Ascorbic Acid Biosensor Based On Nanomaterials/Poly(3,4-ethylenedioxythiophene)Composite

Biosensors are analytical devices in corporating biological materials such as enzymes, tissues, microorganisms, antibodies, cell receptors or biologically derived materials or a biomimic component in intimate contact with a physico-chemical transducer or transducing microsystems. Transducers are the components that convert a biochemical signal into a quantifiable electricalsignal. The transducing microsystem may be electrochemical, thermometric, optical, piezoelectric or magnetic. Biosensors have found immense applications in medical diagnostics, environmental monitoring and genetics, food processing industries and defense. Due to their simplicity, high sensitivity and potential ability for real-time and onsite analysis, biosensors have been widely applied invarious fields including industrial process, clinical detection, environmental control etc. In recent years, researchers have put their efforts to improve the performance of biosensors. There are three parts in our work:multi walled carbon nanotubes (MWCNTs)-poly(3,4-ethylenedioxythiophene)(PEDOT)-ascorbate oxidase (AO) biosensor; single walled carbon nanotube (SWCNT)-PEDOT/AO/nafion biosensor; Au nanoparticles (AuNPs)-PEDOT-AO biosensor.(1) The MWCNTs-PEDOT nanocomposite films were synthesized successfully by electropolymerization of EDOT in aqueous solution. Studies revealed obvious improvement in the electrochemical response of PEDOT matrix after the incorporation of MWCNTs. The experimental results showed that the composite films exhibited better mechanical integrity, electrochemical activity, higher electronic and ionic conductivity, and larger redox capacitance compared with pure PEDOT films. An amperometric AA biosensor fabricated by immobilizing AO in MWCNTs-PEDOT nanocomposite films was reported for the first time. The entrapment of AO in MWCNTs-PEDOT nanocomposite films was performed during an electrochemical polymerization process. The response of the biosensor towards AA under the optimized conditions is linear from0.05to20mmol L-1with a detection limit of15μmol L-1(S/N=3). The biosensor shows a response time of20s and a sensitivity of23.95mA M-1cm-2. Moreover, the biosensor exhibits good anti-interferent ability, good reproducibility and remarkable storage stability.(2) A stable sandwich-type amperometric biosensor based on SWCNT-PEDOT/AO/nafion films for detection of AA was successfully developed. SWCNT-PEDOT nanocomposite and nafion films were used as inner and outer films, respectively. AO was immobilized between these two films. The SWCNT-PEDOT nanocomposite films were characterized by electrochemical impedance spectroscopy and scanning electron microscopy. The influence of detection potential and temperature on the biosensor performance was examined in detail. Despite the multilayer configuration, the biosensor exhibited a relatively fast response (less than10s) and a linear range from1μM to18mmol L-1(a correlation coefficient of0.9974). The sensitivity of the biosensor was found to be28.5mA M-1cm-2. Its experimental detection limit was0.7μM (S/N=3) and the apparent Michaelis-Menten constant (Km) was calculated to be18.35mmol L-1. Moreover, the biosensor exhibited good anti-interferent ability and excellent long-term stability. All the results showed that such sandwich-type SWCNT-PEDOT/AO/nafion films could provide a promising platform for the biosensor designs for AA detection.(3) An amperometric AA biosensor was described based on the immobilization of AO in AuNPs-PEDOT nanocomposite films, which was easily fabricated by a one-step electrochemical method. AuNPs of10nm diameter have been synthesized, using the citrate reduction method, and characterized using transmission electron microscopy and UV-visible absorption spectroscopy. The AuNPs-PEDOT nanocomposite films were characterized by electrochemical impedance spectroscopy and scanning electron microscopy. The biosensor was applied to detect AA with a linear range of1μmol L-1to1.5mmol L-1(R2=0.9979) with a response time of10s. The sensitivity of the biosensor was found to be48.85mA M-1cm-2. Its experimental detection limit was1μmol L-1(S/N=3) and the Km was calculated to be17.85mmol L-1. Moreover, the biosensor shows good reproducibility (a relative standard deviation of3.1%was obtained) and remarkable long-term stability (it retains90%of the original activity after two months). The effects of potential and temperature on the response current of the biosensor are also described. All of these advantages are also suitable for practical applications in the agro-industry.