Detection Of Urea Research Articles

Development of electrochemical biosensors with various types of zeolites

In the work, different types of zeolites were used for the development of enzyme-based electrochemical biosensors. Zeolites were added to the biorecognition elements of the biosensors and served as additional components of the biomembranes or adsorbents for enzymes. Three types of biosensors (conductometric, amperometric and potentiometric) were studied. The developed biosensors were compared with the similar biosensors without zeolites. The biosensors contained the following enzymes: urease, glucose oxidase, glutamate oxidase, and acetylcholinesterase and were intended for the detection of urea, glucose, glutamate, and acetylcholine, respectively. Construction of the biosensors using the adsorption of enzymes on zeolites has several advantages: simplicity, good reproducibility, quickness, absence of toxic compounds. These benefits are particularly important for the standardization and further mass production of the biosensors. Furthermore, a biosensor for the sucrose determination contained a three-enzyme system (invertase/mutatorase/glucose oxidase), immobilized by a combination of adsorption on silicalite and cross-linking via glutaraldehyde; such combined immobilization demonstrated better results as compared with adsorption or cross-linking separately. The analysis of urea and sucrose concentrations in the real samples was carried out. The results, obtained with biosensors, had high correlation with the results of traditional analytical methods, thus the developed biosensors are promising for practical applications.

Non-invasive paper-based microfluidic device for ultra-low detection of urea through enzyme catalysis.

This work describes the design, fabrication and characterization of a paper-based microfluidic device for ultra-low detection of urea through enzyme catalysis. The microfluidic system comprises an entry port, a fluidic channel, a reaction zone and two electrodes (contacts). Wax printing was used to create fluidic channels on the surface of a chromatography paper. Pre-conceptualized designs of the fluidic channel are wax-printed on the paper substrate while the electrodes are screen-printed. The paper printed with wax is heated to cause the wax reflow along the thickness of the paper that selectively creates hydrophilic and hydrophobic zones inside the paper. Urease immobilized in the reaction zone catalyses urea into releasing ions and, thereby, generating a current flow between the electrodes. A measure of current with respect to time at a fixed potential enables the detection of urea. The methodology enabled urea concentration down to 1 pM to be detected. The significance of this work lies in the use of simple and inexpensive paper-based substrates to achieve detection of ultra-low concentrations of analytes such as urea. The process is non-invasive and employs a less cumbersome two-electrode assembly.

Urea impedimetric biosensing using electrospun nanofibers modified with zinc oxide nanoparticles

Reliable analytical techniques to evaluate dairy products, including milk, are of outmost importance to ensure food safety against contaminants. Among possible substances employed as adulterants in milk, urea raises deep concern due to its harmful effects to consumer’s health. In the present study, a biosensing platform was developed to be applied in the electrochemical detection of urea. The sensing platform was fabricated using polymeric electrospun nanofibers of polyamide 6 (PA6) and polypyrrole (PPy) deposited onto fluorine doped tin oxide (FTO) electrodes, which were then modified with zinc oxide nanoparticles (ZnO). This material showed excellent properties for the immobilization of urease enzyme, conferring the FTO/PA6/PPy/ZnO/urease electrode high sensitivity for urea detection within the concentration range between 0.1 and 250 mg dL−1 with a limit of detection of 0.011 mg dL−1. The results achieved evidence the potential of electrospun nanofibers-based electrodes for applications in biosensors aiming at dairy products analysis.

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.

Detection of Paracetamol in Water and Urea in Artificial Urine with Gold Nanoparticle@Al Foil Cost-efficient SERS Substrate.

We demonstrated that a cost-efficient, easy to prepare, hybrid SERS substrate-gold nanoparticles (AuNPs) on untreated Al foil (AlF) can effectively detect pharmaceuticals, such as paracetamol and clinical biomarkers, like urea in artificial urine. The limit of detection (LOD) for paracetamol on AuNPs on AlF is superior (0.1 vs. 1 mM ) to the LOD reported for SERS detection of paracetamol in the literature. For SERS detection of urea in urine, AuNPs on both Al foil and Au film performed much better than AuNPs on glass, in terms of the concentration range, linearity and LOD. However, assay on AuNPs on AlF showed a better semi-logarithmic trendline with R2 = 0.98 than an assay on AuNPs on Au film with R2 = 0.94. They have comparable sensitivity with LOD 0.024 and 0.017 M, respectively. The limit of quantification (LOQ) of the former is 0.026 M, which makes it sufficient for the quantification of urea in urine at both normal and pathophysiological (0.03 - 0.15 M) concentration.

