Near infra-red (NIR) fluorescence is a desirable property for probe particles because such deeply penetrating light enables remote reporting of the local environment in complex surroundings and imaging. Here, two NIR non-radiative energy transfer (NRET) fluorophores (Cy5 and Cy5.5) are coupled to preformed pH-responsive poly(ethylacrylate-methacrylic acid-divinylbenzene) microgel particles (PEA-MAA-5/5.5 MGs) to obtain new NIR fluorescent probes that are cytocompatible and swell strongly. NIR ratiometric photoluminescence (PL) intensity analysis enables reporting of pH-triggered PEA-MAA-5/5.5 MG particle swelling ratios over a very wide range (from 1–90). The dispersions have greatly improved colloidal stability compared to a reference temperature-responsive NIR MG based on poly(N-isopropylacrylamide) (PNP-5/5.5). We also show that the wavelength of maximum PL intensity (λ_max) is a second PL parameter that enables remote reporting of swelling for both PEA-MAA-5/5.5 and PNP-5/5.5 MGs. After internalization the PEA-MAA-5/5.5 MGs are successfully imaged in stem cells using NIR light. They are also imaged after subcutaneous injection into model tissue using NIR light. The new NIR PEA-MAA-5/5.5 MGs have excellent potential for reporting their swelling states (and any changes) within physiological settings as well as very high ionic strength environments (e.g., waste water).

中文翻译：

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用于双模式近红外荧光报告和成像的高溶胀 pH 响应微凝胶

近红外 (NIR) 荧光是探针粒子的理想特性，因为这种深度穿透的光能够远程报告复杂环境和成像中的局部环境。在这里，将两个 NIR 非辐射能量转移 (NRET) 荧光团 (Cy5 和 Cy5.5) 与预制的 pH 响应型聚(丙烯酸乙酯-甲基丙烯酸-二乙烯基苯) 微凝胶颗粒 (PEA-MAA-5/5.5 MGs) 偶联以获得具有细胞相容性和强烈膨胀的新型 NIR 荧光探针。NIR 比率光致发光 (PL) 强度分析能够在非常宽的范围（1-90）内报告 pH 触发的 PEA-MAA-5/5.5 MG 颗粒溶胀比。与基于聚（N-异丙基丙烯酰胺）（PNP-5/5.5）。我们还表明，最大 PL 强度 ( λ _max ) 的波长是第二个 PL 参数，它可以远程报告 PEA-MAA-5/5.5 和 PNP-5/5.5 MG 的膨胀情况。内化后，PEA-MAA-5/5.5 MG 使用 NIR 光成功地在干细胞中成像。它们还在使用 NIR 光皮下注射到模型组织后进行成像。新的 NIR PEA-MAA-5/5.5 MG 在生理环境和非常高的离子强度环境（例如废水）中报告其膨胀状态（和任何变化）具有极好的潜力。