, Raman spectroscopy, DLS, and STEM confirmed successful functionalization and uniform nanoparticle distribution. Electrochemical studies demonstrated enhanced electron transfer kinetics and electrocatalytic activity toward DA oxidation, attributed to the synergistic interaction between AuSNPs and GODA. Under optimized conditions, the sensor exhibited a linear response over a concentration range of 2.5-70 mu M with a detection limit of 1.43 mu M. The platform showed good selectivity, excellent reproducibility (RSD < 4.2%), and long-term stability (>90% signal retention after 30 days). Its applicability was further validated in human serum samples with satisfactory recovery values (99.50-101.73%). These results highlight the potential of the GODA@AuSNPs-based platform as a cost-effective, environmentally friendly electrochemical sensor with potential for portable, real-time biomedical applications.

Measuring the pH of human biofluids provides meaningful information about physiological balance and potential pathological changes. While blood remains the conventional medium for diagnostic evaluation, there has been an increasing focus on external biofluids, such as sweat, that enable non-invasive, continuous health assessment. Recent advances in wearable sensing technologies have resulted in the development of flexible, miniaturized and biocompatible systems that can monitor sweat pH in real time on the body. This review highlights the latest progress in wearable electrochemical and optical sensors designed for sweat pH monitoring. It first outlines the general procedures for sweat pH sensing, including sweat secretion and collection, pH sensing, signal conversion, and data interpretation. Subsequent sections focus on electrochemical approaches, particularly potentiometric sensors based on ion-selective membranes and ion-sensitive field-effect transistor (ISFET) configurations, which are recognized for their high sensitivity and rapid response times. The review further explores optical sensing technologies, such as surface-enhanced Raman scattering (SERS), fluorescence and colorimetric sensors, emphasizing their versatility for visual and spectroscopic detection. Looking ahead, the integration of artificial intelligence, microfluidic systems, and self-powered modules will facilitate the development of fully autonomous, wireless sensing platforms. The convergence of advanced materials, sensor engineering, and digital health technologies is expected to establish wearable sweat pH sensors as a cornerstone of personalized medicine, preventive care, and real-time health tracking.

This study reports the preparation of cobalt-impregnated activated carbon derived from beech wood (Co-ACBH) and its application for the adsorption of Congo Red (CR) from aqueous solution. Activated carbon was synthesized by KOH chemical activation, followed by cobalt impregnation and thermal treatment under a nitrogen atmosphere. The prepared materials were characterized by BET surface area analysis, SEM-EDX, FTIR, XRD, TGA/DSC, and density functional theory (DFT) calculations. BET analysis showed that cobalt impregnation decreased the specific surface area from 436.12 to 337 m2 g−1 while increasing the pore volume from 0.194 to 0.688 cm3 g−1 and the porosity from 13% to 37%. SEM-EDX confirmed the successful incorporation of cobalt onto the activated carbon surface, whereas FTIR and XRD analyses indicated that the surface functional groups and the predominantly amorphous carbon structure were preserved after modification. TGA/DSC results revealed that Co-ACBH exhibited higher thermal stability than the pristine activated carbon. Under the optimized adsorption conditions (pH 7, initial CR concentration of 50 mg L−1, 120 min contact time and at room temperature), Co-ACBH achieved a Congo Red removal efficiency of approximately 98%. Theoretical DFT investigations further clarified the adsorption mechanism through donor–acceptor interactions, electrostatic attractions, and van der Waals forces between the adsorbent and the dye. HOMO-LUMO analysis, molecular electrostatic potential mapping, and QTAIM/NCI analyses confirmed the stability and favorable electronic properties of the adsorption complexes. Overall, the synthesized Co-ACBH material exhibited promising adsorption performance and strong potential as an eco-friendly and cost-effective adsorbent for dye-contaminated wastewater treatment.

Next-generation electronic devices, including embedded microsystems and wearable technologies, require the development of safe, and low-cost energy storage systems to meet the 21st-century society demands. In this context, several ecological binders have been developed and amended in order to achieve high-performance carbon-based supercapacitors. This work demonstrates a solid state-based supercapacitor using Pullulan (Pu)/Polyvinyl Alcohol (PVA) composite as an eco-friendly binder for the first time, for carbon-based electrodes development. Furthermore, PVA/KOH/Glycerol (GCy) blends are used as conductive electrolytes towards safe and light weight devices manufacturing. The electrodes are fabricated through simple and low-cost hand-painting (paint brush) on Nickel foam substrates. The device shows an interesting areal capacitance of 176 mF cm(-2) at 10 mV s(-1), energy and power densities of 25 & micro;Wh cm(-2) and 3.2 mW cm(-2) respectively, at 0.5 A g(-1). More importantly, the device demonstrates robust mechanical strength with excellent reversibility across various bending angles (0 degrees, 90 degrees, 180 degrees), with a capacitance retention of 90% after 10 000 charging/discharging cycles while maintaining an important coulombic efficiency (>95%). The outcomes of this work are quite promising compared to many reported studies, opening wide potential application in the field of handheld electronics.

