Synthesis of mesoporous multiwall ZnO nanotubes by replicating silk and application for enzymatic biosensor

Synthesis of Zinc Oxide Nanoparticles with Bioflavonoid Rutin: Characterisation, Antioxidant and Antimicrobial Activities and In Vivo Cytotoxic Effects on Artemia Nauplii

This study aims to synthesise zinc oxide nanoparticles with rutin (ZnO-R NPs) using a green synthesis approach and characterise the nanostructures for diverse biomedical applications. In this study, the optical and chemical properties of synthesised ZnO-R NPs were verified through Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-Vis) spectroscopy. The FTIR spectroscopy revealed a symmetric bending vibration peak of 460 cm⁻¹ for ZnO-R NPs, whereas UV-Vis spectroscopy showed a distinct absorption band at 395 nm. Moreover, the oval-shaped morphology of ZnO-R NPs was verified through scanning electron microscopy and transmission electron microscopy. The synthesised nanoformulation revealed a wurtzite structure with a crystallite size of 13.22 nm; however, the zeta potential value was recorded as −8.50 ± 0.46 mV for ZnO-R NPs. According to an antioxidant study, ZnO-R NPs demonstrated lower free-radical scavenging activity than pure rutin. The cytotoxicity study was conducted using a human breast cancer cell line (MCF-7). In vitro analysis verified that ZnO-R NPs exhibited significantly higher anticancer and microbial growth inhibition activities than standard ZnO NPs (ZnO Std NPs) and pure rutin. In addition, ZnO-R NPs revealed a significantly lower IC₅₀ value than the commercial ZnO Std NPs and pure rutin in MCF-7 cells (16.39 ± 6.03 μg/mL, 27 ± 0.91 μg/mL and 350 ± 30.1 μg/mL, respectively) after 48 h. However, synthesised ZnO-R NPs demonstrated no significant toxicity towards Artemia nauplii. These results highlight the synthesis of rutin-mediated ZnO NPs and their possible chemotherapeutic potential.

Effect of Electrode Modification with Chitosan and Nafion® on the Efficiency of Real-Time Enzyme Glucose Biosensors Based on ZnO Tetrapods

Noninvasive, continuous glucose detection can provide some insights into daily fluctuations in blood glucose levels, which can help us balance diet, exercise, and medication. Since current commercially available glucose sensors can barely provide real-time glucose monitoring and usually imply different invasive sampling, there is an extraordinary need to develop new harmless methods for detecting glucose in non-invasive body fluids. Therefore, it is crucial to design (bio)sensors that can detect very low levels of glucose (down to tens of µM) normally found in sweat or tears. Apart from the selection of materials with high catalytic activity for glucose oxidation, it is also important to pay considerable attention to the electrode functionalization process, as it significantly contributes to the overall detection efficiency. In this study, the (ZnO tetrapods) ZnO TPs-based electrodes were functionalized with Nafion and chitosan polymers to compare their glucose detection efficiency. Cyclic voltammetry (CV) measurements have shown that chitosan-modified ZnO TPs require a lower applied potential for glucose oxidation, which may be due to the larger size of chitosan micelles (compared to Nafion micelles), and thus easier penetration of glucose through the chitosan membrane. However, despite this, both ZnO TPs modified with chitosan and Nafion membranes, provided quite similar glucose detection parameters (sensitivities, 7.5 µA mM-1 cm-1 and 19.2 µA mM-1 cm-1, and limits of detection, 24.4 µM and 22.2 µM, respectively). Our results show that both electrodes have a high potential for accurate real-time sweat/tears glucose detection.

Low dimensional materials for glucose sensing

Biosensors are essential components for effective healthcare management. Since biological processes occur on molecular scales, nanomaterials and nanosensors intrinsically provide the most appropriate landscapes for developing biosensors. Low-dimensional materials have the advantage of offering high surface areas, increased reactivity and unique physicochemical properties for efficient and selective biosensing. So far, nanomaterials and nanodevices have offered significant prospects for glucose sensing. Targeted glucose biosensing using such low-dimensional materials enables much more effective monitoring of blood glucose levels, thus providing significantly better predictive diabetes diagnostics and management. In this review, recent advances in using low dimensional materials for sensing glucose are summarized. Sensing fundamentals are discussed, as well as invasive, minimally-invasive and non-invasive sensing methods. The effects of morphological characteristics and size-dependent properties of low dimensional materials are explored for glucose sensing, and the key performance parameters such as selectivity, stability and sensitivity are also discussed. Finally, the challenges and future opportunities that low dimensional materials can offer for glucose sensing are outlined.

