Highly fluorescent oligodopamine (F-ODA) for accurate and sensitive detection of the neurotransmitter dopamine

Abstract

Dopamine (DA) is an important neurotransmitter for regulating the central nervous system, hormones, and cardiovascular system. Fluorescence technique is usually applied for the rapid detection of DA neurotransmitter because DA is easily converted to fluorescent products under alkaline condition. However, it is difficult to accurately quantify low levels of DA ( < 10 nM) because the final product of DA conversion, so-called polydopamine (PDA), usually have low fluorescence efficiency. In this study, DA dissolved in Tris-EDTA buffer (pH 8.5) was oxidized and polymerized by adding NaOH as an oxidizing agent. After obtaining products with various degrees of polymerization, the fluorescent oligodopamine (F-ODA) (i.e., indole-5,6-quinone-rich compounds) was separated from non-fluorescent polydopamine (PDA) products. After removing non-fluorescent PDA by centrifugation, the F-ODA in the supernatant exhibited high FL intensity at 470 nm under excitation at 360 nm. At the optimal reaction conditions, the standard curve of the F-ODA exhibited a good linearity over wide range of DA concentration from 1 mu M to 1 nM (limit of detection = similar to 0.1 nM), suggesting a very useful analytical tool for the accurate and sensitive detection of the neurotransmitter DA in bio-fluid.