Investigating the Influence of Temperature on the Kaolinite-Base Synthesis of Zeolite and Urease Immobilization for the Potential Fabrication of Electrochemical Urea Biosensors

Application of zeolites and zeolitic imidazolate frameworks in the biosensor development

Biosensors are advanced devices for analysis of composition of blood, urine, environmental samples, and many other media. Their current development is tightly linked with nanomaterials, such as zeolites and zeolitic imidazolate framework (ZIFs). The present review describes electrochemical (amperometric, conductometric, ISFET) and optical (fluorescent and colorimetric) biosensors that incorporate zeolites and ZIFs in their biorecognition elements. The biosensors are based on immobilized enzymes (such as glucose oxidase, urease, and acetylcholinesterase), antibodies, DNA, and aptamers. The review present reasons for application of these nanomaterials, and discusses advantages of zeolite- and ZIF-containing biosensors over other biosensors. In most cases, the biosensors have improved sensitivity, better limit of detection, wider linear range, and other improved characteristics. It is demonstrated that immobilization of biomolecules such as enzymes or antibodies on the surface of zeolites and ZIFs enables creation of unique advanced biosensors that have a potential for further development and practical applications.

Immobilization of Urease onto Nanochitosan Enhanced the Enzyme Efficiency: Biophysical Studies and in Vitro Clinical Application on Nephropathy Diabetic Iraqi Patients

Immobilization of enzymes is an effective method for improving the properties and applications of modern enzymes. There are several supports for enzyme immobilization. Because of its unique features, such as inertness and high surface area, chitosan was widely used to immobilize enzymes. Immobilization of urease onto chitosan is a promising approach to treating high urea levels in the blood, however, the immobilization conditions for the best kinetics and enzyme efficiency are still challenging. Herein, we tried to immobilize urease onto nanochitosan (chitosan NPs) through a cross-linker and study the kinetics (km and $v_{\max }$ values) and thermodynamics (Ea, ∆H, ∆S, and ∆G) parameters of the enzyme reaction before and after immobilization at different substrate concentration (50, 100, 150, 200, and 250 mg/dl) and incubation temperature (15, 20, 25, 30, 35, and 40°C) under selected optimum conditions. The immobilized urease chitosan NPs was characterized in our previous work using Fourier transform infrared $\text{infrared}$ (FTIR), Atomic force $\text{force}$ microscopy (AFM), and $\text{and}$ imaged here by scanning electron microscopy $\text{microscopy}$ (SEM). Results revealed that the highest efficiency % of immobilization (70.38%) was observed at 750 mg/ml chitosan NPs and phosphate buffer pH 7 at 40°C. With an increase of Km value for the immobilized enzyme, however, the efficiency of the enzyme was significantly higher than the free enzyme, $p<0.001$ . In addition, the activation energy of the reaction catalyzed by the immobilized enzyme was lower than that of the free enzyme, which suggests that the active site geometry of the immobilized enzyme was more favorable to accommodate the substrate and thus required less energy than that of the free enzyme. The reaction was endothermic by means of positive ∆H. The immobilized urease enzyme was in vitro applied to blood samples of Iraq nephropathy diabetic patients (n = 35) to investigate the effect on serum urease activity and urea level compared to healthy volunteers. Interestingly, the activity of serum urease significantly increased after adding the immobilized enzyme and the level of urea significantly decreased ( $p<0.0001$ ) by ∼1.5 folds. Thus, applying an immobilized urease $\text{urease}$ to remove urea from blood could be effective in the blood detoxification or dialysis regeneration system of artificial kidney machines.

Recent advancements in urea biosensors for biomedical applications

The quick progress in health care technology as a recurrent measurement of biochemical factors such as blood components leads to advance development and growth in biosensor technology necessary for effectual patient concern. The review wok of authors present a concise information and brief discussion on the development made in the progress of potentiometric, field effect transistor, graphene, electrochemical, optical, polymeric, nanoparticles and nanocomposites based urea biosensors in the past two decades. The work of authors is also centred on different procedures/methods for detection of urea by using amperometric, potentiometric, conductometric and optical processes, where graphene, polymer etc. are utilised as an immobilised material for the fabrication of biosensors. Further, a comparative revision has been accomplished on various procedures of urea analysis using different materials-based biosensors, and it discloses that electrochemical and potentiometric biosensor is the most promise one among all, in terms of rapid response time, extensive shelf life and resourceful design.

