Synthesis of SnO2 nanowires as a reusable and flexible electrode for electrochemical detection of riboflavin

Biogenic synthesis of CuO/ZnO nanocomposite from Bauhinia variegate flower extract for highly sensitive electrochemical detection of vitamin B2

In this study, we report the preparation of bio-inspired binary CuO/ZnO nanocomposite (bb-CuO/ZnO nanocomposite) via the biological route using Bauhinia variegata flower extract following hydrothermal treatment. The prepared bb-CuO/ZnO nanocomposite was electrophoretically deposited (EPD) on indium tin oxide (ITO) substrate to develop bb-CuO/ZnO/ITO biosensing electrode which is employed for the determination of vitamin B2 (Riboflavin) through electrochemical techniques. Physicochemical assets of the prepared bb-CuO/ZnO nanocomposite have been extensively evaluated and make use of different characterization techniques including powder XRD, FT-IR, AFM, SEM, TEM, EDX, XPS, Raman, and TGA. Electrochemical characteristics of the bb-CuO/ZnO/ITO biosensing electrode have been studied towards vitamin B2 determination. Furthermore, different biosensing parameters such as response time, reusability, stability, interference, and real sample analysis were also estimated. From the linear plot of scan rate, charge transfer rate constant (Ks), surface concentration of electrode (γ), and diffusion coefficient (D) have been calculated, and these are found to be 6.56 × 10-1 s-1, 1.21 × 10-7 mol cm-2, and 6.99 × 10-3 cm2 s-1, respectively. This biosensor exhibits the linear range of vitamin B2 detection from 1 to 40 μM, including sensitivity and limit of detection (LOD) of 1.37 × 10-3 mA/μM cm2 and 0.254 μM, respectively. For higher concentration range detection linearity is 50-100 μM, with sensitivity and the LOD of 1.26 × 10-3 mA/μM cm2 and 0.145 μM, respectively. The results indicate that the bio-inspired nanomaterials are promising sustainable biosensing platforms for various food and health-based biosensing devices.

Metal oxide nanomaterials based electrochemical and optical biosensors for biomedical applications: Recent advances and future prospectives

The amalgamation of nanostructures with modern electrochemical and optical techniques gave rise to interesting devices, so-called biosensors. A biosensor is an analytical tool that incorporates various biomolecules with an appropriate physicochemical transducer. Over the past few years, metal oxide nanomaterials (MONMs) have significantly stimulated biosensing research due to their desired functionalities, versatile chemical stability, and low cost along with their unique optical, catalytic, electrical, and adsorption properties that provide an attractive platform for linking the biomolecules, for example, antibodies, nucleic acids, enzymes, and receptor proteins as sensing elements with the transducer for the detection of signals or signal amplifications. The signals to be measured are in direct proportionate to the concentration of the bioanalyte. Because of their simplicity, cost-effectiveness, portability, quick analysis, higher sensitivity, and selectivity against a broad range of biosamples, MONMs-based electrochemical and optical biosensing platforms are exhaustively explored as powerful early-diagnosis tools for point of care applications. Herein, we made a bibliometric analysis of past twenty years (2004-2023) on the application of MONMs as electrochemical and optical biosensing units using Web of Science database and the results of which clearly reveal the increasing number of publications since 2004. Geographical area distribution analysis of these publications shows that China tops the list followed by the United States of America and India. In this review, we first describe the electrochemical and optical properties of MONMs that are crucial for the creation of extremely stable, specific, and sensitive sensors with desirable characteristics. Then, the biomedical applications of MONMs-based bare and hybrid electrochemical and optical biosensing frameworks are highlighted in the light of recent literature. Finally, current limitations and future challenges in the field of biosensing technology are addressed.

Electrochemical determination of riboflavin in pharmaceuticals using unmodified screen printed carbon electrodes

In this study, we have devised an efficient and rapid approach to detect riboflavin (also known as Vitamin B2 or VB2) utilizing an unaltered screen-printed carbon electrode (SPCE). The unmodified screen-printed electrodes are created within the laboratory, where carbon ink is applied to a ceramic substrate. All experiments pertaining to the investigation of electrochemical behavior and the fine-tuning of crucial experimental parameters were conducted through cyclic voltammetry (CV). For quantitative assessments, square wave voltammetry (SWV) was employed. The findings indicate that unaltered SPCEs exhibit robust current signals during the riboflavin redox reaction. Riboflavin displays a distinct oxidation peak at - 0.136 V (vs. Ag/AgCl, 3.0 M KCl) in a Britton-Robinson buffer solution (BRBS) at pH 2, which was employed for quantification. The electrode demonstrates a broad linear range from 0.05 to 10 µM, boasting a detection limit of 0.03 µM. Repeatability stands at 1.45%, while reproducibility is 6.61%. Testing the influence of common interfering compounds yielded negligible results. The sensor effectively determines riboflavin content in pharmaceutical formulations without any prior treatment. This method presents an economical, modifier-free sensor with exceptional sensitivity and cost-effectiveness, making it suitable for rapid riboflavin quantification.

