Glucose biosensor based on glucose oxidase immobilized at gold nanoparticles decorated graphene-carbon nanotubes

Biopolymer pectin stabilized gold nanoparticles were prepared at graphene and multiwalled carbon nanotubes (GR-MWNTs/AuNPs) and employed for the determination of glucose. The formation of GR-MWNTs/AuNPs was confirmed by scanning electron microscopy, X-ray diffraction, UV–vis and FTIR spectroscopy methods. Glucose oxidase (GOx) was successfully immobilized on GR-MWNTs/AuNPs film and direct electron transfer of GOx was investigated. GOx exhibits highly enhanced redox peaks with formal potential of −0.40 V (vs. Ag/AgCl). The amount of electroactive GOx and electron transfer rate constant were found to be 10.5 × 10⁻¹⁰ mol cm⁻² and 3.36 s⁻¹, respectively, which were significantly larger than the previous reports. The fabricated amperometric glucose biosensor sensitively detects glucose and showed two linear ranges: (1) 10 μM – 2 mM with LOD of 4.1 μM, (2) 2 mM – 5.2 mM with LOD of 0.95 mM. The comparison of the biosensor performance with reported sensors reveals the significant improvement in overall sensor performance. Moreover, the biosensor exhibited appreciable stability, repeatability, reproducibility and practicality. The other advantages of the fabricated biosensor are simple and green fabrication approach, roughed and stable electrode surface, fast in sensing and highly reproducible.     

Electrochemical studies of biocatalytic anode of sulfonated graphene/ferritin/glucose oxidase layer-by-layer biocomposite films for mediated electron transfer

In this study, a bioanode was developed by using layer-by-layer (LBL) assembly of sulfonated graphene (SG)/ferritin (Frt)/glucose oxidase (GOx). The SG/Frt biocomposite was used as an electron transfer elevator and mediator, respectively. Glucose oxidase (GOx) from Aspergillus niger was applied as a glucose oxidation biocatalyst. The electrocatalytic oxidation of glucose using GOx modified electrode increases with an increase in the concentration of glucose in the range of 10–50 mM. The electrochemical measurements of the electrode was carried out by using cyclic voltammetry (CV) at different scan rates (20–100 mV s⁻¹) in 30 mM of glucose solution prepared in 0.3 M potassium ferrocyanide (K₄Fe(CN)₆) and linear sweep voltammetry (LSV). A saturation current density of 50 ± 2 mA cm⁻² at a scan rate of 100 mV s⁻¹ for the oxidation of 30 Mm glucose is achieved.     

Development of electrochemical sulfite biosensor based on SOX/PBNPs/PPY modified Au electrode

A sulfite oxidase (SO_X) (EC 1.8.3.1) purified from Syzygium cumini leaves was immobilized onto Prussian blue nanoparticles/polypyrrole (PBNPs/PPY) nanocomposite film electrodeposited onto the surface of gold (Au) electrode. An electrochemical sulfite biosensor was fabricated using SO_X/PBNPs/PPY/Au electrode as working electrode, Ag/AgCl as standard electrode and Pt wire as auxiliary electrode connected through a potentiostat. The working electrode was characterized by Fourier Transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) at different stages of its construction. The biosensor showed optimum response within 2 s, when operated at 20 mV s⁻¹ in 0.1 M Tris–HCl buffer, pH 8.0 and at 30 °C. Linear range and minimum detection limit were 0.5–1000 μM and 0.1 μM (S/N = 3) respectively. The sensor was evaluated with 95.0% recovery of added sulfite in red wine samples and 1.9% and 3.3% within and between batch coefficients of variation respectively. There was a good correlation (r = 0.96) between red wine samples sulfite value by standard DTNB method and the present method. The sensor was employed for determination of sulfite level in red, white and rose wine samples. The enzyme electrode was used 300 times over a period of 4 months, when stored at 4 °C.     