Silk fibroin-derived carbon aerogels embedded with copper nanoparticles for efficient electrocatalytic CO2-to-CO conversion

Metal-carbon matrix catalyst has attracted a great deal of interest in electrochemical carbon dioxide reduction reaction (CO₂RR) due to its excellent electrocatalytic performance. However, the design of highly active metal-carbon matrix catalyst towards CO₂RR using natural biomass and cheap chemical precursors is still under challenge. Herein, a self-assembly strategy, along with CO₂ gas as acidifying agent, to fabricate silk fibroin (SF) derived carbon aerogels (CA) combining trace copper nanoparticles (SF-Cu/CA) is developed. Zinc nitrate was introduced as a pore-forming agent to further optimize the pore structure of the as-prepared catalysts to form SF-Cu/CA-1. The rich mesoporous structure and unique constitute of SF-Cu/CA-1 is conducive to exposed numerous active sites, fast electron transfer rate, and the desorption of *CO intermediate, thus leading to the electrocatalytic CO₂RR of SF-Cu/CA-1 catalyst with an excellent current density of 29.4 mA cm^-2, Faraday efficiency of 83.06% towards carbon monoxide (CO), high the ratio value of CO/H₂ (19.58), and a long-term stability over a 10-hour period. This performance is superior to that of SF-Cu/CA catalyst (13.0 mA cm^-2, FE_CO=58.43%, CO/H₂ = 2.16). This work not only offers a novel strategy using natural biomass and cheap chemicals to build metal-carbon matrix catalyst for electrocatalytic CO₂-to-CO conversion, but also is expected to promote the industrial-scale implementations of CO₂ electroreduction.

Recent Progress of the Practical Applications of the Platinum Nanoparticle-Based Electrochemistry Biosensors

The detection of biomolecules using various biosensors with excellent sensitivity, selectivity, stability, and reproducibility, is of great significance in the analytical and biomedical fields toward achieving their practical applications. Noble metal nanoparticles are favorable candidates due to their unique optical, surface electrical effect, and catalytic properties. Among these noble metal nanoparticles, platinum nanoparticles (Pt NPs) have been widely employed for the detection of bioactive substances such as glucose, glutamic acid, and hormones. However, there is still a long way to go before the potential challenges in the practical applications of biomolecules are fully overcome. Bearing this in mind, combined with our research experience, we summarized the recent progress of the Pt NP-based biosensors and highlighted the current problems that exist in their practical applications. The current review would provide fundamental guidance for future applications using the Pt NP-based biosensors in food, agricultural, and medical fields.

In situ fabrication of aloe-like Au-ZnO micro/nanoarrays for ultrasensitive biosensing of catechol

Currently, the large-scale and controllable fabrication of nanostructures on substrates remains a great challenge for further practical applications. In this work, a novel 3D aloe-like Au-ZnO nanocomposite was designed for in situ synthesis on an ITO substrate, achieving real-time detection of trace catechol (CC) in water. A seed-assisted hydrothermal approach was proposed to control the crystal distribution and growth direction to build a ZnO aloe-like architecture. To eliminate the natural weak conductivity of ZnO, Au nanoparticles were further deposited on all ZnO arrays to construct Au-ZnO micro/nanostructures. The synergetic effects derived from the aloe-like ZnO with a large specific area and Au nanoparticles with high conductivity resulted in both high electrocatalysis and fast electron transfer in enzymatic reactions. After laccase immobilization, the as-prepared biosensor exhibited specific recognition of catechol among other dihydroxybenzenes and phenol with an ultrahigh sensitivity of 131 μA mM^-1, as well as an extremely wide linear range from 75 nM to 1100 μM and an ultralow detection limit of 25 nM. In addition, in the detection of real lake samples, this biosensor showed satisfactory anti-interference ability and provided reliable assay results.

Fabrication of the Ni/ZnO/BiOI foam for the improved electrochemical biosensing performance to glucose

The Ni foam decorated with ZnO/BiOI core-shell p-n junction nanorods was prepared and employed as an enzyme loading matrix to detect glucose. The detection potential was decreased significantly (0.3 V) and the sensitivity was enhanced largely (115.2 μA mM^-1 cm^-2). The metal-semiconductor foam can afford the porous surface for loading enzymes and achieving the multiple catalysis. More important, the built-in electric field and electron well in the p-n junction interface provide the driving force for electron transport. It was an effective strategy to enhance the biosensing performance by the rational design of p-n junction.

