Unconventional methods of imaging: computational microscopy and compact implementations

Abstract

In the past two decades or so, there has been a renaissance of optical microscopy research and development. Much work has been done in an effort to improve the resolution and sensitivity of microscopes, while at the same time to introduce new imaging modalities, and make existing imaging systems more efficient and more accessible. In this review, we look at two particular aspects of this renaissance: computational imaging techniques and compact imaging platforms. In many cases, these aspects go hand-in-hand because the use of computational techniques can simplify the demands placed on optical hardware in obtaining a desired imaging performance. In the first main section, we cover lens-based computational imaging, in particular, light-field microscopy, structured illumination, synthetic aperture, Fourier ptychography, and compressive imaging. In the second main section, we review lensfree holographic on-chip imaging, including how images are reconstructed, phase recovery techniques, and integration with smart substrates for more advanced imaging tasks. In the third main section we describe how these and other microscopy modalities have been implemented in compact and field-portable devices, often based around smartphones. Finally, we conclude with some comments about opportunities and demand for better results, and where we believe the field is heading.

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.…”

“…3. A holographic on-chip microscope using green illumination (e.g., ~532 nm) and an off-the-shelf standard CMOS image sensor (kept at room temperature) is practically limited to a particle size of ~250 nm as the detection limit50, which can be further reduced to ~40–50 nm using self-assembled nanolenses2829. Assuming that the sensor performance and other noise parameters remain the same, we used RCS analysis to get an estimate on the improvement of this practical detection limit at shorter wavelengths (Fig.…”

Utilizing social media and video games to control #DIY microscopes

“…Several designs and approaches have been developed for creating low cost light microscopes with reasonable magnification (Cybulski, Clements & Prakash, 2014). Such designs have resulted in microscopes that can operate in a variety of modalities including bright field, dark field and fluorescence (Cybulski, Clements & Prakash, 2014;McLeod & Ozcan, 2016). Cellphone based microscopes have been developed in which the phone's camera is simply employed as the imaging sensor (Contreras-Naranjo, Wei & Ozcan, 2016).…”

“…Indeed, the simplest embodiment of a DIY Microscope can be achieved by simply placing a water drop on the cellphone front facing camera. These various approaches are not only important for educational purposes, but also have a significant role to play in developing low cost diagnostic tools for the lab or the field (Landrain et al, 2013;Baden, 2014;Wong et al, 2008;Garvey, 2012;Watts, 2011;Miller, 2010;Long, 2011;Pelling, 2015;Chai Biotechnologies Inc., 2014a;Wong et al, 2015;Chai Biotechnologies Inc., 2014b;Synbiota, 2017;Cybulski, Clements & Prakash, 2014;McLeod & Ozcan, 2016;Contreras-Naranjo, Wei & Ozcan, 2016;Zhu et al, 2011;Skandarajah et al, 2014;Switz, D'Ambrosio & Fletcher, 2014;Smith et al, 2011;Cavanihac, 2006;Ibanez, 2012;Kim, Gerber & Riedel-Kruse, 2016).…”

High-throughput and automated diagnosis of antimicrobial resistance using a cost-effective cellphone-based micro-plate reader

“…Over the past several years, smartphones and other portable consumer electronics devices have demonstrated their capability for serving as a multiplexed platform for building biomedical imaging, sensing and diagnostic systems12131415161718192021222324252627282930313233343536373839404142. These portable measurement tools typically utilize opto-mechanical attachments used in conjunction with the built-in capabilities of the mobile device (e.g., camera, microphone, GPS) to provide cost-effective, rapid, portable, and highly distributable imaging and sensing systems.…”