Nanostructured ZnO for biosensing applications

Potential of Zinc Oxide Nanostructures in Biosensor Application

The burgeoning field of biosensors has seen significant advancements with the induction of zinc oxide (ZnO) nanostructures, because of their unique structural, electrical, and optical properties. ZnO nanostructures provide numerous benefits for biosensor applications. Their superior electron mobility enables effective electron transfer between the bioreceptor and transducer, enhancing sensitivity and reducing detection limits. Furthermore, ZnO's biocompatibility and non-toxicity make it ideal for in vivo applications, reducing the chances of adverse biological responses. This review paper explores the prospects of ZnO nanostructures in the development of biosensors, focusing on their morphological and structural characteristics. Various synthesis techniques, that include sol-gel, sputtering, and chemical vapor deposition, were successfully employed to prepare different ZnO nanostructures, like nanorods, nanotubes, and nanowires. The various findings in this field underscore the efficacy of ZnO nanostructures in enhancing the specificity and sensitivity of biosensors, presenting a promising avenue for the advancement of point-of-care diagnostic devices.

Optical tuning of polymer functionalized zinc oxide quantum dots as a selective probe for the detection of antibiotics

Excess consumption of antibiotics leads to antibiotic resistance that hinders the control and cure of microbial diseases. Therefore, it is crucial to monitor the antibiotic levels in the environment. In this proposed research work, an optical nano-sensor was devised that can sense the ultra-low concentration of antibiotics, in samples like tap water using fluorescent zinc oxide quantum dots (ZnO QDs) based nano-sensor. For this, different polymers (polyvinylalcohol-PVA and polyvinylpyrrolidine-PVP) capped florescent ZnO QDs were synthesized using a modified sol-gel technique. These were used as fluorescent probes to monitor the presence of antibiotics. The optical characterizations of synthesized QDs were performed using UV-visible absorption and fluorescence spectroscopic methods while structural characteristics were analyzed by using Raman spectroscopy and X-ray diffraction spectroscopy. The formation of capped QDs was confirmed by Fourier transform infrared spectroscopy (FTIR). Charge on the synthesized QDs was obtained with the help of ZETA potential. Here ten different antibiotics were checked, Ciprofloxacin and Moxifloxacin have shown excellent sensing and specificity with PVA-ZnO QDs and PVP-ZnO QDs with LOD of 1.4 nM and 0.8 nM, and sensitivity of 36.17 units/mM and 19.33 units/mM respectively. This study also inferred the tuning of the ZnO QDs properties and specificity towards the different antibiotics can be achieved by capping QDs with different polymers.

Eco-Friendly Synthesis of ZnO for Efficient Photodegradation of Pharmaceutical Drug Removal by Photocatalysis

In the present work, a comparative study on eco-friendly synthesis of zinc oxide (ZnO) sample 1 and sample 2 with 3.17 and 4.17 M NaOH, respectively, is reported. Sample 2 with 4.17 M NaOH is applied in the photocatalytic degradation of paracetamol (pure and raw both) using the ultraviolet (UV, 280-400 nm) and UV/H2O2 reaction systems. Pure paracetamol (PCM1) and raw paracetamol (PCM2) from tablets are used for photocatalytic degradation by photocatalysis. Our experimental evidence show that ZnO sample 2 was more active in the UV/H2O2 reaction system than under ultraviolet (UV, 280-400 nm) irradiation only in the photocatalytic degradation process. Field emission scanning electron microscopy (FE-SEM) confirms the homogeneous growth of a rod-like structure for sample 1 and brittle and randomly aggregated rod-like and wire-like nanostructures for sample 2. The peaks observed in the region around 440 to 900 cm-1 in the FTIR spectra for sample 1 and sample 2 annealed at 250 °C confirms the presence of ZnO bonds. UV absorption spectroscopy indicates a red shift in the absorption spectra due to the increase in the molar concentration of NaOH to 4.17 M for sample 2. In this study, the band gap values are found to be 3.33 and 3.01 eV for the synthesized ZnO sample 1 and sample 2, respectively, which are 40 and 360 meV less as compared to that of bulk ZnO (3.37 eV). The oxidation rate is increased in the UV/H2O2 reaction system, producing the highest rate for PCM1 drug removal with rate constant 9.7 × 10-3 min-1 and half-life 71.5 min. The kinetic study results for the removal of PCM1 and PCM2 show good results and follow the pseudo-first-order kinetic model with correlation coefficients 0.69556 and 0.90851, respectively, whereas PCM2 follows the pseudo-second-order kinetic model with correlation coefficient 0.9993. The experimental and calculated values of removal capacity (q e) at equilibrium is found close to those of the pseudo-second order kinetic model for the removal of both the paracetamol forms PCM1 and PCM2 with the catalyst ZnO nanostructure. The photostability of ZnO sample 2 is also tested with a reusability test in photocatalytic degradation of paracetamol at least four times. The absence of a maxima peak at 243 of PCM1 in the UV/H2O2 reaction system indicates nearly 100% successful conversion of 20 ppm PCM1 by using synthesized catalyst ZnO sample 2. The comparative results of both reaction systems, i.e., UV and UV/H2O2, show that the hydroxyl radicals, as the active species, are responsible for major degradation of both paracetamol forms (PCM1 and PCM2).

