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(searched for: doi:10.4236/ojab.2013.21002)
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Nur Izzati Zakaria, , Sharina Abu Hanifah, Khadijah Hilmun Kamarudin, Azrilawani Ahmad
Published: 10 February 2021
Arabian Journal of Chemistry, Volume 14; https://doi.org/10.1016/j.arabjc.2021.103056

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Chetana Vaghela, Mohan Kulkarni, Rohini Aiyer, Meena Karve
IEEE Sensors Journal, Volume 18, pp 7273-7280; https://doi.org/10.1109/jsen.2018.2850909

Abstract:
A simple, reliable, low cost, and portable biosensor has been developed for direct measurement of urea levels in serum samples. It is based on hydrolysis of urea by immobilized urease, generating ammonia that is estimated by modified Berthelot method using simple optical detection system. The immobilization of urease was achieved in agarose guar-gum composite film for the first time which offered an excellent retention of enzyme activity (90%-95%) with negligible leaching and good operational stability. The optical detection system involving LED light, optical fiber, and phototransistor provides simple and portable measurement system. The sensor shows linear response in the wide range of urea concentration from 0.025 to 10 mM with reusability for 10 cycles and superior storage stability of 180 days. The fabricated biosensor was successfully employed for measurement of normal and abnormal urea levels in serum samples with accuracy of 96% using very small sample volume (15 μl). It showed an excellent correlation (r 2 = 0.99) for determination of urea levels with that of using Siemens autoanalyzer.
Published: 3 March 2017
by MDPI
Journal: Biosensors
Biosensors, Volume 7; https://doi.org/10.3390/bios7010013

Abstract:
A potentiometric enzyme biosensor is a convenient detector for quantification of urea concentrations in industrial processes, or for monitoring patients with diabetes, kidney damage or liver malfunction. In this work, poly(3-hexylthiophene-co-3-thiopheneacetic acid) (P(3HT-co-3TAA)) was chemically synthesized, characterized and spin-coated onto conductive indium tin oxide (ITO) glass electrodes. Urease (Urs) was covalently attached to the smooth surface of this copolymer via carbodiimide coupling. The electrochemical behavior and stability of the modified Urs/P(3HT-co-3TAA)/ITO glass electrode were investigated by cyclic voltammetry, and the bound enzyme activity was confirmed by spectrophotometry. Potentiometric response studies indicated that this electrode could determine the concentration of urea in aqueous solutions, with a quasi-Nernstian response up to about 5 mM. No attempt was made to optimize the response speed; full equilibration occurred after 10 min, but the half-time for response was typically <1 min.
Ruska Nenkova, Jiamin Wu, ,
Published: 31 December 2014
Analytical Letters, Volume 48, pp 1297-1310; https://doi.org/10.1080/00032719.2014.979364

Abstract:
Eleven glucose biosensors were prepared by cross-linking, entrapment, and layer-by-layer assembly to investigate the influence of these immobilization methods on performance. The effects of separate nanozeolites combined with magnetic nanoparticles and multiwalled carbon nanotubes in the enzyme composition on the performance of glucose biosensors were compared. Cyclic voltammetric studies were carried out on the biosensors. Acrylonitrile copolymer/nanozeolite/carbon nanotube and acrylonitrile copolymer/nanozeolite/magnetic nanoparticle electrodes prepared by a cross-linking method showed the highest electroactivity. These results indicated that a synergistic effect occurred when multiwalled carbon nanotubes, magnetic nanoparticles, and nanozeolites were combined that greatly improved the electron transfer ability of the sensors. Amperometric measurements by the glucose oxidase electrodes were obtained that showed that the acrylonitrile copolymer/nanozeolite/carbon nanotube electrode was the most sensitive (10.959 microamperes per millimolar). The lowest detection limit for this biosensor was 0.02 millimolar glucose, with a linear dynamic range up to 3 millimolar. The response after thirty days was 81 percent of the initial current.
Published: 1 November 2014
Enzyme and Microbial Technology, Volume 66, pp 48-55; https://doi.org/10.1016/j.enzmictec.2014.08.003

Abstract:
In this article we report a selective urea electrochemical biosensor based on electro-co-deposited zirconia-polypropylene imine dendrimer (ZrO2-PPI) nanocomposite modified screen printed carbon electrode (SPCE). ZrO2 nanoparticles, prepared by modified sol-gel method were dispersed in PPI solution, and electro-co-deposited by cyclic voltammetry onto a SPCE surface. The material and the modified electrodes were characterised using FTIR, electron microscopy and electrochemistry. The synergistic effect of the high active surface area of both materials, i.e. PPI and ZrO2 nanoparticles, gave rise to a remarkable improvement in the electrocatalytic properties of the biosensor and aided the immobilisation of the urease enzyme. The biosensor has an ampereometric response time of ∼4 s in urea concentration ranging from 0.01 mM to 2.99 mM with a correlation coefficient of 0.9985 and sensitivity of 3.89 μA mM(-1) cm(-2). The biosensor was selective in the presence of interferences. Photochemical study of the immobilised enzyme revealed high stability and reactivity.
B.H. Meshram, S.B. Kondawar, A.P. Mahajan, R.P. Mahore, D.K. Burghate
Journal of the Chinese Advanced Materials Society, Volume 2, pp 223-235; https://doi.org/10.1080/22243682.2014.935953

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