Sensor Surface Research Articles

Ligand-Induced Folding in a Dopamine-Binding DNA Aptamer.

Aptamers are often employed as molecular recognition elements in the development of different types of biosensors. Many of these biosensors take advantage of the aptamer having a ligand-induced structure-formation binding mechanism. However, this binding mechanism is poorly understood. Here we use isothermal titration calorimetry, circular dichroism spectroscopy and NMR spectroscopy to study the binding and ligand-induced structural change exhibited by a dopamine-binding DNA aptamer. We analysed a series of aptamers where we shorten the terminal stem that contains the 5´and 3´termini of the aptamer sequence. All aptamers bind dopamine in an enthalpically driven process coupled with an unfavorable entropy. A general trend of the aptamer having a weaker binding affinity is observed as the terminal stem is shortened. For all aptamers studied, numerous signals appear in the imino region of the1H NMR spectrum indicating that new structure forms with ligand binding. However, it is only when this region of structure formation in the aptamer is brought close to the sensor surface that we obtain a functional electrochemical aptamer-based biosensor.

Double-layer optical fiber interferometer with bio-layer-modified reflector for label-free biosensing of inflammatory proteins

This work discusses label-free biosensing application of a double-layer optical fiber interferometer where the second layer tailors the reflection conditions at the external plain and supports changes in reflected optical spectrum when a bio-layer binds to it. The double-layer nanostructure consists of precisely tailored thin films, i.e., titanium (TiO2) and hafnium oxides (HfO2) deposited on single-mode fiber end-face by magnetron sputtering. It has been shown numerically and experimentally that the approach besides well spectrally defined interference pattern distinguishes refractive index (RI) changes taking place in a volume and on the sensor surface. These are of interest when label-free biosensing applications are considered. The case of myeloperoxidase (MPO) detection—a protein, which concentration rises during inflammation—is reported as an example of application. The response of the sensor to MPO in a concentration range of 1 × 10−11–5 × 10−6 g/mL was tested. An increase in the MPO concentration was followed by a redshift of the interference pattern and a decrease in reflected power. The negative control performed using ferritin proved specificity of the sensor. The results reported in this work indicate capability of the approach for diagnostic label-free biosensing, possibly also at in vivo conditions.

Analysis of cow and goat milk by spr: adulteration detection and differences in protein adsorption

The article discusses using Surface Plasmon Resonance (SPR) to detect adulteration of goat milk with cow milk. The SPR technique is based on changes in the refractive index and can be used to monitor the adsorption of proteins on the sensor surface. The SPR technique can differentiate between pure cow milk and pure goat milk by measuring the initial refractive index, which is higher for cow milk. The article then describes the changes in the refractive index that occur when goat milk is adulterated with cow milk and how adding a bovine casein film on the sensor surface can make it more selective for cow milk. The differences in the chemical compositions and molecular structures of cow and goat milk and how these differences affect the adsorption of proteins and fatty acids on the sensor surface. Finally, other proteins, such as α-lactalbumin and β-lactoglobulin, are used as indicators of adulteration.

Impact of Design Dimension Optimization on Capacitive Sensor Performance for Particulate Matter Detection and Measurement

Particulate matter (PM) emissions from exhaust gases are major pollutants and cause serious health problems. Diesel particulate filters (DPF) are used for monitoring and trapping particulates from exhaust gases. For sensing these particulates sensors are used downstream of a DPF. The present study proposes an interdigitated electrode (IDE) capacitive sensor for detecting and measuring deposited particulates on the sensor surface. The sensor dimensions are optimized to detect and measure the least deposition of particulates. The paper presents improvement in sensor performance, a high selectivity of 65.70% with an accuracy of 87.26%. Dimension optimization extracts capacitance of 581 pF manifolds 10 times more than the reference sensor from the literature. The study presents a sensor with a thin sensing layer manufactured by optical lithography and a lift-off method for IDE. Measurements and testing showed that the sensor measures the lowest particulate mass of 0.0045 mg in 3.4 ms

An impedimetric determination of zearalenone on MIP-modified carboceramic electrode

