New Urea Biosensor Based on Urease Enzyme Obtained from Helycobacter pylori

Non-enzymatic disposable electrochemical sensors based on CuO/Co3O4@MWCNTs nanocomposite modified screen-printed electrode for the direct determination of urea

A new electrochemical impedimetric sensor for direct detection of urea was designed and fabricated using nanostructured screen-printed electrodes (SPEs) modified with CuO/Co₃O₄ @MWCNTs. A facile and simple hydrothermal method was achieved for the chemical synthesis of the CuO/Co₃O₄ nanocomposite followed by the integration of MWCNTs to be the final platform of the urea sensor. A full physical and chemical characterization for the prepared nanomaterials were performed including Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), contact angle, scanning electron microscope (SEM) and transmission electron microscopy (TEM). Additionally, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties the modified electrodes with the nanomaterials at different composition ratios of the CuO/Co₃O₄ or MWCNTs. The impedimetric measurements were optimized to reach a picomolar sensitivity and high selectivity for urea detection. From the calibration curve, the linear concentration range of 10^-12-10^-2 M was obtained with the regression coefficient (R²) of 0.9961 and lower detection limit of 0.223 pM (S/N = 5). The proposed sensor has been used for urea analysis in real samples. Thus, the newly developed non-enzymatic sensor represents a considerable advancement in the field for urea detection, owing to the simplicity, portability, and low cost-sensor fabrication.

Advancements in CRISPR-Based Biosensing for Next-Gen Point of Care Diagnostic Application

With the move of molecular tests from diagnostic labs to on-site testing becoming more common, there is a sudden rise in demand for nucleic acid-based diagnostic tools that are selective, sensitive, flexible to terrain changes, and cost-effective to assist in point-of-care systems for large-scale screening and to be used in remote locations in cases of outbreaks and pandemics. CRISPR-based biosensors comprise a promising new approach to nucleic acid detection, which uses Cas effector proteins (Cas9, Cas12, and Cas13) as extremely specialized identification components that may be used in conjunction with a variety of readout approaches (such as fluorescence, colorimetry, potentiometry, lateral flow assay, etc.) for onsite analysis. In this review, we cover some technical aspects of integrating the CRISPR Cas system with traditional biosensing readout methods and amplification technologies such as polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), and recombinase polymerase amplification (RPA) and continue to elaborate on the prospects of the developed biosensor in the detection of some major viral and bacterial diseases. Within the scope of this article, we also discuss the recent COVID pandemic and the numerous CRISPR biosensors that have undergone development since its advent. Finally, we discuss some challenges and future prospects of CRISPR Cas systems in point-of-care testing.

Advanced Sensing Strategies Based on Different Types of Biomarkers toward Early Diagnosis of H. pylori

Helicobacter pylori (H. pylori) is a bacterium that can colonize human gastric epithelial cells and cause H. pylori infection, closely related to many gastric diseases. Compared with conventional H. pylori detection methods, emerging diagnostic approaches (such as biosensors) have become potentially more effective alternatives due to their high sensitivity, good selectivity and noninvasiveness. This review begins with a brief overview of H. pylori infection, the processes that lead to diseases, and current diagnostic methods. Subsequently, advanced biosensors in different target-based for diagnosing H. pylori infection are focused, including the detection of H. pylori-related nucleic acid, H. pylori-related protein (such as the cytotoxin, urease), and intact H. pylori. In addition, prospects for the development of H. pylori detection methods are also discussed in the end.

Advances in diagnosis of Helicobacter pylori through biosensors: Point of care devices

Invasive as well as non-invasive conventional techniques for the detection of Helicobacter pylori (H. pylori) have several limitations that are being overcome by the development of novel, rapid and reliable biosensors. Herein, we describe several biosensors fabricated for the detection of H. pylori. This review aims to provide the principles of biosensors and their components including in the context to H. pylori detection. The major biorecognition elements in H. pylori detection include antigen/antibodies, oligonucleotides and enzymes. Furthermore, the review describes the transducers, such as electrochemical, optical and piezoelectric, also including microfluidics approaches. An overview of the biomarkers associated with H. pylori pathogenesis is also discussed. Finally, the prospects of advancement and commercialization of point-of-care tools are summarized.

Paper-based analytical device with colorimetric detection for urease activity determination in soils and evaluation of potential inhibitors

Urease is an enzyme associated with the degradation of urea, an important nitrogen fertilizer in agriculture. Thus, this current report describes the use of a paper-based analytical device (UrePAD) designed to contain a microzone array for colorimetric determination of urease activity in soils in the absence/presence of potential enzyme inhibitors. The UrePAD can be used at the point-of-need (point-of-care), and it offers advantages such as low cost, simplicity in handling, low sample/reagent volumes, and no use of toxic reagents. The acid-base indicator phenol red was used to monitor the urea hydrolysis reaction catalyzed by urease in the evaluated systems. The images were digitalized in a bench scanner, and the analysis was performed using Corel Draw X8 software. The device offered a LOD of 0.10 U mL^-1 with linearity between 0.25 and 4.0 U mL^-1 and a relative standard deviation ≤ 1.38%. UrePAD was tested in four soil samples of different characteristics and with eight urease inhibitors of varied classes. The results obtained through the proposed device did not differ statistically (95% confidence interval) from those employing the classic method based on the Berthelot reaction, thus indicating that UrePAD was effective for determining urease activity and screening inhibitors, besides showing the capacity to simplify fieldwork involving the application of urea in the soil.

