Recent developments in urea biosensors

A Novel Conductometric Urea Biosensor with Improved Analytical Characteristic Based on Recombinant Urease Adsorbed on Nanoparticle of Silicalite

Development of a conductometric biosensor for the urea detection has been reported. It was created using a non-typical method of the recombinant urease immobilization via adsorption on nanoporous particles of silicalite. It should be noted that this biosensor has a number of advantages, such as simple and fast performance, the absence of toxic compounds during biosensor preparation, and high reproducibility (RSD = 5.1 %). The linear range of urea determination by using the biosensor was 0.05-15 mM, and a lower limit of urea detection was 20 μM. The bioselective element was found to be stable for 19 days. The characteristics of recombinant urease-based biomembranes, such as dependence of responses on the protein and ion concentrations, were investigated. It is shown that the developed biosensor can be successfully used for the urea analysis during renal dialysis.

Table top surface plasmon resonance measurement system for efficient urea biosensing using ZnO thin film matrix

The present report addresses the application of surface plasmon resonance (SPR) phenomenon for urea sensing. The former promises a high sensitivity, label-free detection, and real-time information by monitoring the refractive index change at the metal–dielectric interface. In the present report, a highly sensitive urea biosensor has been developed by integrating a ZnO thin film matrix with the SPR technique. Kretschmann configuration has been used to excite the surface plasmon (SP) modes at the ZnO–metal (gold) interface using an indigeneously developed table top SPR measurement setup. Urease (Urs), the urea-specific enzyme, has been immobilized on the surface of ZnO thin film by physical adsorption technique. The SPR reflectance curves were recorded for the prism/Au/ZnO/Urs system in angular interrogation mode with phosphate-buffered saline (PBS) solution as the liquid media. The SPR resonance angle is found to be shifted toward a lower angle from 49.1 to 42.0 deg with an increase in the urea concentration (0 to 300  mg/dl) in the PBS solution. The developed sensor (prism/Au/ZnO/Urs) is found to be highly sensitive [sensitivity=0.039  deg/(mg/dl) or 203  deg/RIU] with detection accuracy of 0.045(deg)(−1).

A novel potentiometric sensor based on urease/ bovine serum albumin-poly(3,4-ethylenedioxythiophene)/Pt for urea detection

We have presented a potentiometric urea sensor using an urease/bovine serum albumin (BSA)-poly(3,4-ethylenedioxythiophene)(PEDOT)/Pt electrode. A urea detection sensitivity of 15.2 mV/decade (order of magnitude) has been achieved. BSA trapped in the PEDOT matrix was employed to bond urease molecules on the surface of a BSA-PEDOT/Pt electrode via amide bonds formed between the carboxyl functional groups on the enzyme and the amines on the BSA. The effects of PEDOT thickness, pH value of the urea solution, urease concentration, and temperature on the urea detection sensitivity were also studied. The lifetime of the sensor was studied for a period of 10 weeks, and the average sensing degradation rate was about 9 % per week. This sensor displayed a high selectivity to urea over glucose, KCl, and NaCl.

Label-free and pH-sensitive colorimetric materials for the sensing of urea

This communication demonstrates a facile method for naked-eye detection of urea based on the structure color change of pH-sensitive photonic crystals. The insertion of urease provides excellent selectivity over other molecules. The detection of urea in different concentration ranges could be realized by changing the molar ratio between the functional monomer and cross-linker.

Ammonia sensing for enzymatic urea detection using organic field effect transistors and a semipermeable membrane

Organic transistors detect the enzymatic breakdown of ureaviaammonia diffusion into the transistor through a semipermeable parylene-C membrane.

