Zhybak M. The development of the amperometric nanocomposite-based bio-/chemosensors for the detection of low molecular weight metabolites in biological liquids

The PhD thesis is dedicated to the research and development of the amperometric nanocomposite-based bio-/chemosensors for the detection of clinically important low molecular weight metabolites in biological samples. The laboratory prototypes of the biosensors for the detection of choline, ammonium ions, L-arginine, creatinine, urea have been developed using commercial screen-printed electrodes, highly sensitive electro-deposited nanocomposites, and immobilized enzymes. The choline biosensors were developed using two different enzyme immobilization strategies: i) usage of the NH2-modified carbon nanotubes as a structural element of the choline oxidase (ChOx) membrane; ii) electrochemically assisted sol-gel deposition of the ChOx on gold screen-printed electrodes. The application of the sensors with the purpose of identifying choline in the baby milk demonstrated satisfactory metrological characteristics. A novel amperometric biosensor for the amino acid L-arginine (L-Arg) has been fabricated. It is based on the use of a Nafion/Polyaniline (PANi) composite on a platinum screen-printed electrode using a novel recombinant arginine deiminase. The biosensor was applied to the analysis of L-Arg in pharmaceutical samples and in spiked human plasma. A novel composite material for use in ammonium ions detection is described. A carbon electrode was modified with electrodeposited copper, a Nafion membrane and electropolymerized PANi. The chemosensor was applied to the quantification of ammonium ions by amperometry. It was applied to the determination of ammonium ion in human serum where it compared well with the photometric routine approach. The use of a novel ammonium ion-specific copper-polyaniline nano-composite as transducer for creatinine and urea biosensors is proposed. The performance of the biosensors in human serum samples was evaluated and a good correlation with standard spectrophotometric clinical laboratory techniques was found.