Metal Oxide-based Sensors Research Articles

Biotemplate synthesis of single crystal MoO3 hierarchical tubules assembled from nano-rectangles for conductometric sensing of diisopropylamine vapor

The development of metal oxide-based gas sensors with high sensing to carcinogenic organoamines has recently attracted much attention. However, there is no related report on detecting diisopropylamine (DIPA). Herein, renewable poplar branches were selected as bio-template and immersed in ammonium molybdate solution. Subsequently, the above precursors were calcined in air to successfully synthesize two types of MoO3 nano-rectangles with different sizes. Amongst, biomorphic MoO3-500 tubules cross-linked by relatively small nano-rectangles were simply replicated by calcining precursors at 500 °C, which have multistage pores and single-crystal nature. Such structure characteristics can facilitate the fast diffusion of target gas, and increase the conductivity, active sites, as well as content of adsorbed oxygen species in sensing material. Especially, under the synergism of surface unsaturated Mo6+ catalysis, we realized the conductometric detection of DIPA vapor by metal oxide-based sensor for the first time. At 170 °C, MoO3-500 sensor shows high response value (244) and fast response speed (4 s) to 100 ppm DIPA vapor. Meanwhile, it still presents low detection limit, good selectivity and stability. Therefore, MoO3-500 tubules are expected to be a promising material for accurately detecting trace DIPA vapor.

Graphitic carbon-doped SnO2 nanosheets-wrapped tubes for chemiresitive ppb-level nitric oxide sensors operated near room temperature

The development of low-temperature metal oxide-based sensors with high sensing response towards harmful ppb-level gases remains challenging. Based on the idea of biological structure imitation, we choose wooden hydrangea petals as biotemplate and carbon source to controllably replicate graphitic carbon-doped SnO2 material (GC/SnO2-6) by simply calcining the salt solution-soaked precursor at 600 °C. Its morphology is tube bundle wrapped by corrugated sheets that formed by cross-linkage of nanoparticles. The internal surface of tube wall is decorated with nanoaggregates. The fabricated GC/SnO2-6 sensor exhibits response value of 256.3 towards 1 ppm NO at 50 ℃, which is 9.9 times higher than that (S = 26.0) of pure SnO2-7 material obtained by calcining at 700 ℃ in air. Meanwhile, this sensor also has short recovery time (42 s), low actual detection limit (50 ppb), satisfactory moisture resistance and long-term stability. Such excellent comprehensive gas-sensing performance is attributed to the homogeneous mesopore and large specific surface area of its biomorphic structure, as well as the synergism of graphitic carbon doping and abundant oxygen vacancies. In addition, the enhanced sensing mechanism is also explored in detail.

DEVELOPMENT OF DATA ACQUISITION SYSTEM FOR MOBILE ULTRAVIOLET (UV) MONITORING DEVICE

In this age of modernization, smart or self-sufficient frameworks in all domains of work are becoming increasingly important as innovation advances. This involves improving data collecting for UV monitoring system using metal oxide sensors, an underdeveloped market niche. The Data Acquisition (DAQ) system available at the moment is antiquated and frustrating. This project aims to establish a framework for acquiring information about UV monitoring devices using metal oxide sensors. Metal oxide-based sensor uses titanium dioxide nanorod arrays (TNAs). Self-powered UV photosensor creates electricity when exposed to UV light. UV photosensors are photoelectrochemical (PEC). Monitoring the sensor's real-time output voltage in relation to UV intensity evaluates the data acquisition system's performance. A Raspberry Pi is used to evaluate the data security architecture for the Cytron-UNO development board. The sensor's data gathering system detected the current produced and stamped the date and time on it. This paper discusses trait formation and experimental data.

