Simple enzyme based fluorimetric biosensor for urea in human biofluids

As an important biomarker for renal related diseases, detection of urea is playing a vital role in human biofluids on clinical diagnosis concern. In this work, a synthetic salicyaldehyde based imine fluorophore was synthesized using sonication method and conjugated with urease which was used as fluorescent biosensor for the detection of urea in serum samples. This enzyme based biosensor has shown a good selectivity and sensitivity towards urea with the linear range from 2 to 80 mM and the detection limit of 73 µM. The sensing response obtain is highly agreeing with existing analytical technique for urea detection which strongly recommends this biosensor for clinical application.

In Situ Measurement of Urea Concentration With an In-Fiber SPR-MZI Sensor

A fiber-optic urea sensor based on surface plasmon resonance (SPR) and Mach-Zehnder interference (MZI) combined principle was designed and implemented. By plating gold film on the single-mode-no-core-thin-core-single-mode fiber structure, we successfully excited both SPR and MZI, and constructed two parallel detection channels for simultaneously measurement of urea concentration and temperature. Urease was immobilized on the gold film by metal-organic zeolite skeleton (ZIF-8), which can not only fix a large number of urease to improve measurement sensitivity of urea, but also protect urease activity to ensure the sensor stability. Experimental results indicate that the designed urea sensor with temperature compensation function can detect urea solution with concentration of 1-9 mM, and the sensitivity is 1.4 nm/mM. The proposed measurement method provides a new choice for monitoring urea concentration in the field of medical diagnosis and human health monitoring.

A Review of Electroactive Nanomaterials in the Detection of Nitrogen-Containing Organic Compounds and Future Applications

Electrochemical and impedimetric detection of nitrogen-containing organic compounds (NOCs) in blood, urine, sweat, and saliva is widely used in clinical diagnosis. NOC detection is used to identify illnesses such as chronic kidney disease (CKD), end-stage renal disease (ESRD), cardiovascular complications, diabetes, cancer, and others. In recent years, nanomaterials have shown significant potential in the detection of NOCs using electrochemical and impedimetric sensors. This potential is due to the higher surface area, porous nature, and functional groups of nanomaterials, which can aid in improving the sensing performance with inexpensive, direct, and quick-time processing methods. In this review, we discuss nanomaterials, such as metal oxides, graphene nanostructures, and their nanocomposites, for the detection of NOCs. Notably, researchers have considered nanocomposite-based devices, such as a field effect transistor (FET) and printed electrodes, for the detection of NOCs. In this review, we emphasize the significant importance of electrochemical and impedimetric methods in the detection of NOCs, which typically show higher sensitivity and selectivity. So, these methods will open a new way to make embeddable electrodes for point-of-detection (POD) devices. These devices could be used in the next generation of non-invasive analysis for biomedical and clinical applications. This review also summarizes recent state-of-the-art technology for the development of sensors for on-site monitoring and disease diagnosis at an earlier stage.

Green structure orienting and reducing agents of wheat peel extract induced abundant surface oxygen vacancies and transformed the nanoflake morphology of NiO into a plate-like shape with enhanced non-enzymatic urea sensing application

Researchers are increasingly focusing on using biomass waste for green synthesis of nanostructured materials since green reducing, capping, stabilizing and orientation agents play a significant role in final application. Wheat peel extract contains a rich source of reducing and structure orienting agents that are not utilized for morphological transformation of NiO nanostructures. Our study focuses on the role of wheat peel extract in morphological transformation during the synthesis of NiO nanostructures as well as in non-enzymatic electrochemical urea sensing. It was observed that the morphological transformation of NiO flakes into nanoplatelets took place in the presence of wheat peel extract during the preparation of NiO nanostructures and that both the lateral size and thickness of the nanostructures were significantly reduced. Wheat peel extract was also found to reduce the optical band gap of NiO. A NiO nanostructure prepared with 5 mL of wheat peel extract (sample 2) was highly efficient for the detection of urea without the use of urease enzyme. It has been demonstrated that the induced modification of NiO nanoplatelets through the use of structure-orienting agents in the wheat peel has enhanced their electrochemical performance. A linear range of 0.1 mM to 13 mM was achieved with a detection limit of 0.003 mM in the proposed urea sensor. The performance of the presented non-enzymatic urea sensor was evaluated in terms of selectivity, stability, reproducibility, and practical application, and the results were highly satisfactory. As a result of the high surface active sites on sample 2, the low charge transfer resistance, as well as the high exposure to the surface active sites of wheat peel extract, sample 2 demonstrated enhanced performance. The wheat peel extract could be used for the green synthesis of a wide range of nanostructured materials, particularly metal/metal oxides for various electrochemical applications.

