Electrochemically grown Cu,Ni-BTC film for the electrochemical detection of caffeic acid in fruits

Abstract

Caffeic acid (CA) is an important antioxidant often found in many kinds of fruits. In this study, we developed an electrochemical sensor based on an electrochemically grown bimetallic metal–organic framework film (Cu,Ni-BTC) for the in situ determination of CA in fruits. The Cu,Ni-BTC film was grown directly onto a glassy carbon electrode (GCE) via a cathodic electrodeposition method under optimal conditions. The results showed that a uniform film made of Cu,Ni-BTC metal–organic frameworks with a Cu : Ni molar ratio of 3.67 was grown on the electrode surface. It was found that the charge transfer kinetics were much improved on the electrode modified with the Cu,Ni-BTC material. Consequently, the caffeic acid sensor based on the Cu,Ni-BTC film showed a detection limit and sensitivity as low as 0.7 µM (1.5 times less than that of the unmodified electrode) and 0.924 µA µM⁻¹ cm⁻² (13.2 times higher than that of the unmodified electrode), respectively. The developed sensor also exhibited high reproducibility (RSD = 2.61%), good stability (RSD = 6.47%) after 7 days, and good selectivity towards CA. Real sample tests using apple juice showed good recovery (92.2–98.4%). Further studies will be conducted in the near future to better understand the growth mechanism of the MOF films, control their morphology and utilize them in other electronic applications.