We present the design and fabrication of pH responsive ratiometric dual component sensor systems based on multicolor emissive upconversion nanoparticles (UCNP) and pH sensitive BODIPY dyes with tunable pK_a values embedded into a polymeric hydrogel matrix. The use of NIR excitable NaYF₄:Yb³⁺,Tm³⁺ UCNPs enables background free read-out. Furthermore, the spectrally matching optical properties of the UCNPs and the dyes allow the UCNPs to serve as excitation light source for the analyte-responsive BODIPY as well as intrinsic reference. The blue upconversion luminescence (UCL) of NaYF₄:Yb³⁺,Tm³⁺ UCNPs excited at 980 nm, that overlaps with the absorption of the pH-sensitive fluorophore, provides reabsorption based excitation of the dye, the spectrally distinguishable green fluorescence of which is switched ON upon protonation, preventing photoinduced electron transfer (PET) within the dye moiety, and the pH-inert red UCL act as reference. The intensities ratios of the dye’s fluorescence and the analyte-inert red Tm³⁺ UCL correlate directly with pH, which was successfully utilized for monitoring time-dependent pH changes of a suspension of quiescent E. coli metabolizing d-glucose.

中文翻译：

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基于上转换纳米晶体和pH敏感荧光BODIPY染料的简单自参考发光pH传感器

我们介绍了基于多色发射上转换纳米粒子（UCNP）和pH敏感的BODIPY染料的pH响应比例双组分传感器系统的设计和制造，该染料具有可调节的p K _a值嵌入聚合物水凝胶基质中。使用近红外激发NaYF ₄：Yb ³⁺，Tm ³⁺ UCNPs可以实现无背景读出。此外，UCNP和染料的光谱匹配光学特性允许UCNP用作分析物响应BODIPY以及本征参比的激发光源。NaYF ₄：Yb ³⁺，Tm ³⁺的蓝色上转换发光（UCL）在980 nm处激发的UCNP与pH敏感的荧光团的吸收重叠，提供了基于染料的重吸收的激发，其在光谱上可区分的绿色荧光在质子化时被打开，从而防止了染料部分内的光诱导电子转移（PET） ，pH惰性红色UCL作为参考。染料的荧光强度和分析物惰性的红色Tm ³⁺ UCL的强度比与pH值直接相关，这已成功地用于监测静止的代谢d-葡萄糖的大肠杆菌悬浮液随时间的pH变化。