Polydopamine coated copper nanoclusters with aggregation-induced emission for fluorometric determination of phosphate ion and acid phosphatase activity

The preparation of aggregation-induced emission-type copper nanoclusters (CuNCs) capped with polydopamine (PDA) is described. PDA was formed via in situ polymerization of dopamine in the presence of alkaline polyethylenimine. The PDA-capped CuNCs (PDA-CuNCs) exhibit orange fluorescence with maximal emission at 580 nm upon excitation at 340 nm, a storage stability of at least 2 weeks, and a quantum yield (QY) of 2.54% in aqueous solution. The QY is 28-fold higher than that of sole CuNCs. The fluorescence of the PDA-CuNCs is quenched by Fe³⁺ ion while it is recovered by PO₄^3- due to its stronger affinity for Fe³⁺. On this basis, a fluorometric phosphate assay was developed that has a 1.5 nM detection limit and a linear range over 0.003-70 μM. The method was satisfactorily applied to the determination of phosphate in local tap water and human sera, and the results agreed well with those obtained by a colorimetric method. In the presence of acid phosphatase (ACP), PO₄^3- is produced by the catalytic hydrolysis of adenosine triphosphate (ACP substrate). Thus, a fluorogenic assay for screening ACP activity was established. Response is linear over the activity range 0.0012-25 U L^-1, with a detection limit of 0.001 U L^-1 (at S/N = 3). Graphic abstract We proposed an effective polydopamine-templating strategy for the in situ synthesis of highly emissive and stable CuNCs and demonstrated its use as an ion-driven fluorescence switch for the determination of phosphate and acid phosphatase activity.

Phosphate Assay Kit in One Cell for Electrochemical Detection of Intracellular Phosphate Ions at Single Cells

In this paper, phosphate assay kit in one cell is realized for the electrochemical detection of intracellular phosphate ions at single cells. The components of the phosphate assay kit, including maltose phosphorylase, maltose, mutarotase, and glucose oxidase, are electrochemically injected into a living cell through a nanometer-sized capillary with the ring electrode at the tip. These components react with phosphate ions inside the cell to generate hydrogen peroxide that is electrochemically oxidized at the ring electrode for the qualification of intracellular phosphate ions. An average 1.7 nA charge was collected from eight individual cells, suggesting an intracellular phosphate concentration of 2.1 mM. The establishment in the electrochemical measurement of phosphate ions provides a special strategy to monitor the fluctuation of intracellular phosphate at single cells, which is significant for the future investigation of phosphate signal transduction pathway.