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Determining the concentration of biomarkers offers insights into the health condition and performance of the body. The majority of the biosensors applied to measuring biomarkers in biological fluids are electrochemical bases; however, these biosensors suffer from several key drawbacks. These include utilizing complex sensing materials to obtain desirable analytical performance, which prevents their practical application; and operation at a relatively high potential, which leads to inaccurate measurements due to the undesired oxidation of non-target molecules. A novel photo-induced chemiresistive biosensor is introduced here that addresses these challenges. A UV-induced ZnO nanorod (NR) chemiresistive biosensor is developed and applied to monitoring lactate and glucose, as model biomarkers in sweat. The detection mechanism of lactate based on its interaction with ZnO NRs is proposed. Furthermore, the effect of the electrode design and operating parameters, including irradiance, radiation wavelength, and applied potential, are evaluated. The highest response, the shortest response time, and complete recovery are obtained at 5.6 mW/cm2 irradiance of 365 nm and 0.1 V potential. The results indicate that the developed transduction platform utilizing a simple sensing layer is a promising technique with excellent analytical performance for detecting different biomarkers, thereby paving the way toward the emergence of photo-induced chemiresistive biosensors for real-life applications.

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Vertically aligned ZnO nanorods (NRs) were grown hydrothermally on the wide bandgap (∼3.86 - 4.04 eV) seed layers (SLs) of grain size ∼162 ± 35 nm, prepared using ball-milled derived ZnO powder. The synthesized ZnO NRs were further decorated with ZnS nanocrystals to achieve a ZnO NR-ZnS core-shell (CS)-like nano-scaffolds by a subsequent hydrothermal synthesis at 70 °C for 1 h. UV-Vis-NIR spectroscopy, x-ray diffractometry (XRD), Raman spectroscopy and Field emission scanning electron microscopy (FESEM) coupled with Energy dispersive x-ray spectroscopy (EDX) analyses confirmed the formation of ZnS atop the vertically aligned ZnO NR arrays of ∼1.79 ± 0.17µm length and ∼165 ± 27 nm diameter. Transmission electron microscopy (TEM)/EDX analyses revealed that vertically aligned ZnO NRs (core dia. ∼181 ± 12 nm) arrays are conformally coated by an ultrathin ZnS (∼25 ± 7 nm) shell layer with a preferential ZnS{111}/ZnO{10-10}-like partial epitaxy. The ZnO NRs exhibited a sharp band edge near ∼384 nm having optical bandgap energy (Eg) of ∼3.23 eV. However, the ZnO NR-ZnS CS exhibited double absorption bands atEg∼ 3.20 eV (ZnO-core) andEg∼ 3.78 eV (ZnS-shell). The ZnS{111}/ZnO{10-10}-nano-scaffolds could be utilized to facilitate the enhanced absorption of UV photons as well as the radial junction formation between the Pb-free perovskite absorber and ZnS/ZnO NRs layers.

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ZnO nanostructures show great potential in hydrogen sensing at atmospheric conditions for good gas adsorption abilities. However, there is less research on low-pressure hydrogen sensing performance due to its low concentration and in-homogeneous distributions under low-pressure environments. Here, we report the low-pressure hydrogen sensing by the construction of Al-N-co-doped ZnO nanorods based on the adsorption-induced field emission enhancement effect in the pressure range of 10-7 to 10-3 Pa. The investigation indicates that the Al-N-co-doped ZnO sample is the most sensitive to low-pressure hydrogen sensing among all ZnO samples, with the highest sensing current increase of 140% for 5 min emission. In addition, the increased amplitude of sensing current for the Al-N-co-doped ZnO sample could reach 75% at the pressure 7 × 10-3 Pa for 1 min emission. This work not only expands the hydrogen sensing applications to the co-doped ZnO nanomaterials, but also provides a promising approach to develop field emission cathodes with strong low-pressure hydrogen sensing effect.

