Ratiometric "on/off"-type fluorescence sensors based on nitrogen and silicon co-doped graphene quantum dots for identification and semi-quantitative visualized detection of dopamine, epinephrine, and norepinephrine.

Catecholamines (CAs) play pivotal physiological in the human body, and the aberrant levels of them are closely associated with various diseases. Therefore, developing a rapid, simple, and accurate method for CAs determination is of considerable clinical importance for precise disease diagnosis. In this work, a turn-off fluorescence sensor based on nitrogen and silicon co-doped graphene quantum dots (N,Si-GQDs) was first established for the detection of total CAs, leveraging the inner filter effect (IFE). To achieve the selective identification and separate quantification of dopamine (DA), epinephrine (EP), and norepinephrine (NEP), resorcinol (RS) and ethylenediamine (EDA) were subsequently introduced. Taking advantage of the differential reactivity of DA/EP/NEP toward RS/EDA, three distinct fluorescent adducts were generated: DA-RS (λem=460 nm), EP-EDA (λem=510 nm), and NEP-EDA (λem=492 nm). Therefore, two ratiometric "on/off"-type fluorescence sensors, N,Si-GQDs/RS and N,Si-GQDs/EDA, were successfully constructed for identification and on-site semi-quantitative visual detection of DA (F460/F380), EP (F510/F380), and NEP (F492/F380), respectively. Under the optimal conditions, the detection limits of DA, EP, and NEP were respectively as low as 15.9, 14.1, and 6.3 nM. Furthermore, upon irradiation with a 365 nm UV lamp, the color differences observed at different times can be utilized to distinguish DA, EP and NEP, and conduct their rapid, semi-quantitative, on-site visual detection.