Search Results (80)

Point-of-care (POC) diagnostic technologies have become essential for the real-time monitoring and management of chronic wounds, where maintaining a moist environment and controlling pH levels are critical for effective healing. In this study, a flexible pH sensor based on a graphene/molybdenum disulfide (graphene/MoS₂) composite interdigitated electrode (IDE) structure was fabricated using pulsed laser ablation. The pH sensor, with an active area of 30 mm × 30 mm, exhibited good adhesion to the polyethylene terephthalate (PET) substrate and maintained structural integrity under repeated bending cycles. Precise ablation was achieved under optimized conditions of 4.35 J/cm² laser fluence, a repetition rate of 300 kHz, and a scanning speed of 500 mm/s, enabling the formation of defect-free IDE arrays without substrate damage. The influence of laser processing parameters on the surface morphology, electrical conductivity, and wettability of the composite thin films was systematically characterized. The fabricated pH sensor exhibited high sensitivity (~4.7% change in current per pH unit) across the pH 2–10 range, rapid response within ~5.2 s, and excellent mechanical stability under 100 bending cycles with negligible performance degradation. Moreover, the sensor retained > 95% of its stable sensitivity after 7 days of ambient storage. Furthermore, the pH response behavior was evaluated for electrode structures with different pitches, demonstrating that structural design parameters critically impact sensing performance. These results offer valuable insights into the scalable fabrication of flexible, wearable pH sensors, with promising applications in wound monitoring and personalized healthcare systems. Full article

This work represents the first use of a phosphonium salt-functionalized β-Cyclodextrin polymer (β-CDP) as a highly selective sensing membrane for monitoring the safety of drinking water against perchlorate ions (ClO₄⁻) using electrochemical impedance spectroscopy (EIS). Structural confirmation via ¹H NMR, ¹³C NMR, ³¹P NMR, and FT-IR spectroscopies combined with AFM and contact angle measurements demonstrate how the enhanced solubility of modified cyclodextrin improves thin film quality. The innovation lies in the synergistic combination of two detection mechanisms: the “Host-Guest” inclusion in the cyclodextrin cavity and anionic exchange between the bromide ions of the phosphonium groups and perchlorate anions. Under optimized functionalization conditions, EIS reveals high sensitivity and selectivity, achieving a record-low detection limit (LOD) of ~10⁻¹² M and a wide linear range of detection (10⁻¹¹ M–10⁻⁴ M). Sensing mechanisms at the functionalized transducer interfaces are examined through numerical fitting of Cole-Cole impedance spectra via a single relaxation equivalent circuit. Real water sample analysis confirms the sensor’s practical applicability, with recoveries between 96.9% and 109.8% and RSDs of 2.4–4.8%. Finally, a comparative study with reported membrane sensors shows that β-CDP offers superior performance, wider range, higher sensitivity, lower LOD, and simpler synthesis. Full article

Background/Objectives: Extracellular vesicles (EVs) are nanoscale, membrane-enclosed structures that play key roles in intercellular communication and biological regulation. Among them, Lactobacillus paracasei-derived EVs (Lp-EVs) have attracted attention for their anti-inflammatory and anti-aging properties, making them promising candidates for therapeutic and cosmetic use. However, methods for specific detection and quantitative evaluation of Lp-EVs are still limited. This study aims to develop a surface plasmon resonance (SPR)-based sensor system for the precise and selective detection of Lp-EVs. Methods: Anti-p40 antibodies were immobilized on gold thin films to construct an SPR sensing platform. The overexpression of the p40 protein on Lp-EVs was confirmed using flow cytometry and Western blotting. For functional evaluation, Lp-EVs were applied to an artificial skin membrane mounted on a Franz diffusion cell, followed by SPR-based quantification and fluorescence imaging to assess their skin penetration behavior. Results: The developed SPR sensor demonstrated high specificity and a detection limit of 0.12 µg/mL, with a linear response range from 0.1 to 0.375 µg/mL. It successfully discriminated Lp-EVs from other bacterial EVs. In the skin diffusion assay, Lp-EVs accumulated predominantly in the epidermal layer without penetrating into the dermis, likely due to their negative surface charge and interaction with the hydrophobic epidermal lipid matrix. Fluorescence imaging confirmed this epidermal confinement, which increased over 24 h. Conclusions: This study presents a sensitive and selective SPR-based platform for detecting Lp-EVs and demonstrates their potential for targeted epidermal delivery. These findings support the use of Lp-EVs in skin-focused therapeutic and cosmetic applications. Future studies will explore strategies such as microneedle-assisted delivery to enhance transdermal penetration and efficacy. Full article