Microwave induced synthesis of ZnO nanorods and their efficacy as a drug carrier with profound anticancer and antibacterial properties

In the present study, we report the microwave-induced synthesis of fluorescent zinc oxide nanorods (ZnO) and their usage as a cargo material to carry hydrophobic drug, quercetin. TEM and SEM showed the rod-shape morphology of our synthesized ZnO. XRD showed several diffraction peaks correspond to a hexagonal wurtzite structure. The optical and chemical natures of these nanorods were also confirmed from the UV-vis (showed a distinct absorption bands from 361 to 395 nm) and FTIR spectrum (showed absorption band specific to Zn-O stretching). The synthesized ZnO also showed fluorescence emission at around 550 nm when excited under UV irradiation. Quercetin was loaded onto ZnO surface via employing a metal ion-ligand coordination bond, (ZnO/QR), which exhibit pH-sensitive release behavior. ZnO/QR displayed superior drug loading content (42%) and loading efficiency (72.4%). in vitro assays showed that ZnO/QR exhibited higher anticancer, as well as antibacterial activities compared with free quercetin and ZnO. All these results highlight the synthesis of ZnO nanorods under microwave irradiation, which can be used as a plausible therapeutic option for bioimaging and drug delivery purpose.

3D Architectures of Cox P Using Silk Fibroin Scaffolds: An Active and Stable Electrocatalyst for Hydrogen Generation in Acidic and Alkaline Media

Developing nonprecious, highly active, and stable catalysts is essential for efficient electrocatalytic hydrogen evolution reaction in water splitting. In this study, the facile synthesis of a 3D flower-like Co_x P/carbon architecture is proposed composed of an assembly of nanosheets interconnected by silk fibroin that acts as 3D scaffolds and a carbon source. This unique 3D architecture coupled with a carbon matrix enhances catalytic activity by exposing more active sites and increasing charge transport. The flower-like Co_x P/carbon can facilitate a lower overpotential, Tafel slope, charge transfer resistance, and a higher electrochemically active surface than carbon-free and silk-free Co_x P. The nanostructured architecture exhibits excellent catalytic performance with low overpotentials of 109 and 121 mV at 10 mA cm^-2 and Tafel slopes of 55 and 62 mV dec^-1 in acidic and alkaline media, respectively. Furthermore, it minimally degrades the overpotential and current density after long-term stability tests 10 000 cyclic voltammetry cycles and a chronoamperometric test over 40 h, respectively, in acidic media, which confirms the high durability and stability of the flower-like Co_x P/carbon.

Distributed electrochemical sensors: recent advances and barriers to market adoption

Despite predictions of their widespread application in healthcare and environmental monitoring, electrochemical sensors are yet to be distributed at scale, instead remaining largely confined to R&D labs. This contrasts sharply with the situation for physical sensors, which are now ubiquitous and seamlessly embedded in the mature ecosystem provided by electronics and connectivity protocols. Although chemical sensors could be integrated into the same ecosystem, there are fundamental issues with these sensors in the three key areas of analytical performance, usability, and affordability. Nevertheless, advances are being made in each of these fields, leading to hope that the deployment of automated and user-friendly low-cost electrochemical sensors is on the horizon. Here, we present a brief survey of key challenges and advances in the development of distributed electrochemical sensors for liquid samples, geared towards applications in healthcare and wellbeing, environmental monitoring, and homeland security. As will be seen, in many cases the analytical performance of the sensor is acceptable; it is usability that is the major barrier to commercial viability at this moment. Were this to be overcome, the issue of affordability could be addressed. Graphical Abstract ᅟ.

Highly sensitive and selective non-enzymatic monosaccharide and disaccharide sugar sensing based on carbon paste electrodes modified with perforated NiO nanosheets

Fabrication and characterization of enzyme-free electrochemical sensor for the sensing of monosaccharide and disaccharide sugars based on perforated NiO nanosheets (NSs).

Size Controlled Copper (I) Oxide Nanoparticles Influence Sensitivity of Glucose Biosensor

Copper (I) oxide (Cu₂O) is an appealing semiconducting oxide with potential applications in various fields ranging from photovoltaics to biosensing. The precise control of size and shape of Cu₂O nanostructures has been an area of intense research. Here, the electrodeposition of Cu₂O nanoparticles is presented with precise size variations by utilizing ethylenediamine (EDA) as a size controlling agent. The size of the Cu₂O nanoparticles was successfully varied between 54.09 nm to 966.97 nm by changing the concentration of EDA in the electrolytic bath during electrodeposition. The large surface area of the Cu₂O nanoparticles present an attractive platform for immobilizing glucose oxidase for glucose biosensing. The fabricated enzymatic biosensor exhibited a rapid response time of <2 s. The limit of detection was 0.1 μM and the sensitivity of the glucose biosensor was 1.54 mA/cm². mM. The Cu₂O nanoparticles were characterized by UV-Visible spectroscopy, scanning electron microscopy and X-ray diffraction.

