Solution growth of 3D MnO2 mesh comprising 1D nanofibres as a novel sensor for selective and sensitive detection of biomolecules

Nanomaterials-based biosensor and their applications: A review

A sensor can be called ideal or perfect if it is enriched with certain characteristics viz., superior detections range, high sensitivity, selectivity, resolution, reproducibility, repeatability, and response time with good flow. Recently, biosensors made of nanoparticles (NPs) have gained very high popularity due to their excellent applications in nearly all the fields of science and technology. The use of NPs in the biosensor is usually done to fill the gap between the converter and the bioreceptor, which is at the nanoscale. Simultaneously the uses of NPs and electrochemical techniques have led to the emergence of biosensors with high sensitivity and decomposition power. This review summarizes the development of biosensors made of NPssuch as noble metal NPs and metal oxide NPs, nanowires (NWs), nanorods (NRs), carbon nanotubes (CNTs), quantum dots (QDs), and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Electrogenerated chemiluminescence resonance energy transfer between luminol and MnO2 nanosheets decorated with Cu2O nanoparticles for sensitive detection of RNase H

In the present work, a novel approach was developed for the preparation of Cu₂O nanoparticle decorated MnO₂ nanosheets (Cu₂O@MnO₂). Uniformly dispersed Cu₂O nanocrystals were produced on the surface of MnO₂ nanosheets by in situ reduction under refluxing conditions. The unique structure of the used MnO₂ nanosheet support played a vital role in the preparation of such Cu₂O@MnO₂ nanocomposites. The electrogenerated chemiluminescence (ECL) resonance energy transfer can occur between the luminol/H₂O₂ system and Cu₂O@MnO₂ nanocomposites, resulting in a decrease of the ECL intensity, which can be used to fabricate an ECL sensor. Cu₂O@MnO₂ nanocomposite modified heterologous DNA/RNA duplexes were modified on the GCE to construct an ECL-RET system, leading to the decrease of ECL intensity. As a highly conserved damage repair protein, RNase H can specifically hydrolyze RNA in DNA/RNA strands to release Cu₂O@MnO₂ nanocomposites and recover the ECL signal. As a result, an "off-on" mode ECL sensor for sensitive RNase H assay was fabricated. Under the optimal conditions, the detection limit of RNase H is 0.0005 U mL^-1, which is superior to other approaches. The proposed method provides a universal platform for monitoring RNase H, and exhibits great potential in bioanalysis.

Selective Voltammetric Sensor for the Simultaneous Quantification of Tartrazine and Brilliant Blue FCF

Tartrazine and brilliant blue FCF are synthetic dyes used in the food, cosmetic and pharmaceutical industries. The individual and/or simultaneous control of their concentrations is required due to dose-dependent negative health effects. Therefore, the paper presents experimental results related to the development of a sensing platform for the electrochemical detection of tartrazine and brilliant blue FCF based on a glassy carbon electrode (GCE) modified with MnO₂ nanorods, using anodic differential pulse voltammetry. Homogeneous and stable suspensions of MnO₂ nanorods have been obtained involving cetylpyridinium bromide solution as a cationic surfactant. The MnO₂ nanorods-modified electrode showed a 7.9-fold increase in the electroactive surface area and a 72-fold decrease in the electron transfer resistance. The developed sensor allowed the simultaneous quantification of dyes for two linear domains: in the ranges of 0.10-2.5 and 2.5-15 μM for tartrazine and 0.25-2.5 and 2.5-15 μM for brilliant blue FCF with detection limits of 43 and 41 nM, respectively. High selectivity of the sensor response in the presence of typical interference agents (inorganic ions, saccharides, ascorbic and sorbic acids), other food dyes (riboflavin, indigo carmine, and sunset yellow), and vanillin has been achieved. The sensor has been tested by analyzing soft and isotonic sports drinks and the determined concentrations were close to those obtained involving the chromatography technique.

Advances of MnO2 nanomaterials as novel agonists for the development of cGAS-STING-mediated therapeutics

As an essential micronutrient, manganese plays an important role in the physiological process and immune process. In recent decades, cGAS-STING pathway, which can congenitally recognize exogenous and endogenous DNA for activation, has been widely reported to play critical roles in the innate immunity against some important diseases, such as infections and tumor. Manganese ion (Mn²⁺) has been recently proved to specifically bind with cGAS and activate cGAS-STING pathway as a potential cGAS agonist, however, is significantly restricted by the low stability of Mn²⁺ for further medical application. As one of the most stable forms of manganese, manganese dioxide (MnO₂) nanomaterials have been reported to show multiple promising functions, such as drug delivery, anti-tumor and anti-infection activities. More importantly, MnO₂ nanomaterials are also found to be a potential candidate as cGAS agonist by transforming into Mn²⁺, which indicates their potential for cGAS-STING regulations in different diseased conditions. In this review, we introduced the methods for the preparation of MnO₂ nanomaterials as well as their biological activities. Moreover, we emphatically introduced the cGAS-STING pathway and discussed the detailed mechanisms of MnO₂ nanomaterials for cGAS activation by converting into Mn²⁺. And we also discussed the application of MnO₂ nanomaterials for disease treatment by regulating cGAS-STING pathway, which might benefit the future development of novel cGAS-STING targeted treatments based on MnO₂ nanoplatforms.

