Amperometric biosensors based on carboxylated multiwalled carbon nanotubes-metal oxide nanoparticles-7,7,8,8-tetracyanoquinodimethane composite for the determination of xanthine

Carbon Nanomaterials (CNMs) and Enzymes: From Nanozymes to CNM-Enzyme Conjugates and Biodegradation

Carbon nanomaterials (CNMs) and enzymes differ significantly in terms of their physico-chemical properties—their handling and characterization require very different specialized skills. Therefore, their combination is not trivial. Numerous studies exist at the interface between these two components—especially in the area of sensing—but also involving biofuel cells, biocatalysis, and even biomedical applications including innovative therapeutic approaches and theranostics. Finally, enzymes that are capable of biodegrading CNMs have been identified, and they may play an important role in controlling the environmental fate of these structures after their use. CNMs’ widespread use has created more and more opportunities for their entry into the environment, and thus it becomes increasingly important to understand how to biodegrade them. In this concise review, we will cover the progress made in the last five years on this exciting topic, focusing on the applications, and concluding with future perspectives on research combining carbon nanomaterials and enzymes.

Recent Advantages of Mediator Based Chemically Modified Electrodes; Powerful Approach in Electroanalytical Chemistry

Background:

Modified electrodes have advanced from the initial studies aimed at understanding electron transfer in films to applications in areas such as energy production and analytical chemistry. This review emphasizes the major classes of modified electrodes with mediators that are being explored for improving analytical methodology. Chemically modified electrodes (CMEs) have been widely used to counter the problems of poor sensitivity and selectivity faced in bare electrodes. We have briefly reviewed the organometallic and organic mediators that have been extensively employed to engineer adapted electrode surfaces for the detection of different compounds. Also, the characteristics of the materials that improve the electrocatalytic activity of the modified surfaces are discussed.

Objective:

Improvement and promotion of pragmatic CMEs have generated a diversity of novel and probable strong detection prospects for electroanalysis. While the capability of handling the chemical nature of the electrode/solution interface accurately and creatively increases , it is predictable that different mediators-based CMEs could be developed with electrocatalytic activity and completely new applications be advanced.

Nanohybrid electrochemical enzyme sensor for xanthine determination in fish samples

An amperometric biosensor for xanthine was designed, based on covalent immobilization of xanthine oxidase (XO) of Bacillus pumilus RL-2d onto a screen-printed multi-walled carbon nanotubes gold nanoparticle-based electrodes (Nano-Au/c-MWCNT). The carboxyl groups at the electrode surface were activated by the use of 1-Ethyl-3-(3-dimethylaminopropyl carbodiimide) (EDC) and N-hydroxysuccinimide (NHS). The working electrode was then coated with 6 μL of xanthine oxidase (0.273 U/mg protein). The cyclic voltammetry (CV) study was done for the characterization of the sensor using [K₃Fe(CN)₆] as an artificial electron donor. The sensitivity (S) and the limit of detection (LOD) of the biosensor were 2388.88 µA/cm²/nM (2.388 µA/cm²/µM) and 1.14 nM, respectively. The developed biosensor was used for determination of fish meat freshness.

Polyphenazine and polytriphenylmethane redox polymer/nanomaterial-based electrochemical sensors and biosensors: a review

In recent years, an increasing number of studies has demonstrated that redox polymers can be used in simple and effective electrochemical sensing platforms due to their fast electron transfer and electrocatalytic ability. To develop more sensitive and selective electrochemical (bio)sensors, the electrocatalytic properties of redox polymers and the electrical, mechanical, and catalytic properties of various nanomaterials are combined. This review aims to summarize and contribute to the development of (bio)sensors based on polyphenazine or polytriphenylmethane redox polymers combined with nanomaterials, including carbon-based nanomaterials, metal/metal oxide, and semiconductor nanoparticles. The synthesis, preparation, and modification of these nanocomposites is presented and the contribution of each material to the performance of (bio)sensor has been be examined. It is explained how the combined use of these redox polymers and nanomaterials as a sensing platform leads to improved analytical performance of the (bio)sensors. Finally, the analytical performance characteristics and practical applications of polyphenazine and polytriphenylmethane redox polymer/nanomaterial-based electrochemical (bio)sensors are compared and discussed.