Green Synthesis of NiO Nanoflakes Using Bitter Gourd Peel, and Their Electrochemical Urea Sensing Application

To determine urea accurately in clinical samples, food samples, dairy products, and agricultural samples, a new analytical method is required, and non-enzymatic methods are preferred due to their low cost and ease of use. In this study, bitter gourd peel biomass waste is utilized to modify and structurally transform nickel oxide (NiO) nanostructures during the low-temperature aqueous chemical growth method. As a result of the high concentration of phytochemicals, the surface was highly sensitive to urea oxidation under alkaline conditions of 0.1 M NaOH. We investigated the structure and shape of NiO nanostructures using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). In spite of their flake-like morphology and excellent crystal quality, NiO nanostructures exhibited cubic phases. An investigation of the effects of bitter gourd juice demonstrated that a large volume of juice produced thin flakes measuring 100 to 200 nanometers in diameter. We are able to detect urea concentrations between 1-9 mM with a detection limit of 0.02 mM using our urea sensor. Additionally, the stability, reproducibility, repeatability, and selectivity of the sensor were examined. A variety of real samples, including milk, blood, urine, wheat flour, and curd, were used to test the non-enzymatic urea sensors. These real samples demonstrated the potential of the electrode device for measuring urea in a routine manner. It is noteworthy that bitter gourd contains phytochemicals that are capable of altering surfaces and activating catalytic reactions. In this way, new materials can be developed for a wide range of applications, including biomedicine, energy production, and environmental protection.

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.

Fabrication, characterization, and photocatalytic degradation potential of chitosan-conjugated manganese magnetic nano-biocomposite for emerging dye pollutants

The release of toxic dyes from different industries through industrial effluents cause hazardous effects to human and aquatic life. Therefore, the detoxification of such toxic pollutants is very important for a clean environment. In this regard, chitosan conjugated Mn-magnetic nano-biocomposite (Mn-CCMN) was synthesized, characterized, and applied for the photocatalytic decontamination of crystal violet (CV) dye in the contaminated aqueous system and industrial wastewater. The characterization was performed using SEM, XRD, EDX and FTIR spectroscopic techniques and determine PZC. The data shows the successfully synthesis of the resultant nano-biocomposite with amorphous nature and Fe and Mn were present therein. The SEM study revealed the flat and irregular shaped structure with porous surface and 87 ± 4 nm as mean particle size. The application of as-synthesized nano-biocomposite was determined as a photocatalyst for the eradication of CV in the aqueous environment under UV light illumination. The different photocatalysis conditions were studied for maximum degradation of CV and under the best experimental factors, tremendous CV degradation was attained in the real samples and industrial wastewater. The synthesized Mn-CCMN sustain excellent photocatalytic performance for four successive batches. The photocatalytic data was fitted to the pseudo-first-order kinetic model (R² = 0.992) having 0.007672 min^-1 and 0.0549 ppm/min as k and reaction rate, respectively. The statistical models such as response surface methodology (RSM) and artificial neural network-genetic algorithm (ANN-GA) were also applied for confirmation of the experimental data and the results showed a good agreement. It is deduced that the synthesized Mn-CCMN could be an excellent alternative to the present photocatalysts for the decontamination of toxic organic dyes from contaminated water and industrial wastewater.

Core-shell magnetic molecularly imprinted polymer for selective recognition and detection of sunset yellow in aqueous environment and real samples