A new disposable biosensor platform: carbon nanotube/poly(o-toluidine) nanocomposite for direct biosensing of urea

The development of new techniques for rapid and continuous monitoring of urea in biomedical and clinical analysis is very important. Thus, conductive polymer-supported carbon nanotube as an effective electrochemical biosensing platform for direct detection of urea in blood samples was designed. For the assay optimization, several conductive polymers were synthesized and tested as electrode modifiers; among the tested polymers, poly-o-toluidine (PoT) showed the highest electrochemical signals. However, after the enzyme immobilization, direct bioelectrochemical signals were not obtained when the PoT was used alone. Due to the lower electrocatalytic feature of PoT, integration of carbon nanotube, to form a composite with the PoT, was exploited to enable the direct electron transfer. Successfully, using the hybrid, the catalytic activity of the immobilized urease enzyme was retained. Consequently, a sensitive and specific chronoamperometric signals were achieved after the bioassay optimization. Eventually, a standard calibration curve for urea determination was obtained. A linear range was found from 0.1 to 11 mM with the limit of detection of 0.03 mM. Successfully, several blood samples were analyzed and urea level was correlated with the reference analytical method.

Urea Detection Using Commercial Field Effect Transistors

We used an easy method to assemble a biosensor using simple and low cost materials. Commercial SnO2:F thin films were used as the basic sensing part of an extended-gate ion-sensitive field effect transistor. When used as a pH sensor, the oxide film showed a sensitivity of 59 ± 4 mV.pH−1, and linear response in the pH range 2.0 to 10.0. Since urea detection and quantification is important for the control of many pathologies, as proof of concept the samples were further used as platform for urea sensing by immobilizing urease protein onto the surface of the film. For urea sensing, the modified electrodes showed a linear response in the pUrea range of 2.1 to 3.0 (1.00 mM to 7.94 mM, which covers a suitable screening interval for clinical exams) and a sensitivity of 109 ± 3 mV.pUrea−1. A steady-state was reached after about 60 seconds. Varied pHs and buffer concentrations were also investigated to assess the biosensor behavior toward changes in the environmental conditions. The proposed device could be applied in clinical trials in developing countries as well as in areas hit by natural disasters.

Non-Enzymatic Electrochemical Detection of Urea on Silver Nanoparticles Anchored Nitrogen-Doped Single-Walled Carbon Nanotube Modified Electrode

Herein, we demonstrated synthesis and application of silver nanoparticles (Ag-NPs) decorated nitrogen doped single-walled carbon nanotube through a one-step thermal-reduction method using melamine as the nitrogen source. Field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction data confirmed the successful synthesis of Ag-NPs functionalized nitrogen doped single-walled carbon nanotubes(Ag-N-SWCNTs). The nitrogen-doping notably modified the properties of the SWCNT and it showed stronger affinity for the attachment of Ag-NPs. By integrating the high surface area and electrical properties of N-SWCNTs with Ag-NPs, the obtained Ag-N-SWCNTs nanocomposite showed high catalytic activity than N-SWCNTs and pristine-SWCNTs. The enzyme-based methods have some disadvantages. For example, high fabrication cost and poor stability, due to these intrinsic disadvantages, non-enzymatic sensors have received more interest in fabrication of sensors. A non-enzymatic electrochemical urea sensor was developed by modifying glassy carbon electrode (GCE) with Ag-N-SWCNTs and a layer of Nafion (Nf). Thus, the fabricated sensor exhibited lower limit of detection (4.7 nM), with an enhanced sensitivity of 141 μAmM−1cm−2 for urea detection in the range of 66 nM to 20.6 mM(R2 = 0.966). The reliability of the as-fabricated sensor was successfully investigated by using it to detect urea in tap water and milk samples. The NF/Ag-N-SWCNTs based urea sensor offers several advantages such as simple fabrication procedure, non-enzymatic and low-cost, so this sensor can be applied to detect urea in various samples from food, fertilizer industries and environmental fields. Moreover, the modified electrode showed phenomenal stability with no loss in activity of storage under ambient conditions. In addition, the novel hybrid NF/Ag-N-SWCNTs/GCE showed high selectivity toward urea with good repeatability and reproducibility further confirmed that this method can be utilized for detection of urea.