A highly efficient urea detection using flower-like zinc oxide nanostructures

A novel matrix based on flower-like zinc oxide nanostructures (ZnONF) has been fabricated using hydrothermal method and exploited successfully for the development of urea biosensor. Urease (Urs) is physically immobilized onto the ZnO nanostructure matrix synthesized over platinized silicon substrate. The surface morphology and crystallographic structure of the as-grown ZnONF have been characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. The fabricated amperometric biosensor (Urs/ZnONF/Pt/Ti/Si) exhibits a linear sensing response towards urea over the concentration range 1.65 mM to 16.50mM with an enhanced sensitivity (~132 μA/mM/cm(2)) and a fast response time of 4s. The relatively low value of Michaelis-Menten constant (Km) of 0.19 mM confirms the high affinity of the immobilized urease on the nanostructured ZnONF surface towards its analyte (urea). The obtained results demonstrate that flower-like ZnO nanostructures serve as a promising matrix for the realization of efficient amperometric urea biosensor with enhanced response characteristics.

Catalytic Oxidative Carbonylation of Amino Moieties to Ureas, Oxamides, 2-Oxazolidinones, and Benzoxazolones

The direct syntheses of ureas, oxamides, 2-oxazolidinones, and benzoxazolones by the oxidative carbonylation of amines, β-amino alcohols, and 2-aminophenols allows us to obtain high value added molecules, which have a large number of important applications in several fields, from very simple building blocks. We have found that it is possible to perform these transformations using the PdI2 /KI catalytic system in an ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate, as the solvent, the solvent/catalyst system can be recycled several times with only a slight loss of activity, and the product can be recovered easily by crystallization.

A high-performance nonenzymatic piezoelectric sensor based on molecularly imprinted transparent TiO2 film for detection of urea

Transparent photocatalytic surfaces are of ever increasing importance for the enhancement of the photocatalytic efficiency. Here, the highly ordered transparent TiO2 nanotube arrays were prepared by the anodization and thermal annealing of titanium layer deposited onto the glass substrate, and a novel nonenzymatic piezoelectric sensor was developed for urea detection based on the modification of molecularly imprinted TiO2 thin film onto transparent TiO2 nanotube arrays. The performance of the fabricated sensor was evaluated and the results indicated that the sensor exhibited high sensitivity in urea detection, with a linear range from 0.04 to 120 μM and a limit of detection of 0.01 μM. Moreover, the sensor presented outstanding selectivity while used in coexisting systems containing various interferents with high concentration. The analytical application of the urea sensor confirmed the feasibility of urea detection in urine sample.

Enzymatic-reaction induced production of polydopamine nanoparticles for sensitive and visual sensing of urea

A novel method to use the enzymatically driven polymerization of dopamine for urea biosensing through spectroscopic or particle size analysis is developed.

Fabrication of nickel oxide nanostructures with high surface area and application for urease-based biosensor for urea detection

NiO nanostructures with high surface area were used to fabricate urease-based NiO biosensors for urea detection.

Application of electrochemical biosensors in clinical diagnosis

Analyses in the clinical area need quick and reliable analytical methods and devices. For this purpose, biosensors can be a suitable option, whereas they are constructed to be simple for use, specific for the target analyte, capable of continuous monitoring and giving quick results, potentially low-costing and portable. In this article, we describe electrochemical biosensors developed for clinical diagnosis, namely for glucose, lactate, cholesterol, urea, creatinine, DNA, antigens, antibodies, and cancer markers assays. Chosen biosensors showed desirable sensitivity, selectivity, and potential for application on real samples. They are often designed to avoid interference with undesired components present in the monitored systems.

A nonenzymatic biosensor based on gold electrodes modified with peptide self-assemblies for detecting ammonia and urea oxidation

