Dopamine biosensors was developed using gold nanoparticles (AuNPs) at carbon dots (CDs) sheathed by the chitosan (CHIT) (AuNPs@CDs-CHIT) and the tyrosinase enzymes (Tyr) on the surface of glassy carbon electrode (GCE) (Tyr/AuNPs@CDs-CHIT/GCE). CDs were synthesized and tested by scanning electron microscope (SEM). It founds that the shape of CDs like a tapered bar with the size of 2 x 5 micrometers. The other type is found in the sheet, which is approximately 5 x 5 micrometers. The energy-dispersive x-ray spectroscopy (EDX) study found the peak of the K-Carbon occurs at 0.25 keV with 61.94 percent of carbon as the main element. The AuNPs and CDs were combined and formed a cluster of AuNPs@CDs. The CHIT was added in the AuNPs@CDs, the functionalized net of AuNPs@CDs with CHIT (AuNPs@CDs-CHIT) was formed. The SEM image found that the particles of AuNPs@CDs dissolved in the surface of the CHIT at approximately 1 micrometer. The film thickness of Tyr/AuNPs@CDs-CHIT on the GCE has 20 micrometers.
The Tyr/AuNPs@CDs-CHIT/GCE analysis using electrochemical impedance spectroscopy (EIS) technique found that it has a resistance of 1,800 ohms. This biosensor showed a good response to dopamine by the signal-to-background ratio of 137.0 times. It is also showed high repeatability and repeatability. The developed biosensors provide high sensitivity to dopamine at 0.0379 microamperes per micromolar. It has a wide linearity range (0.05 - 1,000 ?M), with a very low detection limit of 0.020 ?M and without interfered from ascorbic acid, aspirin, cholesterol, choline, glucose, sucrose, and uric acid
The stability test of the developed dopamine biosensor found that the current reduced to 90 percent at 19 times usage and still more than 50 percent when 35 times usage. In conclusion, the developed electrode is stable for 35 times. Moreover, the developed dopamine biosensors had been tested with real blood samples without having sample preparation. It provided a percentage recovery in the range of 96.00 - 98.80 percent.