Effect of the carboxyl functional group at the edges of graphene on the signal sensitivity of dopamine detection

Abstract

Sensitive and selective detection of dopamine (DA) is important for the early diagnosis of diseases associated with abnormal DA levels. This study investigated the effect of the degree of carboxyl (−COOH) functional groups at the edges of graphene on the signal sensitivity of electrochemical DA detection in the presence of ascorbic acid (AA) and uric acid (UA). We prepared edge carboxylated graphene (ECG) nanoplatelets with a high proportion of oxygen functional groups (26.40%) and heat-treated ECG (HECG) with a low proportion of oxygen functional groups (2.35%), which were used to modify a fluorine-doped tin oxide (FTO) electrodes through the electrospray method. The ECG/FTO electrode showed excellent catalytic activity in separating AA, DA, and UA signals, potentially owing to the strong chemical interactions of these analytes with −COOH groups of ECG. While the HECG/FTO electrode displayed the oxidation signals suppression of AA and UA from those of DA signals with low sensitivity; this can be ascribed to decreased chemical interactions of these analytes with HECG induced by the low proportion of −COOH functional groups. Concurrently, the ECG/FTO sensor showed high sensitivity (ca. 2.11 μA/cm2/μM) and low detection limit (ca. 0.26 μM) for DA detection in the presence of AA and UA, while it was ca. 0.55 μA/cm2/μM and 1.0 μM, respectively, for the HECG/FTO sensor. These results suggest that the dense distribution of oxygen functional groups at the edges of graphene plays a vital role in ensuring high sensitivity and a low limit of DA detection.