The surface enhanced fluorescence effect of acridine orange fluorophore in the proximity of Au nanoparticles has been investigated experimentally in the system of aqueous solution. Significant enhancement of the fluorescence intensity was observed when the system was excited with 532 nm or 442 nm CW lasers. The influence of the distances between neighboring Au particles as well as that between the fluorophore molecules and the Au surface were explored experimentally. The results demonstrated that a compact distribution of metallic particles was able to produce stronger fluorescence enhancement. Proper separation between the fluorophore molecules and the metal surface was favorable for a better enhancement. surface enhanced fluorescence, local field enhancement, acridine orange, hydrophilic Au nanoparticle PACS: 42.62.Fi, 68.49.Uv, 33.50.Dq, 87.64.NiAs a powerful and broadly used method, fluorescence emission and detection enable the revolution in medical diagnostics, DNA sequencing, and genomics [1]. But it is often limited by low quantum yields and poor photostability in many practical applications [2]. To overcome these difficulties, new approaches for increasing the sensitivity of the detection on the target have been developed [3]. It has been found that the metallic surface has the ability to drastically alter emission of vicinal fluorophores and to enhance the fluorescence intensity [2]. The phenomenon is termed surface enhanced fluorescence (SEF) or metal enhanced fluorescence (MEF) [4]. Investigation of the influence of a metallic surface on the fluorescence emission has a long scientific history, perhaps starting with Drexhage's work [5,6]. Possible mechanisms proposed for understanding experimental observations of SEF include the lighting rod effect, local field effect induced by surface plasmon resonance [7],
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