Characterization of the fullerene end-functionalized ZnO nanotube: A computational study

The electronic and field emission properties of the fullerene end-functionalized zinc oxide nanotube (ZnONT) are investigated by density functional theory (DFT) to search for novel field emitter nano material. The interaction energies of ZnONT/fullerenes complexes gradually increase, with increasing the nanotube lengths which indicate that ZnONTs with higher lengths could improve the stability of the complexes. The band gaps of connected construction of fullerene molecules with ZnONTs gradually reduced by increasing the tube length, but were not sensitive to the tubes diameter. It is found that the ionization potentials of ZnONT/fullerenes complexes mainly decrease compared to that of pristine nanotube in the presence of 0, 0.002, 0.004[Formula: see text]a.u. electric field. The reduction of the ionization potential means the enhancement of the field emission properties of ZnONT/fullerenes complexes compared with simple ZnONT and fullerene molecules. The calculations show that the combination of ZnONT with fullerene molecules indeed improves the field emission by controlling the tube size and electric field strength.

Sustainable waste mitigation: biotemplated nanostructured ZnO for photocatalytic water treatment via extraction of biofuels from hydrothermal carbonization of banana stalk

Working at the food-energy-water nexus, we identified an abundant agricultural waste with little intrinsic value – banana stalk – that can be converted to biofuels and a template for water treatment materials via hydrothermal carbonization.

An amperometric glucose biosensor based on a MnO2/graphene composite modified electrode

In this paper, a novel composite of graphene/MnO₂ (GR/MnO₂) was successfully synthesized by a simple one-step hydrothermal method.

Direct and indirect sonication affect differently the microstructure and the morphology of ZnO nanoparticles: Optical behavior and its antibacterial activity

In the present study, the sono-synthesis of ZnO nanoparticles (NPs) was performed by simple, low-cost, and the environmentally friendly method. The synthesis of zinc oxide as an antibacterial agent was performed by an ultrasonic bath (low intensity) for the indirect sonication and a horn system (high intensity) for the direct sonication. The samples synthesized by these two kinds of sonication were compared with each other. Crystallographic structures and the morphologies of the resultant powders were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns showed that both ZnO samples were crystallized in their pure phase. The TEM images confirmed that the morphologies of the products were completely different from each other. Based on the obtained analysis, the probable growth mechanisms were proposed for crystallization of both samples. The antibacterial activity of the synthesized species was evaluated by the colony count method against Escherichia coli O157:H7. Moreover, the optical behavior of the samples was studied by UV-vis spectroscopy and the variation of the ZnO band gap was compared.

Electrospun Porous ZnO Nanofibers for Glucose Biosensors

Porous 1 dimensional (1D) ZnO nanofibers were synthesized by electrospinning technology and sequent annealing process. The ZnO nanofibers have many nanopores in it and connect to each other to form a porous film. The diameters of the nanofibers are about 100 nm, and their lengths are so long as tens of millimeters. Owing to the porous nanofibers based matrix has 1D channels and high isoelectric point, the prepared ZnO porous film is wonderful platform to immobilize glucose oxidase enzyme for glucose biosensing. The as-fabricated biosensor exhibited high sensitivity (69 μA/mMcm-2), fast response (3 s) and low detection limit (10 μM), due to the nanomaterial with large surface-to-volume ratio for enzyme immobilization and excellent electrical properties. The biosensors can be fabricated controllably and repeatedly. These excellent results indicate the biosensors are attractive for application.

Introducing heterojunction barriers into single kinked nanowires for the probe-free detection of proteins and intracellular recording

A nanoprobe based on a single nanowire (NW) possesses substantial potential for biological and in vivo determination. With regard to intracellular detection, minimal invasion and an adjustable detection depth have become crucial challenges. Nanoprobes with small, sharp tips, and long arms are thus desired. Here, we demonstrate a general strategy to prepare a single kinked NW heterojunction with a continuously adjustable angle, length and sharp line-type tip. It is found that heterojunction barriers introduced into kinked NWs can be used as a functional factor to interact with biomolecules and cells. The prepared kinked NW nanosensor is successfully used for the highly-sensitive probe-free detection of hemoglobin and real-time intracellular recording with minimal invasion. The sensing performance is dependent on the amount of heterojunction barriers. Integrated nanoprobes with multi-shaped structures are further designed for multi-functional applications. Introducing heterojunction barriers to kinked NWs provides a substantial opportunity for fabricating functional and integrated nanoprobes for applications in the life sciences.

Nanosheet-based 3D hierarchical ZnO structure decorated with Au nanoparticles for enhanced electrochemical detection of dopamine

A novel sensor based on well-dispersed Au nanoparticles on a nanosheet-based three-dimensionally hierarchical ZnO matrix was fabricated to sensitively detect DA.