This study aims to develop a sustainable electrochemical sensor integrated with machine learning (ML) for the simultaneous prediction of serotonin (5-HT) and dopamine (DA) concentrations, two key biomarkers of neurological disorders. The novelty of this work lies in the combination of green-synthesized nanomaterials and advanced ML algorithms within a miniaturized, eco-friendly, and cost-effective sensing platform. This integration improves diagnostic accuracy, reduces analysis time, and minimizes reliance on manual interpretation, offering significant potential for clinical applications. Monitoring neurotransmitters is crucial for the early diagnosis of neurological diseases, yet conventional methods are often costly, time-consuming, and dependent on specialized expertise. Electrochemical sensors based on nanomaterials provide a promising alternative, particularly when enhanced by ML to enable accurate, real-time prediction of analyte concentrations. In this work, a screen-printed electrode (SPE) functionalized with green-synthesized silver nanoparticles decorated reduced graphene oxide (AgNPs-rGO) was employed for the simultaneous neurotransmitter detection. Experimental electrochemical signals were systematically collected and used as input features for ML models, with 80% of the dataset applied for training and 20% for validation. Among the tested algorithms, Random Forest Regression (RFR) achieved the highest predictive accuracy, with R 2 values of 0.984 for 5-HT and 0.897 for DA. By integrating eco-friendly nanomaterials with ML-based predictive modeling on a miniaturized platform, this study provides a rapid, efficient, and sustainable approach with strong potential for improving early diagnosis of neurological disorders.

The green synthesis of zinc oxide nanoparticles (ZnO NPs) using Retama raetam leaf extract via microwave irradiation was investigated. The biosynthesized NPs were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectrophotometry. An XRD pattern confirmed the formation of a hexagonal wurtzite structure. An FTIR analysis indicated the interactions of the NPs with bioactive molecules involved in their synthesis. SEM and STEM imaging determined the morphology of the NPs with an average size of 14 nm. Furthermore, the biosynthesized ZnO NPs were used as a sensitive layer for detecting volatile organic compounds (VOCs) at low concentrations ranging from 0.5 to 5 ppm. The response sensor measured at an optimum operating temperature of 250 °C and 50% relative humidity (RH). The sensor exhibited a strong response to 5 ppm ethanol (325%), a detection limit as low as 4 ppb and an excellent stability across varying humidity levels.

Electrochemical sensors based on molecularly imprinted polymers (MIPs) have attracted interest due to their high selectivity, which is achieved through cavities that complement the structure, size, and chemical functionality of the target analyte. However, functional groups located outside the imprinted sites within the polymer matrix can promote non-specific binding, which reduces the performance of the sensor. In this context, the present study aims to develop strategies to reduce non-specific adsorption phenomena in both conductive (polypyrrole and polyaniline) and non-conductive polymers (polydopamine and o-phenylenediamine), thereby enhancing the selectivity of MIP-based sensors. This approach was applied to two model analytes, tryptophan and tyramine, both of which have important biomedical relevance. Non-specific adsorption was eliminated by electrostatically immobilizing SDS on conductive polymer-based MIPs. For non-conductive MIPs, the analyte interacts with the electrode surface solely through the imprinted cavities. The lack of conductivity in the polymer allows the selectivity of the sensor to be enhanced simply by optimizing the number of scans, without polymer modification. Finally, MIP-based sensor using polyaniline polymer were applied to evaluate the analytical performance of the developed strategy, using tryptophan as a model analyte. The sensor demonstrated a sensitivity of 0.015 mu A mu M -1, a detection limit of 6.7 mu M and high selectivity in the presence of a wide range of interferents. This work demonstrates strong potential for the development of low-cost, highly selective, and environmentally friendly sensors for the detection of a wide range of analytes.