Amperometric Detection of Urea by Polyaniline and Poly(O-anisidine) Film under Galvanostatic Method: A Comparative Study

Amperometric Detection of Urea by Polyaniline and Poly(O-anisidine) Film under Galvanostatic Method: A Comparative Study

An ammonia-based etchant for attaining copper nanoclusters with green fluorescence emission.

Luminescent copper nanoclusters (CuNCs) constitute a very active research topic due to their unique properties and lower cost than gold and silver NCs. In this study, we report a new, facile, and rapid top-down etching method for synthesizing luminescent CuNCs, using Cu nanoparticles (CuNPs) as the precursor and ammonia (NH3) as the etchant. The etching mechanism is systematically investigated and the optical and structural properties of the obtained CuNCs are carefully studied. The NH3-triggered etching process is very fast and the newly generated CuNCs can emit strong green fluorescence with a high quantum yield. Moreover, by coupling the urease-catalyzed hydrolysis of urea with the NH3-induced etching of CuNPs, we developed a novel fluorescence turn-on assay for urea. The linear range for urea detection is from 0.25 to 5 mM, and the limit of detection is 0.01 mM. This novel sensing approach, with good sensitivity and excellent selectivity, is then successfully utilized to detect urea in human serum samples, demonstrating its great potential in clinical diagnosis. In addition, the proposed coupling method can be extended to monitor other analytes that influence the size-focusing etching process, allowing metal NCs to be used to construct diverse chemosensors and biosensors.

Abstract B003: Development of OAT-1746, a novel arginase 1 and 2 inhibitor for cancer immunotherapy

Abstract Depletion of arginine represents an important mechanism of immunosuppression, and high plasma and tumor arginase (ARG) activity has been demonstrated in patients with a wide spectrum of cancers and correlated with a poor prognosis. Low arginine levels inhibit proliferation and activation of cytotoxic T and NK cells. Preclinical and clinical studies show that simultaneous interference with multiple mechanisms of immunosuppression results in a strongly improved antitumor efficacy. In this context, we have developed OAT-1746, a novel, potent, and selective small-molecule inhibitor of ARG1 and ARG2 with profound antitumor efficacy as a monotherapy and in combinations with gemcitabine and PD-L1 inhibitor. The IC50 of OAT-1746 was determined against the recombinant human and murine ARG1 and ARG2. Cellular activity was evaluated in M2-polarized, bone marrow-derived murine macrophages, and CHO cells transfected with human ARG1 or ARG2. The in vivo antitumor efficacy of OAT-1746 was evaluated in syngeneic mouse models and in an orthotopic C6 rat glioma model after oral administration. In the rat model, C6 glioma cells were implanted by stereotactic intracranial inoculation and the tumor size was measured by bioluminescence in vivo imaging or immunohistochemistry. Quantitative real-time PCR was used to determine inflammatory markers. The tumor arginase activity was assessed using the urea detection assay. L-Arginine and drug levels in plasma and tumor were evaluated by LC/MS method. We have developed potent, selective, orally active inhibitors of ARG1 and ARG2. The clinical candidate, OAT-1746, has IC50=32 nM and 50 nM against human ARG1 and ARG2, respectively, and a potent cellular activity (M2 macrophages IC50=32 nM, CHO-K1 hARG1 IC50=55 nM). In vivo, OAT-1746 showed good pharmacologic properties and demonstrated significant antitumor efficacy as a monotherapy in 4 tumor models: B16 (melanoma), LLC (lung carcinoma), CT26 (CRC), and C6 glioma with TGI=34-53%. The antitumor efficacy correlated with sustained pharmacodynamic (PD) effects: suppression of tumor arginase activity and 3-6 fold increases in plasma and tumor arginine concentrations. Induction of inflammatory markers in tumors confirmed reversal of immunosuppression. Combinations of OAT-1746 with PD-L1 checkpoint inhibitor and gemcitabine showed increased efficacy. Administration of OAT-1746 with anti-PD-L1 antibody resulted in a “controlled” tumor growth with 55% of tumors remaining under 500 mm3 at day 24 versus 36% for PD-L1 monotherapy. Full regression was observed in 20% of the animals treated in combination with gemcitabine in comparison to 0% for monotherapy. OAT-1746 also demonstrated efficacy and PD effects in the orthotopic model of GBM, confirming its ability to cross the blood-brain barrier. Together these results support the clinical development of OAT-1746 for cancer therapy. Citation Format: Paulina Seweryna Stanczak, Marcin Mikolaj Grzybowski, Paulina Wolska, Anna Maria Zdziarska, Marcin Mazurkiewicz, Paulina Pilanc, Anna Gieryng, Bozena Kaminska, Anna Gzik, Marek Dziegielewski, Karol Jedrzejczak, Bartlomiej Borek, Roman Blaszczyk, Adam Golebiowski, Pawel Dobrzanski, Karolina Dzwonek. Development of OAT-1746, a novel arginase 1 and 2 inhibitor for cancer immunotherapy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B003.

