Acridine orange and silica nanoparticles facilitated novel robust fluorescent hollow microcapsules toward DNA bio-sensor

Tuning optical properties by nanotechnology has become a topic of larger interest as these materials can be of extraordinary sensitivity, selectivity and robustness toward sensing applications. Here we report novel fluorescent hollow microcapsules via congregation of poly (l-lysine) interceded by silica nanoparticles and acridine orange. Scanning tunneling microscope images confirm spherical nature of microcapsules with size of 1–3 μm. The hollow structures are verified by fluorescent images, which indicate acridine orange is intermingled in the shell wall of the microcapsules. The excitation fluorescence spectra reveal that acridine orange exists in monomeric and aggregated form within the microcapsules. But at pH 8.5, monomeric acridine orange diffuses out of microcapsules. Association of acridine orange with poly (l-lysine) and SiO2 nanoparticles in monomeric or aggregated form does not limit intercalation of acridine orange with DNA. Thus, the acridine orange based fluorescent hollow microcapsule could easily sense DNA in 100 ng mL−1 concentration ranges. The excited state lifetime of fluorescent hollow microcapsules is shorter than acridine orange in neutral form, which further establishes a strong association of acridine orange with poly (l-lysine). However, the excited state lifetime is marginally quenched in the presence of DNA but independent of DNA concentration that rules out the possibility of intercalation in the excited state rather than a ground state complex formation.