Cupric oxide nanoparticles incorporated poly(hydroxybutyrate) nanocomposite for potential biosensing application

We report the synthesis of a novel electrochemical biosensor comprising of cupric oxide (CuO) nanoparticles (NPs) mediated poly(hydroxybutyrate) (PHB) composite film with polyvinyl alcohol (PVA) as a binder/template support using the solution casting method for the detection of a biomolecule i.e., ascorbic acid (AA). The specimens were characterized for surface, chemical, mechanical, optical, and electrochemical attributes. The results expressed regular mediation of CuO NPs in the PHB/PVA matrix towards nanobiocomposite formation with enhanced crystallinity, inter-molecular interactions, mechanical, and electrochemical attributes, and decreased hydrophilicity and bandgap, thus being useful in potential optoelectronic devices. The synthesized biocomposite film exhibited a tensile strength of 86.24 ± 4.10 N which might be due to reinforcement/uniform dispersion of the CuO nanofiller in the PHB-based matrix. The PHB/CuO composite, then, deposited on a glassy carbon electrode surface exhibited good electrocatalytic activity towards the AA in the aqueous media even at low analyte concentrations. Such modified electrode surfaces with metal/biopolymer complex could find possible applications in the detection of other bioactive molecules.

Morphology Effect of One-Dimensional MnO2 Nanostructures on Heteroatom-Doped Carbon Dot-Based Biosensors for Selective Detection of Glutathione

Structural versatility of MnO₂ nanostructures plays a significant role in biosensing applications. So, we have prepared simple and selective "turn-off-on" sensing probes for the detection of glutathione (GSH), based on nitrogen, sulfur codoped carbon dots (N, S-Cdots) and different morphologies of one-dimensional (1-D) MnO₂ nanostructures. N, S-Cdots with a high fluorescence quantum yield (73.42%) were prepared by a green approach through high-temperature pyrolysis in just 5 min. The different morphologies of 1-D MnO₂ nanostructures (nanowires with varying aspect ratios and nanorods) were synthesized through a hydrothermal method by varying the reaction period (8, 10, and 12 h). MnO₂ nanowires prepared at 8 h showed a high specific surface area (34 m² g^-1) with a large aspect ratio. They showed significant fluorescence quenching, Stern-Volmer constants, and binding constants in the presence of N, S-Cdots. Further, ultraviolet-visible absorption, zeta potential, and time decay studies showed that the quenching mechanism of the developed sensing system was the inner filter effect, which was further confirmed by using the Parker equation. The N, S-Cdots-MnO₂ nanowire (with a high aspect ratio) sensing system showed the best limit of detection, i.e., 28.5 μM for GSH. This fast, simple, eco-friendly, and cost-effective sensing system can be further used for real-time biosensing and bioimaging application.

Morphology-Dependent Performance of MnO2 Nanostructure-Carbon Dot-Based Biosensors for the Detection of Glutathione

Herein, we develop a facile, sensitive, and selective fluorescent nanosensor for the detection of glutathione (GSH). In this protocol, carbon dots (Cdots) with a fairly high quantum yield were synthesized by a microwave-assisted pyrolysis technique. Moreover, different shapes of the MnO₂ nanostructure were also prepared by the hydrothermal technique. A comparative photophysical study of different morphology-dependent Cdots@MnO₂ nanostructure-based biosensors was explored, which showed different results for the quenching values of ("turn-off") fluorescence intensity, quantum yields, electron transfer rate, and average lifetime. The structure, property, and performance of nanomaterials are interdependent. Therefore, the different shapes of MnO₂, that is, nanoflowers (NFs), nanorods (NRs), and a mixture of NFs/NRs was prepared by the hydrothermal method owing to different specific surface areas (23-69 m² g^-1) which put the impact on their sensing activity. It was observed that the variation in the different photophysical parameters of fluorescent Cdots such as quantum yield (Φ), average lifetime values [τ_av (ns)], radiative (k_r) rate constant, nonradiative (k_nr) rate constant, rate of electron transfer (k_ET), the efficiency of electron transfer (Φ_EET), FRET efficiency (E), and Förster distance (R₀) were dependent on the different shapes of the MnO₂ nanostructure. These results indicate that the transfer of energy occurs between the Cdots and different shapes of MnO₂ nanostructures based on fluorescence resonance energy transfer at different charge-transfer rates. The recovery rate ("turn-on") of fluorescence of Cdots with the addition of GSH was obtained best for the NF structure by conversion of MnO₂ to Mn²⁺, and the limit of detection was obtained as ∼19 μM for GSH. The developed sensing probes were rapid, easy, cheap, and eco-friendly for the determination of GSH.