Preparation of sulfonated poly(ether–ether–ketone) functionalized ternary graphene/AuNPs/chitosan nanocomposite for efficient glucose biosensor

A facile method of preparing water-dispersible sulfonated graphene (SPG) using sulfonated poly(ether–ether–ketone) organic polymer as a modifier was realized. A glucose biosensor was fabricated by immobilizing glucose oxidase (GO_x) on the surface of AuNPs used to modify SPG and chitosan (CH) deposited on an indium tin-oxide (ITO) glass electrode by a solution casting method. Morphological and structural characterizations confirm that the AuNPs can be efficiently applied to the SPG–CH matrix. The amperometric response of the GO_x/SPG–AuNPs–CH/ITO bioelectrode shows a broad linear range of 0.5 to 22.2 mM, with a limit of detection of 0.13 mM and a high sensitivity of 6.51 μA/(mM cm²). The excellent performance of the constructed biosensor is attributed to the large surface-to-volume ratio and electron transfer ability of SPG, the high catalytic activity of the AuNPs, and the good biocompatibility of CH. In addition, the sensor has important advantages, such as its simple preparation, fast response time (10 s), good stability (70 days), and high reproducibility. Favorable results upon examining the electrochemical response for the determination of glucose in human blood serum were obtained, without the assistance of a negligible effect of interfering bio-analytes. The results of studies show that the ternary SPG–AuNPs–CH nanocomposite may offer a new approach for developing novel types of highly sensitive and stable electrochemical biosensors.     

Immobilization of lysine oxidase on a gold–platinum nanoparticles modified Au electrode for detection of lysine

A commercial lysine oxidase (LyOx) from Trichoderma viride was immobilized covalently onto gold nanoparticles (AuNPs) and platinum nanoparticles (PtNPs) electrodeposited onto Au electrode using 3-aminopropyltriethoxy silane (3-APTES) and glutaraldehyde cross linking chemistry. A lysine biosensor was fabricated using LyOx/3-APTES/AuNPs-PtNPs/Au electrode as a working electrode, Ag/AgCl (3 M KCl) as standard electrode and Pt wire as auxiliary electrode connected through a potentiostat. The enzyme electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The cumulative effect of AuNPs and PtNPs showed excellent electrocatalytic activity at low applied potential for detection of H₂O₂, a product of LyOx reaction. The sensor showed its optimum response within 4 s, when polarized at 0.2 V vs. Ag/AgCl in 0.1 M phosphate buffer, pH 7.5 at 30 °C. The linear range and detection limit of the sensor were 1.0–600 μM and 1.0 μM (S/N = 3), respectively. Biosensor measured lysine level in sera, milk and amino acid tablet, which correlated well with those by standard HPLC method. The enzyme electrode lost 50% of its initial activity after 200 uses over a period of 4 months.     

An amperometric H2O2 biosensor based on cytochrome c immobilized onto nickel oxide nanoparticles/carboxylated multiwalled carbon nanotubes/polyaniline modified gold electrode

Cytochrome c was immobilized covalently onto nickel oxide nanoparticles/carboxylated multiwalled carbon nanotubes/polyaniline composite (NiO-NPs/cMWCNT/PANI) electrodeposited on gold (Au) electrode. An amperometric H₂O₂ biosensor was constructed by connecting this modified Au electrode along Ag/AgCl as reference and Pt wire as counter electrode to the galvanostat. The modified Au electrode was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and Fourier transform infra-red spectroscopy (FTIR). Cyclic voltammetric (CV) studies of the electrode at different stages demonstrated that the modified Au electrode had enhanced electrochemical oxidation of H₂O₂, which offered a number of attractive features to develop an amperometric biosensor based on split of H₂O₂. There was a good linear relationship between the current (mA) and H₂O₂ concentration in the range 3–700 μM. The sensor had a detection limit of 0.2 μM (S/N = 3) with a high sensitivity of 3.3 mA μM^?1 cm^?2. The sensor gave accurate and satisfactory results, when employed for determination of H₂O₂ in different fruit juices.     