In silico study of interaction of (ZnO)12 nanocluster to glucose oxidase-FAD in absence and presence of glucose

Diabetes mellitus is one of the foremost global concerns, as it has impacted millions of lives. Therefore, there is an urgent need to develop a technology for continuous glucose monitoring in vivo. In the current study, we employed computational methods such as docking, MD simulations, and MM/GBSA, to obtain molecular insights into the interaction between (ZnO)12 nanocluster and glucose oxidase (GOx) that cannot be obtained through experiments alone. For this, theoretical modeling of the 3D cage-like (ZnO)12 nanocluster in ground state configuration was performed. Further docking of (ZnO)12 nanocluster with GOx molecule was carried out to find the nano-bio-interaction of (ZnO)12-GOx complex. To understand the whole interaction and dynamics of (ZnO)12-GOx-FAD-with and without glucose, we performed MD simulation and MM/GBSA analysis of (ZnO)12-GOx-FAD complex and glucose-(ZnO)12-GOx-FAD complex separately. The interaction was found to be stable, and the binding energy of (ZnO)12 to GOx-FAD increases in the presence of glucose by 6 kcal mol-1. This may be helpful in nano probing of the interaction of GOx with glucose. It can help in making a device like fluorescence resonance energy transfer (FRET) based nano-biosensor to monitor the glucose level in pre and post diabetic patient.Communicated by Ramaswamy H. Sarma.

Exploring the photoexcited electron transfer dynamics in artificial sunscreen PBSA-coupled biocompatible ZnO quantum dots

Frequent exposure to ultraviolet (UV) radiation without any protection turns out to be a fatal threat leading to skin cancer, necessitating the use of sunscreen cosmetic product with enhanced efficiency to dissipate the UV absorbed energy.

The Decoration of ZnO Nanoparticles by Gamma Aminobutyric Acid, Curcumin Derivative and Silver Nanoparticles: Synthesis, Characterization and Antibacterial Evaluation

Zinc oxide nanoparticles (ZnO NPs) are applied in various applications in catalysis, biosensing, imaging, and as antibacterial agents. Here we to prepare ZnO nanomaterials decorated by γ-amino butyric acid (GABA), curcumin derivatives (CurBF₂) and silver nanoparticles (CurBF₂-AgNPs). The structures of all ZnO nanostructures were characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), UV-VIS spectrophotometry, fluorescence spectrophotometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). Further, their antibacterial activities against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria were investigated through analysis of minimum inhibitory concentration (MIC) method. Among the prepared nanostructures, the ZnO NPs-GABA/CurBF₂-AgNPs showed excellent antibacterial activity against both Gram-positive and -negative bacteria. ZnO NPs fabricated here may have potential use in future anti-bacterial compositions and coatings technologies.

A Review on Biosensors and Recent Development of Nanostructured Materials-Enabled Biosensors