Bioengineered Polymer/Composites as Advanced Biological Detection of Sorbitol: An Application in Healthcare Sector

Bioengineered polymers and nanomaterials have emerged as promising and advanced materials for the fabrication and development of novel biosensors. Nanotechnology-enabled biosensor methods have high sensitivity, selectivity and more rapid detection of an analyte. Biosensor based methods are more rapid and simple with higher sensitivity and selectivity and can be developed for point-of-care diagnostic testing. Development of a simple, sensitive and rapid method for sorbitol detection is of considerable significance to efficient monitoring of diabetes-associated disorders like cataract, neuropathy, and nephropathy at initial stages. This issue encourages us to write a review that highlights recent advancements in the field of sorbitol detection as no such reports have been published till the date. The first section of this review will be dedicated to the conventional approaches or methods that had been playing a role in detection. The second part focused on the emerging field i.e. biosensors with optical, electrochemical, piezoelectric, etc. approaches for sorbitol detection and the importance of its detection in healthcare application. It is expected that this review will be very helpful for readers to know the different conventional and recent detection techniques for sorbitol at a glance.

Convenient synthesis of three-dimensional hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide for non-enzymatic electrochemical sensing of xanthine

A novel hybrid with three-dimensional (3D) hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide (CuS@Pd/N-RGO) has been prepared by a facile wet-chemical route without utilizing any template molecules and surfactants. The characterization results reveal that the 3D flower-like structure of CuS "core" is composed of interconnecting nanoplates, which is conductive to the loading of Pd nanoparticles' "shell" and results in the robust interaction between the core and shell for the formation of CuS@Pd cauliflowers. Anchoring such appealing CuS@Pd cauliflowers on the two-dimensional N-RGO can efficaciously inhibit the aggregation of CuS@Pd cauliflowers and accelerate the kinetics of xanthine oxidation. Benefiting from the multi-functional properties and unique morphology, the sensor constructed by CuS@Pd/N-RGO exhibits excellent performance for non-enzymatic detection of xanthine including a wide detection range of 0.7-200.0 μM (0.94 V vs. SCE), a low detection limit of 28 nM (S/N = 3), high reproducibility (relative standard deviation (RSD) = 4.1%), and commendable stability (retained 90% of the initial electrochemical responses after storage for 30 days), which is amongst the best of various electrochemical sensors reported for xanthine assays till date. Reliable and satisfying recoveries (95-105%, RSD ≤ 4.1%) are achieved for xanthine detection in real samples. The inspiring results make the uniquely structural CuS@Pd/N-RGO greatly promising in non-enzymatic electrochemical sensing applications. Graphical abstract A high-performance non-enzymatic xanthine sensor has been constructed by the three-dimensional hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide.

Monodispersed gold nanoparticles entrapped in ordered mesoporous carbon/silica nanocomposites as xanthine oxidase mimic for electrochemical sensing of xanthine

Monodispersed Au nanoparticles in ordered mesoporous carbon/silica (Au/OMCS) nanocomposites were prepared by the solvent evaporation induced self-assembly. Au/OMCS nanocomposites were characterized through XRD, BET, and TEM. The obtained nanocomposites exhibit uniform mesopores with the size of 18 ± 2 nm. And ultrafine Au nanoparticles with the size of 3~7 nm are well dispersed in the cavities. An ultrasensitive nanoenzyme sensor was fabricated based on a Au/OMCS-modified electrode. The Au/OMCS-modified electrode displays high xanthine oxidase-like catalytic activity evaluated through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The DPV response currents are linearly dependent on concentrations of xanthine (Xa) in the range 0.10-20 μM, along with a high sensitivity of 6.84 μA μM^-1 cm^-2 and very low detection limit of 0.006 μM (S/N = 3) under the optimal working potential of 0.64 V vs. SCE. Interference experiments show that the nanoenzyme sensor has no obvious responses to most potentially interfering species at a potential of 0.64 V. The fabricated sensor has been applied to the determination of Xa in spiked urine samples with recoveries ranging from 98.26 to 101.4%. Graphical abstract.

Amperometric determination of heavy metal using an HRP inhibition biosensor based on ITO nanoparticles-ruthenium (III) hexamine trichloride composite: Central composite design optimization

A novel horseradish peroxidase (HRP) enzyme inhibition biosensor based on indium tin oxide (ITO) nanoparticles, hexaammineruthenium (III) chloride (RUT), and chitosan (CH) modified glassy carbon electrode (GCE) was developed. The biosensor fabrication process was investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The amounts of ITO nanoparticles and RUT were optimized using a 2² central composite design for the optimization of electrode composition. The detection limits were determined as 8 nM, 3 nM, and 1 nM for Pb²⁺, Ni²⁺, and Cd²⁺, respectively. The inhibition calibration curves of the biosensor were found to be within the range of 0.009-0.301 µM with a sensitivity of 11.97 µA µM^-1 cm^-2 (0.85 µA µM^-1) for Pb²⁺, 0.011-0.368 µM with a sensitivity of 10.84 µA µM^-1 cm^-2 (0.77 µA µM^-1) for Ni²⁺, and 0.008-0.372 µM with a sensitivity of 10.99 µA µM^-1 cm^-2 (0.78 µA µM^-1) for Cd²⁺. The type of HRP inhibition by Pb²⁺, Ni²⁺ and Cd²⁺ was investigated by the Dixon and Cornish-Bowden plots. The effects of possible interfering species on the biosensor response were examined. The analysis of Pb²⁺, Ni²⁺, and Cd²⁺ in tap water was demonstrated using the HRP/ITO-RUT-CH/GCE with satisfactory experimental results. The proposed method agreed with the atomic absorption spectrometry results.

