Refractive index (RI) sensing as a label-free and non-invasive method has been playing an important role in industrial metrology, biochemical detection, and environmental analysis. Due to the combined advantages of microoptics and microfluidics, optofluidic RI sensors have attracted growing interest. Despite a variety of prototypes of optofluidic RI sensors, comprehensive improvement in sensitivity, detection range, fabrication procedures and cost can still bring substantial benefits to the field. In this work, we fabricated a 3D-cascade-microlens optofluidic chip (3DCMOC) for RI sensing. Two-photon stereolithography was employed to fabricate the chip mold, with which the 3DCMOC could be easily manufactured via mold replication. By virtue of integrating four detection channels configured with different numbers (1, 3, 5, and 7) of cascaded microlenses within the 3DCMOC, adjustable sensitivity for RI sensing has been demonstrated through measuring standard sucrose solutions. It was found that the seven-microlens configuration achieved an excellent sensitivity (mean: 21 ± 5 AU·RIU (refractive index unit)⁻¹) and resolution (mean: 3.8 × 10⁻⁵ ± 0.9 × 10⁻⁵ RIU) at a cost of a narrow linear dynamic range (LDR, 1.3326–1.3548). In contrast, the single-microlens configuration led to an extended LDR (1.3326–1.5120 tested) despite the lower sensitivity (mean: 2.6 ± 0.2 AU·RIU⁻¹) and resolution (mean: 1.5 × 10⁻⁴ ± 0.1 × 10⁻⁴ RIU). Furthermore, the use of the 3DCMOC was investigated via real-time salinity sensing and analysis of urine specific gravity.

中文翻译：

---

用于折光测定的 3D 级联微透镜光流控芯片，灵敏度可调

折射率 (RI) 传感作为一种无标记和非侵入性的方法，在工业计量、生化检测和环境分析中发挥着重要作用。由于微光学和微流体的综合优势，光流体 RI 传感器引起了越来越多的兴趣。尽管有各种光流体 RI 传感器的原型，但在灵敏度、检测范围、制造程序和成本方面的全面改进仍然可以为该领域带来实质性的好处。在这项工作中，我们制造了用于 RI 传感的 3D 级联微透镜光流体芯片 (3DCMOC)。双光子光固化物用于制造芯片的模具，利用该3DCMOC可以容易地制造通过模具复制。通过在 3DCMOC 内集成配置有不同数量（1、3、5 和 7）级联微透镜的四个检测通道，通过测量标准蔗糖溶液证明了 RI 传感的可调灵敏度。结果发现，七微透镜的配置来实现优良的灵敏度（平均：21±5 AU·RIU（折射率单位）^-1）和分辨率（平均值：3.8×10 ^-5 ±0.9×10 ^-5 RIU）在一个窄线性动态范围（LDR，1.3326–1.3548）的成本。相比之下，尽管灵敏度（平均值：2.6 ± 0.2 AU·RIU ^-1）和分辨率（平均值：1.5 × 10 ^-4 ± 0.1 × 10⁻⁴ RIU）。此外，通过实时盐度传感和尿液比重分析研究了 3DCMOC 的使用。