Magnetic Molecularly imprinted polymers (MMIPs) have been recently recognized as an exceptional tool for monitoring and decontamination of environmental and biological samples of diverse nature. Based on the potential applications as sorbents and biomimetic sensors, herein, a core-shell magnetic-molecularly imprinted polymer (MMIP) was developed as a selective material for separation and sensing of sunset yellow (SY) dye in an aqueous environment and real samples. The MMIP was synthesized via precipitation polymerization using SY as a template, MAA as a functional monomer (chosen based on simulation studies), EGDMA as a cross-linking agent, and AIBN as an initiator. To elaborate the specificity of MMIP, a comparative agent, magnetic non-imprinted polymer (MNIP) was also synthesized. The XRD results showed that the MMIP showed both crystalline and amorphous structure attributed to the presence and polymeric and non-polymeric groups. The FTIR spectra confirmed synthesis of intermediate and final MMIP product. The SEM results showed spherical morphology and porous structure of the MMIP with an average particle size of 0.636 μm in diameter. The MMIP was first employed as a sorbent for the removal of SY from the aqueous environment. The binding experiments performed at optimized operating conditions (pH 2; time 30 min; sorbent dosage 3 mg; sorbate concentration 80 ppm) showed more selectivity when compared with MNIP. The data fitted best to Langmuir's sorption isotherm (Q_o 359.8 mg/g) and followed the pseudo-second-order kinetic model. The synthesized MMIP was also used as an electrochemical sensor for detection of SY dye in the aqueous environment, which exhibited a linear range of detection as (1.51 × 10^-6 - 1.5 × 10^-3 M). The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.00413 M and 0.0137 M, respectively. While the R² value was found to be 0.997 at optimized analytical conditions. These results suggested that the synthesized MMIP can be applied for the selective separation and quantification of SY dye in sample of diverse nature.

3-D printed electrode integrated sensing chip and a PoC device for enzyme free electrochemical detection of blood urea

Herein we report a novel electrochemical sensing chip and a point-of-care device (PoC) for enzyme-free electrochemical detection of urea in human blood. The electrochemical sensing chip was developed by 3-D printing of conductive Ag ink and subsequent electrodeposition of AuNP-rGO nanocomposite. Material characterization of the sensing chip was conducted to find a plausible mechanism for the electrochemical reaction with urea. Subsequently, the response with varying concentrations of urea in solution and human blood samples was tested. High peak response current (~5 times than that of the highest reported value), low impedance, rapid sensor fabrication procedure, high selectivity towards urea, excellent linear response (R² = 0.99), high sensitivity of 183 μA mM^-1 cm^-2, the fast response indicated by high diffusion coefficient, the limit of detection of 0.1 µM, tested shelf life of more than 6 months and recovery rate of >99% ensured the application of the developed sensor chip towards PoC urea detection test kit. A PoC device housing an electronic circuitry following the principles of linear sweep voltammetry and compatible with a sensing chip was developed. A maximum percentage error of 4.86% and maximum RSD of 3.63% confirmed the use of the PoC device for rapid urea measurements in human blood.

Design and fabrication of green and sustainable vapochromic cellulose fibers embedded with natural anthocyanin for detection of toxic ammonia

Exposure to colorless ammonia gas may lead to damage in human organs or even death. Herein, we describe facile fabrication of an environmentally-friendly, portable, reversible, and sensitive solid-state colorimetric cellulose (Cell)/anthocyanin (Anth) vapochromic sensor that exhibits instant visual color change to both gaseous and aqueous phases of ammonia. The naturally occurring anthocyanin can be easily extracted from the red-cabbage plant and applied as a direct dyestuff onto viscose fibers in the presence of potassium aluminum sulfate as mordant to generate nanoparticles of mordant/anthocyanin coordinated complex. Thus, upon exposure to aqueous ammonia, an instant color change of the smart (Cell-Anth) diagnostic assays, from purple to colorless, was noted and quantitatively probed via both CIE Lab coordinates and UV-Vis spectral measurements. Importantly, the fabricated (Cell-Anth) viscose fabric showed rapid responses, fraction of second, with a good limit of detection (LOD) in the range of 200-1200 mg L^-1. This receptor also demonstrated ratiometric changes in the UV-Vis absorbance spectra, giving a hypsochromic shift from 611 to 375 nm upon increasing the total content of ammonia in an aqueous media. The morphologies of Cell-Anth fabrics as well as particle size of the generated mordant/dye complex on the fabric surface have been characterized by transmission electron microscopic (TEM), scan electron microscopy (SEM), energy-dispersive X-ray patterns (EDX) and Fourier-transform infrared spectroscopic (FT-IR). The comfortability of the dyed cellulose fibers was also investigated in terms of their bend length, air-permeability and colorfastness properties. Significantly, the present study offers a promising onsite vapochromic device that enables detection of ammonia in either aqueous or gas phase in various environments and products.