Development of a paper-based microanalysis device doped with multi-walled carbon nanotubes for in vitro evaluation of fluorene cytotoxicity

Developing a cost-effective and simple micro-analysis tool has long been an important objective in the toxicological detection of fluorene. In this study, a disposable paper-based micro-analysis device (μ-PAD) was designed using graphite doped with multi-walled carbon nanotubes (MWCNTs) to hand draw the electrode (MWCNTs/μ-PAD). We investigated the feasibility of the designed MWCNTs/μ-PAD as a cell-sensing platform using voltammetry measurements. Its application for evaluating the cytotoxicity of fluorene was studied based on the electrochemical determination of human breast cancer cells induced by fluorene. The results showed a dose-dependent toxicity effect of fluorene on cellular activity. The measurements were comparable with those obtained using a methyl-thiazolyl-tetrazolium assay. The detection limit of the MWCNTs/μ-PAD for human breast cancer cells was as low as 4.00 × 10³ cells·mL^-1 owing to the enhanced catalytic activity of the MWCNTs. Notably, the MWCNTs/μ-PAD-which had a diameter of 7.00 mm-allowed a sampling volume of 10.0 μL, which is 50.0 times less than the sampling volume required with a conventional electrode (500 μL). Advantages such as the simplicity of manufacture, low consumption, low cost, rapid detection, and disposability, suggest that the MWCNTs/μ-PAD could provide new opportunities and directions for in vitro microanalysis.

A polypyrrole-coated eightfold-helical Wells-Dawson POM-based Cu-FKZ framework for enhanced colorimetric sensing

To explore a novel colorimetric biosensor with high sensibility and selectivity, a new Wells-Dawson-type polyoxometalate (POM)-based metal-organic framework (MOF) with an eightfold helix, [Cu₉(FKZ)₁₂(H₂O)₈][H₃P₂W₁₈O₆₂]₂·4H₂O (CuFKZP₂W₁₈) (HFKZ = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-1-yl)methyl] ethanol), was successfully synthesized; then, polypyrrole (PPy) was introduced to fabricate CuFKZP₂W₁₈/PPy(n) nanocomposites (n = 7%, 15%, 30%) via a facile in situ oxidation polymerization process. All the results indicate that CuFKZP₂W₁₈/PPy(15%) as a colorimetric biosensor exhibits lower limits of detection (0.07 μM towards H₂O₂ and 0.627 μM towards ascorbic acid), smaller K_m values (0.106 mM for H₂O₂ and 0.042 mM for o-phenylenediamine) and higher sensitivity (0.0227 1 μM^-1 towards H₂O₂ and 0.0025 1 μM^-1 to ascorbic acid) than most reported enzyme mimetics to the best of our knowledge.

Enzyme Immobilization on Maghemite Nanoparticles with Improved Catalytic Activity: An Electrochemical Study for Xanthine

Generally, enzyme immobilization on nanoparticles leads to nano-conjugates presenting partially preserved, or even absent, biological properties. Notwithstanding, recent research demonstrated that the coupling to nanomaterials can improve the activity of immobilized enzymes. Herein, xanthine oxidase (XO) was immobilized by self-assembly on peculiar naked iron oxide nanoparticles (surface active maghemite nanoparticles, SAMNs). The catalytic activity of the nanostructured conjugate (SAMN@XO) was assessed by optical spectroscopy and compared to the parent enzyme. SAMN@XO revealed improved catalytic features with respect to the parent enzyme and was applied for the electrochemical studies of xanthine. The present example supports the nascent knowledge concerning protein conjugation to nanoparticle as a means for the modulation of biological activity.