Significant improvement in the acetone sensing performance of Ag-decorated ZnO porous nanosheets through defect engineering by Li-ion implantation

Defect engineering by Li-ion implantation has been extensively studied in electrocatalysis, photocatalysis, and energy storage devices. Here, we provide the first experimental evidence that Li-ion implantation improves the acetone sensing performance of ZnO-based sensors. The morphological structure of the solvothermally synthesized Ag-decorated ZnO porous nanosheets (Ag-ZnO PNSs) was controlled by Li-ion insertion/extraction at various discharge voltages. The generation of nanocracks caused by the electrochemical reaction between ZnO and Li significantly improved the sensing performance. The nanocracked Ag-ZnO PNSs had a much higher sensing response (∼319) to 10 ppm acetone than the ZnO nanoparticles, bare ZnO PNSs, and bare Ag-ZnO PNSs. At the optimum operating temperature of 400 °C, the low detection limit was 0.1 ppm. The significant improvement in the acetone sensing performance of nanocracked sample is attributed to the simultaneous increase in oxygen vacancies and specific surface area, as well as the Ag catalytic effect. Furthermore, the nanocrack structures were found to be stable even after repeated measurements at high temperatures. Our research found that Li-ion implantation is an effective method for improving the gas sensing performance of metal oxide-based sensors, and that nanocracked Ag-ZnO PNSs can be a promising candidate material for use as acetone sensor applications.

Recent Advances in Ethylene Gas Detection.

The real-time detecting and monitoring of ethylene gas molecules could benefit the agricultural, horticultural and healthcare industries. In this regard, we comprehensively review the current state-of-the-art ethylene gas sensors and detecting technologies, covering from preconcentrator-equipped gas chromatographic systems, Fourier transform infrared technology, photonic crystal fiber-enhanced Raman spectroscopy, surface acoustic wave and photoacoustic sensors, printable optically colorimetric sensor arrays to a wide range of nanostructured chemiresistive gas sensors (including the potentiometric and amperometric-type FET-, CNT- and metal oxide-based sensors). The nanofabrication approaches, working conditions and sensing performance of these sensors/technologies are carefully discussed, and a possible roadmap for the development of ethylene detection in the near future is proposed.

In Vivo Sensing of pH in Tomato Plants Using a Low-Cost and Open-Source Device for Precision Agriculture.

The development of sensing devices for precision agriculture is crucial to boost crop yields and limit shortages in food productions due to the growing population. However, current approaches cannot provide direct information about the physiological status of the plants, reducing sensing accuracy. The development of implanted devices for plant monitoring represents a step forward in this field, enabling the direct assessment of key biomarkers in plants. However, available devices are expensive and cannot be used for long-term applications. The current work presents the application of ruthenium oxide-based nanofilms for the in vivo monitoring of pH in plants. The sensors were manufactured using the low-cost electrodeposition of RuO2 films, and the final device could be successfully incorporated for the monitoring of xylem sap pH for at least 10 h. RuO2 nanoparticles were chosen as the sensing material due to its biocompatibility and chemical stability. To reduce the noise rates and drift of the sensors, a protective layer consisting of a cellulose/PDMS hybrid material was deposited by an aerosol method (>GBP 50), involving off-the-shelf devices, leading to a good control of film thickness. Nanometrically thin films with a thickness of 80 nm and roughness below 3 nm were fabricated. This film led to a seven-fold decrease in drift while preserving the selectivity of the sensors towards H+ ions. The sensing devices were tested in vivo by implantation inside a tomato plant. Environmental parameters such as humidity and temperature were additionally monitored using a low-cost Wio Terminal device, and the data were sent wirelessly to an online server. The interactions between plant tissues and metal oxide-based sensors were finally studied, evidencing the formation of a lignified layer between the sensing film and xylem. Thus, this work reports for the first time a low-cost electrochemical sensor that can be used for the continuous monitoring of pH in xylem sap. This device can be easily modified to improve the long-term performance when implanted inside plant tissues, representing a step forward in the development of precision agriculture technologies.

Biomorphic ZnO Nanotubes for n-Pentanol Sensing

It is of great practical significance to develop portable and conductometric sensors for detecting flammable and explosive high-energy n-pentanol vapor. In view of the very few reports on metal oxide-based n-pentanol sensors, herein, biomorphic ZnO nanotubes were synthesized through a zinc salt impregnation–calcination method using poplar branch as a biotemplate. The multistage porous ZnO-500 tube arrays obtained from calcination at 500 °C are cross-linked by small-size nanoparticles, which are beneficial to the rapid adsorption and diffusion of n-pentanol vapor with a long alkyl chain. A ZnO-500-based sensor presents high and fast response (S = 221.0; Tres = 4 s) to 100 ppm n-pentanol vapor at 252 °C, as well as a low detection limit (100 ppb) and a wide linear relationship. Under the synergistic effect of inherent characteristics of the biomorphic structure and biotemplate imprinting, the above comprehensive gas-sensing indicators are significantly superior to those of the reported metal oxide-based sensors. Thus, the porous ZnO-500 nanomaterials prepared by a simple, low-cost, and controllable biotemplate method have the potential to be fabricated as candidates for the rapid and accurate detection of trace amounts of n-pentanol.

