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 (∼   130   nm), 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 pH   4.0 to pH   7.4). As a luminescence probe for Co 2   + ions, the detection limit of AgNCs@PEI is as low as 0.25   nM, 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 0.5   nM–50   μM is achieved for Co 2   + when using 20   μM AgNCs@PEI in BR buffer solution (neutral condition pH   7.4). Incubation time of AgNCs@PEI toward Co 2   + is only 2   min 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.