A Review on Recent Trends and Future Developments in Electrochemical Sensing

Electrochemical methods and devices have ignited prodigious interest for sensing and monitoring. The greatest challenge for science is far from meeting the expectations of consumers. Electrodes made of two-dimensional (2D) materials such as graphene, metal-organic frameworks, MXene, and transition metal dichalcogenides as well as alternative electrochemical sensing methods offer potential to improve selectivity, sensitivity, detection limit, and response time. Moreover, these advancements have accelerated the development of wearable and point-of-care electrochemical sensors, opening new possibilities and pathways for their applications. This Review presents a critical discussion of the recent developments and trends in electrochemical sensing.

Growth kinetics of crumb-like structure formation on SnO2 nanowires during direct oxidation

A facile AAO (anodic aluminum oxide) template-assisted vacuum die-casting technique was used to create Sn nanowires and convert them into SnO2 without degrading the wires nanostructure. As a function of time and temperature, the controlled oxidation on the Sn nanowires of two different spatial configurations (100 and 250 nm in diameter) revealed distinct oxidation mechanisms. The 250-SnO2 nanowires exhibits a peculiar crumb-like structure formation over the surface due to the higher level of Sn atom dislocation. Conversely, the sub-100 nm SnO2 nanowires shows a highly crystalline, homogenous, and defect-free surfaces. The optical properties of the sub-100 nm SnO2 nanowires were characterized using UV-Vis spectroscopy. The heat-treated tin oxides nanowires samples at temperatures of 300, 500, and 700 °C for 7 h exhibited optical energy bandgaps of 1.8, 2.6, and 3.3 eV, respectively. The observed variation in bandgap is attributed to the unique phase compositions achieved in each of the heat-treated samples. Moreover, the obtained results showed exceptional structural integrity and optical properties that are inherently interconnected with the diverse phases achieved under precise heat treatment conditions.

Tailoring SnO2 Defect States and Structure: Reviewing Bottom-Up Approaches to Control Size, Morphology, Electronic and Electrochemical Properties for Application in Batteries

Tin oxide (SnO₂) is a versatile n-type semiconductor with a wide bandgap of 3.6 eV that varies as a function of its polymorph, i.e., rutile, cubic or orthorhombic. In this review, we survey the crystal and electronic structures, bandgap and defect states of SnO₂. Subsequently, the significance of the defect states on the optical properties of SnO₂ is overviewed. Furthermore, we examine the influence of growth methods on the morphology and phase stabilization of SnO₂ for both thin-film deposition and nanoparticle synthesis. In general, thin-film growth techniques allow the stabilization of high-pressure SnO₂ phases via substrate-induced strain or doping. On the other hand, sol-gel synthesis allows precipitating rutile-SnO₂ nanostructures with high specific surfaces. These nanostructures display interesting electrochemical properties that are systematically examined in terms of their applicability to Li-ion battery anodes. Finally, the outlook provides the perspectives of SnO₂ as a candidate material for Li-ion batteries, while addressing its sustainability.

Natrium Diacid Phosphate-Manganese-Lead Vitroceramics Obtained from Spent Electrodes

NaH₂PO₄-MnO₂-PbO₂-Pb vitroceramics were studied usinginfrared (IR), ultraviolet-visible (UV-Vis) and electron paramagnetic resonance (EPR) spectroscopies to understand the structural modifications as potential candidates for electrode materials. The electrochemical performances of the NaH₂PO₄-MnO₂-PbO₂-Pb materials were investigated through measurements of cyclic voltammetry. Analysis of the results indicates that doping with a suitable content of MnO₂ and NaH₂PO₄ removes hydrogen evolution reactions and produces a partial desulphatization of the anodic and cathodic plates of the spent lead acid battery.

Ag NPs/PMMA nanocomposite as an efficient platform for fluorescence regulation of riboflavin

The fluorescence detection platform has broad application in many fields. In this paper, we report a simple and efficient fluorescence detection platform based on the synergistic effects of Ag nanoparticles (Ag NPs) and polymethylmethacrylate (PMMA). Ag NPs were introduced to realize the plasmon enhancement fluorescence and a thin PMMA layer was used to adjust the distance between Ag NPs and riboflavin. The thin PMMA layer not only enhances the fluorescence by enhancing adhesion of substrate, but also optimizes the plasmon enhancement fluorescence effect by serving as the spacer. The fluorescence enhancement factor based on this platform shows a trend of increasing with the decrease of the concentration of riboflavin, and the detection of riboflavin is realized based on this feature, the lowest detectable concentration is as low as 0.27 µM. In addition to the detection based on plasmon enhancement fluorescence, the detection of riboflavin at low concentrations can also be realized by the shift and broadening of the fluorescence peak due to the Ag NPs. The combination of the two ways of plasmon enhancement fluorescence and shift of the fluorescence spectra is used for the detection of riboflavin. These results show that the platform has great potential applications in the field of detection and sensing.