An Ultrasensitive Room-Temperature H₂S Gas Sensor Based on 3D Assembly of Cu₂O Decorated WS₂ Nanomaterial

Herein, we report for the first time on the fabrication of a hybrid material consisting of Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O nanoparticles-decorated multilayered tungsten disulfide nanostructures and demonstrate their remarkable gas sensing characteristics towards hydrogen sulfide gas. In the first step, a continuous film of WS2 was deposited directly on commercial alumina substrate by adopting a facile route combining aerosol-assisted chemical vapor deposition with H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> free atmospheric pressure CVD technique. For functionalization an additional step of synthesis was added where copper oxide nanoparticles were grown and deposited directly over as-grown tungsten disulfide at low temperature (i.e., 150 °C) using a simple and cost-effective technique. The morphological, structural and chemical characteristics were investigated using FESEM, TEM, and EDX spectroscopy. The gas-sensing studies performed shows that this hybrid nanomaterial has excellent sensitivity towards hydrogen sulfide (11-times increase in response compared to that of pristine WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor) at moderate temperature (150 °C). Additionally, functionalization of pristine WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor with Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O nanoparticles further enhances the gas sensing performance towards the targeted gas even at room temperature (13-times increase in response compared with that of pristine WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor). Moreover, results obtained from humidity cross-sensitivity of Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O-WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor indicates superior gas sensing response (with a negligible decrease in response) as compared to pristine WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor, when ambient humidity is increased to 50%, which is rarely found in metal oxide-based sensors. This study could add a significant research value in the gas sensor domain.

Study Design and Development Gas Sensor Technology for Motor Vehicle Exhaust Emissions

Metal oxide-based gas sensors, have been used in the detection of gaseous pollutants emitted from motor vehicles, such as CO, SO2, NH3, NOx, hydrocarbons (HC) etc. However, the problems that up to now are still faced by the metal oxide-based sensors are reviews their low sensitivity, low selectivity and lack of stability. Therefore, it is difficult, to the make such an accurate metal oxide-based sensor and stable over a long period of time. In this short review, it will be described the state-of-the-art technology, design and fabrication methods and various techniques that can be applied to improve the performance of metal oxide-based sensors. Keywords: gaseous pollutants, the motor vehicle emission, gas sensors, metal oxide

Hydrangea-type bismuth molybdate as a room-temperature smoke and humidity sensor

Detecting smoke at room-temperature using unrealistic metal oxide-based sensor is the most important component in a fire alarm system. We report on highly sensitive and selective chemically grown porous hydrangea-type bismuth molybdate (Bi2MoO6) room-temperature smoke and humidity sensor. The as-synthesized Bi2MoO6 sensor has been initially screened for its structure, morphology, surface elemental composition, type of conductivity and porosity measurements by various means and then is exposed to different gases like ammonia, acetone, ethanol, methanol, and benzaldehyde as a room-temperature i.e., 25 ºC. Hydrangea-type nanocrystalline and mesoporous n-type Bi2MoO6 sensor demonstrates a sensitive response of 59% towards 40 vol% smoke with a fast response/recovery time of 60/14 s at room-temperature which would find a potential use in a fire alarm system. Despite of n-type semiconducting nature, Bi2MoO6 sensor endows quite good response after the exposure of smoke. Effect of smoke concentration and relative humidity on sensor resistance followed performance has also been explored. The alterations in band bending, under various operation conditions, are illustrated using schematic structural views with the help of possible structural images.