Hybrid synthetic receptor composed of molecularly imprinted polydopamine and aptamers for impedimetric biosensing of urea

An electrochemical aptamer-based method is described for highly specific sensing of urea. Urea-imprinted polydopamine was obtained by electropolymerization of dopamine (DA). The molecularly imprinted polymer (MIP) also contains DNA aptamers on gold nanoparticles decorated with a carbon nanotube network (AuNP/CNT). The material was placed on a glassy carbon electrode (GCE). After removal of urea from the MIP cavities, the GCE display double recognition capability which makes it superior to conventional MIP-only or aptamer-only based assays. On exposure of the modified electrode to urea, the interfacial charge transfer of the redox probe hexacyanoferrate is traced, typically measured at a peak voltage of 0.22 V vs. Ag/AgCl. The change in charge transfer resistance depends on the urea concentration. The assay has a 900 fM detection limit, and response is the linear up to 500 nM urea concentrations. Graphical abstract ᅟ.

A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles

We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo₂O₄) nanoneedles.

Ultrathin nickel-metal–organic framework nanobelt based electrochemical sensor for the determination of urea in human body fluids

Ni-MOF ultrathin nanobelts in alkaline media can be used as an efficient catalyst for urea electrooxidation.

Synthesis of novel amperometric urea-sensor using hybrid synthesized NiO-NPs/GO modified GCE in aqueous solution of cetrimonium bromide

In this study NiO nanostructures were synthesized via combinational synthetic method (ultrasound-assisted biosynthesis) and immobilized on the glassy carbon electrode (GCE) as a highly sensitive and selective enzyme-less sensor for urea detection. NiO-NPs were fully characterized using SEM, EDX, XRD, BET, TGA, FT-IR, UV-vis and Raman methods which revealed the formation of NiO nanostructures in the form of cotton like porous material and crystalline in nature with the average size of 3.8 nm. GCE was modified with NiO-NPs in aqueous solution of cetrimonium bromide(CTAB). Highly adhesive NiO/CTAB/GO nanocomposite membrane has been formed on GCE by immersing NiO/CTAB modified GCE in GO suspension. CTAB has a major role in the production and immobilization of the nanocomposites on the GCE surface and the binding NiO nanoparticles on GO plates. In addition, CTAB/GO composition made a highly adhesive surface on the GCE. The resulting NiO/CTAB/GO/GCE contains potently sensitive to urea in aqueous environments. The response of as developed amperometric sensor was linear in the range of 100-1200 µM urea with R² value of 0.991 and limit of detection (LOD), 8 µM. The sensor responded negligibly to various interfering species like glucose, uric acid and ascorbic acid. This sensor was applied successfully for determining urea in real water samples such as mineral water, tap water and river water with acceptable recovery.

Miniaturized Bio-and Chemical-Sensors for Point-of-Care Monitoring of Chronic Kidney Diseases

This review reports the latest achievements in point-of-care (POC) sensor technologies for the monitoring of ammonia, creatinine and urea in patients suffering of chronic kidney diseases (CKDs). Abnormal levels of these nitrogen biomarkers are found in the physiological fluids, such as blood, urine and sweat, of CKD patients. Delocalized at-home monitoring of CKD biomarkers via integration of miniaturized, portable, and low cost chemical- and bio-sensors in POC devices, is an emerging approach to improve patients’ health monitoring and life quality. The successful monitoring of CKD biomarkers, performed on the different body fluids by means of sensors having strict requirements in term of size, cost, large-scale production capacity, response time and simple operation procedures for use in POC devices, is reported and discussed.

Spectrophotometric methods for the determination of urea in real samples using silver nanoparticles by standard addition and 2nd order derivative methods

In this work, we have developed simple, sensitive and inexpensive methods for the spectrophotometric determination of urea in urine samples using silver nanoparticles (AgNPs). The standard addition and 2nd order derivative methods were adopted for this purpose. AgNPs were prepared by chemical reduction of AgNO₃ with hydrazine using 1,3-di-(1H-imidazol-1-yl)-2-propanol (DIPO) as a stabilizing agent in aqueous medium. The proposed methods were based on the complexation of AgNPs with urea. Using this concept, urea in the urine samples was successfully determined spectrophotometric methods. The results showed high percent recovery with ±RSD. The recoveries of urea in the three urine samples by spectrophotometric standard addition were 99.2%±5.37, 96.3%±4.49, 104.88%±4.99 and that of spectrophotometric 2nd order derivative method were 115.3%±5.2, 103.4%±2.6, 105.93%±0.76. The results show that these methods can open doors for a potential role of AgNPs in the clinical determination of urea in urine, blood, biological, non-biological fluids.