Department of Chemistry, Clemson University, Clemson, SC 29634, USA.
Department of Electrical and Computer Engineering, Clemson University, Clemson, SC 29634, USA.
Sensors (Basel). 2021 May 20;21(10):3554. doi: 10.3390/s21103554.
We describe a method to measure micron to millimeter displacement through tissue using an upconversion spectral ruler. Measuring stiffness (displacement under load) in muscles, bones, ligaments, and tendons is important for studying and monitoring healing of injuries. Optical displacement measurements are useful because they are sensitive and noninvasive. Optical measurements through tissue must use spectral rather than imaging approaches because optical scattering in the tissue blurs the image with a point spread function typically around the depth of the tissue. Additionally, the optical measurement should have low background and minimal intensity dependence. Previously, we demonstrated a spectral encoder using either X-ray luminescence or fluorescence, but the X-ray luminescence required an expensive X-ray source and used ionizing radiation, while the fluorescence sensor suffered from interference from autofluorescence. Here, we used upconversion, which can be provided with a simple fiber-coupled spectrometer with essentially autofluorescence-free signals. The upconversion phosphors provide a low background signal, and the use of closely spaced spectral peaks minimizes spectral distortion from the tissue. The small displacement noise level (precision) through tissue was 2 µm when using a microscope-coupled spectrometer to collect light. We also showed proof of principle for measuring strain on a tendon mimic. The approach provides a simple method to study biomechanics using implantable sensors.
我们描述了一种使用上转换光谱标尺测量组织中微米到毫米位移的方法。测量肌肉、骨骼、韧带和肌腱的刚度（负载下的位移）对于研究和监测损伤愈合非常重要。光学位移测量是有用的，因为它们是敏感的和非侵入性的。光学穿过组织的测量必须使用光谱而不是成像方法，因为组织中的光散射用点扩散函数通常在组织深度周围使图像模糊。此外，光学测量应该具有低背景和最小的强度依赖性。以前，我们使用 X 射线发光或荧光演示了一种光谱编码器，但 X 射线发光需要昂贵的 X 射线源和电离辐射，而荧光传感器受到自发荧光的干扰。在这里，我们使用了上转换，它可以通过一个简单的光纤耦合光谱仪提供，具有基本上无自发荧光的信号。上转换荧光粉提供了低背景信号，并且使用紧密间隔的光谱峰值最小化了来自组织的光谱失真。当使用显微镜耦合光谱仪收集光时，通过组织的小位移噪声水平（精度）为 2 µm。我们还展示了用于测量肌腱模拟物应变的原理证明。该方法提供了一种使用可植入传感器研究生物力学的简单方法。