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Water pollutants harm ecosystems and degrade water quality. At the same time, many pollutants carry potentially valuable chemical energy, measured by chemical oxygen demand (COD). This study highlights the potential for energy harvesting during remediation using photocatalytic fuel cells (PCFCs), stressing the importance of economically viable and sustainable materials. To achieve this, this research explores alternatives to platinum cathodes in photocathodes and aims to develop durable, cost-effective photoanode materials. Here, zinc oxide nanorods of high density are fabricated on carbon fiber surfaces using a low-temperature aqueous chemical growth method that is simple, cost-efficient, and readily scalable. Alternatives to the Pt cathodes frequently used in PCFC research are explored in comparison with screen-printed PEDOT:PSS cathodes. The fabricated ZnO/carbon anode (1.5 × 2 cm2) is used to remove the model pollutant used here and salicylic acid from water (30 mL, 70 µM) is placed under simulated sunlight (0.225 Sun). It was observed that salicylic acid was degraded by 23 ±0.46% at open voltage (OV) and 43.2 ± 0.86% at 1 V with Pt as the counter electrode, degradation was 18.5 ± 0.37% at open voltage (OV) and 44.1 ± 0.88% at 1 V, while PEDOT:PSS was used as the counter electrode over 120 min. This shows that the PEDOT:PSS exhibits an excellent performance with the full potential to provide low-environmental-impact electrodes for PCFCs.

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Optoelectronic devices have various applications in medical equipment, sensors, and communication systems. Photodetectors, which convert light into electrical signals, have gained much attention from many research teams. This study describes a low-cost photodetector based on CuO nanoparticles and ZnO nanorods operating in a wide range of light wavelengths (395, 464, 532, and 640 nm). Particularly, under 395 nm excitation, the heterostructure device exhibits high responsivity, photoconductive gain, detectivity, and sensitivity with maximum values of 1.38 A·W-1, 4.33, 2.58 × 1011 Jones, and 1934.5% at a bias of 2 V, respectively. The sensing mechanism of the p-n heterojunction of CuO/ZnO is also explored. Overall, this study indicates that the heterostructure of CuO nanoparticles and ZnO nanorods obtained via a simple and cost-effective synthesis process has great potential for optoelectronic applications.

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Rapid and sensitive detection of Dengue virus remains a critical challenge in global public health. This study presents the development and evaluation of a Zinc Oxide nanorod (ZnO NR)-surface-integrated microfluidic platform for the early detection of Dengue virus. Utilizing a seed-assisted hydrothermal synthesis method, high-purity ZnO NRs were synthesized, characterized by their hexagonal wurtzite structure and a high surface-to-volume ratio, offering abundant binding sites for bioconjugation. Further, a comparative analysis demonstrated that the ZnO NR substrate outperformed traditional bare glass substrates in functionalization efficiency with 4G2 monoclonal antibody (mAb). Subsequent optimization of the functionalization process identified 4% (3-Glycidyloxypropyl)trimethoxysilane (GPTMS) as the most effective surface modifier. The integration of this substrate within a herringbone-structured microfluidic platform resulted in a robust device for immunofluorescence detection of DENV-3. The limit of detection (LOD) for DENV-3 was observed to be as low as 3.1 × 10-4 ng/mL, highlighting the remarkable sensitivity of the ZnO NR-integrated microfluidic device. This study emphasizes the potential of ZnO NRs and the developed microfluidic platform for the early detection of DENV-3, with possible expansion to other biological targets, hence paving the way for enhanced public health responses and improved disease management strategies.

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In this study, the integration of carbon nanotube (CNT), graphene, and biochar (BC) with zinc oxide nanorods (ZnO NRs) was investigated for efficient water pollutant removal. Two types of ZnO NRs/BC hybrids (BC on top and bottom of ZnO NRs) were synthesized and compared to other carbon material-based ZnO NRs combinations. Methylene blue (MB) adsorption efficiency was evaluated for various carbon material-based ZnO NRs composites, revealing good performance in ZnO NRs/BC hybrids, particularly with BC on top. The adsorption efficiency reached an impressive 61.79% for ZnO NRs/BC, surpassing other configurations. MB removal by ZnO NRs/BC fitted well with pseudo-first-order kinetics and the rate constants of MB adsorption is 9.19 × 10-2 1/min (R2 = 0.9237). Surface characterizations revealed a distinctive distribution of BC grains, with denser aggregation observed on top of ZnO NRs. This unique distribution contributed to higher MB adsorption rates, substantiated by Fourier transform infrared spectroscopy (FTIR) analysis that showcased stronger MB adsorption in ZnO NRs/BC hybrids. Notably, the enhanced MB adsorption rates were attributed to the population of BC grains. This research establishes ZnO NRs/BC composites as promising candidates for effective water pollutant removal. The developed materials can be combined with the existed conventional wastewater treatment systems to further purify the water quality. PRACTITIONER POINTS: ZnO NRs/BC hybrids achieve a remarkable 61.79% efficiency in removing MB pollutants, surpassing other carbon materials. MB removal using BC-based materials follows pseudo-first-order kinetics. BC grains exhibit unique distribution patterns on ZnO NRs, with densely packed grains atop contributing to higher MB removal. FTIR analysis confirms increased MB-related bond vibration, supporting the effectiveness of ZnO NRs/BC hybrids for water pollutant removal.