ATMP-induced three-dimensional conductive polymer hydrogel scaffold for a novel enhanced solid-state electrochemiluminescence biosensor

Reliable and sensitive detection of xanthine has important medical and biological significance. In this work, a novel three-dimensional (3D) conductive polymer hydrogel of polyaniline (PAni) was feasibly prepared using aniline (Ani), amino trimethylene phosphonic acid (ATMP) and ammonium persulfate ((NH₄)₂S₂O₈) as monomer, gelatinizing agent and oxidizing agent, respectively. Protonation of aniline can be achieved by ATMP, inducing good conductivity of the obtained hydrogel. ATMP remained the chelating abilities in the conductive hydrogel, enabling further immobilization with silver nanoparticles (AgNPs) functionalized by a luminol derivative, N-(aminobutyl)-N-(ethylisoluminol) (ABEI). ABEI-Ag@PAni-ATMP exhibited an enhanced performance of solid-state electrochemiluminescence (ECL). Integrated with xanthine oxidase (XOD), the proposed biosensor can be applied in the detection of xanthine via in-situ generated hydrogen peroxide (H₂O₂), and present a low detection limit of 9.6 nM, a wide linear range (from 0.01 to 200 μM) and excellent stability.

Tyrosinase-immobilized CNT based biosensor for highly-sensitive detection of phenolic compounds

Highly sensitive phenol biosensor was developed by using well-dispersed carbon nanotubes (CNTs) in enzyme solution and adding CNTs in enzyme electrodes. First, the intact CNTs were dispersed in aqueous tyrosinase (TYR) solution, and TYR molecules were precipitated and crosslinked to prepare the sample of enzyme adsorption, precipitation and crosslinking (EAPC). EAPC exhibited 10.5- and 5.4-fold higher TYR activity per mg of CNTs as compared to enzyme adsorption (EA) and enzyme adsorption/crosslinking (EAC), respectively. EAPC retained 29% of its initial activity after incubation at 40 °C for 128 h, while EA and EAC showed no residual activities, respectively. In biosensing a model phenolic compound of catechol, the sensitivities of EA, EAC and EAPC electrodes on glassy carbon electrode (GCE) were 34, 281 and 675 µA/mM/cm², respectively. When 90 w/w% CNTs were added to the enzyme electrodes, the sensitivities of EA, EAC, and EAPC electrodes were 146, 427, and 1160 µA/mM/cm², respectively, and the EAPC electrode showed a 2.3-fold increase in sensitivity upon CNT addition. Catechol and phenol could also be detected by EAPC on the screen-printed electrode (SPE), with sensitivities of 1340 and 1170 µA/mM/cm², respectively. The sensitivity of EAPC-SPE for phenol detection in the effluent from real municipal wastewater treatment plant was 1100 µA/mM/cm². The sensitivity of EAPC-SPE retained 74% of its initial sensitivity after incubation at 40 °C for 12 h. The combination of EAPC immobilization and CNT addition has great potential for application in the development of sensitive enzyme biosensors for various analytes and phenols in water environments.

Aluminium oxide nanoparticles induce structural changes in tau and cytotoxicity of the neuroblastoma cell line

The application of nanomaterials in the healthy system may induce some neurodegenerative diseases initiated by tau folding and neuronal cell death. Herein, aluminium oxide nanoparticles (Al₂O₃ NPs) were synthesized and characterized by XRD, TEM, DLS and zeta potential investigations. Afterwards, the interaction of Al₂O₃ NPs with tau protein was investigated by fluorescence and CD spectroscopic methods. The molecular docking and molecular dynamic were also run to explore the binding site and conformational changes of tau after interaction with Al₂O₃ cluster. Moreover, the MTT, LDH, caspase-9/-3 and flow cytometry assays were done to explore the Al₂O₃ NPs-induced cytotoxicity against SH-SY5Y cells. It was revealed that Al₂O₃ NPs bind to tau protein and form a static complex and fold the structure of tau toward a more packed structure. Molecular docking and molecular dynamic investigations revealed that NPs bind to the hydrophilic residues of the tau segments and promote some marginal structural folding of tau segment. The cellular assays displayed that Al₂O₃ NPs can elicit cell mortality through membrane leakage, caspase-9/-3 activations, and induction of both apoptosis and necrosis. This data may indicate that NPs can induce some adverse effects on the biological systems.

Progress in utilisation of graphene for electrochemical biosensors

This review discusses recent graphene (GR) electrochemical biosensor for accurate detection of biomolecules, including glucose, hydrogen peroxide, dopamine, ascorbic acid, uric acid, nicotinamide adenine dinucleotide, DNA, metals and immunosensor through effective immobilization of enzymes, including glucose oxidase, horseradish peroxidase, and haemoglobin. GR-based biosensors exhibited remarkable performance with high sensitivities, wide linear detection ranges, low detection limits, and long-term stabilities. Future challenges for the field include miniaturising biosensors and simplifying mass production are discussed.