Enantioselective sensors and biosensors for clinical analysis

Abstract

The enantioanalysis of compounds of biological importance with a chiral moiety is very important because each enantiomer is a marker for a different disease. Accordingly, very reliable methods of enantioanalysis should be employed for the correct diagnosis of the diseases. The utilization of amperometric biosensors and enantioselective, potentiometric membrane electrodes made the assay of a single enantiomer faster, easier and more reliable if one compare with the chromatographic techniques which are widely proposed for this kind of analyses. Monocrystalline diamond was proposed as matrix for amperometric electrodes and amperometric biosensors design. The advantages of using such material for electrode design are: (a) lower background currents and noise signals, which lead to improve S/B and S/N ratios, and lower detection limits; (b) good electrochemical activity (pre-treatment is not necessary); (c) wide electrochemical potential window in aqueous media; (d) very low capacitance; (e) extreme electrochemical stability; and (f) high reproducibility of analytical information. The design selected for the electrodes is simple, fast and reproducible. The carbon or diamond powders were mixed with paraffine oil to give the carbon or diamond paste which can act alone as electroactive material in the electrodes or it can be modified with a chiral selector (e.g., cyclodextrins, maltodextrins or antibiotics) or enzyme (e.g., L(D)-aminoacid oxidase, L-lysine oxidase). The results obtained by employing the amperometric electrodes and biosensors and the enantioselective, potentiometric membrane electrodes proved a high sensitivity, selectivity, accuracy and high reliability. These characteristics made them suitable to be used for the enantioanalysis of different compounds of biological importance (e.g., pipecolic acid, glyceric acid, 2-hydroxyglyceric acid, fucose, L-vesamicol and L-lysine) in serume and/or urine samples. The features of the proposed enantioselective, amperometric and potentiometric electrodes proposed in this thesis are their utilization for in vivo measurements and as detectors in flow systems (flow injection analysis or/and sequential injection analysis). This will simplify the enantioanalysis and will improve considerable the reliability of the analytical information favorazing a fast and accurate diagnosis of the diseases associated with the marker determined.