Zearalenone (ZEN) is a mycotoxin that poses significant risks to human and animal health due to its mutagenic, immunosuppressive, and carcinogenic properties. This study presents a novel analytical method for detecting ZEN using electrochemical impedance spectroscopy (EIS) combined with a molecularly imprinted polymer (MIP). ZEN, used as the template molecule, was incorporated into polypyrrole on screen-printed electrodes (SPE), and a ZEN-sensitive MIP sensor was created through template removal. The modified sensor surfaces were characterized by EIS and scanning electron microscopy (SEM). An impedimetric MIP sensor for ZEN was developed, offering a detection range from 1 pM to 500 pM. The method's limit of detection (LOD) was established at 1 pM (0.3 pg/mL) with a signal-to-noise ratio of 3 (S/N = 3). The method demonstrated high precision and accuracy, with a maximum relative standard deviation (RSD) of less than 4.4% at a 95% confidence level, and relative error (RE) values ranging from −0.8% to −2.7%. The selectivity of the developed MIP sensor was evaluated using ochratoxin A, ochratoxin B, and aflatoxin B1, with no significant interference observed. ZEN recovery from spiked samples was between 95% and 105%, indicating that the method was successfully applied to grain samples, including corn, rice, and wheat.

Morphology and Wettability of Polystyrene film on QCM Sensor Caused by Oxygen Plasma with DC Bias

Surface wettability and morphology are important aspects of developing QCM sensors for chemical sensors and biosensors. The functionality and morphology of the sensitive coating on the sensor surface affect the sensor sensitivity and selectivity. Various materials and methods to improve the functionality and morphology of the sensor surface have been developed, one of which is plasma. Species and parameters of the generated plasma play an important role in the treatment. One parameter is the DC-bias voltage of RF plasma, which plays an important role in plasma generation and bombardment on the surface being modified. This work shows the effect of the DC bias of the 2 MHz RF plasma with oxygen species. Surface functionality and morphology modification of the polystyrene film on the QCM sensor was done by surface modification using oxygen plasma. Partial etching of the polystyrene film occurred when treated with oxygen plasma generated using 2 MHz with negative DC-bias. CII, CO+, and CO were detected during the exposure of oxygen plasma on polystyrene film, indicating a chemical reaction between the plasma species, oxygen plasma, and the polystyrene. Observation by optical microscope and SEM showed the occurrence of partial etching on the polystyrene film. As there is no masking, the partial etching occurred randomly. The average size of the etched film increased with the DC bias voltage, but the percentage of the etched area was not. The oxygen plasma converts the polystyrene film from hydrophobic to hydrophilic, but hydrophobicity increases with the DC bias voltage. HIGHLIGHTS Polystyrene surface treatment using oxygen plasma can be used to alter the surface hydrophobicity. The DC bias plays important role in the surface modification. High DCV bias gives stronger plasma energy which may etched the polystyrene film. Observation using SEM shows part of the polystyrene film was etched as the DC bias voltage increase. The amount of the etched surface can be measured using optical microscope and processed using ImageJ. Increasing the DC bias result in a wider etched film. GRAPHICAL ABSTRACT

Super-resolution lensless on-chip microscopy based on array illumination and scattering multiplexing with polystyrene microspheres layer

The resolution of lensless on-chip microscopy is mainly limited by the pixel size of the image sensor. Many super-resolution techniques have emerged to solve the problem of insufficient imaging resolution. Most existing pixel super-resolution technologies rely on precise electric translation stage for hundreds of high-precision displacements, or on expensive tunable lasers to generate diffraction diversity. Conventional ptychography iterative engine (PIE) is considered an effective method for improving imaging resolution, but it is prone to oscillations in the early stage of iteration. In this paper, we propose a ptychography imaging technique based on scattering multiplexing, which involves coating the surface of the image sensor with a layer of polystyrene microspheres, and utilizing a 4 × 3 LED array to sequentially illuminate the sample. An innovative ptychography reconstruction algorithm based on dual amplitude gradient descent (DAGD) is designed for the reconstruction from the holograms, which effectively avoids the problems of slow convergence speed and obvious oscillation. Compared with other similar technologies, our system has no moving parts and uses inexpensive partially coherent light illumination. It only records 12 holograms and reaches the imaging resolution of 1.23 μm, which is 1.36 times pixel super-resolution compared with the pixel size of the sensor.