Theoretical study on W-Co3O4 (1 1 1) surface: Acetone adsorption and sensing mechanism

Volatile organic compounds are highly toxic, and need advanced sensing technology for detection. The morphology, composition and surface characteristics are critical parameters to enhance the gas sensing of metal oxide-based sensors. However, the experimental results only reflect macroscopic phenomena, but cannot explain the sensing mechanism in depth. In this study, the acetone sensing performance of pristine and W modified Co3O4 (111) surface have been studied using DFT methods. Various adsorption sites have been investigated on top of the clean and O adsorped W-Co3O4 (111) surfaces. Our results show the decorated W atom in direct vicinity of pre-adsorbed oxygen is the best site for acetone adsorption. The modification of W atom makes energy band-gap narrower, alters the electronic properties, and enhances the number of transferred electrons. Our study provides a theoretical basis for finding better modified p-type semiconductor sensors toward acetone.

Experimental verification of mixed metal oxide-based sensor for multiple sensing application

Mixed Metal Oxide (MMO) based piezoelectric sensor was fabricated using Zinc Oxide (ZnO) and Ferric Oxide (Fe2O3). The X-Ray diffraction pattern shows the presence of ZnO and Fe2O3 with the respective characteristic peaks. Field Emission Scanning Electron Microscope confirms the ZnO nanorods grown using the hydrothermal method and shows the deposition of Fe2O3 nanoparticles on the ZnO nanorods. The electrical analysis using photoconductivity study reveals the formation of p-n junction in both the samples. The fabricated MMO sensor when subjected to piezoelectric sensing set up gave an improved output voltage of 1.32 V for 1 g input acceleration compared to the other. Similarly, when both the sensors were exposed to gas sensing setup, improved sensitivity of 7.66 and 0.791 for 100 ppm of Carbon Monoxide and Methane at room temperature respectively was obtained when compared to the other sensor fabricated.

Absorbent cotton derived mesoporous CeO2 hollow tubule for enhanced detection of p-xylene at low energy consumption

Ultra-sensitive detection of flammable and carcinogenic p-xylene gas at relatively low energy consumption through metal oxide-based sensors remains a great challenge due to its high stability. Herein, mesoporous CeO2 hollow microtubules with cubic fluorite structure were simply prepared by immersing absorbent cotton into cerium salt and subsequent calcination. The effect of calcination temperature on the microstructure and gas-sensing performance was also studied. The CeO2-500 hierarchical structure calcinated at 500 °C is composed of cross-linked nanoparticles with small size (12 nm), which possesses relatively large specific surface area (60.8 m2·g−1), well-distributed mesopores (15.0 nm) and abundant oxygen vacancy defects. At a relatively low operating temperature of 133 °C, CeO2-500 sensor shows a fast response to 100 ppm p-xylene (Tres = 5.4 s) and detection limit of 100 ppb, which represents the lowest value in reported CeO2-based sensors. Such excellent gas-sensing performance is highly related to the intrinsic structural properties of mesoporous CeO2-500 hollow microtubule, surface adsorbed oxygen and oxygen vacancy defects caused by Ce3+ ions.

Metal-organic framework-derived highly dispersed Pt nanoparticles-functionalized ZnO polyhedrons for ppb-level CO detection

Abstract Metal oxides-based CO sensors with ppb-level detection limit are highly desirable in the application of air quality monitoring and exhaled breath detection. Synthesis of porous nanostructure unit with a large number of active sites has been deemed as an effective way to lower the detection limit of metal oxides-based sensors. This work reports a regular approach for the synthesis of highly dispersed Pt nanoparticles-functionalized ZnO polyhedrons (Pt NPs@ZnO) using metal-organic framework (ZIF-8) as a template. Nanoscale Pt NPs with a narrow size distribution (2−5 nm) were in-situ loaded on the cavities of porous ZnO. The prepared Pt NPs@ZnO polyhedrons exhibited good CO response ((Ra-Rg)/Ra·100 % = 9%–500 ppb), long-term stability, ultra-low detection limit (100 ppb) and superior CO selectivity. To the best of our knowledge, the detection limit toward CO reported in this work is the lowest experimental value among those metal oxide-based sensors reported so far. The enhanced CO sensing properties are owing to the porous nanostructures, high specific surface area, the catalytic effects and electron sensitization effects of highly dispersed Pt NPs. The Pt NPs@ZnO sensor has a great potential application for detecting low-concentration CO.