Investigation of Various Influencing Factors of Hydrothermal Synthesis of Analcime Zeolite

This study presents an investigation of the use of the natural mineral of Nakhchivan Autonomous Republic to produce analcime zeolite of potential practical importance. The influence of temperature and crystallization time, the concentration of alkaline solution and mineralizer on the process of synthesis of analcime has been evaluated. The optimal conditions established for the synthesis of pure analcime with a 100% degree of crystallinity are as follows: temperature of 180°C, alkaline and mineralizer solution of 10-15% KOH and 5-10% KCl and processing time of 50 hours. It has been shown that the presence of the KCl mineralizer promotes the production of pure analcime with a 100% crystallinity, and the natural mineral of Nakhchivan represents a good source for the synthesis process.

Poly(azomethine-urethane) and zeolite-based composite: Fluorescent biosensor for DNA detection

In the present paper, a highly selective and sensitive fluorescent biosensor based on poly(azomethine-urethane) and zeolite for the determination of DNA molecules was developed. Zeolite was chosen to enhance with anionic or cationic functional groups in polymer matrix and interaction between polymer and DNA. Several parameters such as polymer concentration, pH and incubation time effect on the sensitivity of the fluorescent biosensor were optimized. Linear range was determined between 2.50 and 25.00 nmol/L DNA concentration and limit of detection (LOD) of the biosensor was calculated as 0.095 nmol/L under the optimal conditions. Interference study was also performed in the presence of different amino acids, cations and organic compounds. The results clearly indicated that the tested cations and compounds were not induced a significant fluorescence change and the proposed zeolite-based biosensor was shown a good selectivity for DNA.

Electrochemical Response of Saccharomyces cerevisiae Corresponds to Cell Viability upon Exposure to Dioclea reflexa Seed Extracts and Antifungal Drugs

Dioclea reflexa bioactive compounds have been shown to contain antioxidant properties. The extracts from the same plant are used in traditional medical practices to treat various diseases with impressive outcomes. In this study, ionic mobility in Saccharomyces cerevisiae cells in the presence of D. reflexa seed extracts was monitored using electrochemical detection methods to link cell death to ionic imbalance. Cells treated with ethanol, methanol, and water extracts were studied using cyclic voltammetry and cell counting to correlate electrochemical behavior and cell viability, respectively. The results were compared with cells treated with pore-forming Amphotericin b (Amp b), as well as Fluconazole (Flu) and the antimicrobial drug Rifampicin (Rif). The D. reflexa seed water extract (SWE) revealed higher anodic peak current with 58% cell death. Seed methanol extract (SME) and seed ethanol extract (SEE) recorded 31% and 22% cell death, respectively. Among the three control drugs, Flu revealed the highest cell death of about 64%, whereas Amp b and Rif exhibited cell deaths of 35% and 16%, respectively, after 8 h of cell growth. It was observed that similar to SWE, there was an increase in the anodic peak current in the presence of different concentrations of Amp b, which also correlated with enhanced cell death. It was concluded from this observation that Amp b and SWE might follow similar mechanisms to inhibit cell growth. Thus, the individual bioactive compounds from the water extracts of D. reflexa seeds could further be purified and tested to validate their potential therapeutic application. The strategy to link electrochemical behavior to biochemical responses could be a simple, fast, and robust screening technique for new drug targets and to understand the mechanism of action of such drugs against disease models.

Applications of zeolites in biotechnology and medicine – a review

Zeolites are microporous natural or synthetic tectosilicates, promising for organism detoxification, improvement of the nutrition status and immunity, separation of various biomolecules and cells, detection of biomarkers of various diseases, controlled drug and gene delivery, radical scavenging, haemostasis, tissue engineering and biomaterial coating.