Polyethyleneimine protected silver nanoclusters luminescence probe for sensitive detection of cobalt (II) in living cells.

A simple luminescence sensor, based on polyethyleneimine protected silver nanoclusters (AgNCs@PEI) is successfully fabricated via one-pot reduction method. The obtained AgNCs@PEI are characterized by high-resolution transmission electron microscopy (HR-TEM), Dynamic light scattering (DLS), transient and steady-state fluorescence, and UV-vis spectroscopy. The NCs show large Stocks-shift (∼130nm), high tolerability to extreme pH and high ionic strengths, and excellent photo-stability under UV irradiation, laying the basement for the practical applications. In addition, the sensor is used to detect the Co(2+) basing on the luminescence quenching, which is interfered by pH conditions (from pH4.0 to pH7.4). As a luminescence probe for Co(2+) ions, the detection limit of AgNCs@PEI is as low as 0.25nM, which is much lower than that of many other reports. Additionally, the AgNCs@PEI possess the advantages of good selectivity, fast response and abroad linear detection. A linear response range in 0.5nM-50μM is achieved for Co(2+) when using 20μM AgNCs@PEI in BR buffer solution (neutral condition pH7.4). Incubation time of AgNCs@PEI toward Co(2+) is only 2min and it can distinguish Co(2+) from other 13 metal ions. Furthermore, the probe (AgNCs@PEI) is applied to sensing and imaging of HeLa cells, showing low cytotoxicity and good sensitivity.