A biosensor is an integrated receptor-transducer device, which can convert a biological response into an electrical signal. The design and development of biosensors have taken a center stage for researchers or scientists in the recent decade owing to the wide range of biosensor applications, such as health care and disease diagnosis, environmental monitoring, water and food quality monitoring, and drug delivery. The main challenges involved in the biosensor progress are (i) the efficient capturing of biorecognition signals and the transformation of these signals into electrochemical, electrical, optical, gravimetric, or acoustic signals (transduction process), (ii) enhancing transducer performance i.e., increasing sensitivity, shorter response time, reproducibility, and low detection limits even to detect individual molecules, and (iii) miniaturization of the biosensing devices using micro-and nano-fabrication technologies. Those challenges can be met through the integration of sensing technology with nanomaterials, which range from zero- to three-dimensional, possessing a high surface-to-volume ratio, good conductivities, shock-bearing abilities, and color tunability. Nanomaterials (NMs) employed in the fabrication and nanobiosensors include nanoparticles (NPs) (high stability and high carrier capacity), nanowires (NWs) and nanorods (NRs) (capable of high detection sensitivity), carbon nanotubes (CNTs) (large surface area, high electrical and thermal conductivity), and quantum dots (QDs) (color tunability). Furthermore, these nanomaterials can themselves act as transduction elements. This review summarizes the evolution of biosensors, the types of biosensors based on their receptors, transducers, and modern approaches employed in biosensors using nanomaterials such as NPs (e.g., noble metal NPs and metal oxide NPs), NWs, NRs, CNTs, QDs, and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Nephron ultrastructural alterations induced by zinc oxide nanoparticles: an electron microscopic study

Due to their unique properties, zinc oxide nanoparticles (ZnO NPs) are invested in many industries, commercial products, and nanomedicine with potential risk for human health and the environment. The present study aims to focus on alterations that might be induced by ZnO NPs in the nephron ultrastructure. Male Wister Albino rats were subjected to ZnO NPs at a daily dose of 2 mg/kg for 21 days. Kidney biopsies were processed to transmission electron microscopy (TEM) and ultrastructural pathology examinations. Exposure to ZnO NPs‐induced ultrastructural alterations in the proximal convoluted tubules (PCTs) and to lesser extent in the distal ones (DCTs), while the loops of Henle were almost not affected. The glomeruli demonstrated dilatation, partial mesangial cells loss, matrix ballooning, slits filtration widening, and basement membrane thickening. Moreover, PCT revealed cytoplasmic necrosis, vacuolation, erosion, and disorganisation of the apical microvilli together with mitochondrial swelling and cristae destruction. The nuclei of the renal cells exhibited nuclear deformity, heterochromatin accumulation, and apoptotic activities. The findings indicate that ZnO nanomaterial have the potential to affect the nephron ultrastructure suggesting alteration in the kidney functions. More work is needed for better understanding the toxicity and pathogenesis of ZnO oxide nanomaterial.

Light-Addressable Potentiometric Sensors Using ZnO Nanorods as the Sensor Substrate for Bioanalytical Applications

Light-addressable potentiometric sensors (LAPS) are of great interest in bioimaging applications such as the monitoring of concentrations in microfluidic channels or the investigation of metabolic and signaling events in living cells. By measuring the photocurrents at electrolyte-insulator-semiconductor (EIS) and electrolyte-semiconductor structures, LAPS can produce spatiotemporal images of chemical or biological analytes, electrical potentials and impedance. However, its commercial applications are often restricted by their limited AC photocurrents and resolution of LAPS images. Herein, for the first time, the use of 1D semiconducting oxides in the form of ZnO nanorods for LAPS imaging is explored to solve this issue. A significantly increased AC photocurrent with enhanced image resolution has been achieved based on ZnO nanorods, with a photocurrent of 45.7 ± 0.1 nA at a light intensity of 0.05 mW, a lateral resolution as low as 3.0 μm as demonstrated by images of a PMMA dot on ZnO nanorods and a pH sensitivity of 53 mV/pH. The suitability of the device for bioanalysis and bioimaging was demonstrated by monitoring the degradation of a thin poly(ester amide) film with the enzyme α-chymotrypsin using LAPS. This simple and robust route to fabricate LAPS substrates with excellent performance would provide tremendous opportunities for bioimaging.

Gentamicin-Releasing Mesoporous ZnO Structures

Among metal oxides, zinc oxide (ZnO) is one of the most attractive materials thanks to its biocompatible and biodegradable properties along with the existence of various morphologies featuring piezoelectric, semiconducting and photocatalytic activities. All of these structures were successfully prepared and tested for numerous applications, including optoelectronics, sensors and biomedical ones. In the last case, biocompatible ZnO nanomaterials positively influenced cells growth and tissue regeneration as well, promoting wound healing and new bone formation. Despite showing high surface areas, ZnO morphologies generally lack an intrinsic mesoporous structure, strongly limiting the investigation of the corresponding drug loading and release properties. Within this scope, this study focuses on the adsorption and release properties of high surface area, mesoporous ZnO structures using gentamicin sulfate (GS), a well known antibiotic against bacterial infections especially in orthopedics. The particular ZnO morphology was achieved starting from sputtered porous zinc layers, finally converted into ZnO by thermal oxidation. By taking advantage of this mesoporous framework, GS was successfully adsorbed within the ZnO matrix and the kinetic release profile evaluated for up to seven days. The adsorption of GS was successfully demonstrated, with a maximum amount of 263 mg effectively loaded per gram of active material. Then, fast kinetic release was obtained in vitro by simple diffusion mechanism, thus opening further possibilities of smart pore and surface engineering to improve the controlled delivery.

