TU Braunschweig, Institute of Microtechnology, 38124 Braunschweig, Germany.
Lab Chip. 2017 Dec 5;17(24):4265-4272. doi: 10.1039/c7lc00929a.
Measuring small changes in refractive index can provide both sensitive and contactless information on molecule concentration or process conditions for a wide range of applications. However, refractive index measurements are easily perturbed by non-specific background signals, such as temperature changes or non-specific binding. Here, we present an optofluidic device for measuring refractive index with direct background subtraction within a single measurement. The device is comprised of two interdigitated arrays of nanofluidic channels designed to form an optical grating. Optical path differences between the two sets of channels can be measured directly via an intensity ratio within the diffraction pattern that forms when the grating is illuminated by a collimated laser beam. Our results show that no calibration or biasing is required if the unit cell of the grating is designed with an appropriate built-in asymmetry. In proof-of-concept experiments we attained a noise level equivalent to ∼10 refractive index units (30 Hz sampling rate, 4 min measurement interval). Furthermore, we show that the accumulation of biomolecules on the surface of the nanochannels can be measured in real-time. Because of its simplicity and robustness, we expect that this inherently differential measurement concept will find many applications in ultra-low volume analytical systems, biosensors, and portable devices.
测量小的折射率变化可以为广泛的应用提供敏感和非接触式的分子浓度或过程条件信息。然而，折射率测量很容易受到非特异性背景信号的干扰，如温度变化或非特异性结合。在这里，我们提出了一种用于测量折射率的光流控器件，该器件在单次测量中可以直接进行背景扣除。该器件由两个叉指状纳米通道阵列组成，设计用于形成光学光栅。当光栅被平行激光束照射时，两个通道之间的光程差可以通过衍射图案中的强度比直接测量，该衍射图案形成于光栅处。我们的结果表明，如果光栅的单元结构具有适当的内置不对称性，则不需要校准或偏置。在概念验证实验中，我们达到了等效于约 10 个折射率单位的噪声水平（30 Hz 采样率，4 分钟测量间隔）。此外，我们还展示了可以实时测量纳米通道表面上生物分子的积累。由于其简单性和鲁棒性，我们预计这种固有差分测量概念将在超微量分析系统、生物传感器和便携式设备中找到许多应用。
