Inexpensive Compact Microscope Diagnoses Tuberculosis

The microscope has been tested on samples from patients with TB and performed as well as a reference-standard fluorescence microscope. The microscope weighs 1.1 kg and is inexpensive, transportable, and flexible. It could be used in clinics in developing countries that have limited access to laboratory equipment and may lack electricity.

The Global Focus microscope uses a battery-operated LED-based flashlight as the light source and achieves a maximum spatial resolution of 0.8 µm at 1000× magnification in fluorescence mode. The resolution of the microscope is 3.2 times larger than the predicted resolution of 0.25 µm for the system. No condenser lens is used and the parabolic reflector in the flashlight housing serves to direct and shape light towards the sample.

The microscope was used to analyze smear samples from 19 patients suspected of having TB, an infectious disease that usually attacks the lungs and can be fatal if not treated. The TB smear samples came from Tehran, Iran, and they were tested in The Methodist Hospital Research Institute (TMHRI; Houston, TX, USA). Slides were stained with auramine orange and evaluated as being positive or negative for Mycobacterium tuberculosis with both the new portable fluorescence microscope and a laboratory-grade fluorescence microscope. Similar findings were obtained in 98.4% of the samples tested when compared with those from a standard reference microscope. M. tuberculosis bacilli could be clearly resolved at 400× magnification.

Rebecca Richards-Kortum, Ph.D., at Rice University (Houston, TX, USA), where the microscope was first constructed, said, "The microscope, which is portable, durable and inexpensive, could be used to diagnose tuberculosis in community or rural health centers with limited infrastructure in the developing world, promoting early detection and successful treatment of the disease.” The results of the study were published online in 2010 in PloS ONE.

Related Links:
The Methodist Hospital Research Institute