Preparation and application of single polyelectrolyte microcapsules possessing tunable autofluorescent properties

Autofluorescent single polyelectrolyte microcapsules, exemplified by poly-l-lysine (PLL), have been prepared through glutaraldehyde-mediated covalent layer-by-layer (LbL) assembly and subsequent core removal. CaCO3 microparticles were used as template cores for the LbL deposition and removed by treatment of ethylenediamine tetraacetic acid disodium salt (EDTA). The prepared microcapsules, without conjugating an exterior fluorochrome, exhibited evenly distributed fluorescence. The fluorescence properties of PLL microcapsules were investigated by fluorescence spectroscopy and confocal laser scanning microscopy. The fluorescence color could be modulated with different excitation wavelengths. Autofluorescent PLL microcapsules were used as fluorescence tracers for cell imaging after cell ingestion. Sodium borohydride (NaBH4) reduction was also used to alter fluorescence character of PLL microcapsules.