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In recent years, defect engineering has shown great potential to improve the properties of metal oxide nanomaterials for various applications thus received extensive investigations. While traditional techniques mostly focus on controlling the defects during the synthesis of the material, laser irradiation has emerged as a promising post-deposition technique to further modulate the properties of defects yet there is still limited information. In this article, defects such as oxygen vacancies are tailored in ZnO nanorods through nanosecond (ns) laser irradiation. The relation between laser parameters and the temperature rise in the ZnO due to laser heating was established based on the observation in the SEM and the simulation. Raman spectra indicated that the concentration of the oxygen vacancies in the ZnO is temperature-dependent and can be controlled by changing the laser fluence and exposure time. This is also supported by the absorption spectra and the photoluminescence spectra of ZnO NRs irradiated under these conditions. On the other hand, the distribution of the oxygen vacancies was studied by XPS depth profiling, and it was confirmed that the surface-to-bulk ratio of the oxygen vacancies can be modulated by varying the laser fluence and exposure time. Based on these results, four distinctive regimes containing different ratios of surface-to-bulk oxygen vacancies have been identified. Laser-processed ZnO nanorods were also used as the catalyst for the photocatalytic degradation of rhodamine B (RhB) dye to demonstrate the efficacy of this laser engineering technique.

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Photo(electro)-piezo catalysis has emerged as one of the most effective strategies for sustainable environmental remediation. While various (nano)materials have been investigated for enhancing the intrinsic properties related to the interfacial band structure, increasing the efficiency by integration of materials with rational design for stress-strain applications has not yet been considered. Herein, we introduce kirigami strain engineering to photopiezo catalysts for enhancing efficiency by increasing the magnitude of applied strain and density of bends. Macroscale stretching motion is converted into localized bending by a pliable kirigami structure using similar or even lower input energy, which can be easily modulated by natural waves. The kirigami structure leads to a significant enhancement (∼250%) in the degradation of dyes, and we discovered the significant contribution of the oxygen reduction pathway in the charge-transfer mechanism, which corresponds to the observed enhancement. The photopiezo catalytic effects of kirigami were further highlighted by the small water reservoir test, showing its feasibility in nature for self-sustainable environmental remediation that can be modulated using motions of winds, waves, and life vibrations.

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Dilute magnetic semiconductor Zn1-xCuxO (x = 0, 1.5, 3.0, and 4.5%) nanorods were prepared by hydrothermal method. The impact of dopant concentration on the physical properties was investigated along with the anti-bacterial and photocatalytic activities. Synthesis of ZnO nanorods was confirmed by the characteristic band at 380 nm in UV-Visible spectra of the synthesized samples. A red shift in absorbance spectra was observed from 380 to 465 nm with an increase in dopant concentration. The hexagonal wurtzite geometry and rod-like morphology of Cu-doped ZnO nanorods having an average size of 29 nm were confirmed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM), respectively. An increase in the crystallinity of the material was observed with an increase in the dopant (Cu) ratio without any alteration in geometry. EDX analysis was used to confirm the purity of samples. FTIR spectra were recorded to explore the functional group present in samples. The hysteresis loop drawn by a vibrating-sample magnetometer (VSM) was utilized to analyze the ferromagnetic behavior. As-synthesized pure and Cu-ZnO nanorods were evaluated for their photocatalytic behavior for the photodegradation of methyl orange (MO) dye. Zn1 - xCuxO with x = 4.5%, pH 3, and catalyst dosage of 0.5 g has shown the maximum efficiency. Results elucidated > 81% degradation of MO dye with a rate constant (k) value of - 1.930 × 10-2 min-1 in just 90 min of exposure to a visible light source. ZnO nanorods have also exhibited anti-bacterial potential against gram-positive and gram-negative strains of bacteria. However, smaller size nanorods were found more effective to suppress the growth of gram-negative bacteria. A slight decrease (11%) in catalytic potential was observed in the 5th cycle during recycling and reuse experiments.