The detection of hydrogen gas is crucial for both industrial fields, as a green energy carrier, and biomedical applications, where it is a biomarker for diagnosis. TiO₂ nanomaterials are stable and sensitive to hydrogen gas, but their gas response can be negatively affected by external factors such as humidity. Therefore, a strategy is required to mitigate these influences. The utilization of organic–inorganic hybrid gas sensors, specifically metal oxide gas sensors coated with ultra-thin copolymer films, is a relatively novel approach in this field. In this study, we examined the performance and long-term stability of novel TiO₂-based sensors that were coated with poly(trivinyltrimethylcyclotrisiloxane-co-tetrafluoroethylene) (P(V3D3-co-TFE)) co-polymers. The P(V3D3-co-TFE)/TiO₂ hybrid sensors exhibit high reliability even for more than 427 days. They exhibit excellent hydrogen selectivity, particularly in environments with high humidity. An optimum operating temperature of 300 °C to 350 °C was determined. The highest recorded response to H₂ was approximately 153% during the initial set of measurements at a relative humidity of 10%. The developed organic–inorganic hybrid structures open wide opportunities for gas sensor tuning and customization, paving the way for innovative applications in industry and biomedical fields, such as exhaled breath analysis, etc. Full article

This review article’s primary aim is to discuss different thin-film deposition technique methods and their important uses. The histories of thin-film technology, thin-film growth, thin-film classification, and thin-film preparation techniques are also covered in this review article. The preparation and characterization of functional thin films and nanostructured materials, as well as various devices based on these materials and recent developments are also focused on in this review. The properties of the materials and several thin-film deposition techniques are also covered in this article. This review article also discusses the classification and application of thin-film sensors. Furthermore, the formation of thin films and their physical properties are impacted by deposition conditions such as pH, temperature, deposition time, and deposition parameters, which are analyzed. This article discusses how a wide range of potential uses in structural, mechanical, and protective coatings; sensing; energy storage systems; catalysis; optoelectronics; and biomedicine are made possible by the special qualities of thin films and nanostructured materials, including their high surface area to volume ratio, structure, surface charge, anisotropic nature, and tunable functionalities. Full article

Dissolved oxygen (DO) is a crucial parameter in water quality monitoring because it directly affects the health of aquatic ecosystems. This study explored electrodeposited Cu₂O thin-film semiconductors for DO sensing. Cu₂O was chosen for its low cost, eco-friendliness, and non-toxic nature. Cu₂O films were electrodeposited on titanium (Ti) substrates using an acetate bath (0.1 M sodium acetate and 0.01 M cupric acetate) at −200 mV versus Ag/AgCl for 30 min, with a bath temperature of 55 °C, stirred at 50 rpm. The bath pH was systematically adjusted from 5.8 to 6.8 in 0.2 steps using NaOH and Acetic acid. A range of analyses including synchrotron X-ray diffraction (SXRD), scanning electron microscopy (SEM), surface wettability, capacitance–voltage (C-V), Raman spectroscopy, Fourier-transform infrared (FTIR) spectrum, and Electrochemical Impedance Spectroscopy (EIS) was performed to assess their properties and sensing performance. The results showed that Cu₂O films deposited at pH 6.4 exhibited optimal performance for DO sensing, with a strong linear response, marking this pH, deposition time, and temperature as ideal for creating effective DO sensors. This study introduces a novel, cost-effective approach to dissolved oxygen sensing using electrodeposited n-Cu₂O thin-film semiconductors, marking the first application of this material in such sensors and showcasing its potential for scalable and environmentally sustainable sensing technologies. Full article

