Ozcan’s Lensfree Holographic Microscopy and Cellphone Fluorescent Microscopy
Optical microscopy is one of the oldest and most important scientific tools widely used in research and a variety of applications. It is today over $1 billion industry. Professional grade microscopes today are bulky and sensitive instruments, ranging in price from thousands to tens of thousands of dollars , and largely confined to laboratory use. On the other hand there is a great need for portable, inexpensive, microscopes that would allow widespread applications in the field and remote locations, including telemedicine, global health, and environmental monitoring. This is where lensfree holographic microscopy comes in.
LUCAS technology (Lensfree Ultra wide-field Cell Monitoring Array Platform based on Shadow Imaging) invented by Professor Aydogan Ozcan at UCLA and his research group is based on a brilliant insight that light passing through translucent objects like biological samples interferes with itself and creates an interference pattern which can be used to mathematically reconstruct the microscopic image of the object- without any lenses. In practical terms this means that a microscope’s expensive and bulky optics and precision mechanics is replaced by computational resources, which are these days inexpensive and ubiquitous in cell phones, laptops, and the Internet. The result: an inexpensive, small, and robust portable microscope that can be used anywhere. Several early prototypes are shown below.
Research and development continue in several directions: to develop new devices using the same technology platform, to improve performance, and to study new applications.
Prof. Aydogan Ozcan and his PhD student Onur Mudanyali, together with their collaborators in Ozcan’s Research Group at UCLA, have developed an Integrated Rapid-Diagnostic- Test (RDT) reader on a cellphone. RDTs are an important class of relatively inexpensive diagnostics for point-of-care or home applications; largely based on the lateral flow immunoassay technology they have found widespread application at home (i.e. home pregnancy tests), physicians’ offices (thyroid RDT), and public health ( HIV, malaria, influenza, and many other RDTs). The problem is that RDTs today are either qualitative and prone to operator error or require expensive readers, and in any case test results are not automatically recorded and are unavailable to healthcare authorities. The Holomic Rapid Diagnostic Reader (HRDR) on a cellphone, together with its backoffice software application, solves all these problems. It will enable accurate and cost-effective large scale use of RDTs for better healthcare delivery, monitoring and geo-tracking of emerging epidemics, and help public health authorities with epidemics preparedness. For more information see Lab on a Chip 2012, DOI:10.1039/C2LC40235A. Holomic LLC introduced this reader to the market at the AACC Annual Meeting in Los Angeles, July 17-19, 2012. The HRDR is now commercially available.
This microscope is the original implementation of LUCAS technology based on partially-coherent inline transmission digital holography. It is a sophisticated device in terms of design theory and mathematical processing but it is built with inexpensive parts on top of conventional CMOS cameras. It does not require any lenses and precision mechanical parts and it is very small (<6 cuin) and light. And yet, it provides resolution comparable to a quality 20X objective and a field-of-view 20X to 100X larger than a conventional microscope. This means that a search for that rare object– a cell, an organism, or a bacteria– in a sea of other objects can be performed digitally on a single image, rather than with slow and expensive scanning over a large number of images.
In addition to low cost, size, and portability LUCAS technology provides another significant advantage with its ultra-wide field-of-view. But there is a tradeoff in resolution which is typically between one and two microns– still adequate for counting and observation of cells and microorganisms. Resolution can be improved by additional image processing and with only a small increase in cost. This “pixel super resolution” model is shown here, and it achieves a submicron resolution suitable for observation of sub-cellular features.
This microscope adds a reflection mode which is a better choice for imaging dense or connected samples such as tissue slides in histopathology labs. This configuration is still lensfree, small, cost effective, and it has much larger field-of-view than conventional microscopes (albeit smaller than the transmission mode). Wide field of view is especially important when searching for rare cells, for example cancerous cells in pap smears.
Fluorescent microscopy has become very important in recent decades with the development of a wide range of fluorescent markers. The idea here is to engineer fluorescent compounds that would selectively bind to the target cell or bacteria or protein. Detection of that fluorescence can provide significantly higher sensitivity and selectivity than the regular bright field microscopy. The Ozcan Research Group has developed this fluorescent microscope as an attachment to a cellphone. It does not use lensfree holographic technology but it is made possible by innovative engineering and the usual focus on low cost, simplicity, and portability. It has a very wide field-of-view of 81 mm2 allowing significantly larger sample volume than conventional fluorescent microscopes.
Using a similar fluorescen microscope design and a capillary array for a liquid sample cuvette it was possible to detect E. Coli. Capillaries were functionalized with an anti- E. Coli O157:H7 antibody and with quantum dots used as signal reporters. For more details see H. Zhu, U. Sikora, A. Ozcan, Analyst 2012, DOI:10.1039/C2AN35071H
Even larger sample volumes are possible with this device. It images cells dynamically as they flow through a microfluidic channel past the image sensor. A “movie’ is captured as the cells flow and processed mathematically to derive cell count and density. Sample volume is limited only by how much time can be allocated for the test. An important application for this type of testing might be for monitoring HIV+patients. It is expected that this model will play significant role in global health and environmental monitoring.
In biology there is a great need for three dimensional imaging of certain optically accessible model organisms, such as C. Elegans and Zebra fish. What is needed is high throughput and the ability to examine multiple layers and reconstruct a 3-D model. This lensfree tomographic microscope embodies the same principles as in other devices with the additional feature of capturing a series of images at different angles of illumination. Its capability to image a volume of 15mm2 with 1 to 3 micron resolution with a microscope so compact is unparalleled.
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