In situ hierarchical encapsulation of bimetallic selenides into honeycomb-like nitrogen doped porous carbon nanosheets for highly sensitive and selective guanosine detection

An innovative electrochemical nanocomposite for the detection of guanosine (Gua) was proposed by in situ encapsulation of nickel-iron bimetallic selenides confined into honeycomb-like nitrogen doped porous carbon nanosheets, denoted as (Ni,Fe)Se₂/N-PCNs. The porous carbon nanosheets were prepared by utilizing nickel-iron layered double hydroxide (Ni-Fe LDH) as the substrate and zeolitic imidazolate frameworks (ZIF-67) nanocrystals as the sacrificial templates via hydrothermal synthesis, followed by a process of acid etching and pyrolysis selenylation. Interestingly, the nickel-ferric bimetallic selenides material (Ni,Fe)Se₂, is rarely fabricated successfully using selenylation treatment, which is a highly conductive and robust support to promote the electron transport. Meanwhile, the obtained (Ni,Fe)Se₂/N-PCNs have the favorable architectural features of both unique three-dimensional (3D) porous structural and hierarchical connectivity, which are expected to provide more active sites for electrochemical reactions and ease of electron, ion, and biomolecule penetration. Benefiting from the inherent virtues of its composition, together with unique structural advantages, the (Ni,Fe)Se₂/N-PCNs possess ideal sensing properties for guanosine detection with a low detection limit of 1.20 × 10^-8 M, a wide linear range of 5.30 × 10^-8 ~ 2.27 × 10^-4 M and a good stability. Superb selectivity for potential interfering species and superb recoveries in serum suggests its feasibility for practical applications.

Surfactant-assisted synthesis of copper oxide nanorods for the enhanced photocatalytic degradation of Reactive Black 5 dye in wastewater

In this study, copper oxide nanorods were synthesized via surfactant-assisted chemical precipitation method and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV-Visible spectrometer. XRD result reveals that CuO nanorods were structured in the monoclinic phase. SEM image suggested that synthesized CuO were shaped like nanorod with approximately 20-40 nm width and 500-800 nm length. The observed band gap calculated from UV-Visible absorption studies is 1.45 eV. As-prepared CuO nanorods were applied as a photocatalyst for the degradation of textile dye Reactive Black 5 (RB-5) in aqueous solution under the presence of visible light. The result exhibited that an enhanced degradation of RB-5 was achieved around 98% within 300 min and the experimental values were well matched with the linear fit model (R² = 0.97) and the observed rate constant found to be 5 × 10^-3 min^-1. Therefore, as-synthesized CuO nanorods can be applied as a potential photocatalyst material for the degradation of organic pollutants in the wastewater.

Solution growth of 1D zinc tungstate (ZnWO4) nanowires; design, morphology, and electrochemical sensor fabrication for selective detection of chloramphenicol

Development of 1D nanostructures with novel morphology is a recent scientific attraction, so to say yielding unusual materials for advanced applications. In this work, we have prepared solution grown, single-pot 1D ZnWO₄ nanowires (NWs) and the morphology is assessed for label-free but selective detection of chloramphenicol. This is the first report where, such structures are being investigated for this purpose. Transmission electron microscopy shows the presence of strands of ZnWO₄ of about 20 nm in diameter. The formed NWs were highly dispersed in nature with uniform size and shape. X-ray diffraction analysis confirmed high purity of the designed NWs despite solution synthesis. X-ray photoelectron spectroscopy confirmed surface valence state of ZnWO₄. Fourier transform infrared spectroscopy was employed for the ascription of functional groups, whereas, optical properties were investigated using photoluminescence. NWs were employed for the detection of a model antibiotic, chloramphenicol. The developed sensor exhibited excellent limit of detection, 0.32 μM and 100% specificity as compared to its structural and functional analogues such as thiamphenicol and clindamycin. This work can broaden new opportunities for the researchers to explore unconventional nanomaterials bearing unique morphologies and quantum phenomenon for the label-free detection of other bioanalytes.