Two water-soluble near-infrared luminescent probes, which possess both conventional intense Stokes fluorescence and unique single-photon frequency upconversion luminescence (FUCL), were developed for sensitive and selective detection of pH changes in live cells. The water solubility and biocompatibility of these probes were achieved by introducing mannose residues through 2,2′-(ethylenedioxy)diethylamine tethered spacers to a near-infrared conventional fluorescence (CF) and FUCL organic fluorophore. At a pH higher than 7.4, the probes have ring-closed spirocyclic lactam structures, thus are colorless and nonfluorescent. Nevertheless, they sensitively respond to acidic pH values, with a drastic structural change to ring-opened spirocyclic lactam forms, which cause significant absorbance increases at 714 nm. Correspondingly, their near-infrared CF and FUCL intensities at 740 nm are also significantly enhanced when excited by 690 and 808 nm, respectively. The probes hold a variety of advantages such as high sensitivity, excellent reversibility and selectivity to pH over metal ions, low cellular autofluorescence background interference, good cell membrane permeability and photostability, as well as low cytotoxicity. Our results have successfully proven that these probes can visualize intracellular lysosomal pH changes in live cells by monitoring both near-infrared CF and FUCL changes.

中文翻译：

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通过两个近红外发光通道灵敏检测活细胞pH变化的发光探针

已开发出两种具有常规斯托克斯荧光强度和独特的单光子频率上转换发光（FUCL）的水溶性近红外发光探针，用于灵敏和选择性地检测活细胞的pH变化。这些探针的水溶性和生物相容性是通过将甘露糖残基通过2,2'-（乙二氧基）二乙胺系留的间隔基引入近红外常规荧光（CF）和FUCL有机荧光团来实现的。在高于7.4的pH值下，探针具有闭环的螺环内酰胺结构，因此是无色且无荧光的。但是，它们对酸性pH值敏感，对开环的螺环内酰胺形式有剧烈的结构变化，这会导致在714 nm处的吸光度显着增加。相应地，当分别被690和808 nm激发时，它们在740 nm处的近红外CF和FUCL强度也显着增强。该探针具有多种优势，例如灵敏度高，对金属离子的pH值具有优异的可逆性和选择性，低的细胞自发荧光背景干扰，良好的细胞膜通透性和光稳定性以及低细胞毒性。我们的结果已成功证明，这些探针可通过监测近红外CF和FUCL的变化来可视化活细胞中细胞内溶酶体的pH变化。良好的细胞膜通透性和光稳定性，以及低细胞毒性。我们的结果已成功证明，这些探针可通过监测近红外CF和FUCL的变化来可视化活细胞中细胞内溶酶体的pH变化。良好的细胞膜通透性和光稳定性，以及低细胞毒性。我们的结果已成功证明，这些探针可以通过监测近红外CF和FUCL的变化来观察活细胞中细胞内溶酶体的pH变化。