Fabrication of surface functionalized QCM sensor for BTX detection at ambient conditions

Developing optimized gas sensors for detecting low concentrations of Benzene, Toluene, and Xylene (BTX) in ambient conditions is advantageous for health and environment monitoring applications. This study reports on the feasibility of using Quartz Crystals Microbalance (QCM) coated by Tungsten Oxide (WO3) to detect BTX compounds. A WO3 layer was deposited on the QCM surface using DC magnetron sputtering. Optical Profilometry (OP), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) were employed to analyze sensor surface morphology and structure. Adsorption properties were studied through the Langmuir adsorption isotherm. Thermal stability was evaluated by thermogravimetric analysis. The response to BTX vapours was investigated using a laboratory-designed gas-sensing setup in ambient conditions. The optimized film thickness was 200.81 ± 0.39 nm for 540 s of sputtering. XRD pattern confirms the amorphous nature, and SEM images of WO3 show the granular microstructure with 200 nm diameter. The developed sensor shows the highest sensitivity for xylene (5.10 ± 0.08 Hz/ppm), followed by toluene (5.69 ± 0.22 Hz/ppm) and benzene (3.36 ± 0.24 Hz/ppm). The limit of detection for BTX was 1.48 ppm, 0.79 ppm, and 0.33 ppm, respectively. The sensor exhibited faster response times of 30 s, 32 s, and 43 s for BTX, respectively. Repeatability of 99 % and reproducibility of 98 % were observed for BTX vapours. The fabricated WO3-coated QCM sensor can detect BTX vapour at room temperature with high sensitivity and response time. Thus, it can play a significant role in detecting BTX in the workplace for health and environment monitoring systems.

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.

Enhanced gas sensing performance of ZnO and Pt-doped ZnO nanostructured films by chemical spray pyrolysis

This study focuses on the preparation and characterization of zinc oxide (ZO) and platinum-doped zinc oxide (Pt-ZO) nanostructured thin films using the chemical spray pyrolysis technique. Structural and morphological properties of the films were investigated via X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). To understand the semiconducting nature and carrier dynamics, UV-Vis spectroscopy, electrical conductivity measurements, and a static gas sensing system were employed. The films exhibited crystallization in the hexagonal wurtzite structure with a preferred orientation along the (002) plane. FESEM images revealed the presence of small bright particles, particularly abundant in the 5 wt% Pt-doped ZO thin film, indicating the presence of platinum catalysts. Electrical conductivity measurements confirmed the semiconducting nature of the films. Optical parameters such as band gap and absorption index were obtained from UV-Vis spectroscopy. Gas sensing performance towards liquefied petroleum gas (LPG) showed that the 5 wt% Pt-doped ZO thin film exhibited a high response (69.9) to a 50 ppm concentration of LPG at 350 °C. The gas response and recovery times were observed to be 8 s and 12 s, respectively. These results are attributed to interactions between LPG molecules and adsorbed oxygen species on the sensor surface. Platinum atoms on the oxide surface facilitate the formation of oxygen vacancies and the dissociation of oxygen molecules at low temperatures, leading to increased adsorption and reaction with LPG molecules. This results in significant changes in the sensor's resistance, thereby amplifying the sensor response. The findings demonstrate the potential of Pt-doped ZO thin films for practical gas sensing applications.

