We present the optical coupling of the silver nanoparticles (AgNPs)-conjugated dye molecule into fiber optical modes for detecting fluorescence with the enhanced signal-to-noise (S/N) ratio. This near field coupling of the excited state of organic dye (FAM) molecules into the fiber multimodes occurs by immobilizing them on the exposed surface of fiber core, permitting the coupled light to be guided along the fiber for detection. This fiber based scheme is the first attempt to single out the fluorescence using fiber modes not for carrying excitation light but only for collecting emission light via the dye-fiber coupling. The emission-selective coupling into fiber modes turns out to be effective in reducing the unwanted background noise arising from both the false detection of excitation light and bulk autofluorescence.

This scheme differs from the previously reported fluorescence sensors based on waveguides where guided modes at ${\lambda }_{\text{ex}}$ excite dye molecules via their evanescent fields. In addition, the local fields enhanced by AgNPs in close proximity to FAM molecules on the fiber core surface increase the rates of dye excitation and radiative decay/AgNP supported surface plasmon coupled emission. While focusing on demonstrating the proof-of-concept of the scheme presented, we obtain the maximum of 4.2-fold enhancement of the signal-to-noise (S/N) ratio in detecting fluorescence as compared to a conventional fluorescence detection scheme. The results presented in the fiber-based scheme may find an application where high S/N ratio fluorescence based biochemical assay is required in a small-sized device with remote sensing capability.

我们介绍了银纳米粒子（AgNPs）共轭的染料分子到光纤光学模式的光学耦合，用于检测具有增强的信噪比（S / N）的荧光。通过将有机染料（FAM）分子的激发态固定在纤维芯的裸露表面上，可以将它们激发态耦合到纤维多模中，从而使耦合光沿着纤维被引导进行检测。这种基于光纤的方案是首次尝试使用光纤模式来挑选荧光，该模式不用于承载激发光，而仅用于通过染料-光纤耦合收集发射光。事实证明，发射选择性耦合到光纤模式可有效减少由于错误检测激发光和大量自发荧光而产生的有害背景噪声。

该方案与先前报道的基于波导的荧光传感器不同，后者的波导模式为 ${\lambda }_{\text{前}}$通过其消逝场激发染料分子。另外，由AgNP增强的局部场紧邻纤维芯表面上的FAM分子，增加了染料激发和辐射衰减/ AgNP支持的表面等离激元耦合发射的速率。在专注于演示所提出的方案的概念验证的同时，与传统的荧光检测方案相比，我们在检测荧光时获得了最大4.2倍的信噪比（S / N）增强。基于光纤的方案中提出的结果可能会发现一种在具有遥感功能的小型设备中需要高信噪比的基于荧光的生化分析的应用。