Construction And Performance Of Electrochemical Biosensors Based OnPolyaniline-graphene Nanocomposite

In recent years, bisoensors have attracted much more attention due to their accurate detection, portable features, cheap raw material as well as simple preparation techniques, and thus have been used in various fields such as medical science, biology, water quality online monitoring, etc. In this paper, polyaniline (PANI), graphene (GRA) and their composite were used to construct glucose and phenol biosensors, and the properties of the resultant biosensors were studied. Controllable synthesis of nanostructured PANI with different morphologies by cyclic voltammety was also investigated in this paper.A biosensor was fabricated by immobilizing glucose oxidase (GOD) into nanostructured GRA-conducting PANI nanocomposite, which was based on electrochemical polymerization of aniline in the presence of GRA. Scanning electron spectroscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the morphology and performance of the as-prepared biosensor. Amperometric measurements were carried out to optimize test conditions (pH and applied potential) of the biosensor. Under the optimal condition, the biosensor showed a linear range from 10.0 μM to 1.48 mM (R2=0.9988) with a sensitivity of 22.1 μA mM-1 cm-2, and a detection limit of 2.769 μM (S/N=3). The apparent Michaelis-Menten constant (KMa) was estimated to be 3.26 mM. The interference from glycine (Gly), D-galactose (D-Gal), urea (Urea), L-phenylalanine (L-Phe), ascorbic acid (AA), and L-tyrosine (L-Tyr) was also investigated. The results indicated that the biosensor exhibit high sensitivity and superior selectivity, providing a hopeful candidate for glucose biosensing.PANI could be used as an immobilization matrix for enzymes, and its morphology had great effects on the properties of biosensors. Therefore, the morphology and properties of PANI were also studied in this paper. Eight kinds of PANI were synthesized using cyclic voltammety by controlling the concentration of aniline monomers and potential scan rate. Results from SEM showed that PANI presented flower-shape, sea urchin-shape and rob-like nanostructures in different electrochemical polymerization conditions, so it’s possible to control the morphology of PANI by controlling experimental conditions. Results from ultraviolet-visible (UV-VIS) spectra and Fourier transform infrared (FTIR) spectra indicated that polymerization conditions of the concentration of aniline and scan rate had no obvious effects on the electronic structure and chemical structure of PANI, but with little infuluences on the oxidation degree of PANI. X-ray diffraction (XRD) patterns showed that the as-synthesized PANI was highly HCl-doped and semicrystalline emeraldine salt (ES-PANI). The relative crystallinity of ES-PANI increased with the concentration of aniline monomers increasing at a scan rate of 5 mV/s, but stayed almost constant when the potential scan rate was 10,20 or 30 mV/s with an aniline concentration of 0.1 M.In addition, phenol biosensors were constructed by using GRA and polyacrylonitrile (PAN)-GRA composite as carriers to immobilize and load polyphenol oxidase (PPO). For PAN-GRA/CS-PPO based biosensor, the effect of electrode material on the amperometric response of the biosensor to p-cresol was investigated. The results showed that the biosensor using glass carbon electrode (GCE) exhibited a higher sensitivity than the biosensor using platinium disk electrode (Pt), which suggested that GCE be more suitable to construct PAN-GRA/CS-PPO based biosensor. For GRA-CS-PPO based biosensor, the effect of pH of CS solution on the amperometric response of the biosensor was studied. It was found that the response of the biosensor was affected by both the activity of PPO and the dispersibility of graphene. The fabricated biosensor showed higher ampermetric response to p-cresol under lower pH conditions. However, these two kind biosensors showed signal shift and attenuation. The problem of signal shift could be improved by modifying the fabricated biosensor using glutaraldehyde (GA) vapor crosslinking, but signal attenuation still existed, which needs to be futher explored.