Zhang Bohong, Mumtaz Farhan, Roman Muhammad, Alla Dinesh Reddy, Gerald Ii Rex E, Huang Jie
Opt Express. 2024 Jan 29;32(3):4228-4241. doi: 10.1364/OE.511190.
In biochemistry, the absence of a compact, assembly-free pH sensor with high sensitivity and signal-to-noise ratio has been a persistent hurdle in achieving accurate pH measurements in real time, particularly in complex liquid environments. This manuscript introduces what we believe to be a novel solution in the form of a miniaturized pH sensor utilizing an assembly-free ball lens on a tapered multimode optical fiber (TMMF), offering the potential to revolutionize pH sensing in biochemical applications. A multimode optical fiber (MMF) was subjected to tapering processes, leading to the creation of an ultra-thin needle-like structure with a cross-sectional diameter of about 12.5 µm and a taper length of 3 mm. Subsequently, a ball lens possessing a diameter of 20 µm was fabricated at the apex of the taper. The resultant structure was coated utilizing the dip-coating technique, involving a composite mixture of epoxy and pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF), thereby ensconcing the tapered ball lens with dye molecules for pH sensing. This study encompassed the fabrication and evaluation of six distinct fiber structures, incorporating the cleaved endface, the convex lens, and the ball lens structures to compare light focal lengths and propagation intensities. Computational simulations and numerical analyses were conducted to elucidate the encompassing light focal distances across the full array of lens configurations. The efficacy of the proposed pH sensor was subsequently assessed through its deployment within a complex liquid medium spanning a pH spectrum ranging from 6 to 8. Real-time data acquisition was performed with a fast response time of 0.5 seconds. A comparative analysis with a pH sensor predicated upon a single TMMF embedded with the fluorescent dye underscored the substantial signal enhancement achieved by the proposed system twice the fluorescence signal magnitude. The proposed assembly-free miniaturized pH sensor not only substantiates enhanced signal collection efficiency but also decisively addresses the persistent challenges of poor signal-to-noise ratio encountered within contemporary miniaturized pH probes.
在生物化学领域，缺乏一种紧凑、无需组装且具有高灵敏度和信噪比的pH传感器，一直是实时进行精确pH测量的一个长期障碍，尤其是在复杂液体环境中。本论文介绍了一种我们认为新颖的解决方案，即一种利用锥形多模光纤（TMMF）上无需组装的球透镜的小型化pH传感器，它有可能彻底改变生化应用中的pH传感。对一根多模光纤（MMF）进行了拉锥处理，形成了一种超薄的针状结构，其横截面直径约为12.5 µm，拉锥长度为3 mm。随后，在拉锥顶端制作了一个直径为20 µm的球透镜。利用浸涂技术对所得结构进行涂层处理，该技术涉及环氧树脂和pH敏感染料2',7'-双（2-羧乙基）-5-（和-6）-羧基荧光素（BCECF）的复合混合物，从而用染料分子包裹锥形球透镜以进行pH传感。本研究包括制造和评估六种不同的光纤结构，包括切割端面、凸透镜和球透镜结构，以比较光焦距和传播强度。进行了计算模拟和数值分析，以阐明整个透镜配置阵列的光焦距。随后，通过将所提出的pH传感器部署在pH范围为6至8的复杂液体介质中，评估了其有效性。以0.5秒的快速响应时间进行了实时数据采集。与基于嵌入荧光染料的单个TMMF的pH传感器进行的对比分析强调了所提出系统实现的显著信号增强——荧光信号强度提高了两倍。所提出的无需组装的小型化pH传感器不仅证实了增强的信号收集效率，而且果断地解决了当代小型化pH探头中持续存在的信噪比差的挑战。