Synthesis of Cu–Ti thin film multilayers on silicon substrates

Metal-oxide-based sensors (MOS) can be used for several technological applications in microelectronics, due to their low cost and sensitive capabilities to different chemical species. On the perspective to develop CuO–TiO2 MOS, our goal was to obtain a homogeneous intermixing of Cu and Ti in the bulk structure of the detectors, exploring the most promising combination between such elements and avoiding the presence of Cu–Ti–O compounds. To do that, several Cu and Ti thin layers were alternatively deposited by Ar+ sputtering on silicon wafers and, subsequently, oxidized by thermal annealing. The obtained samples were characterized in terms of %at. Cu–Ti ratios (by RBS and SIMS analyses) and morphology (by AFM and SEM investigations), showing the abundance ratios of such elements in the whole structure. In particular, SIMS maps allowed to study the spatial distribution and thickness of each phase of the Cu–Ti multilayers and further to observe the Cu diffusion and the mixing with Ti, as well as phase separation of CuO and TiO2 in the samples. This unwanted effect represents an open issue that has to be investigated, in order to improve the MOS fabrication.

Fast Selective Sensing of Nitrogen-Based Gases Utilizing δ-MnO2-Epitaxial Graphene-Silicon Carbide Heterostructures for Room Temperature Gas Sensing

Real-time toxic gas mapping in complex urban environments have become increasingly possible with improvements in data analysis and network infrastructures. Hindering this is the cost and operation requirements of commercial gas sensors, requiring sensors with high sensitivity and selectivity that are robust and capable of operating at room temperature. Transition metal oxide-based sensors are of historical significance in the production of commercial gas sensors due to their low cost and high selectivity to target gases. The low inherent conductivity of metal oxides, however, requires operating temperatures higher than 150 °C, limiting their operation to controlled environments. To overcome this limitation, heterostructures have been formed between graphene and transition metal oxides, seeking to couple the conductivity of graphene with the reactivity of transition metal oxides. Among these transition metal oxides, manganese dioxide exhibits unique properties that can be leveraged to improve gas sensing. Its wide variety of synthesized structural polymorphs ( $1\times 1$ tunnel ( $\beta$ ), $1\times 2$ tunnel ( $\alpha$ ), spinel ( $\gamma$ ), and layered ( $\delta)$ ) allow for control over the available reactive surface area to enhance gas response. By utilizing defect rich $\delta $ -phase, the reactivity of the material can be improved. Here we present a $\delta $ -MnO2/epitaxial graphene/silicon carbide heterostructure for use as a room temperature gas sensor. We confirm the composition through Raman spectroscopy and surface morphology through scanning electron microscopy and atomic force microscopy. We then demonstrate its room-temperature detection by testing against NO2, NH3, IPA, and CH3OH at room temperature. [2020-0144]

Atomic Layer Deposition of SnO2-Coated Anodic One-Dimensional TiO2 Nanotube Layers for Low Concentration NO2 Sensing.

The continuous emission of nitrous oxides contributes to the overall air pollution and deterioration of air quality. In particular, an effective NO2 sensor capable of low concentration detection for continuous monitoring is demanded for safety, health, and wellbeing. The sensing performance of a metal oxide-based sensor is predominantly influenced by the availability of surface area for O2 adsorption and desorption, efficient charge transport, and size or thickness of the sensing layer. In this study, we utilized anodic one-dimensional (1D) TiO2 nanotube layers of 5 μm thick which offer large surface area and unidirectional electron transport pathway as a platform to accommodate thin SnO2 coatings as a sensing layer. Conformal and homogeneous SnO2 coatings across the entire inner and outer TiO2 nanotubes were achieved by atomic layer deposition with a controlled thickness of 4, 8, and 16 nm. The SnO2-coated TiO2 nanotube layers attained a higher sensing response than a reference Figaro SnO2 sensor. Specifically, the 8 nm SnO2-coated TiO2 nanotube layer has recorded up to ten-fold enhancement in response as compared to the blank nanotubes for the detection of 1 ppm NO2 at an operating temperature of 300 °C with 0.5 V applied bias. This is attributed to the SnO2/TiO2 heterojunction effect and controlled SnO2 thickness within the range of the Debye length. We demonstrated in this work, a tailored large surface area platform based on 1D nanotubes with thin active coatings as an efficient approach for sensing applications and beyond.

