This simple and portable diagnosis method uses the change in position of small beads levitating between two magnets to detect T. cruzi antibodies. To run a test, a single drop of blood is extracted by the finger of the patient and deposited in a test tube filled with a solution of Magnetic Levitating Microbeads (MLBs). MLBs attract T.cruzi antibodies, which attach to their surface and modify the density of the beads. When the test tube containing the MLBs is placed between two antialigned magnets, they levitate according to their density. The higher density of MLBs with T. cruzi antibodies attached makes them to levitate at a lower height, allowing the visual diagnosis of Chagas disease by the naked eye. (Graphic provided by the Purdue FlexiLab)

"Chagas, a chronic disease found predominantly in Latin America, is typically asymptomatic at its early stages of infection," explained Ramses Martinez, assistant professor of industrial engineering and biomedical engineering. "This makes its early diagnosis and effective treatment very difficult, and significantly decreases the patient's survival chances. Conventional parasitic tests for the diagnosis of the disease are highly specific but cannot provide enough sensitivity during the chronic stage of the disease due to the reduced parasite load. As a consequence, clinical tests for Chagas disease commonly used in hospitals for diagnosis and the screening of blood donations are based on the sensitive detection of the specific antibodies that infected patients develop when they get infected. Unfortunately, these blood tests must be performed by highly trained personnel in relatively well-equipped laboratories, making it impossible to diagnose patients living in resource-limited settings." 

"Portable and power-free serodiagnosis of Chagas disease using magnetic levitating microbeads" (Advance Article published in Analyst, 31 Jul 2018)

Abstract

This work describes the detection of anti-T. cruziti- antibodies in whole blood solutions using magnetic levitating microbeads (MLμBs). This simple diagnostic method can be easily performed by minimally trained personnel using an inexpensive and portable magnetic stage that requires no electricity. A multi-phase test tube containing the MLμBs facilitates the sequential incubation, filtering, and reading of the immunoassays. The diagnostic method starts by adding a blood sample to the top phase of the test tube where the anti-T. cruzi antibodies present in the blood attach to the T. cruzi antigens on the surface of the MLμBs. Shaking the test tube after incubation mixes the top layer with a paramagnetic medium loaded with SiO 2 microcrystals. The attachment of SiO 2 microcrystals to those MLμBs bound to T. cruzi antibodies decreases their levitation height once the tube is placed between two antialigned permanent magnets. Measuring the levitation height of MLμBs enables the accurate detection and quantification of anti-T. cruzi antibodies in the blood across the clinically relevant range, with a detection limit of 5 μg mL − 1 . The small size of the test tubes facilitates the simultaneous analysis of over 50 different samples. MLμBs act as partial collimators for non-polarized light, facilitating their visual identification by the naked eye or by projecting incident light on a thin paper screen. A machine-vision algorithm was created to automatically interpret the results of the MLμB tests from a digital image, resulting in a rapid, accurate, and user-friendly assay for Chagas disease that can be used in resource-limited settings.