A simple sonochemical approach to fabricate a urea biosensor based on zinc phthalocyanine/graphene oxide/urease bioelectrode

A novel zinc phthalocyanine/graphene oxide (ZnPh/GO) nanocomposite modified glassy carbon electrode (GCE) was prepared by using sonochemical approach and simple drop casting method. Urease (Urs) was used as the specific enzyme for urea detection and was physically immobilized onto the surface of ZnPh/GO nanocomposite. The fabricated ZnPh/GO/Urs matrix was successfully characterized by UV–vis-spectroscopy, FT-IR spectroscopy, scanning electron microscopy (SEM), raman spectrum, thermogravimetric analysis, cyclic voltammetric (CV) and amperometric techniques. The electrocatalytic performance of the ZnPh/GO/Urs electrode was investigated by urea biosensor. Our results demonstrate that the modified electrode has excellent electrocatalytic activity towards the sensing of urea in 0.1 M phosphate buffer solution (PBS, pH 7.2). The biosensor tolerated a wide linear concentration range for urea from 0.4 to 22 μM (R2 = 0.991), with a detection limit of 0.034 µM (S/N = 3). The ZnPh/GO/Urs bioectrode has several excellent properties, including a fast response time, high reproducibility and stability.

Novel I–V Disposable Urea Biosensor Based on a Dip‐coated Hierarchical Magnetic Nanocomposite (Fe3O4@SiO2@NH2) on SnO2:F Layer

Silicon oxide was initially loaded on a Fe3O4 magnetic nanoparticle substrate (Fe3O4@SiO2) and then functionalized with ─NH2 group (Fe3O4@SiO2@NH2) to construct a novel hierarchical magnetic nanocomposite. A sensitive urea biosensor medium involving a dip‐coated hierarchical magnetic nanocomposite on F‐doped SnO2 conducting glass was designed (Fe3O4@SiO2@NH2/SnO2:F) to achieve an excellent platform for urease (Urs) enzyme immobilization via covalent linking to the exposed NH2 groups through glutaraldehyde (Urs/Fe3O4@SiO2@NH2/SnO2:F). The hierarchical magnetic nanocomposite selection criteria were based on enhancement of urea biosensing by Urs immobilization via covalent linking to the exposed NH2 groups, while the SnO2:F selection as substrate was based on its ability to afford high electronic density to the biosensor surface as an electrostatic repulsion layer for the anionic interferents in the biological environment. FE‐SEM, TEM, FTIR, CV, EIS, and I–V techniques established the morphology of the modified electrode's surface and electrochemical behavior of urea on the fabricated Urs/Fe3O4@SiO2@NH2/SnO2:F biosensor. The sensing mechanism can be clarified on the basis of the two reactions, namely (1) catalytic reaction and (2) oxidation or reduction of metal oxides, same as in the case of solid‐state gas sensors. The I–V results display high sensitivity for urea detection of within 5–210 mg/dL and a limit of detection of 3 mg/dL.

Development of sensitive impedimetric urea biosensor using DC sputtered Nano-ZnO on TiO2 thin film as a novel hierarchical nanostructure transducer