Development of a label-free electrochemical aptasensor based on diazonium electrodeposition: Application to cadmium detection in water

In this study we have developed a new aptasensor for cadmium (Cd²⁺) detection in water. Gold electrode surface has been chemically modified by electrochemical reduction of diazonium salt (CMA) with carboxylic acid outward from the surface. This was used for amino-modified cadmium aptamer immobilization through carbodiimide reaction. Chemical surface modification was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This latter was also used for Cd²⁺ detection. The aptasensor has exhibited a good linear relationship between the logarithm of the Cd²⁺ concentration and the impedance changes in the range from 10^-3 to 10^-9 M with a correlation R² of 0.9954. A high sensitivity was obtained with a low limit of detection (LOD) of 2.75*10^-10 M. Moreover, the developed aptasensor showed a high selectivity towards Cd²⁺ when compared to other interferences such as Hg²⁺, Pb²⁺ and Zn²⁺. The developed aptasensor presents a simple and sensitive approach for Cd²⁺detection in aqueous solutions with application for trace Cd²⁺ detection in spring water samples.

Extracellular urease from Arthrobacter creatinolyticus MTCC 5604: scale up, purification and its cytotoxic effect thereof

Urease is a potent metalloenzyme with diverse applications. This paper describes the scale up and purification of an extracellular urease from Arthrobacter creatinolyticus MTCC 5604. The urease production was scaled-up in 3.7 L and 20 L fermentor. A maximum activity of 27 and 27.8 U/mL and a productivity of 0.90 and 0.99 U/mL/h were obtained at 30 h and 28 h in 3.7 and 20 L fermentor, respectively. Urease was purified to homogeneity with 49.85-fold purification by gel filtration and anion exchange chromatography with a yield of 36% and a specific activity of 1044.37 U/mg protein. The enzyme showed three protein bands with molecular mass of 72.6, 11.2 and 6.1 kDa on SDS-PAGE and ~ 270 kDa on native PAGE. The cytotoxic effect of urease was assessed in vitro using cancer cell lines (A549 and MG-63) and normal cell line (HEK 293). Urease showed its inhibitory effects on cancer cell lines through the generation of toxic ammonia, which in turn increased the pH of the surrounding medium. This increase in extracellular pH, enhanced the cytotoxic effect of weak base chemotherapeutic drugs, doxorubicin (50 µM) and vinblastine (100 µM) in the presence of urease (5 U/mL) and urea (0-4 mM) significantly.

Determination of urea with special emphasis on biosensors: A review

Urea is the major end product of nitrogen metabolism in humans, which is eliminated from the body mainly by the kidneys through urine but is also secreted in body fluids such as blood and saliva. Its level in urine ranges from 7 to 20 mg/dL, which drastically rises under patho-physiological conditions thus providing key information of renal function and diagnosis of various kidney and liver disorders. Increase in urea levels in blood, also referred to as azotemia or uremia. The chronic kidney disease (CKD) or end stage renal disease (ESRD) is generally caused due to the progressive loss of kidney function. Hence, there is an urgent need of determination of urea in biological fluids to diagnose these diseases at their early stage. Among the various methods available for detection of urea, most are complicated and require time-consuming sample pre-treatment, expensive instrumental set-up and trained persons to operate, specifically for chromatographic methods. The biosensing methods overcome these drawbacks, as these are simple, fast, specific and highly sensitive and can also be applied for detection of urea in vivo. This review presents the principles of various analytical methods for determination of urea with special emphasis on biosensors. The use of various nanostructures and electrochemical microfluidic paper based analytical device (EμPAD) are suggested for further development of urea biosensors.

A novel approach for simultaneous sensing of urea and glucose by SPR based optical fiber multianalyte sensor

A novel design is presented for the sensing of urea and glucose simultaneously by surface plasmon resonance (SPR) based optical fiber multianalyte sensor using gel entrapment technique in a fluid for biomedical applications. Sensing surfaces are prepared by coating of different metals and high index dielectric over-layers (silver and silicon in channel 1 and copper and tin-oxide in channel 2) over two small and well separated unclad portions of an optical fiber. Enzymes urease and glucose oxidase are immobilized over respective surfaces using gel entrapment method for the sensing of urea and glucose, respectively. Wavelength interrogation technique is used for the calibration of the sensor. The concentration of urea and glucose are selected in the range 0-180 mM and 0-260 mg dl(-1), respectively, to mimic the physiological range of urea and glucose in human blood. Mixed solutions of urea and glucose with varying concentrations are prepared in buffer solution for the calibration of the sensor. The resonance wavelengths are determined corresponding to two channels responding independently to the interaction of analytes in solution on sensing channels. It is observed that the resonance wavelengths in the case of both the sensing channels decrease with the increasing concentrations of urea and glucose in solutions. The sensor gives 8.51 nm and 13.04 nm total shifts in resonance wavelength for 0 mM to 180 mM urea and 0 mg dl(-1) to 260 mg dl(-1) glucose concentrations in a sample, respectively. The advantages of the present sensor are cascaded design with multiple sensing channels on a single platform, inexpensive, simultaneous sensing of two parameters, possibility of online monitoring and remote sensing.

Immobilization of glutaminase enzyme from Hypocria jecorina on polyacrylic acid: preparation and biochemical characterization

L-glutaminase enzyme produced from Hypocrea jecorina pure culture and polyacrylic acid (PAA) in the presence (Cu2+) ions were composed the ternary complex at pH 7. The properties of free and immobilized enzyme were defined. The effect of various factors such as pH, temperature, heat, and storage stability on immobilized enzyme were investigated. The properties of immobilized enzyme were investigated and compared to those of free enzyme. Optimum pH and temperature of both enzyme were determined to be 8.0 and 50°C, respectively. Kinetic parameters of the immobilized enzyme (Km and Vmax values) were also determined as 0.38 mM of the Km and 10.9 U/L of the Vmax. No drastic change was observed in the Km and Vmax values. Thermal and storage stability experiments were carried out. The thermal stability studies indicated that the immobilization process tends to stabilize the enzyme.