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In the context of ZnO nanorods (NRs) grown on Si and indium tin oxide (ITO) substrates, this study aimed to compare their degradation effect on methylene blue (MB) at different concentrations. The synthesis process was carried out at a temperature of 100 °C for 3 h. After the synthesis of ZnO NRs, their crystallization was analyzed using X-ray diffraction (XRD) patterns. The XRD patterns and top-view SEM observations demonstrate variations in synthesized ZnO NRs when different substrates were used. Furthermore, cross-sectional observations reveal that ZnO NRs synthesized on an ITO substrate exhibited a slower growth rate compared to those synthesized on a Si substrate. The as-grown ZnO NRs synthesized on the Si and ITO substrates exhibited average diameters of 110 ± 40 nm and 120 ± 32 nm and average lengths of 1210 ± 55 nm and 960 ± 58 nm, respectively. The reasons behind this discrepancy are investigated and discussed. Finally, synthesized ZnO NRs on both substrates were utilized to assess their degradation effect on methylene blue (MB). Photoluminescence spectra and X-ray photoelectron spectroscopy were employed to analyze the quantities of various defects of synthesized ZnO NRs. The effect of MB degradation after 325 nm UV irradiation for different durations can be evaluated using the Beer-Lambert law, specifically by analyzing the 665 nm peak in the transmittance spectrum of MB solutions with different concentrations. Our findings reveal that ZnO NRs synthesized on an ITO substrate exhibited a higher degradation effect on MB, with a rate of 59.5%, compared to NRs synthesized on a Si substrate, which had a rate of 73.7%. The reasons behind this outcome, elucidating the factors contributing to the enhanced degradation effect are discussed and proposed.

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The influence of Mo on the electronic states and crystalline structure, as well as morphology, phase composition, luminescence, and defects in ZnO rods grown as free-standing nanoparticles, was studied using a variety of experimental techniques. Mo has almost no influence on the luminescence of the grown ZnO particles, whereas shallow donors are strongly affected in ZnO rods. Annealing in air causes exciton and defect-related bands to drop upon Mo doping level. The increase of the Mo doping level from 20 to 30% leads to the creation of dominating molybdates. This leads to a concomitant drop in the number of formed ZnO nanorods.

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Nanomaterials are gaining increasing attention as innovative materials in medicine. Among nanomaterials, zinc oxide (ZnO) nanostructures are particularly appealing because of their opto-electrical, antimicrobial, and photochemical properties. Although ZnO is recognized as a safe material and the Zn ion (Zn2+) concentration is strictly regulated at a cellular and systemic level, different studies have demonstrated cellular toxicity of ZnO nanoparticles (ZnO-NPs) and ZnO nanorods (ZnO-NRs). Recently, ZnO-NP toxicity has been shown to depend on the intracellular accumulation of ROS, activation of autophagy and mitophagy, as well as stabilization and accumulation of hypoxia-inducible factor-1α (HIF-1α) protein. However, if the same pathway is also activated by ZnO-NRs and how non-cancer cells respond to ZnO-NR treatment, are still unknown. To answer to these questions, we treated epithelial HaCaT and breast cancer MCF-7 cells with different ZnO-NR concentrations. Our results showed that ZnO-NR treatments increased cell death through ROS accumulation, HIF-1α and endothelial PAS domain protein 1 (EPAS1) activation, and induction of autophagy and mitophagy in both cell lines. These results, while on one side, confirmed that ZnO-NRs can be used to reduce cancer growth, on the other side, raised some concerns on the activation of a hypoxic response in normal cells that, in the long run, could induce cellular transformation.

