All buffers were prepared with purified water from a Milli-Q water purification system (Millipore Corp., Bedford, USA). Fluorescence measurements were performed with Cary Eclipse Fluorescence Spectrophotometer (Agilent Technologies, Germany). UVvis spectrometry was carried out using a Cary 60 UV-vis spectrophotometer (Agilent Technologies, USA). SEM was carried out using JEOL JSM 6700F scanning electron microscope (Japan).