3D hierarchical Nano-ZnO/TiO2 on conductive fluorinated-tin oxide (FTO) layer was fabricated by reactive direct current (DC) magnetron sputtering of ZnO, at the optimized instrumental deposition conditions, on a pre-covered TiO2 surface with Polyvinyl Alcohol (PVA) as an omissible polymer in a pattern of parallel strips (Nano-ZnO/PVA/TiO2/FTO) following by PVA omission via annealing process, which resulted in an efficient porous media for urease (Urs) enzyme immobilization (Urs/Nano-ZnO/TiO2/FTO) designed for urea biosensing. The criteria for TiO2 selection as substrate was based on: (i) its ability to promote electron transfer between ZnO to FTO substrate, (ii) affording high electronic density to the biosensor surface as an electrostatic repulsion layer for the anionic interferents at the biological media, and (iii) enhancement of urea biosensing by the formation of heterojunctions with ZnO. Characterization of the surface morphology of 3D hierarchical Nano-ZnO/TiO2 film by field emission-scanning electron microscopy (FE-SEM) exhibits cavities of nanoporous ZnO film as an effective biosensing area for Urs enzyme immobilization. Step by step monitoring of Urs/Nano-ZnO/TiO2/FTO biosensor fabrication was performed using electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Fabricated Urs/Nano-ZnO/TiO2/FTO biosensor was used for urea determination using impedimetric assessment. The impedimetric results show high sensitivity for urea detection within 5–205mgdl−1 and limit of detection as 2mgdl−1. A fast response of fabricated biosensor can usually allow a real-time analysis.

Simultaneous determination of ethyl carbamate and urea in Korean rice wine by ultra-performance liquid chromatography coupled with mass spectrometric detection.

In this study, a rapid method for simultaneous detection of ethyl carbamate (EC) and urea in Korean rice wine was developed. To achieve quantitative analysis of EC and urea, the conditions for Ultra-performance liquid chromatography (UPLC) separation and atmospheric-pressure chemical ionization tandem mass spectrometry (APCI-MS/MS) detection were first optimized. Under the established conditions, the detection limit, relative standard deviation and linear range were 2.83μg/L, 3.75-5.96%, and 0.01-10.0mg/L, respectively, for urea; the corresponding values were 0.17μg/L, 1.06-4.01%, and 1.0-50.0μg/L, respectively, for EC. The correlation between the contents of EC and its precursor urea was determined under specific pH (3.5 and 4.5) and temperature (4, 25, and 50°C) conditions using the developed method. As a result, EC content was increased with greater temperature and lower pH. In Korean rice wine, urea was detected 0.19-1.37mg/L and EC was detected 2.0-7.7μg/L. The method developed in this study, which has the advantages of simplified sample preparation, low detection limits, and good selectivity, was successfully applied for the rapid analysis of EC and urea.

Fabrication of novel compound SERS substrates composed of silver nanoparticles and porous gold nanoclusters: A study on enrichment detection of urea

Abstract A new type of surface-enhanced Raman scattering (SERS) substrate was fabricated through the layer-by-layer self-assembly of silver nanoparticles (AgNPs, av. 45 nm in diameter) and porous gold nanoclusters/nanoparticles (AuNPs, av. 143 nm in diameter). The development of the porosity of the AuNPs was investigated, and successful SERS applications of the porous AuNPs were also examined. As compared with AgNP films, the enhancement factor of Ag-Au compound substrates is increased 6 times at the concentration of 10−6 M. This additional enhancement contributes to the trace-amount-detection of target molecules enormously. The contribution is generated through the increase of the usable surface area arising from the nanoscale pores distributed three-dimensionally in the porous AuNPs, which enrich the adsorption sites and hot spots for the adsorption of probe molecules, making the developed nanofilms highly sensitive SERS substrates. The substrates were used for the detection of a physiological metabolite of urea molecules. The results reached to a very low concentration of 1 mM and exhibited good quantitative character over the physiological concentration range (1 ∼ 20 mM) under mimicking biophysical conditions. These results show that the prepared substrate has great potential in the ultrasensitive SERS-based detection and in SERS-based biosensors.

