Upconversion fluorescence has triggered extensive efforts in the past decade because of its superior physicochemical features and great potential in biomedical and biophotonic studies. However, practical applications of upconversion fluorescence are often hindered by its relatively low luminescence efficiency (<1%). Here, we employ a living yeast or human cell as a natural bio-microlens to enhance the upconversion fluorescence. The natural bio-microlens, which was stably trapped on a fiber probe, could concentrate the excitation light into a subwavelength region so that the upconversion fluorescence of core–shell NaYF₄:Yb³⁺/Tm³⁺ nanoparticles was enhanced by 2 orders of magnitude. As a benefit of the fluorescence enhancement, single-cell imaging and real-time detection of the labeled pathogenic bacteria, such as Escherichia coli and Staphylococcus aureus, were successfully achieved in the dark fields. This biocompatible, sensitive, and miniature approach could provide a promising powerful tool for biological imaging, biophotonic sensing, and single-cell analysis.

中文翻译：

---

用天然生物微透镜增强上转换荧光

在过去的十年中，上转换荧光因其卓越的理化特性以及在生物医学和生物光子学研究中的巨大潜力而​​引发了广泛的努力。但是，上转换荧光的实际应用通常由于其相对较低的发光效率（<1％）而受到阻碍。在这里，我们采用活酵母或人类细胞作为天然生物微透镜，以增强上转换荧光。天然生物微透镜被稳定地捕获在纤维探针上，可以将激发光集中在亚波长区域，从而使核-壳NaYF ₄：Yb ³⁺ / Tm ³⁺的上转换荧光纳米颗粒增加了两个数量级。作为增强荧光的一项优势，在暗视野中成功实现了单细胞成像和实时检测标记的病原细菌，例如大肠杆菌和金黄色葡萄球菌。这种生物相容，灵敏且微型的方法可以为生物成像，生物光子传感和单细胞分析提供有前途的强大工具。