We present for the first time a lens-free, oblique illumination imaging platform for on-sensor dark- field microscopy and shadow-based 3D object measurements. It consists of an LED point source that illuminates a 5-megapixel, 1.4 µm pixel size, back-illuminated CMOS sensor at angles between 0° and 90°. Analytes (polystyrene beads, microorganisms, and cells) were placed and imaged directly onto the sensor. The spatial resolution of this imaging system is limited by the pixel size (∼1.4 µm) over the whole area of the sensor (3.6×2.73 mm). We demonstrated two imaging modalities: (i) shadow imaging for estimation of 3D object dimensions (on polystyrene beads and microorganisms) when the illumination angle is between 0° and 85°, and (ii) dark-field imaging, at >85° illumination angles. In dark-field mode, a 3-4 times drop in background intensity and contrast reversal similar to traditional dark-field imaging was observed, due to larger reflection intensities at those angles. With this modality, we were able to detect and analyze morphological features of bacteria and single-celled algae clusters.

中文翻译：

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CMOS芯片上的基于反射的无透镜暗场显微镜（RDFM）

我们首次展示了用于传感器暗场显微镜和基于阴影的3D对象测量的无透镜倾斜照明成像平台。它由一个LED点光源组成，该光源以0°至90°的角度照亮5兆像素，1.4 µm像素大小的背照式CMOS传感器。放置分析物（聚苯乙烯珠，微生物和细胞）并将其直接成像到传感器上。该成像系统的空间分辨率受到传感器整个区域（3.6×2.73 mm）的像素大小（约1.4 µm）的限制。我们展示了两种成像方式：（i）阴影成像，用于在照明角度介于0°和85°之间时估算3D对象尺寸（在聚苯乙烯珠和微生物上），以及（ii）在大于85°的照明下进行暗场成像角度。在暗场模式下，观察到背景强度下降了3-4倍，并且与传统的暗场成像类似，对比度反转也有所下降，这是由于在这些角度处的反射强度更大。通过这种方式，我们能够检测和分析细菌和单细胞藻类簇的形态特征。