Polydopamine Dots-Based Fluorescent Nanoswitch Assay for Reversible Recognition of Glutamic Acid and Al³⁺ in Human Serum and Living Cell

We developed a facile and feasible fluorescent nanoswitch assay for reversible recognition of glutamate (Glu) and Al3+ in human serum and living cell. The proposed nanoswitch assay is based on our recently developed method for controlled synthesis of fluorescent polydopamine dots (PDADs) at room temperature with dopamine as the sole precursor. The fluorescence of nanoswitch assay could be quickly and efficiently quenched by Glu (turn-Off), and the addition of Al3+ could recover the fluorescence of the PDADs–Glu system (turn-On). Meanwhile, the reversible recognition of Glu and Al3+ in this nanoswitch system was stable after three cycles. Additionally, the system displayed excellent performance for Glu and Al3+ determination with a low detection limit of 0.12 and 0.2 μM, respectively. Moreover, PDADs are successfully applied to determine Glu and monitor Al3+ in human serum. Noteworthy, the nanoswitch assay is transported into HepG2 cells and realized “Off” detection of Glu and “On” sensing Al3+ in the living cells. Therefore, this PDADs-based nanoswitch assay provides a strategy to develop reversible recognition biosensors for intracellular and external molecular analysis.