Rare earth-tuned oxygen vacancies in gadolinium-doped tin oxide for selective detection of volatile organic compounds

The gas sensing characteristics of metal oxide-based sensors are found to be influenced by the oxygen vacancies (OVs) that act as selective sites for gas adsorption. To ascertain the effect of OVs on gas sensing properties of tin oxide (SnO2), rare earth (gadolinium)-doped SnO2 thin films have been prepared via electron beam evaporation technique and characterized for structural, optical, and gas sensing properties. Spectroscopic studies revealed the doping dependence of in-plane and sub-bridging OVs that influence the gas interaction properties of Gd-doped SnO2 films. The dominance of sub-bridging OVs leads to enhanced sensing characteristics of 3% Gd-doped SnO2 film towards isopropanol. The gas sensing characteristics of metal oxide-based sensors are found to be influenced by the OVs that act as selective sites for gas adsorption. Among the tested volatile organic compounds (VOCs), the dominance of sub-bridging OVs leads to enhanced sensing characteristics of 3% Gd-doped SnO2 film towards isopropanol.

P-p Heterojunction Sensors of p-Cu3Mo2O9 Micro/Nanorods Vertically Grown on p-CuO Layers for Room-Temperature Ultrasensitive and Fast Recoverable Detection of NO2.

High sensitivity, low limit of detection (LOD), and short response and recovery times at room temperature (RT) are critical for gas sensors. For NO2, different binary metal oxide-based sensors were developed to achieve superior performance at elevated temperatures instead of RT. Herein, we report on CuO@CuO and Cu3Mo2O9@CuO sensors with CuO and Cu3Mo2O9 micro/nanorods vertically aligned on the CuO layers, which were directly fabricated using a facile, low-cost, and catalyst-free chemical vapor deposition (CVD) technique. Their sensing performance tests revealed that the Cu3Mo2O9@CuO p-p heterojunction sensors exhibited a high response of 160% to 5 ppm NO2, an excellent sensitivity of 50% ppm-1, a low LOD of 2.30 ppb, a short response time of 49 s, and a rapid recovery of 241 s at RT, obviously better than those for CuO@CuO sensors. The superior performance of Cu3Mo2O9@CuO sensors could be attributed to the Schottky heterojunction formed between p-Cu3Mo2O9 micro/nanorods and p-CuO films, the catalytic effect, and the anisotropic nature of Cu3Mo2O9 micro/nanorods. This study not only provides a simple, low-cost, and batchable fabrication method of homo/heterojunction sensors with micro/nanorods vertically aligned on films but also opens an avenue for sensor design by tuning the Schottky barrier height to enhance RT performance.

Cerium oxide-monoclonal antibody bioconjugate for electrochemical immunosensing of HER2 as a breast cancer biomarker

Metal oxide-based sensors have the advantage of rapid response and of high sensitivity to detect specific active biological species and are relatively inexpensive. This report of the present study concerns the development of a cerium oxide – monoclonal antibody bioconjugate for its application as a sensitive immunosensor to detect a breast cancer biomarker. A cerium oxide-anti HER2 bioconjugate was constructed by adding anti HER2 onto cerium oxide that had been previously reacted with APTMS and PEG-NHS-Maleimide. The FTIR spectra of the reaction product showed that the cerium oxide-anti HER2 bioconjugate was successfully synthesized. The resulted bioconjugate was then immobilized on a screen-printed carbon‑gold nanoparticles electrode surface by using the amine coupling bonding systems. The interaction of the synthesized cerium oxide-anti-HER2 bioconjugate with HER2 was found to inhibit an electron transfer and a decrease in the voltammetric Fe(CN)63-/4- peak current, which was proportional to the concentration of HER2. The optimal response of the current signal was generated at an anti-HER2 concentration of 5.0 μg/mL. The two linear ranges of HER2 concentration were found: that were 0.001 to 0.5 ng/mL and 0.5 to 20.0 ng/mL. By using the first calibration curve, the limit of detection was 34.9 pg/mL. The developed label-free immunosensor was used to determine HER2 in a human serum sample with satisfactory results, as shown by a consistent result with the addition of standard. Thus, the resulted immunosensor in this study is promising and has a potential application in clinical bio-analysis.