An acetylcholinesterase biosensor based on graphene–gold nanocomposite and calcined layered double hydroxide

In this study, a novel acetylcholinesterase-based biosensor was fabricated. Acetylcholinesterase (AChE) was immobilized onto a glassy carbon electrode (GCE) with the aid of Cu–Mg–Al calcined layered double hydroxide (CLDH). CLDH can provide a bigger effective surface area for AChE loading, which could improve the precision and stability of AChE biosensor. However, the poor electroconductibility of CLDHs could lead to the low sensitivity of AChE biosensor. In order to effectively compensate the disadvantages of CLDHs, graphene–gold nanocomposites were used for improving the electron transfer rate. Thus, the graphene–gold nanocomposite (GN-AuNPs) was firstly modified onto the GCE, and then the prepared CLDH-AChE composite was immobilized onto the modified GCE to construct a sensitive AChE biosensor for pesticides detection. Relevant parameters were studied in detail and optimized, including the pH of the acetylthiocholine chloride (ATCl) solution, the amount of AChE immobilized on the biosensor and the inhibition time governing the analytical performance of the biosensor. The biosensor detected chlorpyrifos at concentrations ranging from 0.05 to 150 μg/L. The detection limit for chlorpyrifos was 0.05 μg/L.     

A novel electrochemical biosensor based on horseradish peroxidase immobilized on Ag-nanoparticles/poly(l-arginine) modified carbon paste electrode toward the determination of pyrogallol/hydroquinone

A novel electrochemical biosensor for the determination of pyrogallol (PG) and hydroquinone (HQ) has been constructed based on the poly l-arginine (poly(l-Arg))/carbon paste electrode (CPE) immobilized with horseradish peroxidase (HRP) and silver nanoparticles (AgNPs) through the silica sol–gel (SiSG) entrapment. The electrochemical properties of the biosensor were characterized by employing the electrochemical techniques. The proposed biosensor showed a high sensitivity and fast response toward the determination of PG and HQ around 0.18 V. Under the optimized conditions, the anodic peak current of PG and HQ was linear with the concentration range of 8 μM to 30 × 10^?5 M and 1–150 μM. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 6.2 μM, 20 μM for PG and 0.57 μM, 1.92 μM for HQ respectively. The electrochemical impedance spectroscopy (EIS) studies have confirmed that the occurrence of electron transfer at HRP-SiSG/AgNPs/poly(l-Arg)/CPE was faster. Moreover the stability, reproducibility and repeatability of the biosensor were also studied. The proposed biosensor was successfully applied for the determination of PG and HQ in real samples and the results were found to be satisfactory.     

A novel ternary NiFe2O4/CuO/FeO-chitosan nanocomposite as a cholesterol biosensor

We report the results of studies relating to the in situ synthesis of a novel ternary NiFe₂O₄/CuO/FeO-chitosan nanocomposite, which could be utilized as a cholesterol biosensor. The phase identification, morphology and particle size of the NiFe₂O₄/CuO/FeO nanocomposite have been investigated via X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy. The quantification of cholesterol was accomplished by immobilizing cholesterol oxidase (ChOx) onto a chitosan-NiFe₂O₄/CuO/FeO nanocomposite (NiFe₂O₄/CuO/FeO-CH NC) deposited onto an indium-tin-oxide (ITO) glass substrate via the sol–gel technique. The electrochemical study results of the biocompatible ChOx/NiFe₂O₄/CuO/FeO-CH/ITO electrode reveal good linearity (50–5000 mg/L), a low detection limit (313 mg/L), high sensitivity (0.043 μA/(mg/L cm^?2)), a fast response time (10 s) and a shelf-life of 3 months. The low Michaelis–Menten constant (K_m) of 80 mg/L (0.21 mM) indicates the high affinity of ChOx for the analytes. Further, this bioelectrode has been used in clinical applications to estimate cholesterol levels with negligible interference (2%) from analytes present in human serum samples.     

