Preparation and properties of silver-deposited magnetically responsive colloidal photonic crystals for significant fluorescence enhancement

Fluorescence detection is actually available on measuring substances by using metal-based micro or nano structures which produce a great surface enhanced fluorescence (SEF) effect in quick response to endless diseases and environmental problems recently. However, traditional SEF substrates are expensive, as well as inefficient due to single-component detection mode. Therefore, SEF substrates with controllable fluorescence enhancement formed by magnetically responsive CoFe₂O₄@SiO₂@Ag colloidal photonic crystals were designed in this work. The fluorescence spectra were enhanced selectively at different wavelength owing to photonic band gap adjusted by magnetic field so as to detect Rhodamine B (RB) and fluorescein isothiocyanate (FITC) which had quite different fluorescence emission wavelength. As-prepared composites showed that the highest enhancement factors were 12.6 and 17.6 fold for RB and FITC, respectively, only when the tunable photonic band gap matched with the fluorescence emission wavelength of fluorescent molecules. The mechanism of significant fluorescence enhancement was explained in detail. The CoFe₂O₄@SiO₂@Ag substrates were confirmed to be reliable, sensitive and reproducible in detecting a variety of fluorescent molecules. The results played an important role in effective fluorescence detection, such as chemical analysis, biological sensing and cell imaging.