Synthesis of encapsulated ZnO nanowires provide low impedance alternatives for microelectrodes

Microelectrodes are commonly used in electrochemical analysis and biological sensing applications owing to their miniaturised dimensions. It is often desirable to improve the performance of microelectrodes by reducing their electrochemical impedance for increasing the signal-to-noise of the recorded signals. One successful route is to incorporate nanomaterials directly onto microelectrodes; however, it is essential that these fabrication routes are simple and repeatable. In this article, we demonstrate how to synthesise metal encapsulated ZnO nanowires (Cr/Au-ZnO NWs, Ti-ZnO NWs and Pt-ZnO NWs) to reduce the impedance of the microelectrodes. Electrochemical impedance modelling and characterisation of Cr/Au-ZnO NWs, Ti-ZnO NWs and Pt-ZnO NWs are carried out in conjunction with controls of planar Cr/Au and pristine ZnO NWs. It was found that the ZnO NW microelectrodes that were encapsulated with a 10 nm thin layer of Ti or Pt demonstrated the lowest electrochemical impedance of 400 ± 25 kΩ at 1 kHz. The Ti and Pt encapsulated ZnO NWs have the potential to offer an alternative microelectrode modality that could be attractive to electrochemical and biological sensing applications.

Metal-Oxide Nanomaterials Synthesis and Applications in Flexible and Wearable Sensors

Metal-oxide nanomaterials (MONs) have gained considerable interest in the construction of flexible/wearable sensors due to their tunable band gap, low cost, large specific area, and ease of manufacturing. Furthermore, MONs are in high demand for applications, such as gas leakage alarms, environmental protection, health tracking, and smart devices integrated with another system. In this Review, we introduce a comprehensive investigation of factors to boost the sensitivity of MON-based sensors in environmental indicators and health monitoring. Finally, the challenges and perspectives of MON-based flexible/wearable sensors are considered.

First-Principles Exploration into the Physical and Chemical Properties of Certain Newly Identified SnO2 Polymorphs

Tin dioxide (SnO₂) is one of the transparent conductive oxides that has aroused the interest of researchers due to its wide range of applications. SnO₂ exists in a variety of polymorphs with different atomic structures and Sn-O connectivity. However, there are no comprehensive studies on the physical and chemical properties of SnO₂ polymorphs. For the first time, we investigated the structural stability and ground-state properties of 20 polymorphs in the sequence of experimental structures determined by density functional theory. We used a systematic analytical method to determine the viability of polymorphs for practical applications. Among the structurally stable polymorphs, Fm3̅m, I4₁/amd, and Pnma-II are dynamically unstable. As far as we know, no previous research has investigated the electronic properties of SnO₂ polymorphs from the hybrid functional of Heyd, Scuseria, and Erhzerhof (HSE06) except P4₂/mnm, with calculated band gap values ranging from 2.15 to 3.35 eV. The dielectric properties of the polymorphs have been reported, suggesting that SnO₂ polymorphs are also suitable for energy storage applications. The bonding nature of the global minimum rutile structure is analyzed from charge density, charge transfer, and electron localization function. The Imma-SnO₂ polymorph is mechanically unstable, while the remaining polymorphs met all stability criteria. Further, we calculated Raman and IR spectra, elastic moduli, anisotropic factors, and the direction-dependent elastic moduli of stable polymorphs. Although there are many polymorphic forms of SnO₂, rutile is a promising candidate for many applications; however, we investigated the feasibility of the remaining polymorphs for practical applications.

Rational design of ruddlesden–popper phase Mn2SnO4 for ultra-sensitive and highly selective detection of chloramphenicol in real-life samples

A low-cost and eco-friendly Mn2SnO4/GCE electrochemical sensor was fabricated to detect chloramphenicol present in milk powder and eye drops.

A ratiometric fluorescent sensor based on g-CNQDs@Zn-MOF for the sensitive detection of riboflavin via FRET

A novel ratiometric fluorescent sensor based on Förster resonance energy transfer (FRET) platform was designed for riboflavin (RF) detection. The graphitic carbon nitrides quantum dots - Zn-MOF composite (g-CNQDs@Zn-MOF) was used as the fluorescent probe. In the FRET system, g-CNQDs@Zn-MOF and RF acted as donor and acceptor, respectively. The probe exhibited high sensitivity and good selectivity to RF, and had been successfully used for the detection of RF in milk and vitamin B₂ tablets. The detection limit of the sensor was 15 nM. The strategy expanded the application of MOF in sensing filed and provided a new method for the detection of RF.