Lensfree Optofluidic Microscopy and Tomography

Abstract

Microfluidic devices aim at miniaturizing, automating, and lowering the cost of chemical and biological sample manipulation and detection, hence creating new opportunities for lab-on-a-chip platforms. Recently, optofluidic devices have also emerged where optics is used to enhance the functionality and the performance of microfluidic components in general. Lensfree imaging within microfluidic channels is one such optofluidic platform, and in this article, we focus on the holographic implementation of lensfree optofluidic microscopy and tomography, which might provide a simpler and more powerful solution for three-dimensional (3D) on-chip imaging. This lensfree optofluidic imaging platform utilizes partially coherent digital in-line holography to allow phase and amplitude imaging of specimens flowing through micro-channels, and takes advantage of the fluidic flow to achieve higher spatial resolution imaging compared to a stationary specimen on the same chip. In addition to this, 3D tomographic images of the same samples can also be reconstructed by capturing lensfree projection images of the samples at various illumination angles as a function of the fluidic flow. Based on lensfree digital holographic imaging, this optofluidic microscopy and tomography concept could be valuable especially for providing a compact, yet powerful toolset for lab-on-a-chip devices.

Microfluidics for sperm research

“…Improvements in microfluidic technology will greatly improve upon current pointof-care ART, ultimately making ART more affordable and accessible worldwide for couples affected by male-factor infertility. [52][53][54][55][56][57][58][62][63][64] have emerged since the first work on microfluidic shadow-imaging with CCD sensors to visualize Caenorhabditis elegans [63]. The CMOS sensor is preferred over CCDs for point-of-care sperm research because it is low in cost, gives a higher-resolution image, and has low heat dissipation [65].…”

Lensless microscope based on iterative in-line holographic reconstruction

“…Phase retrieval algorithm based on iteration between sample plane and detection plane is one of the important image reconstruction methods to suppress the twin-image of in-line holography [5][6][7]. A popular method is to choose a threshold to define the sample support [8], which was used as constraint in the iteration. However, there are two limitations for this method.…”

Spectral Demultiplexing in Holographic and Fluorescent On-chip Microscopy

“…2. Under the assumption that the illumination is sufficiently narrow-band (e.g., ~3–5 nm), these spatial under-sampling artifacts can be well addressed by implementing pixel super resolution293031 methods on lensfree geometries based on e.g., source293132 or object shifting2433. Another challenge with on-chip imaging is due to the absence of lenses; i.e., one needs to reconstruct diffracted fields of the objects, which constitute (i) partially-coherent fields as in the case of holography and (ii) incoherent fields as in the case of fluorescent objects.…”