Electrochemical detection of xanthine in fish meat by xanthine oxidase immobilized on carboxylated multiwalled carbon nanotubes/polyaniline composite film

A commercial xanthine oxidase (XOD) was immobilized covalently onto carboxylated multiwalled carbon nanotubes (c-MWCNT) and polyaniline (PANI) composite film electrodeposited on the surface of a Pt electrode, using N-ethyl-N′-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) chemistry. A xanthine biosensor was fabricated using XOD/c-MWCNT/PANI/Pt electrode as a working electrode, Ag/AgCl (3 M KCl) as standard electrode and Pt wire as auxiliary electrode connected through a potentiostat. The enzyme electrode was characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectrophotometry and electrochemical impedance spectroscopy (EIS). The biosensor showed optimum response within 4 s at pH 7.0 and 35 °C, when polarized at 0.4 V. The optimized xanthine biosensor showed linear response range of 0.6–58 μM, with a detection limit of 0.6 μM (S/N = 3), and a correlation coefficient of 0.98. The biosensor was applied to determine xanthine in fish meat. The biosensor lost 50% of its initial activity after its 200 uses over a period of 100 days.     

Ethanol/O2 biofuel cell using a biocathode consisting of laccase/ HOOC-MWCNTs/polydiallyldimethylammonium chloride

In the present report we focused on the substitution of metallic catalysts by biocatalysts to develop a high efficient biofuel cell. A bioanode and a biocathode were designed using ADH and laccase, respectively. Carboxylated multiwall carbon nanotubes (HOOC-MWCNTs) and polydiallyldimethylammonium chloride (PDDA) were used for immobilizing the enzymes on either polymethylene green (PMG) modified glassy carbon or graphite electrodes. In this way, an ethanol–oxygen biofuel cell was designed in which PDDA/ADH/PDDA/HOOC-MWCNTs/PMG/GC and PDDA/Lac/PDDA/HOOC-MWCNTs/PMG/Gr operated as bioanode and biocathode, respectively. In the optimized condition of O₂ saturated PBS (0.1 M, pH 7.5) containing 1 mM ethanol and 1 mM NAD⁺ the open-circuit voltage reached to a plateau at 504 mV based of which the power density of 3.98 mW cm⁻² was obtained.     

Ultrasensitive DNA sensor based on gold nanoparticles/reduced graphene oxide/glassy carbon electrode

We have designed a simple and novel electrochemical biosensor based on glassy carbon electrode (GCE) for DNA detection. GCE was modified with reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) by the electrochemical method, which is helpful for immobilization of thiolated bioreceptors. The electrode modification processes were characterized by scanning electron microscopy (SEM) and electrochemical methods. Then a single-stranded DNA (ssDNA) probe for BRCA1 5382 insC mutation detection was immobilized on the modified electrode for a specific time. The experimental conditions, such as probe immobilization time and target DNA (complementary DNA) hybridization time and temperature with probe DNA, were optimized using electrochemical methods. The electrochemical response for DNA hybridization and synthesis was measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) methods. The calibration graph contains two linear ranges; the first part is in the range of 3.0 × 10⁻²⁰ to 1.0 × 10⁻¹² M, and the second segment part is in the range of 1.0 × 10⁻¹² to 1.0 × 10⁻⁷ M. The biosensor showed excellent selectivity for the detection of the complementary sequences from noncomplementary sequences, so it can be used for detection of breast cancer.     

A high-sensitivity electrochemical immunosensor based on mobile crystalline material-41-polyvinyl alcohol nanocomposite and colloidal gold nanoparticles

