Lensless Imaging and Sensing

Abstract

High-resolution optical microscopy has traditionally relied on high-magnification and high-numerical aperture objective lenses. In contrast, lensless microscopy can provide high-resolution images without the use of any focusing lenses, offering the advantages of a large field of view, high resolution, cost-effectiveness, portability, and depth-resolved three-dimensional (3D) imaging. Here we review various approaches to lensless imaging, as well as its applications in biosensing, diagnostics, and cytometry. These approaches include shadow imaging, fluorescence, holography, superresolution 3D imaging, iterative phase recovery, and color imaging. These approaches share a reliance on computational techniques, which are typically necessary to reconstruct meaningful images from the raw data captured by digital image sensors. When these approaches are combined with physical innovations in sample preparation and fabrication, lensless imaging can be used to image and sense cells, viruses, nanoparticles, and biomolecules. We conclude by discussing several ways in which lensless imaging and sensing might develop in the near future.

Machine Learning Based Single-Frame Super-Resolution Processing for Lensless Blood Cell Counting

“…For example, the counts of red blood cells (RBC, erythrocytes), white blood cell (WBC, leukocytes), and platelets help the diagnosis of anemia; the CD4+ lymphocyte count is used to monitor the progression of HIV/AIDS [3]. Existing techniques for blood cell counting mainly include manual counting using high magnification optical microscopy with high–numerical aperture objective lenses, or automated counting using commercial flow cytometers.…”

Computational On-Chip Imaging of Nanoparticles and Biomolecules using Ultraviolet Light

“…The direct interference of the background illumination light with the scattered object light creates in-line holograms of the specimen, which are then recorded/digitized by the image sensor chip. The 3D information of the sample is encoded within these holographic interference patterns, which can be extracted by digitally back propagating the holograms to the sample plane revealing microscopic reconstructions, both as amplitude and phase images, of the target objects19224950.…”

“…In order to fully benefit from these technological advances and extend our measurement capabilities outside the laboratory, it is necessary to develop more accessible alternatives to these laboratory-bound devices18. Towards this direction, on-chip holographic microscopy1920212223 offers a robust, cost-effective and high-throughput alternative to some of the existing imaging and sensing techniques. In an on-chip computational microscope, the sample is placed very close (i.e., ≤0.5–1 mm) to an opto-electronic image sensor chip without any imaging lenses in between.…”

Computational sensing of herpes simplex virus using a cost-effective on-chip microscope

“…A unique feature of this lensfree imaging platform is that both amplitude and phase information of the objects are digitally reconstructed from the holographic diffraction patterns captured by the image sensor chip. In this computational microscope, a set of e.g., 20 sub-pixel shifted images is captured and then a super-resolved hologram is obtained by using a lateral-shift based pixel super-resolution method 31–33 . Following the reconstruction of the super-resolved hologram, quantitative phase information of the captured particles is also obtained.…”