This paper reports a Sonogel-Carbon electrode modified with pine leaf extract-derived gold sononanoparticles (AuSNPs) for the simultaneous detection of serotonin (5-HT) and dopamine (DA), key neurotransmitters in human health. To our knowledge, this is the first time AuSNPs have been greenly synthesized using pine leaf extract coupled with ultrasound technology in only a few minutes. The obtained AuSNPs (56 ± 14 nm) were characterized through several techniques: UV/vis spectroscopy, Fourier infrared spectroscopy, X-ray energy dispersive spectroscopy, and electron microscopy. The green AuSNPs were drop-cast onto the Sonogel-Carbon electrode (SNGCE) for the simultaneous determination of DA and 5-HT. The proposed sensor exhibited low limits of detection, good sensitivity (421.80 pM for DA and 192.55 pM for 5-HT), and reproducibility (RSD 4%). Proof of concept was demonstrated by their successful detection in human blood serum, obtaining recovery rates close to 100% for both analytes in all cases, demonstrating that this sensor has great potential for applications in neurodegenerative diseases and early-stage cancer diagnosis.

This article presents a convenient method for fabricating hybrid heterojunctions using poly (N-vinylcarbazole) (PVK) and a 1-D zinc oxide nanorod (ZnO NR) array for photodetector (PD) development. In this context, PVK and ZnO NRs were employed as electron donor and acceptor, respectively. First, ZnO NRs were hydrothermally synthesized through a two-step procedure at low temperatures on an n-type silicon substrate. Ohmic contacts were integrated by incorporating graphite and eutectic In-Ga (eGaIn) in to the PVK film and Si substrate, respectively. The eGaIn/Si/ZnO NRs/PVK/graphite PD structures’ fundamental electrical parameters were extracted from the $\textit{I}$ – $\textit{V}$ response in dark and under illumination conditions. It was found that the device displayed remarkable sensitivity to ultraviolet (UV) light exposure, owing to a responsivity of 35 mA $\cdot$ W $^{-\text{1}}$ , with notable reproducibility. What is more, the structure demonstrates an open-circuit voltage, short-circuit current density, and ideality factor of 0.28 V, 237.2 $\mu$ A $\cdot$ cm $^{-\text{2}}$ , and 2.3, respectively. The origin of the ZnO/PVK photoconductive properties is explained using the carrier transport mechanism at the interfaces. Moreover, the photoelectrical parameters of the PVK/ZnO NR structure were precisely evaluated through a combined physical–mathematical–numerical approach to unravel the physical mechanisms governing the operation of such PDs. The results of this research reveal promising avenues for flexible and highly sensitive PDs, opening wide potential applications in advanced communication systems, and/or environmental monitoring.

The cost and environmental impact of supercapacitor materials highlight the need for sustainable alternatives. In this context, this paper is the first to explore the use of hydrothermally synthesized activated carbons derived from Tunisian pistachio shells for the development of low-cost supercapacitors using aqueous and/or solid-state electrolytes. More importantly, we provide insights into optimizing the salt content in PVA-based solid-state electrolytes to maximize performance in supercapacitor applications, an area that remains largely unexplored. The prepared carbon material demonstrates a surface area of 797 m2/g with phosphorus and oxygen functional groups, showing promising potential for application in both liquid and/or solid-state supercapacitors. In aqueous electrolytes, the fabricated supercapacitors demonstrate maximum specific capacitances of 175.19 F/g and an energy density of 6.08 Wh/Kg in 1M H2SO4 at 1 A/g. Moreover, the solid-state supercapacitors show specific capacitances of 167.78 F/g and an energy density of 5.82 Wh/Kg in PVA:H2SO4 and 153.70 F/g and 5.33 Wh/Kg in PVA:KOH, at mass ratios of 1/1 and 1/3 respectively. Also, the solid-state devices retain 82 % and 98.6 % of capacitances after 3000 cycles for PVA:H2SO4 and PVA:KOH respectively, demonstrating good stability. This work advances sustainable and low-cost materials for energy storage to meet 21st century energy demands.

We report the development of a novel electrochemical sensor for serotonin (5-HT) detection, based on a glassy carbon electrode (GCE) modified with a newly synthesized manganese(III) porphyrin complex (triflato)[(meso-tetra(para-tolylphenyl)porphyrinato)]manganese(III), denoted as [MnIII(TTP)(SO3CF3)]. To the best of our knowledge, this is the first study utilizing this specific complex as an electroactive material for serotonin sensing. The complex was thoroughly characterized by FTIR, Raman, and UV-visible spectroscopy. Key experimental parameters, including the mass percentage of the modifier, pH, and scan rate, were systematically optimized. The electrochemical detection of 5-HT was performed using differential pulse voltammetry (DPV), yielding a limit of detection of 5.3 μM and a linear detection range of 10-250 μM. The modified electrode showed high selectivity toward serotonin in the presence of common interferents such as dopamine, glucose, uric acid, ascorbic acid, NaCl, and KCl. It also demonstrated excellent reproducibility (RSD = 1.34%) and repeatability (RSD = 0.8%). Moreover, the sensor's practical applicability was validated through successful detection of 5-HT in artificial urine samples. The originality of the sensing interface and the promising analytical performance highlight the potential of this platform for clinical diagnostics and neurochemical research.