A novel competitive immunosensor was developed as a model system using anti-human serum albumin (HSA)-conjugated gold nanoparticles (AuNPs) as an electrochemical label and mobile crystalline material-41 (MCM-41)–polyvinyl alcohol (PVA) mesoporous nanocomposite as an immobilization platform. However, no attempt has yet been made to use the MCM-41 as the supporting electrolyte for the electrosynthesis of nonconducting polymer nanocomposite. This hybrid membrane was evaluated extensively by using field emission scanning electron microscopy (FESEM), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) to determine its physicochemical and electrochemical properties in immunosensor application. FESEM revealed an appropriate and stable attachment between HSA and MCM-41 and also a dense layer deposition of MCM-41–HSA–PVA film onto the electrode surfaces. DPV was developed for quantitative determination of antigen in biological samples. A decrease in DPV responses was observed with increasing concentrations of HSA in standard and real samples. In optimal conditions, this immunosensor based on MCM-41–PVA nanocomposite film could detect HSA in a high linear range (0.5–200 μg ml^?1) with a low detection limit of 1 ng ml^?1. The proposed method showed acceptable reproducibility, stability, and reliability and could also be applied to detect the other antigens.     

Effect of changing the nanoscale environment on activity and stability of nitrate reductase

Nitrate reductase (NR) is employed for fabrication of nitrate sensing devices in which the enzyme in immobilized form is used to catalyze the conversion of nitrate to nitrite in the presence of a suitable cofactor. So far, instability of immobilized NR due to the use of inappropriate immobilization matrices has limited the practical applications of these devices. Present study is an attempt to improve the kinetic properties and stability of NR using nanoscale iron oxide (nFe₃O₄) and zinc oxide (nZnO) particles. The desired nanoparticles were synthesized, surface functionalized, characterized and affixed onto the epoxy resin to yield two nanocomposite supports (epoxy/nFe₃O₄ and epoxy/nZnO) for immobilizing NR. Epoxy/nFe₃O₄ and epoxy/nZnO support could load as much as 35.8 ± 0.01 and 33.20 ± 0.01 μg/cm² of NR with retention of about 93.72 ± 0.50 and 84.81 ± 0.80% of its initial activity respectively. Changes in surface morphology and chemical bonding structure of both the nanocomposite supports after addition of NR were confirmed by scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). Optimum working conditions of pH, temperature and substrate concentration were ascertained for free as well as immobilized NR preparations. Further, storage stability at 4 °C and thermal stability between 25–50 °C were determined for all the NR preparations. Analytical applications of immobilized NR for determination of soil and water nitrates along with reusability data has been included to make sure the usefulness of the procedure.     

Construction of d-amino acid biosensor based on d-amino acid oxidase immobilized onto poly (indole-5-carboxylic acid)/zinc sulfide nanoparticles hybrid film

d-Amino acid oxidase (DAAO) purified from goat kidney was immobilized covalently via N-ethyl-N-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) chemistry onto poly indole 5-carboxylic acid (Pin5-COOH)/zinc sulfide nanoparticles (ZnSNPs) hybrid film electrodeposited on surface of an Au electrode. A highly sensitive d-amino acid biosensor was constructed using this enzyme electrode as working electrode, Ag/AgCl as reference electrode, and Pt wire as auxiliary electrode connected through potentiostat. The biosensor showed optimum response within 3 s at pH 7.5 and 35 °C, when polarized at 0.15 V vs. Ag/AgCl. There was a linear relationship between biosensor response (mA) and d-alanine concentration in the range 0.001–2.0 mM. The sensitivity of the biosensor was 58.85 μA cm^?2 mM^?1 with a detection limit of 0.001 mM (S/N = 3). The enzyme electrode was used 120 times over a period of 2 months when stored at 4 °C. The biosensor has an advantage over earlier enzyme sensors that it has no leakage of enzyme during reuse and is unaffected by the external environment due to the protective layer of poly indole-5-carboxylic acid film. The biosensor was evaluated and employed for measurement of d-amino acid level in fruits and vegetables.     