Gas sensors based on metal oxide semiconductors (MOS) have been widely used for the detection and monitoring of flammable and toxic gases. In this paper, p-type Cr₂O₃ and Ti-doped Cr₂O₃ (CTO) thin films were synthesized using an aerosol-assisted chemical vapor deposition (AACVD) method. Detailed analysis of the thin films deposited, including structural information, their elemental composition, oxidation state, and morphology, was investigated using XRD, Raman analysis, SEM, and XPS. All the gas sensors based on pristine Cr₂O₃ and CTO exhibited a reversible response and good sensitivity to isobutylene (C₄H₈) and ammonia (NH₃) gases. Doping Ti into the Cr₂O₃ lattice improves the response of the CTO-based sensors to C₄H₈ and NH₃. We describe a novel mechanism for the gas sensitivity of p-type metal oxides based on variations in the oxygen vacancy concentration. Full article

Conducting polymers used in chemical sensors are attractive because of their ability to confer reversible properties controlled by the doping/de-doping process. Polyaniline (PANI) is one of the most prominent materials used due to its ease of synthesis, tailored properties, and higher stability. Here, PANI thin films deposited by the drop-casting method on fluorine-doped tin oxide (FTO) substrates were used in electrochemical and optical sensors for pH measurement. The response of the devices was correlated with the deposition parameters; namely, the volume of deposition solution dropped on the substrate and the concentration of the solution, which was determined by the weight ratio of polymer to solvent. The characterisation of the samples aimed to determine the structure–property relationship of the films and showed that the chemical properties, oxidation states, and protonation level are similar for all samples, as concluded from the cyclic voltammetry and UV–VIS spectroscopic analysis. The sensing performance of the PANI film is correlated with its relative physical properties, thickness, and surface roughness. The highest electrochemical sensitivity obtained was 127.3 ± 6.2 mV/pH, twice the Nernst limit—the highest pH sensitivity reported to our knowledge—from the thicker and rougher sample. The highest optical sensitivity, 0.45 ± 0.05 1/pH, was obtained from a less rough sample, which is desirable as it reduces light scattering and sample oxidation. The results presented demonstrate the importance of understanding the structure–property relationship of materials for optimised sensors and their potential applications where high-sensitivity pH measurement is required. Full article

An optical fiber scale sensor based on the detection principle of surface plasmon resonance (SPR) was developed for the rapid, high-sensitivity, real-time evaluation of scale precipitation in geothermal fluids. The optical fiber SPR scale sensor was fabricated by depositing a gold thin film onto the surface of an optical fiber with an exposed core. The optimal gold film thickness of the sensor was determined to be 30 nm, which achieved a refractive index sensitivity of 2140 nm per refractive index unit. A field test was conducted using geothermal brine from the Obama Binary Geothermal Power Plant in Unzen, Nagasaki Prefecture. A conventional optical fiber scale sensor and the SPR sensor were simultaneously assessed using raw and pH-adjusted brines. For the SPR sensor, a peak shift of 0.27 nm/min was observed at a response time of 1 min, whereas no change in transmittance was observed for the conventional sensor until 180 min. After the experiments, a scanning electron microscopy-energy-dispersive spectroscopy analysis was conducted on the sensors, and the findings showed that the deposition of Mg-SiO₂ scale did not significantly differ between the two sensors. The developed SPR sensor achieved faster scale precipitation detection (tens of minutes to hours) than the conventional sensor. Full article

