Lanthanide-based upconversion nanoparticles (UCNPs) generally require high power laser excitation. Here, we report wide-field upconversion microscopy at single-nanoparticle sensitivity using incoherent excitation of a 970 nm light-emitting diode (LED). We show that due to its broad emission spectrum, LED excitation is about 3 times less effective for UCNPs and generates high background compared to laser illumination. To counter this, we use time-gated luminescence detection to eliminate the residual background from the LED source, so that individual UCNPs with high sensitizer (Yb³⁺) doping and inert shell protection become clearly identified under LED excitation at 1.18 W cm^–2, as confirmed by correlated electron microscopy images. Hydrophilic UCNPs are obtained by polysaccharide coating via a facile ligand exchange protocol to demonstrate imaging of cellular uptake using LED excitation. These results suggest a viable approach to bypassing the limitations associated with high-power lasers when applying UCNPs and upconversion microscopy to life science research.

中文翻译：

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上转换显微镜的发光二极管激发：定量评估。

基于镧系元素的上转换纳米颗粒（UCNP）通常需要高功率激光激发。在这里，我们报道了使用970 nm发光二极管（LED）的非相干激发在单纳米粒子灵敏度下进行的宽视野上转换显微镜。我们显示，由于其宽的发射光谱，与激光照明相比，LED激发的UCNP效率低约3倍，并且产生高背景。为了解决这个问题，我们使用时间门控发光检测技术消除了LED光源的残留背景，因此在1.18 W cm ^–2的LED激励下，具有高敏化度（Yb ³⁺）掺杂和惰性外壳保护的单个UCNP变得清晰可见。，如相关电子显微镜图像所证实。亲水性UCNPs是通过简便的配体交换方案通过多糖包被获得的，以证明使用LED激发对细胞摄取的成像。这些结果表明，在将UCNP和上转换显微镜应用于生命科学研究中时，一种可行的方法可以绕过与高功率激光器相关的限制。