Effect of some redox mediators on FAD fluorescence of glucose oxidase from Penicillium adametzii LF F-2044.1

Glucose oxidase (GOx) of Penicillium adametzii LF F-2044.1 recovered by ultrafiltration, was characterized by spectrophotometric and spectrofluorometric methods. It was shown that spectra of GOx from P. adametzii are typical for flavoproteins. Optimal buffer composition was chosen. It was determined that the GOx is the most efficiently interacting with substrate (glucose) in phosphate buffer at pH 7.0 with k_kat/K_M = 15,217 ± 550 M⁻¹ s⁻¹. P. adametzii GOx fluorescence in the presence of different redox mediators (9,10-phenanthroline-5,6-dione, 9,10-phenanthrenequinone, 1,4-benzoquinone, methylene blue, ferrocene, ferrocenecarboxylic acid, α-methylferrocenemethanol, ferrocenecarboxaldehyde) was evaluated. Maximal differences in fluorescence emission intensity were observed in the presence of ferrocene and 9,10-phenanthrenequinone.     

Investigation of switch from ATM to ATR signaling at the sites of DNA damage induced by low and high LET radiation

Upon induction of DNA damage by ionizing radiation (IR), members of the phosphatidylinositol 3-kinase-like kinase family of proteins namely ataxia-telangiectasia mutated (ATM), DNA-PKcs, and ATM- and Rad3-related (ATR) maintain genomic integrity by mounting DNA damage response (DDR). Recent reports suggest that activation of ATM and ATR are oppositely regulated by the length of single stranded overhangs generated during end processing by nucleases at the break sites. These stretches of single stranded overhangs hold the clue for the transition from ATM to ATR signaling at broken DNA ends. We investigated whether differential processing of breaks induced by low and high LET radiation augments the phenomenon of switching from ATM to ATR kinase and hence a concomitant NHEJ to HR transition at the sites of DNA damage. 82-6 human fibroblasts were irradiated with 1 or 2 Gy of γ-rays and particle radiation of increasing LET in order to increase the complexity and variability of DNA double strand breaks (DSB) structures. The activation kinetics of ATM and ATR kinases along with their downstream substrates were determined utilizing Western blotting and immunofluorescence techniques. Our data provide evidence of a potential switch from ATM to ATR kinase signaling in cells treated with γ-rays at approximately 2 h post irradiation, with induction and completion of resection denoted by Rad51 foci resolution kinetics and observed with a significant decline of phosphorylated ATR kinase 8 h after IR. On the other hand, irradiation with high LET 600 MeV/u ⁵⁶Fe (180 keV/μm) and 170 MeV/u ²⁸Si (99 keV/μm) particles show a similar Rad51 foci decay kinetics, however, exhibiting prolonged resection, evident by the persistent phosphorylated ATM and ATR kinase until 24 h post irradiation. This residual effect, however, was significantly reduced for 250 MeV/u ¹⁶O particles of moderate LET (25 keV/μm) and absent for γ-rays. Hence, our results support the hypothesis that the transition from ATM to ATR signaling at DNA break sites is extended for longer periods of time, indicated by sustained resection due to the complex type of damage induced, a hallmark of high LET radiation, which may contribute to its increased biological effectiveness.     

Amperometric hydrogen peroxide biosensor based on the immobilization of HRP on nano-Au/Thi/poly (p-aminobenzene sulfonic acid)-modified glassy carbon electrode

A novel hydrogen peroxide biosensor was fabricated for the determination of H₂O₂. The precursor film was first electropolymerized on the glassy carbon electrode with p-aminobenzene sulfonic acid (p-ABSA) by cyclic voltammetry (CV). Then thionine (Thi) was adsorbed to the film to form a composite membrane, which yielded an interface containing amine groups to assemble gold nanoparticles (nano-Au) layer for immobilization of horseradish peroxidase (HRP). The electrochemical characteristics of the biosensor were studied by CV and chronoamperometry. The factors influencing the performance of the resulting biosensor were studied in detail. The biosensor responded to H₂O₂ in the linear range from 2.6 × 10^− 6 mol/L to 8.8 × 10^− 3 mol/L with a detection limit of 6.4 × 10^− 7 mol/L. Moreover, the studied biosensor exhibited good accuracy and high sensitivity. The proposed method was economical and efficient, making it potentially attractive for the application to real sample analysis.     

Zirconia-poly(propylene imine) dendrimer nanocomposite based electrochemical urea biosensor

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.