We have developed a nonenzymatic biosensor for the detection of ammonia and urea oxidation based on the deposition of peptide microstructures onto thiolated gold electrodes. FF-MNSs/MCP/Au assemblies were obtained by modifying gold substrates with 4-mercaptopyridine (MCP), followed by coating with l,l-diphenylalanine micro/nanostructures (FF-MNSs) grown in the solid-vapor phase. Benzene rings and amide groups with peptide micro/nanostructures interact with synthetic NH4(+) receptors through cation-π and hydrogen bonding. AuOH clusters on the Au surface provided the catalytic sites. The application of a predetermined concentration of analytes at the peptide interfaces activated the catalytic sites. We observed a relationship between the stability of films and the crystal structure of peptides, and we organized the FF-MNSs into an orthorhombic symmetry that was the most suitable assembly for creation of our biosensors. At 0.1 mol L(-1) NaOH, these FF-MNSs/MCP/Au electrodes have electrocatalytic properties regarding ammonia and urea oxidation that are comparable to those of enzyme-based architectures. Under optimal conditions, the electrocatalytic response is proportional to the ammonia and urea concentration in the range 0.1-1.0 mmol L(-1). The sensitivity was calculated as 2.83 and 81.3 μA mmol L(-1) cm(-2) for ammonia and urea, respectively, at +0.40 V (vs SCE). Our detection method is easy to follow, does not require a mediator or enzyme, and has strong potential for detecting urea via nonenzymatic routes.

Acetylcholinesterase biosensors for electrochemical detection of organophosphorus compounds: a review

The exponentially growing population, with limited resources, has exerted an intense pressure on the agriculture sector. In order to achieve high productivity the use of pesticide has increased up to many folds. These pesticides contain organophosphorus (OP) toxic compounds which interfere with the proper functioning of enzyme acetylcholinesterase (AChE) and finally affect the central nervous system (CNS). So, there is a need for routine, continuous, on spot detection of OP compounds which are the main limitations associated with conventional analytical methods. AChE based enzymatic biosensors have been reported by researchers as the most promising tool for analysis of pesticide level to control toxicity and for environment conservation. The present review summarises AChE based biosensors by discussing their characteristic features in terms of fabrication, detection limit, linearity range, time of incubation, and storage stability. Use of nanoparticles in recently reported fabrication strategies has improved the efficiency of biosensors to a great extent making them more reliable and robust.

Potentiometric urea biosensor based on an immobilised fullerene-urease bio-conjugate

A novel method for the rapid modification of fullerene for subsequent enzyme attachment to create a potentiometric biosensor is presented. Urease was immobilized onto the modified fullerene nanomaterial. The modified fullerene-immobilized urease (C₆₀-urease) bioconjugate has been confirmed to catalyze the hydrolysis of urea in solution. The biomaterial was then deposited on a screen-printed electrode containing a non-plasticized poly(n-butyl acrylate) (PnBA) membrane entrapped with a hydrogen ionophore. This pH-selective membrane is intended to function as a potentiometric urea biosensor with the deposition of C₆₀-urease on the PnBA membrane. Various parameters for fullerene modification and urease immobilization were investigated. The optimal pH and concentration of the phosphate buffer for the urea biosensor were 7.0 and 0.5 mM, respectively. The linear response range of the biosensor was from 2.31 × 10⁻³ M to 8.28 × 10⁻⁵ M. The biosensor's sensitivity was 59.67 ± 0.91 mV/decade, which is close to the theoretical value. Common cations such as Na⁺, K⁺, Ca²⁺, Mg²⁺ and NH₄⁺ showed no obvious interference with the urea biosensor's response. The use of a fullerene-urease bio-conjugate and an acrylic membrane with good adhesion prevented the leaching of urease enzyme and thus increased the stability of the urea biosensor for up to 140 days.

Acetylcholinesterase inhibition-based biosensors for pesticide determination: a review

Pesticides released intentionally into the environment and through various processes contaminate the environment. Although pesticides are associated with many health hazards, there is a lack of monitoring of these contaminants. Traditional chromatographic methods-high-performance liquid chromatography, capillary electrophoresis, and mass spectrometry-are effective for the analysis of pesticides in the environment but have certain limitations such as complexity, time-consuming sample preparation, and the requirement of expensive apparatus and trained persons to operate. Over the past decades, acetylcholinesterase (AChE) inhibition-based biosensors have emerged as simple, rapid, and ultra-sensitive tools for pesticide analysis in environmental monitoring, food safety, and quality control. These biosensors have the potential to complement or replace the classical analytical methods by simplifying or eliminating sample preparation and making field-testing easier and faster with significant decrease in cost per analysis. This article reviews the recent developments in AChE inhibition-based biosensors, which include various immobilization methods, different strategies for biosensor construction, the advantages and roles of various matrices used, analytical performance, and application methods for constructing AChE biosensors. These AChE biosensors exhibited detection limits and linearity in the ranges of 1.0×10(-11) to 42.19 μM (detection limits) and 1.0×10(-11)-1.0×10(-2) to 74.5-9.9×10(3)μM (linearity). These biosensors were stable for a period of 2 to 120days. The future prospects for the development of better AChE biosensing systems are also discussed.