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Zinc oxide (ZnO) nanorods have attracted considerable attention in recent years owing to their piezoelectric properties and potential applications in energy harvesting, sensing, and nanogenerators. Piezoelectric energy harvesting-based nanogenerators have emerged as promising new devices capable of converting mechanical energy into electric energy via nanoscale characterizations such as piezoresponse force microscopy (PFM). This technique was used to study the piezoresponse generated when an electric field was applied to the nanorods using a PFM probe. However, this work focuses on intensive studies that have been reported on the synthesis of ZnO nanostructures with controlled morphologies and their subsequent influence on piezoelectric nanogenerators. It is important to note that the diatomic nature of zinc oxide as a potential solid semiconductor and its electromechanical influence are the two main phenomena that drive the mechanism of any piezoelectric device. The results of our findings confirm that the performance of piezoelectric devices can be significantly improved by controlling the morphology and initial growth conditions of ZnO nanorods, particularly in terms of the magnitude of the piezoelectric coefficient factor (d33). Moreover, from this review, a proposed facile synthesis of ZnO nanorods, suitably produced to improve coupling and switchable polarization in piezoelectric devices, has been reported.

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The quantum dot light-emitting diode (QLED) represents one of the strongest display technologies and has unique advantages like a shallow emission spectrum and superior performance based on the cumulative studies of state-of-the-art quantum dot (QD) synthesis and interfacial engineering. However, research on managing the device's light extraction has been lacking compared to the conventional LED field. Moreover, relevant studies on top-emitting QLEDs (TE-QLEDs) have been severely lacking compared to bottom-emitting QLEDs (BE-QLEDs). This paper demonstrates a novel light extraction structure called the randomly disassembled nanostructure (RaDiNa). The RaDiNa is formed by detaching polydimethylsiloxane (PDMS) film from a ZnO nanorod (ZnO NR) layer and laying it on top of the TE-QLED. The RaDiNa-attached TE-QLED shows significantly widened angular-dependent electroluminescence (EL) intensities over the pristine TE-QLED, confirming the effective light extraction capability of the RaDiNa layer. Consequently, the optimized RaDiNa-attached TE-QLED achieves enhanced external quantum efficiency (EQE) over the reference device by 60%. For systematic analyses, current-voltage-luminance (J-V-L) characteristics are investigated using scanning electron microscopy (SEM) and optical simulation based on COMSOL Multiphysics. It is believed that this study's results provide essential information for the commercialization of TE-QLEDs.

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The piezo-/photocatalytic effects of ZnO have been in the limelight because of their great potential in environmental remediation and energy conversion. However, the poor recyclability of the suspended catalysts can cause inevitable secondary pollution, which is one of the major issues that limit the practical application of these materials. To address this problem, a magnetically retrievable Fe3O4@SiO2@ZnO nanocomposite was designed and successfully synthesized by multi-step reactions. The ZnO nanorods were vertically grown on the surface of the magnetic Fe3O4@SiO2 microspheres, while SiO2 served as an insulator to protect the inner core and to inhibit charge transfer across the core/shell interface. The Fe3O4@SiO2@ZnO nanocomposite can be easily collected and separated by using a magnetic field. Along with the good recyclability, the material also exhibited high efficiencies in piezocatalytic, photocatalytic and piezo-photocatalytic dye degradation processes. The rate constant of piezo-photocatalysis reached 95.9 × 10-3 min-1, which was 2.2 and 6.1 times that of the individual piezocatalysis and photocatalysis, respectively. The present result confirmed the existence of a synergetic effect between piezo- and photocatalytic processes. Hereby, we demonstrated that incorporation of a magnetic carrier is a feasible strategy to achieve retrievable and highly efficient piezo-/photocatalyst.

