University of Maryland College Park (UMCP), College Park, MD 20742, USA.
Analyst. 2012 Nov 7;137(21):5011-7. doi: 10.1039/c2an35729a. Epub 2012 Sep 12.
To address the needs of medical diagnostics in resource-poor settings, it is necessary to develop low cost, simple and portable Point of Care detectors for integrated medical diagnostics. Previously, we have described a simple lensless fluorometer with sensitivity in the range of current ELISA plate readers. The key to the lensfree fluorometer is the uniform spatial distribution of light, which we achieved using a simple optical collimator based on a "stack of pinholes" (a stack of black PMMA plates with arrays of pinholes machined via laser) enabling the light to be collimated from the LED light source through the necessary wavelength filters and the assay's microfluidics directly onto the CCD without a lens. In this paper, we describe the optical principle for designing these Söller collimators for lensfree CCD-based fluorometry. The illuminating surface was modeled as a collection of differential areas emitting uniformly and spherically, and the intensity contribution of each emitting area was summed over the detector surface. To compute the final light intensity distribution from such a differential model we derived an integral equation to sum the individual intensity contributions from the two-dimensional emitting surface. The equation is for a single-hole collimator. Light intensity measurements were taken by placing a collimator with a particular aspect ratio (the ratio of hole length to diameter (L/d)) over the CCD image sensor and capturing an image. The resulting image is the 2D light intensity profile generated by the collimator. As the aspect ratio is increased the slope of the light intensity profile increases, corresponding to an increased degree of collimation. To test the model, the measured maximum and mean light intensities were compared with the theoretical predictions generated from the model. There was an agreement between the variation of the mean (R(2) = 0.990) and maximum (R(2) = 0.938) values of light intensities with aspect ratios based modeling. These profile measurements suggest an excellent agreement with the theoretical predictions. The integral equation presented here can be used to perfect the design of the optical Söller collimator. These results may lead to the development of more effective Söller collimators for lensfree CCD-based fluorometry for use in simple low cost lensfree optical detectors with the potential to enhance the accessibility and the quality of health care for underserved populations.
为了满足资源匮乏环境下的医学诊断需求，有必要开发用于集成医学诊断的低成本、简单且便携的即时检测设备。之前，我们已经描述了一种具有与当前 ELISA 板读数器相当的灵敏度的简单无透镜荧光计。无透镜荧光计的关键是光的均匀空间分布，我们通过使用基于“堆叠针孔”的简单光学准直器实现了这一点（堆叠的黑色 PMMA 板，上面通过激光加工有阵列针孔），从而使光从 LED 光源通过必要的波长滤波器和分析物的微流控器件直接准直到 CCD 上，无需透镜。在本文中，我们描述了为无透镜基于 CCD 的荧光计设计这些 Söller 准直器的光学原理。照明表面被建模为一个均匀且球状发射的微分面积集合，并且从每个发射区域到探测器表面的强度贡献被求和。为了从这种微分模型计算最终的光强分布，我们推导出了一个积分方程来对二维发射表面的各个强度贡献求和。该方程适用于单孔准直器。通过将具有特定纵横比（孔长与直径之比 (L/d)）的准直器放置在 CCD 图像传感器上并捕获图像来进行光强测量。得到的图像是准直器生成的 2D 光强轮廓。随着纵横比的增加，光强轮廓的斜率增加，对应于准直程度的增加。为了测试模型，将测量的最大和平均光强与模型生成的理论预测进行比较。基于模型的光强纵横比变化具有很好的一致性（平均值的 R(2) = 0.990，最大值的 R(2) = 0.938）。这些轮廓测量结果表明与理论预测具有极好的一致性。本文提出的积分方程可用于完善光学 Söller 准直器的设计。这些结果可能导致更有效的 Söller 准直器用于无透镜基于 CCD 的荧光计，用于简单的低成本无透镜光学探测器，从而有可能提高服务不足人群的医疗保健的可及性和质量。