High enzymatic activity preservation with carbon nanotubes incorporated in urease-lipid hybrid Langmuir-Blodgett films

The search for optimized architectures, such as thin films, for the production of biosensors has been challenged in recent decades, and thus, the understanding of molecular interactions that occur at interfaces is essential to improve the construction of nanostructured devices. In this study, we investigated the possibility of using carbon nanotubes in hybrid Langmuir-Blodgett (LB) films of lipids and urease to improve the catalytic performance of the immobilized enzyme. The molecular interactions were first investigated at the air-water interface with the enzyme adsorbed from the aqueous subphase onto Langmuir monolayers of dimyristoylphosphatidic acid (DMPA). The transfer to solid supports as LB films and the subsequent incorporation of carbon nanotubes in the hybrid film permitted us to evaluate how these nanomaterials changed the physical properties of the ultrathin film. Colorimetric measurments indicated that the presence of nanotubes preserved and enhanced the enzyme activity of the film, even after 1 month. These results show that the use of such hybrid films is promising for the development of biosensors with an optimized performance.

Immobilization of enzyme and antibody on ALD-HfO2-EIS structure by NH3 plasma treatment

Thin hafnium oxide layers deposited by an atomic layer deposition system were investigated as the sensing membrane of the electrolyte-insulator-semiconductor structure. Moreover, a post-remote NH3 plasma treatment was proposed to replace the complicated silanization procedure for enzyme immobilization. Compared to conventional methods using chemical procedures, remote NH3 plasma treatment reduces the processing steps and time. The results exhibited that urea and antigen can be successfully detected, which indicated that the immobilization process is correct.

Functionalized multilayered graphene platform for urea sensor

Multilayered graphene (MLG) is an interesting material for electrochemical sensing and biosensing because of its very large 2D electrical conductivity and large surface area. We propose a less toxic, reproducible, and easy method for producing functionalized multilayer graphene from multiwalled carbon nanotubes (MWCNTs) in mass scale using only concentrated H(2)SO(4)/HNO(3). Electron microscopy results show the MLG formation, whereas FTIR and XPS data suggest its carboxylic and hydroxyl-functionalized nature. We utilize this functionalized MLG for the fabrication of a novel amperometric urea biosensor. This biosensor shows linearity of 10-100 mg dL(-1), sensitivity of 5.43 μA mg(-1) dL cm(-2), lower detection limit of 3.9 mg dL(-1), and response time of 10 s. Our results suggest that MLG is a promising material for electrochemical biosensing applications.

Bacterial attachment on optical fibre surfaces

Optical fibres have received considerable attention as high-density sensor arrays suitable for both in vitro and in vivo measurements of biomolecules and biological processes in living organisms and/or nano-environments. The fibre surface was chemically modified by exposure to a selective etchant that preferentially erodes the fibre cores relative to the surrounding cladding material, thus producing a regular pattern of cylindrical wells of approximately 2.5 mum in diameter and 2.5 mum deep. The surface hydrophobicity of the etched and non-etched optical fibres was analysed using the sessile pico-drop method. The surface topography was characterised by atomic force microscopy (AFM), while the surface chemistry was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Six taxonomically different bacterial strains showed a consistent preference for attachment to the nano-scale smoother (R(q) = 273 nm), non-etched fibre surfaces (water contact angle, theta = 106 degrees +/- 4 degrees). In comparison, the surfaces of the etched optical fibres (water contact angle, theta = 96 degrees +/- 10 degrees) were not found to be amenable to bacterial attachment. Bacterial attachment on the non-etched optical fibre substrata varied among different strains.