Detection of riboflavin concentration by sol-gel silica coated dual-peak long period fiber grating sensor

A dual-peak long period fiber grating (DP-LPFG)-based sensor was designed and fabricated for the sensitive detection of riboflavin concentration. LPFGs with a period of 163 μm and a cladding mode of LP0, 12 were inscribed on a standard single-mode silica fiber using a femtosecond laser direct writing technique. Coatings of silica-based materials doped with β-cyclodextrin (β-CD), prepared via the sol-gel method, were applied to the surface of the LPFGs for the detection of riboflavin. To investigate the impact of coating thickness on the sensing sensitivity, sol-gel coatings of different thicknesses were applied to the surface of the LPFG sensor. Experimental findings revealed that the sensor with a thickness of approximately 540 nm sol-gel coatings exhibited superior sensing performance. The detection limit of the prepared DP-LPFG sensor was tested to be 0.08 nM, and it exhibits a response time of less than 3 minutes, along with high sensitivity, excellent repeatability, and selectivity. Thus, this sensor holds significant promise for applications in disease treatment and diagnosis, as well as in ensuring food quality.

High performance chemiresistive carbon-nanotube ammonia gas sensor surface modified by tantalum oxide (Ta2O5) metal nanoparticles

High performance chemiresistive carbon-nanotube ammonia gas sensor surface modified by tantalum oxide (Ta2O5) metal nanoparticles

3D printed oxygen gas sensor with a Pt-nanoparticles decorated N-doped carbon catalyst and an amine-polymer composited ionic liquid gel electrolyte

A 3D-printed electrochemical oxygen gas sensor was developed using a Pt nanoparticle-decorated N-doped carbon (PtNC) catalyst and an ionic liquid gel electrolyte incorporated with polyethyleneimine. At first, N-doped carbon particles were synthesized hydrothermally, followed by the decoration of a tiny amount of Pt nanoparticles using a microwave reactor. The working electrode was printed with a composite of high-impact polystyrene (HIPs), graphite powder (Gr), and a PtNC catalyst (HIPs/Gr/PtNC), then counter and reference electrodes were separately printed without the PtNC catalyst. The sensing materials were characterized using various analytical methods, including SEM, XPS, Raman, ICP-AES, CV, and EIS. Prior to detecting oxygen gas, the 3D sensor surface was pretreated with potential cycling in an acidic solution. Additionally, a composite gel electrolyte was prepared by incorporating polyethyleneimine into an ionic liquid, which was then coated onto the sensor surface to enhance sensitivity and ensure long-term stability. The analytical parameters using the final sensor were optimized in terms of Pt contents, 3D-printing polymer type, and ionic liquid gel concentration. The amperometric measurements demonstrated a wide dynamic range from 0.1 % to 100 % with the detection limit of 0.13 ± 0.05 % at a 90 % response time of 3.6 ± 0.4 s. To validate the reliability of the proposed sensor, the measurement of O2 content was performed for room air and standard oxygen gas, revealing reliable and stable results for six months.

A novel electrochemical sensor based on aspartic acid polymer and carbonized-ZIF-67 for rapid sensing of arbutin

A novel electrochemical sensor modified by aspartic acid polymer and carbonized-ZIF-67 was prepared for arbutin detection. ZIF-67 was synthesized and carbonized, and then used as the substrate supporting of electrochemical sensor. Carbonized-ZIF-67 had a large specific surface and good electrical conductivity, which provided large electroactive area and promoted the electron transfer at the sensing interface. Aspartic acid polymer was prepared by cyclic voltammetry. Aspartic acid polymer could effectively absorb arbutin, resulting in the preconcentration of arbutin on sensor surface. Benefiting from the synergistic effect between carbonized-ZIF-67 and aspartic acid polymer, the prepared electrochemical sensor exhibited sensitive electrochemical response for arbutin. Under the optimum conditions, the electrochemical sensor achieved a wide linear range in the range from 5 to 110 μmol/L and a low detection limit of 0.41 μmol/L for arbutin. In practical application, the electrochemical sensor was employed to detect arbutin in green tea and whitening cream samples, exhibiting satisfactory recovery rates. With the outstanding features of easy operation, rapid response and high sensitivity, the prepared electrochemical sensor provided a convenient and effective tool for arbutin detection.

