A Novel Capacitive Biosensor for Urea Assay Based on Modified Magnetic Nanobeads

In this report we describe a new urea capacitive biosensor made by the immobilization of urease on functionalized Fe3O4 nanoparticles (NPs) using BSA, cationic (PAH), anionic (PSS) polyelectrolytes and glutaraldehyde as a cross-linking agent. The establishment of the biomembrane is done layer by layer (LbL) method on Si/SiO2 transducer. The response of the developed biosensor to urea addition is assessed using capacitance potential measurements. The presence of the magnetic nanobeads results in a super high sensitivity to pH change for urea addition. The electrochemical response is. measured as a function of urea concentration in PBS solution pH 7.0. As a result, it has been found that the biosensor showed a linear response ranging from 0.01 to 0.3 mM of urea. The developed urea biosensor demonstrates a high sensitivity, good reproducibility and considerable lifetime. After several optimization steps it was shown that the urease enzyme retains its good bioactivity when being immobilized on magnetic nanobeads in presence of additional cationic and anionic polyelectrolytes.