We report on a simple and low-cost method for the surface modification of polymers by ultrasonic chemical treatment at atmospheric pressure and room temperature. Polyimide films (Kapton) were immersed in different solvents for various durations. After being subjected to ultrasonic cleaning, the surface energies of the Kapton films were determined by the wettability method to improve the adhesion of the films to a suitable coating. The results show that the surface energy of the polyimide films has an optimum value of approximately 55.1 mJ/m2 obtained for ethanol cleaning for 25 min. These values are comparable to those achieved with higher-cost and more complex techniques such as plasma treatment. The optical band gap (Eg) and the number of carbon atoms were measured by using UV-visible spectroscopy on Kapton samples to analyze their absorption. Notably, the optical band gap decreased from 2.30 to 2.24 eV after 25 min of ethanol treatment, indicating improved electronic properties. This reduction in Eg enhances light absorption and is crucial for optimizing the material’s performance in optoelectronic applications. The vibration peaks of the chemical bonds present in these films were identified using FTIR spectroscopy, which was used to characterize the films and track their progression over time. Following the use of the optimized ultrasonic cleaning method, the FTIR analysis showed an increase in the C=O symmetrical and asymmetrical stretching peaks at 1713 and 1774 cm−1, respectively, as well as C–O–C bond stretching at 1240 cm−1. Mechanical tensile tests (MTSs) were used to measure elastic parameters such as Young’s modulus, tensile strength, and strain to failure for untreated and treated samples.

Recent developments in surface plasmon resonance (SPR) sensors based on photonic crystal fiber (PCF) technology have greatly enhanced sensitivity. Nevertheless, existing configurations often face challenges related to design complexity and real-time application optimization. In this study, we present a straightforward and highly sensitive circular PCF-SPR biosensor tailored for the detection of early-stage cancer cells, with efficient performance across both visible and near-infrared spectrums. Using the Taguchi ${L} _{{27}}$ (35) orthogonal array approach, we optimized five critical structural parameters: air hole diameters, pitch, and the thickness of the gold (Au) and titanium dioxide (TiO2) layers. The resulting sensor achieved a remarkable spectral sensitivity of 18 000 nm/RIU and an amplitude sensitivity of 681.655 RIU-1. Designed to function across a wide refractive index (RI) range (1.29-1.40), the biosensor is particularly effective for identifying cervical, blood, and skin cancer cells, reaching a peak sensitivity of 7500 nm/RIU for cervical cancer detection. In addition, performance prediction utilized machine learning techniques, specifically multiple linear regression (MLR) and multi-layer perceptron artificial neural network (MLP-ANN) models. The MLP-ANN model demonstrated superior predictive accuracy, highlighting the potential of artificial intelligence (AI) in optimizing biosensor configurations for advanced cancer diagnostics.

The evolution of wearable technology extends beyond fitness to offer transformative tools with the potential to significantly impact lives. Moreover, the incorporation of sustainable materials, extracted from biomass residues, for the elaboration of bendable energy storage devices, is becoming a global strategy adopted by several research laboratories, with the aim of satisfying modern needs while respecting ecological and economic considerations. In this context, this work proposes the synthesis of mesoporous activated carbon (AC) from Tunisian Hazelnuts shells through chemical carbonization, for the fabrication of carbon-based electrodes on flexible and low-cost graphite paper substrates. Symmetrical electrodes were used for the manufacturing of solid-state micro supercapacitors using Polyvinyl alcohol:sulfuric acid (PVA:H 2 SO 4 ) hydrogel electrolytes. Not to mention, PVA was incorporated as a biocompatible binder for electrode manufacturing, then as a bendable film forming agent for the solid-state electrolyte synthesis. Therefore, this work supports the low-cost manufacturing through affordable supercapacitors for consumers, unlocking widespread adoption and utilization of this energy storage technology. More importantly, the fabricated device showed a maximum areal capacitance of $42.76\ \text{mF}.\text{cm}^{-2}$ at $5\ \text{mV}.\mathrm{s}^{-} 1$ , an energy and power densities of $6.32\ \mu \text{Wh}.\text{cm}^{-2}$ and 3.4 $\text{mW}.\text{cm}^{-2}$ respectively. The obtained energetic performances were compared with other studies and revealed consistently similar or even superior results in some instances. This study unlocks significant potential applications in wearable devices and/or flexible systems such as robots, exoskeletons and others.