An antifouling electrochemical sensor based on a U-shaped four-in-one peptide and poly(3,4-ethylenedioxythiophene) for vancomycin detection in fresh goat milk

Nonspecific adsorption of biomolecules (notably, proteins) and bacteria from unsterilized food may occur on sensor surfaces, which is still a challenge for food safety sensing. To achieve sensitive detection of unsterilized raw-food materials, in this study, a U-shaped four-in-one peptide with the sequence Ac-FLKLLKKLL-DOPA3-PPPPEEKDQDKEKaa that exhibited anchoring, antifouling, antibacterial, and recognition properties was designed. The peptide-modified sensor surface effectively prevented bacterial adhesion and proliferation while resisting biomolecule adsorption (signal inhibition rate as low as 0.51 % in single-protein solutions). A highly conductive polymer layer of poly(3,4-ethylenedioxythiophene) was introduced to improve the electrochemical performance before U-shaped four-in-one peptide anchoring. The proposed sensor could accurately detect vancomycin, with a wide linear range and limit of detection of 0.05–10 μg mL−1 and 2.06 ng mL−1 (S/N = 3), respectively. Satisfactory recovery rates (101.3–105.3 %) were achieved using diluted fresh goat milk.

REFRACTIVE INDEX BASED DETECTION WITH A HIGH SENSITIVITY BIOSENSOR ENHANCED BY GRAPHENE

Over the past decade, optical sensors have made significant advances. An optical sensor examines the environmental impact through the change of an optical signal and offers advantages such as low cost and label-free detection. In this study, a sensor consisting of a single graphene layer and a slit positioned on the substrate is proposed. The strip gap made to improve the excitation of graphene plasmons allowed to achieve 96.2% high transmission resonance mode. This demonstrates the ability of the sensor surface to detect changing environmental conditions. The results show that the sensitivity of the sensor is 6282 nm/RIU when the sensor surface is exposed to analytes with different refractive indices. The use of a single graphene sheet eliminates the need for a metal resonator and achieves a higher sensitivity compared to some experiments recently published in the literature. Thus, the disadvantage of significant ohmic losses in metal resonators is avoided. Furthermore, a thorough discussion of various factors, including the modification of the strip gap width on the graphene layer and electrical tunability, led to the achievement of optimal sensitivity.

Biometric-Tuned E-Skin Sensor with Real Fingerprints Provides Insights on Tactile Perception: Rosa Parks Had Better Surface Vibrational Sensation than Richard Nixon.

The dense mechanoreceptors in human fingertips enable texture discrimination. Recent advances in flexible electronics have created tactile sensors that effectively replicate slowly adapting (SA) and rapidly adapting (RA) mechanoreceptors. However, the influence of dermatoglyphic structures on tactile signal transmission, such as the effect of fingerprint ridge filtering on friction-induced vibration frequencies, remains unexplored. A novel multi-layer flexible sensor with an artificially synthesized skin surface capable of replicating arbitrary fingerprints is developed. This sensor simultaneously detects pressure (SA response) and vibration (RA response), enabling texture recognition. Fingerprint ridge patterns from notable historical figures - Rosa Parks, Richard Nixon, Martin Luther King Jr., and Ronald Reagan - are fabricated on the sensor surface. Vibration frequency responses to assorted fabric textures are measured and compared between fingerprint replicas. Results demonstrate that fingerprint topography substantially impacts skin-surface vibrational transmission. Specifically, Parks' fingerprint structure conveyed higher frequencies more clearly than those of Nixon, King, or Reagan. This work suggests individual fingerprint ridge morphological variation influences tactile perception and can confer adaptive advantages for fine texture discrimination. The flexible bioinspired sensor provides new insights into human vibrotactile processing by modeling fingerprint-filtered mechanical signals at the finger-object interface.

Quantum Dot/TiO2 Nanocomposite-Based Photoelectrochemical Sensor for Enhanced H2O2 Detection Applied for Cell Monitoring and Visualization.