Sensors break out of the lab

Sensors break out of the lab

Non-Enzymatic Urea Detection Via Using Ag/ZnO Nanorod-Based Catalyst

The level of biological molecules, such as urea, glucose, dopamine, and creatinine has been measured by various sensing platform for biomedical applications. For example, the urea level deviated from the reference values which causes several diseases such as renal and hepatic issues, is closely related to our life. Monitoring of urea is also important for fertilizer production as well as development of indirect hydrogen storage materials. Various types of urea sensors, including enzymatic sensors, have been researched to measure abovementioned molecules, courtesy of high selectivity and sensitivity. However, enzymatic sensors have the stability problems caused by denaturation of enzyme. A various metals or metal oxides, such as Pt, Cu/CuO, Ni/NiO, Zn/ZnO, have been widely investigated for the detection of different molecules. Among them, Ni based catalyst presents better performance in the electro-catalytic oxidation of molecules such as urea and glucose. Although Ni based catalyst has shown a good performance, problems such as degradation and expansion of the Ni based catalyst structure during the oxidation still exist. Moreover, the level of pH to operate the electrode for detecting the bio molecules indicates the alkaline the solution which is inability to perform in the physiological condition of approximately pH 7. In other words, the concentration of OH-anions is a dominant factor in Ni based catalyst. In this study, silver catalyst deposited on a synthesized ZnO rods/ carbon substrate was prepared at low-temperature process for the enzyme-free urea sensor. The morphologies and structural properties of Ag catalyst deposited ZnO rods were analyzed by SEM and XRD, and the quantity of the silver catalyst was measured by EDS. Thereafter electrochemical properties of the electrode were performed. The catalytic effect of Ag/ZnO rods electrode for urea sensing was investigated in terms of sensitivity and selectivity. Detailed discussion on the mechanism of Ag/ZnO rods catalytic effect will be given. References R. Lan, J.T.S. Irvine, S. Tao. “Ammonia and related chemicals as potential indirect hydrogen storage materials.” Int. J. Hydrogen Energy, 37 (2012), pp. 1482–1494D. Aronson, M.A. Mittleman, A.J. Burger. “Elevated blood urea nitrogen level as a predictor of mortality in patients admitted for decompensated heart failure.” Am. J. Med., 116 (2004), pp. 466–473G. Dhawan, G. Sumana, B.D. “Malhotra Recent developments in urea biosensors.” J. Biochem. Eng., 44 (2009), pp. 42–45Y. Wang, H. Xu, J. Zhang, J.G. Li. “Electrochemical sensors for clinic analysis.” Sensors, 8 (2008), pp. 2043–2081M. Singh, N. Verma, A.K. Garg, N. Redhu. “Urea biosensors.” Sens. Actuators B, 134 (2008), pp. 345–351V. Vedharathinam, G.G. Botte. “Understanding the electro-catalytic oxidation mechanism of urea on nickel electrodes in alkaline medium.” Electrochim. Acta, 81 (2012), pp. 292–300Q.F. Yi, W. Huang, W.Q. Yu, L. Li, X.P. Liu. “Hydrothermal synthesis of titanium-supported nickel nanoflakes for electrochemical oxidation of glucose.” Electroanalysis, 20 (2008), pp. 2016–2022 Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD).

Magnetic nanofluid based non-enzymatic sensor for urea detection

We demonstrate a simple, inexpensive and non-enzymatic optical probe for the detection of urea using functionalized magnetic nanofluid. The nanofluid used here is an oil-in-water magnetic nanoemulsion containing superparamagnetic iron oxide nanoparticles of size ∼10nm. Under a constant magnetic field (∼90G), the magnetic emulsion, forms a one dimensional Bragg diffraction grating with a fixed interparticle spacing. In the presence of urea, the probe showed a large wavelength shift in the visible wavelength range of 880–600nm, due to complexation of urea with the functional moieties that dramatically changes the electrostatic repulsion between emulsion droplets or conformation of adsorbed polymer. The functional moieties, sodium dodecyl sulphate, poly acrylic acid and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymer are found to be suitable for the measurement of urea in the concentrations range 0.003–0.6, 0.18–33.3 and 2.4–334g/L, respectively. PAA stabilized emulsion is found to be suitable for the selective detection of urea in the presence of biologically important cations such as Na+ and Ca2+. The fast response time of the sensor (less than a second) and the wide urea detection capability are the unique features of the new sensor.

Hydrogel Based Sensors for Biomedical Applications: An Updated Review.

Biosensors that detect and convert biological reactions to a measurable signal have gained much attention in recent years. Between 1950 and 2017, more than 150,000 papers have been published addressing the applications of biosensors in different industries, but to the best of our knowledge and through careful screening, critical reviews that describe hydrogel based biosensors for biomedical applications are rare. This review discusses the biomedical application of hydrogel based biosensors, based on a search performed through Web of Science Core, PubMed (NLM), and Science Direct online databases for the years 2000–2017. In this review, we consider bioreceptors to be immobilized on hydrogel based biosensors, their advantages and disadvantages, and immobilization techniques. We identify the hydrogels that are most favored for this type of biosensor, as well as the predominant transduction strategies. We explain biomedical applications of hydrogel based biosensors including cell metabolite and pathogen detection, tissue engineering, wound healing, and cancer monitoring, and strategies for small biomolecules such as glucose, lactate, urea, and cholesterol detection are identified.