Industrial wastes (IWs) present severe environmental risks by contaminating soil and water sources with hazardous chemicals, which can have harmful effects on ecosystems and human health. Concurrently, the energy storage sector is crucial for enabling renewable energy integration, improving grid stability, and supporting the transition to a sustainable energy future. In this context, this paper provides an overview of how IWs can be explored, particularly focusing on the valuable materials that can be repurposed as alternatives in the energy storage sector, thereby reducing waste generation and promoting circular economy principles by minimizing reliance on finite resources. Notably, we report the use of carbon derived from industrial tire wastes for the development of solid-state micro-supercapacitors on textile substrates through simple and low-cost drop-casting/drying procedures. The device showed capacitive response, with an aerial capacitance of 19.04 mF.cm- 2 , energy density of 1.7 Wh.cm- 2 and a maximum coulombic efficiency of 81.1 % at 1 mA.cm-2 respectively. This work opens the door to potential opportunities for pioneering advancements in e-textile systems and wearable devices supply.

Tryptophan, an essential amino acid playing a pivotal role in various biological processes, stands as a focal point in our investigation. In this study, we introduce a groundbreaking electrochemical sensor that integrates a nanocomposite comprising carbon black (CB) and zinc oxide nanoparticles (ZnO-NPs) for the selective detection of L-tryptophan (Trp). The synthesis of ZnO-NPs, accomplished through the sol-gel technique, was meticulously characterized using XRD, FTIR, and UV-visible methods to unveil their structural and optical properties. The construction of the sensing electrode involved the deposition of a CB/ZnO-NP nanocomposite onto a glassy carbon electrode (GCE) utilizing the drop-coating method. Rigorous evaluation and analysis of the modified glassy carbon electrode were carried out through scanning electron microscopy (SEM), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The resulting CB/ZnO-NPs/GCE electrode exhibited an augmented surface area and outstanding electrocatalytic activity. Significantly, the CB/ZnO-NP sensor displayed remarkable analytical performance for tryptophan detection over an extensive concentration range from 0.01 to 100 µmol.L −1 , featuring a low detection limit of 0.017 µmol.L −1 . Moreover, the proposed electrochemical sensor exhibited notable selectivity, specifically targeting tryptophan, emphasizing its potential for diverse analytical applications. This work not only expands our understanding of tryptophan detection but also offers a highly sensitive and selective tool with broad applications in biomedical and environmental fields, underscoring the significance of this innovative sensor in advancing analytical methodologies.

The identification and quantification of antibiotics in different types of water is of growing interest due to the resistance their presence can induce in many bacterial species. Although the electrochemical analysis of electroactive antibiotics via voltammetric techniques is rapid, simple and cost-effective, their simultaneous detection is often challenging due to their overlapping oxidation peaks. To address this issue, we have developed a voltammetric electronic tongue for the discrimination and quantification of antibiotic mixtures in tap water. For that purpose, three different screen-printed carbon electrodes were modified with “green”-synthesized metallic nanoparticles (NPs) of copper and silver, and commercial titanium dioxide NPs. The electrochemical behavior of the electrodes against the detection of six antibiotics was first investigated by cyclic voltammetry, proving the catalytic effect of the selected NPs. Next, principal component analysis and artificial neural networks (ANNs) were used to achieve the accurate discrimination and quantification of three selected antibiotics, cefepime, daptomycin, and vancomycin, at the mg/L level with a normalized root mean square error (NRMSE) of 0.055 for the test subset. Finally, after validation of the ANN model, the analysis of tap water samples spiked with the three selected antibiotics was carried out to test its applicability for water quality monitoring, showing a good agreement with the expected values (average recovery of 95%, and NRMSE of 0.034).

An electrochemical sensor based on eco-friendly green synthesized silver nanoparticles decorated reduced graphene oxide (AgNPs-rGO) modified screen-printed carbon electrode (SPCE) for the simultaneous detection of serotonin (5-HT) and dopamine (DA) is reported for the first time. The experimental parameters affecting the sensor performance were optimized in terms of AgNPs-rGO coating amount, scan rate and electrolyte pH (6–8). Under optimal conditions, the AgNPs-rGO/SPCE was employed to individually determine both analytes using DPV technique. The sensor was also efficient in the simultaneous detection of these species and reported well-resolved oxidation peaks with a linear range of 10–100 μ M and detection limits of 7 μ M and 7.41 μ M, respectively. The developed device showed good selectivity, reproducibility, and repeatability. Furthermore, it was successfully applied to the determination of both biomolecules in artificial urine samples with good recovery. The main advantages of the designed sensor are its simplicity, portability, and low cost.