This workexploits the possibility of using CdSe/ZnS quantum dot (QD)-electrodes to monitor the metabolism of living cells based on photoelectrochemical (PEC) measurements. To realize that, the PEC setup is improved with respect to an enhanced photocurrent signal, better stability, and an increased signal-to-noise ratio, but also for a better biocompatibility of the sensor surface on which cells have been grown. To achieve this, a QD-TiO2 heterojunction is introduced with the help of atomic layer deposition (ALD). The heterojunction reduces the charge carrier recombination inside the semiconductor nanoparticles and improves the drift behavior. The PEC performance is carefully analyzed by adjusting the TiO2 thickness and combining this strategy with multilayer immobilizations of QDs. The optimal thickness of this coating is ≈5nm; here, photocurrent generation can be enhanced significantly (e.g., for a single QD layer electrode by more than one order of magnitude at 0V vs Ag/AgCl). The resulting optimized electrode is used for hydrogen peroxide (H2O2) sensing with a good sensitivity down to µmolar concentrations, reusability, stability, response rate, and repeatability. Finally, the sensing system is applied to monitor the activity of cells directly grown on top of the electrode surface.

Significance of nanoparticle aggregation for thermal transport over magnetized sensor surface

Abstract This article explores the dynamics of nanofluids consisting of copper (TiO2) nanoparticles suspended in water, as they interact with sensor surfaces between two parallel squeezing plates with porous characteristics. This research specifically targets applications involving enhanced heat transfer and magnetohydrodynamic (MHD) control in nanofluid systems. The primary aim is to analyze the effects of nanoparticle aggregation and non-aggregation on sensor surfaces, considering MHD formations and heat transfer in the energy and momentum equations. The research adopts a steady-state fluid condition and utilizes similarity transformations to convert partial differential equations into more manageable ordinary differential equations. The methodology involves shooting methods for solving these nonlinear ordinary differential equations and employs graphical analyses to study the impacts of various parameters such as permeability, magnetic influence, squeeze flow, and radiation on the temperature and velocity profiles of the nanofluid. The results reveal significant dependencies of temperature and velocity profiles on the studied parameters, illustrating varied behaviors in scenarios of both aggregation and non-aggregation of nanoparticles. The findings emphasize how each parameter distinctively influences the heat and flow characteristics of the nanofluid, offering insights into optimizing conditions for better performance and control in practical applications. Future research could focus on extending the model to include transient fluid states and exploring the effects of other nanoparticle materials and shapes. There is also potential to investigate the interactions under different environmental conditions and to incorporate more complex boundary conditions to simulate real-world applications more accurately. Further experimental validation of the theoretical predictions would be beneficial to enhance the reliability and applicability of the findings.

In Situ Live Monitoring of Extracellular Acidosis near Cancer Cells Using Digital Microfluidics with an Integrated Optical pH Sensor Film.

We demonstrate the live monitoring of extracellular acidification on digital microfluidics using a chip-integrated fluorescent pH sensor film. The metabolism of various types of live cells including cancer and healthy cells were investigated through recording the extracellular pH (pHe) change. An optical pH sensor array was integrated onto a digital microfluidic (DMF) interface with a diameter of 2 mm per pH-sensing spot. Miniaturized, label-free, and noninvasive monitoring of extracellular acidosis on DMF was realized within a pH range of 5.0-8.0 with good sensitivity and rapid response. The pH sensitive probe fluorescein-5-isothiocyanate was covalently bound to poly-2-hydroxyethyl methacrylate and immobilized on a circularly exposed indium tin oxide interface on the DMF top plate. The surface of the fabricated pH sensor spots was modified with polydopamine via self-polymerization. Direct cell attachment on the sensor surfaces enabled rapid pH detection near the cell membranes. Automatic medium exchange on cell-attached pH sensing sites was achieved though solution passive dispensing on DMF. The developed DMF platform was used to monitor the pHe decrease during MCF-7 and A549 cancer cell proliferation due to abnormal glycolysis metabolism. A rapid pH decrease at the pH sensing area in the presence of cancer cells could be detected within 2 min after fresh medium exchange, while no obvious pHe change was observed with HUVEC healthy cells. Real-time detection of cell acidification and cellular response to different metabolic conditions such as higher glucose levels or administered anticancer drugs was possible.