Plastic Fluorescence Microscope Brings Diagnostic Care to Rural Poor

A miniature plastic digital fluorescence microscope that can quantify white blood cell levels in patients aims to improve disease detection in rural parts of the world.

The inexpensive point-of-care device examines blood smears, allowing health care workers to identify and quantify lymphocytes, monocytes and granulocytes — three types of white blood cells — in a drop of blood mixed with the staining compound acridine orange.

"One of the driving aspects of the project is the cost of the sample or sample preparation," said Tomasz Tkaczyk, an associate professor in the department of bioengineering at Rice University. "Many systems which work for point-of-care applications have quite expensive cartridges. The goal of this research is to make it possible for those in impoverished areas to be able to get the testing they need at a manageable price point."

An assembled 3D-printed white blood cell microscope on an optical bench, with 1-in. spacing between the holes for reference. Courtesy of Alessandra Forucci/Rice University.

Also involved in the project was Rice professor Rebecca Richards-Kortum, whose research involves translating molecular imaging research to point-of-care diagnostics.

The staining compound is repelled by water at neutral pH, which allows it to easily diffuse through cellular and nuclear membranes, where it turns green or red when encountering DNA or RNA, respectively, with emission maximums at 525 and 650 nm. By optimizing a microscope for these emission peaks, the researchers were able to quantify the white blood cells in a sample consisting only of 20 μL of dye, 20 μL of whole blood and a glass slide with a coverslip.

The ratio in color allows health care workers to differentiate between the white blood cell types; quantifying this three-part white blood cell count is an essential first step in diagnosing a number of disorders.

To fabricate the microscope's objective — which consists of one polystyrene lens and two polymethyl methacrylate aspheric lenses — the researchers used a single-point diamond turning lathe. The lenses were then enclosed in an all-plastic, 3D-printed microscope housing and objective. Once constructed, the microscope provided a field of view of 1.2 mm, allowing for at least 130 cells to be present for statistical significance when quantifying white blood cells. Additionally, the microscope doesn't require any manual adjustment between samples once constructed.

The prototype microscope, which comprises an LED light source, power supply, control unit, optical system and image sensor, costs less than $3,000 to construct. At production levels upwards of 10,000 units, the researchers estimate the price would fall to around $600 for each unit, with a per-test cost of a few cents.

The research was funded by a Bill and Melinda Gates Foundation challenge grant, and was published in Biomedical Optics Express (doi: 10.1364/boe.6.004433).