Fluorescence enhancement based on cooperative effects of a photonic nanojet and plasmon resonance

Developing a universal and simple structure with an excellent fluorescence enhancement is a highly desirable goal for the practical applications in optical detection and imaging. Herein, a hybrid structure composed of melamino-formaldehyde (MF) microspheres covering an Au nanorods (AuNRs) film (MS/AuNR for short) is reported to enhance fluorescence, which is based on the cooperative effects of a photonic nanojet and plasmon resonance. Moreover, to obtain an excellent plasmonic property, an additional poly(methyl methacrylate) (PMMA) spacing layer with an optimal thickness of 8 nm is added to prevent the fluorescence from directly contacting the AuNRs film. Using the proposed hybrid structure and taking the quantum dots (QDs) as fluorescence materials, a maximum enhancement of fluorescence of up to 260 folds is measured. Besides, the hybrid structure is also proven to apply in fluorescence imaging. Utilizing the fluorescence enhancement and pattern magnification effects of the hybrid structure, a clear imaging of the 100-nm-fluorescent particles is achieved. The above results have important academic value and application prospects in many fields such as weak fluorescence detection and nano-fluorescence imaging.