Due to the presence of the boronic acid moieties, poly-3-thienylboronic acid has an affinity for saccharides and other diol-containing compounds. Thin films of this novel chemosensitive polymer were synthesized electrochemically on the gold surface. The adhesion of the polymer was enhanced by the deposition of a monomolecular layer of thiophenol. The technology was used to fabricate conductometric sensors for glucose and other diol-containing compounds. Simultaneous two- and four-electrode conductivity measurements were performed. The chemical sensitivity to sorbitol, fructose, glucose, and ethylene glycol was studied at different pH and electrode potentials, and the corresponding binding constants were obtained. Depending on the electrode potential, the reciprocal values of the binding constants of glucose to poly-3-thienylboronic acid at neutral pH are in the range of 0.2 mM–1.0 mM. The affinity for glucose has been studied in buffer solutions and in solutions containing the major components of human blood. It was shown that the presence of human serum albumin increases the affinity of poly-3-thienylboronic acid for diol-containing compounds. Full article

Quickly sensing humidity changes is required in some fields, such as in fuel cell vehicles. The micro humidity sensor used for the relative humidity (RH) measurement with fast response characteristics, and its numerical model and method are rare. This paper firstly presents a numerical model and method for a parallel plate capacitor and a numerical analysis of its dynamic characteristics. The fabrication of this sensor was carried out based on the numerical results, and, the main characteristics of its moisture-sensitive element are shown. This parallel plate capacitor is made using complementary metal-oxide semiconductor (CMOS)-compatible technology, with a P-type monocrystalline silicon wafer used as the substrate, a thin polyimide film (PI) between the upper grid electrode and the lower parallel plate electrode, and electrodes with a molybdenum–aluminum bilayer structure. The shape of the micro sensor is square with 3 mm on the side of the source field. The humidity sensor has a linearity of 0.9965, hysteresis at 7.408% RH, and a sensitivity of 0.4264 pF/%RH. The sensor displays an average adsorption time of 1 s and a minimum adsorption time of 850 ms when the relative humidity increases from 33.2% RH to 75.8% RH. The sensor demonstrates very good stability during a 240 h test in a 25 °C environment. The numerical model and method provided by this study are very useful for predicting the performance of a parallel plate capacitor. Full article

In this paper, we presented a novel, compact, conceptually simple, and fully functional low-cost prototype of a pH sensor with a PANI thin film as a sensing layer. The PANI deposition process is truly low-cost; it performs from the liquid phase, does not required any specialized equipment, and comprises few processing steps. The resulting PANI layer has excellent stability, resistance to solvents, and bio- and chemical compatibility. The pH sensor’s sensing part includes only a few components such as a red-light-emitting diode (LED) as a light source, and a corresponding photodiode (PD) as a detector. Unlike other PANI-based sensors, it requires no sophisticated and expensive techniques and components such lasers to excite the PANI or spectrometry to identify the PANI color change induced by pH variation. The pH sensor is sensitive in the broad pH range of 3 to 9, which is useful for numerous practical applications. The sensor requires a tiny volume of the test specimen, as little as 55 µL. We developed a fully integrated packaging solution for the pH sensor that comprises a limited number of components. The pH sensor comprises exclusively commercial off-the-shelf (COTS) components and standard printed circuit boards. The pH sensor is assembled using standard surface mounting technology (SMT). Full article

To realize simple and intelligent electrochemical ammonia (NH₃) detection in water, highly dense colloidal copper nanoparticles (CuNPs) were prepared and subsequently deposited onto a glassy carbon electrode (GCE). The CuNPs/GCE was then placed in an oven at 60 °C to intelligently transform CuNPs into cuprous oxide (Cu₂O) thin film. The colloidal CuNPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, whereas the fabricated Cu₂O/GCE was subjected to Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The XRD of Cu₂O/GCE showed the crystalline nature of the thermally converted Cu₂O thin film, whereas XPS demonstrated that the thin film formed on the surface of GCE was primarily composed of Cu₂O. The SEM images of Cu₂O/GCE revealed Cu₂O crystals with hexapod morphology. The EIS study exhibited substantially higher charger transfer activity of Cu₂O/GCE compared to bare GCE. The drop coating of ammonia (NH₃) solution onto Cu₂O/GCE enabled the fabricated electrode to be utilized as an electrochemical sensor for NH₃ detection in water. The cyclic voltammetric (CV) behavior of NH₃/Cu₂O/GCE was investigated in 0.1 M pH 7 phosphate buffer, which led to the formation of a copper-ammonia complex and revealed the nobility of the fabricated electrode. The square wave voltammetric (SWV) response was linear over the 10 µM and 1000 µM ranges with a detection limit of 6.23 µM and good reproducibility. The NH₃/Cu₂O/GCE displayed high selectivity for the detection of NH₃ in the presence of various coexisting cations and anions in 0.1 M pH 7 phosphate buffer. The recovery of NH₃ in the drinking water sample varied from 98.2% to 99.1%. Full article