ZnO Nanowire Application in Chemoresistive Sensing: A Review

This article provides an overview of the recent development of ZnO nanowires (NWs) for chemoresistive sensing. Working mechanisms of chemoresistive sensors are unified for gas, ultraviolet (UV) and bio sensor types: single nanowire and nanowire junction sensors are described, giving the overview for a simple sensor manufacture by multiple nanowire junctions. ZnO NW surface functionalization is discussed, and how this effects the sensing is explained. Further, novel approaches for sensing, using ZnO NW functionalization with other materials such as metal nanoparticles or heterojunctions, are explained, and limiting factors and possible improvements are discussed. The review concludes with the insights and recommendations for the future improvement of the ZnO NW chemoresistive sensing.

A review on ZnO-based electrical biosensors for cardiac biomarker detection

Over the past few decades zinc oxide (ZnO)-based thin films and nanostructures have shown unprecedented performance in a wide range of applications. In particular, owing to high isoelectric point, biocompatibility and other multifunctional characteristics, ZnO has extensively been studied as a transduction material for biosensor development. The fascinating properties of ZnO help retain biological activity of the immobilized biomolecule and help in achieving enhanced sensing performance. As a consequence of recent advancements in this multidisciplinary field, diagnostic biosensors are expanding beyond traditional clinical labs to point-of-care and home settings. Label-free electrical detection of biomarkers has been demonstrated using ZnO-sensing platforms. In this review we highlight the characteristics of ZnO that enable realization of its use in development of point-of-care biosensors toward disease diagnosis, in particular cardiovascular diseases.

Sol-Gel Synthesis of Carbon Xerogel-ZnO Composite for Detection of Catechol

Carbon xerogel-zinc oxide (CXZnO) composites were synthesized by a simple method of sol-gel condensation polymerization of formaldehyde and resorcinol solution containing zinc salt followed by drying and thermal treatment. ZnO nanoparticles were observed to be evenly dispersed on the surfaces of the carbon xerogel microspheres. The as-prepared CXZnO composites were mixed with laccase (Lac) and Nafion to obtain a mixture solution, which was further modified on an electrode surface to construct a novel biosensing platform. Finally, the prepared electrochemical biosensor was employed to detect the environmental pollutant, catechol. The analysis result was satisfactory, the sensor showed excellent electrocatalysis towards catechol with high sensitivity (31.2 µA·mM⁻¹), a low detection limit (2.17 µM), and a wide linear range (6.91–453 µM). Moreover, the biosensor also displayed favorable repeatability, reproducibility, selectivity, and stability besides being successfully used in the trace detection of catechol existing in lake water environments.

SnO2 nanoparticle-coated ZnO nanotube arrays for high-performance electrochemical sensors

Novel 1D nanostructures offer new opportunities for improving the performance of electrochemical sensors. In this study, highly ordered 1D nanostructure array electrodes composed of SnO2 nanoparticle-coated ZnO (SnO2 @ZnO) nanotubes are designed and fabricated. The composite nanotube array architecture not only endows the electrochemical electrodes with large surface areas, but also allows electrons to be quickly transferred along the nanotubes. Modifying the SnO2 @ZnO nanotube arrays with negatively charged polymer film and employing them as a working electrode, sensitive and selective electrochemical detection of an important neurotransmitter, i.e., dopamine, is realized via the cycle voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Interference from ascorbic acid can be successfully eliminated. The oxidative peak currents recorded from CV linearly depend on the dopamine concentrations from 0.1 to 100 μM with a sensitivity of 2.16 × 10(-7) A μM(-1) cm(-2) and detection limit of 45.2 nM. Using the DPV technique, an improved sensitivity and detection limit of 1.94 × 10(-6) A μM(-1) cm(-2) and 17.7 nM are respectively achieved. Moreover, the SnO2 @ZnO nanotube array electrodes can be reused through simple ultrasonical cleaning and no obvious deterioration is observed in the performance.