Amperometric creatinine biosensor based on covalently coimmobilized enzymes onto carboxylated multiwalled carbon nanotubes/polyaniline composite film

A mixture of commercial creatinine amidohydrolase (CA), creatine amidinohydrolase (CI), and sarcosine oxidase (SO) was coimmobilized covalently via N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) chemistry onto carboxylated multiwalled carbon nanotube (c-MWCNT)/polyaniline (PANI) nanocomposite film electrodeposited over the surface of a platinum (Pt) electrode. A creatinine biosensor was fabricated using enzyme/c-MWCNT/PANI/Pt as working electrode, Ag/AgCl as reference electrode, and Pt wire as auxiliary electrode connected through potentiostat. The enzyme electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and electrochemical impedance spectroscopy (EIS). The biosensor detected creatinine levels as low as 0.1 μM, estimated at a signal-to-noise ratio of 3, within 5 s at pH 7.5 and 35 °C. The optimized biosensor showed a linear response range of 10 to 750 μM creatinine with sensitivity of 40 μA/mM/cm2. The fabricated biosensor was successfully employed for determination of creatinine in human serum. The biosensor showed only 15% loss in its initial response after 180 days when stored at 4 °C.