A novel approach to fabricating a transparent and flexible one-transistor–one-diode (1T-1D) image sensor array on a flexible colorless polyimide (CPI) film substrate is successfully demonstrated with laser lift-off (LLO) techniques. Leveraging transparent indium tin oxide (ITO) electrodes and amorphous indium gallium zinc oxide (a-IGZO) channel-based thin-film transistor (TFT) backplanes, vertically stacked p-i-n hydrogenated amorphous silicon (a-Si:H) photodiodes (PDs) utilizing a low-temperature (<90 °C) deposition process are integrated with a densely packed 14 × 14 pixel array. The low-temperature-processed a-Si:H photodiodes show reasonable performance with responsivity and detectivity for 31.43 mA/W and 3.0 × 10¹⁰ Jones (biased at −1 V) at a wavelength of 470 nm, respectively. The good mechanical durability and robustness of the flexible image sensor arrays enable them to be attached to a curved surface with bending radii of 20, 15, 10, and 5 mm and 1000 bending cycles, respectively. These studies show the significant promise of utilizing highly flexible and rollable active-matrix technology for the purpose of dynamically sensing optical signals in spatial applications. Full article

Because of the expensive nature of sensors used to detect heavy metals and the severe health risks associated with certain heavy metals, there is a pressing need to develop cost-effective materials that are highly efficient in detecting these metals. A flower-shaped WO₂I₂-Poly(1H-pyrrole) (WO₂I₂/P1HP) nanocomposite thin film is synthesized through the oxidation of 1-H pyrrole using iodine and subsequent reaction with Na₂WO₄. The nanocomposite exhibits a distinctive flower-like morphology with an average size of 20 nm. Elemental composition and chemical structure are confirmed via X-ray photoelectron spectroscopy (XPS) analyses, while X-Ray diffraction analysis (XRD) and Fourier-transform infrared spectroscopy (FTIR) analyses provide further evidence of crystalline peaks and functional groups within the composite. The potential of the nanocomposite as a sensor for Cd²⁺ ions is determined using two approaches: simple potentiometric (two-electrode cell) and cyclic voltammetric (three-electrode cell) methods, over a concentration range spanning from 10⁻⁶ to 10⁻¹ M. From the simple potentiometric method, the sensor showcases strong sensing capabilities in the concentration span of 10⁻⁴ to 10⁻¹ M, displaying a Nernstian slope of 29.7 mV/decade. With a detection limit of 5 × 10⁻⁵ M, the sensor proves adept at precise and sensitive detection of low Cd²⁺ ion concentrations. While using the cyclic voltammetric method, the sensor’s selectivity for Cd²⁺ ions, demonstrated through cyclic voltammetry, reveals a sensitivity of 1.0 × 10⁻⁵ A/M and the ability to distinguish Cd²⁺ ions from other ions like Zn²⁺, Ni²⁺, Ca²⁺, K⁺, Al³⁺, and Mg²⁺. This selectivity underscores its utility in complex sample matrices and diverse environments. Furthermore, the sensor’s successful detection of Cd²⁺ ions from real samples solidifies its practical viability. Its reliable performance in real-world scenarios positions it as a valuable tool for Cd²⁺ ion detection across industries and environmental monitoring applications. These findings advocate for its utilization in commercial settings, highlighting its significance in Cd²⁺ ion detection. Full article