Bifunctional Fluorescence Aptasensor Based on Target-Induced Strand Displacement Enables Simultaneous Detection of Dopamine and Serotonin in Multiple Body Fluids

Simultaneous detection of dopamine (DA) and serotonin (5-HT) provides useful information in the early diagnosis of neurological diseases. However, existing approaches have to be conducted in centralized laboratories with assay complexity. Herein, we developed a bifunctional fluorescence aptasensor based on target-induced strand displacement, which enables the simultaneous detection of DA and 5-HT in multiple body fluids. Cy5/FAM-tagged aptamers were first hybridized with a Dabcyl-quenched complementary strand ss-DNA1-(Dabcyl)₂ to form a low fluorescence background complex Cy5-ds-DNA-(Dabcyl)₂-FAM. Upon target binding (DA/5-HT), the tagged aptamers were selectively displaced, restoring Cy5 (red) and FAM (green) fluorescence upon excitation with 600 and 465 nm, respectively. The aptasensor exhibits high sensitivity, with a limit of detection of 0.3 nM for DA and 0.5 nM for 5-HT in solution. Good recovery in artificial cerebrospinal fluid and urine and results consistent with those of high-performance liquid chromatography (HPLC) were achieved. With the success in solution-based detection, we further transferred the aptasensor onto glass fiber paper (GFP) to develop a paper-based aptasensor. Good recovery in tears and urine and results matching those of HPLC were also obtained. This simple and bifunctional fluorescence aptasensor offers a promising point-of-care platform for the detection of multiple neurotransmitters in diverse body fluids.