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Zinc oxide nanorods were grown on an aluminum-doped zinc oxide seeds layer using the chemical bath deposition method. The effects of growth reaction time on the structural, optical, and photocatalytic properties of zinc oxide nanorods were investigated. It was clearly observed that the growth direction of zinc oxide nanorods were dependent on the crystallinity of the as-deposited aluminum-doped zinc oxide seed layer. The crystallinity of the obtained zinc oxide nanorods was improved with the increase in reaction times during the chemical bath deposition process. The mechanism of zinc oxide nanorod growth revealed that the growth rate of nanorods was influenced by the reaction times. With increasing reaction times, there were much more formed zinc oxide crystalline stacked growth along the c-axis orientation resulting in an increase in the length of nanorods. The longest nanorods and the high crystallinity were obtained from the zinc oxide nanorods grown within 5 h. The optical transmittance of all zinc oxide nanorods was greater than 70% in the visible region. Zinc oxide nanorods grown for 5 h showed the highest degradation efficiency of methyl red under ultraviolet light and had a high first-order degradation rate of 0.0051 min-1. The photocatalytic mechanism was revealed as well.

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Herein, the detection of aspartic acid by doped Co3O4-ZnO nanorod materials was proposed using differential pulse voltammetry. The nano-composite metal oxide was synthesized by the wet precipitation method in basic media. Aspartic acid is a non-essential amino acid naturally synthesized in the body with lot of health significance, including as a biomarker for several health deficiencies. The synthesized composite Co3O4-ZnO nanorod was well-investigated by using FESEM, XRD, XPS, FTIR, UV/vis., EIS, and CV. The synthesized composite exhibited a low limit of detection (0.03 µM, high sensitivity (0.0014 µA µM-1 cm-2) and wide linear range (0.05-50 µM) for aspartic acid. The substrate, the Co3O4-ZnO nanorod, enhanced the electro-catalytic oxidation of aspartic acid as a result of its catalytic and conductivity properties. The developed sensor based on Co3O4-ZnO has a repeatable, reproducible and stable current response for aspartic acid. Additionally, other electroactive compounds did not interfere with the sensor's current response. The suitability of the developed sensor for real sample analysis was also established. Therefore, this study proposed the potential use of Co3O4-ZnO nanorod material in healthcare management for the maintenance of human well-being.

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Phase change materials (PCMs) with ideal light-to-thermal conversion efficiency play an important role in solar energy storage and conversion. Hence, we report the fabrication of a novel composite PCMs (CPCMs) device based on ZnO nanorods deposited indium tin oxide (ITO) glass loading with fatty amines. ZnO nanorods were deposited on the ITO glass using a three-electrode electrodeposition method, and 1-Hexadecylamine (HDA) was loaded on the ITO glass via spin-coating, followed by spraying polypyrrole (ppy) on the surface of CPCM device to improve thermal conductivity and solar absorption. The as-prepared CPCM device exhibits excellent light-to-thermal conversion efficiency, achieving a high conversion efficiency of 90.2% obtained at 1sun owing to its high light absorption (80%), enhanced thermal conductivity (improved by 57.8%), and the unique vertical aligned nanorods structure which could significantly decrease tortuosity, thereby reducing thermal route and lowering thermal response time. Furthermore, the electro-to-thermal conversion efficiency of the CPCMs device has also been investigated and the results show that it can reach up to 69.8% under a low voltage of 5 V, indicating that the CPCM device has a high potential in the field of electro-to-thermal conversion. Based on the benefits listed above, the CPCM device may serve an ideal platform for a wide range of solar energy storage and conversion applications.

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Piezoelectric semiconductor zinc oxide (ZnO) shows promising applications in many fields, however, its excellent piezoelectric performance is limited by the intrinsic screening effect. Forming p-n junction through interface engineering is an effective strategy to enhance its piezoelectric output, but the unclear regulation mechanism is a bottleneck in developing high-performance devices. In this work, the enhancement mechanism of interface engineering on the piezoelectric performance of ZnO nanorods (NRs) based devices is revealed from the perspective of carrier concentration. Both the theoretical and experimental results show that the piezoelectric output is significantly correlated with the carrier concentration, which is mainly attributed to the suppression of screening effect and the modulation of the device capacitance. After a reasonable matching design of carrier concentration, the piezoelectric potential of the ZnO NRs-based device is greatly enhanced by about 12 times. Apparently, these findings provide a fresh insight to further understand the enhancement mechanism of interface engineering on the electrical output of piezoelectric semiconductor devices, and provide effective support for the design of p-n junction piezoelectric devices.