Los Angeles, CA--In July 2010, Laser Focus World reported that a lensless microscope developed by researchers at the University of California, Los Angeles (UCLA) was being tested in Africa, and we reported again in April 2011 that lensless tomographic 3D imaging using the same technique was demonstrated. Now, the same lensless microscope technique has been used to identify malaria parasites.

The field-portable lensless optical microscope, which can image large sample areas with sub-micron resolution, is based on an imaging technique termed ‘partially-coherent digital in-line holography.’ The method light-emitting diodes (LEDs) and off-the-shelf digital image sensors with no need for lenses or other bulky optical components; the sensor is held in close proximity to the specimen. The process can even be used to image with a cell phone. UCLA uses a digital image processing technique called pixel super-resolution to convert multiple low-resolution microscope images to a single high-resolution one.

During operation, the light reaching the sensor is either scattered from the object or transmitted unaltered through the sample. The sensor records the intensity of the interference pattern between the scattered and undisturbed light, forming a hologram. The phase of the light field is lost because the sensor responds only to intensity, but iterative phase retrieval algorithms enable recovery of the phase. This allows the field to propagate back to the sample plane, which enables recovery of a microscopic image of the object in both the amplitude and phase channels.

The proximity of the sample to the sensor in this configuration allows the use of the entire FOV of the sensor as the microscope's FOV. This area can be orders of magnitude larger than that of a traditional microscope. With a useful magnification 10-40X, the UCLA approach is appropriate for imaging applications that require testing a large sample volume. In fact, the system was used to image red blood cells infected with malaria parasites. Note that a traditional microscope, due to its limited FOV, would require multiple scans to get a statistically significant number of cells to diagnose malaria.

SOURCE: SPIE; http://spie.org/x51571.xml?ArticleID=x51571