In this project an electrochemical biosensor based on a glassy carbon electrode was prepared using f-MWCNT and polydopamine via electropolymerization method. FT-IR, Raman spectroscopy, FE-SEM, AFM, XRD, EDS and elemental mapping techniques were used for the electrocatalyst characterization and investigation of its surface features. Afterwards, the efficiency of the electrocatalyst was investigated using cyclic voltametry and electrochemical impedance spectroscopy. The biosensor was used for morphine and ciprofloxacin determination using differential pulse voltammetry method. Subsequently, different parameters affecting the sensitivity and selectivity of the method including pH, pre-concentration time and potential, f-MWCNT suspension drop size and dopamine electropolymerization cycles number in cyclic voltammetry method, were optimized. The linear dynamic range for morphine determination was 0.075-7.5 and 7.5-75 µM with a detection limit of 0.06µM. The repeatability and reproducibility were calculated to be 3.7% and 4.3% respectively for morphine determination. The linear dynamic range for ciprofloxacin determination was 0.075-10 and 10-100 µM with a detection limit of 0.04 µM. The repeatability and reproducibility were calculated to be 3.2% and 3.3% respectively for ciprofloxacin determination. Afterwards, the selectivity of these methods in the presence of different interferer species were studied. Finally, the sensor was successfully used for morphine and ciprofloxacin determination in blood plasma and urine samples with satisfactory results.