Point of care diagnostic tools are essential in providing timely guidance for the identification of disease and the choice of appropriate treatment options. While accurate and rapid diagnostic tests at the time and place of patient care are needed both for the developed and developing world, the lack of infrastructure such as stable electricity and trained staffs add additional challenges to design affordable, user-friendly, robust, and equipment-free devices that can be used in poor-resource settings¹. Conventional approaches using lateral flow assays and paper microfluidics offer cost-effective options; however, the application is often limited to the diseases that can be detected with small sample volume².

Over the last decade, we have developed a handful of centrifugal microfluidic technologies for “sample-in and answer-out” type devices. Directly from raw biological samples, fully automated assays for molecular analysis of pathogens³, immunoassays⁴, and enrichment of circulating biomarkers for liquid biopsy^5-8 have been demonstrated. However, none of these previous devices can be deployed in extreme point of care conditions where electricity is often intermittent or non-existent.

Inspired by the fidget spinner, a boomerang-shaped toy with a ball bearing in the center to spin freely with little friction, we developed a diagnostic fidget spinner (Dx-FS) that allows filtration of 1-mL of undiluted urine samples in 5 minutes (Movie1, 2). Regardless the highly variable spinning speed depending on the operator, with just one or two spins by hand, anyone could be able to enrich the pathogens 100-fold allowing naked-eyes detection and identification without the need of laborious bacteria culture processes.

Movie 1. fidget spinner toy (left) and a diagnostic-fidget spinner (right).

The secret to the rapid, clog-free, and robust enrichment of pathogen is in the fluid-assisted separation technology (FAST) that we have previously developed for the isolation of circulating tumor cells from whole blood⁵. In FAST-based particle filtration, the fluid flow caused by the centrifugal force is perpendicular to the filtration flow through the membrane where the drainage chamber underneath remains fully filled. This ensures uniform filtration across the entire membrane and significantly reduces the hydrodynamic resistance.

The current diagnosis of UTIs in rural areas takes about a week, which includes healthcare visits, empirical antibiotic prescription, urine shipment to the laboratory, and urinalysis and culturing at the laboratory. The required infrastructure is unfortunately absent in many places and thus symptom-based diagnosis is common, which results in overuse or misuse of antibiotics. With all doubts we stepped out of the lab to check if the device works in real world. It was a very interesting part of our journey to work along patients and clinical staff. A picture of the box with many devices that were used for testing is shown in Figure 1.

Figure 1. Photographs of diagnostic-fidget spinners used in hospitals in India.

In collaboration with doctors in local hospitals in India, we tested urine samples from 39 UTI suspects and confirmed that symptom-based diagnosis combined with a Dx-FS can identify patients who need antimicrobials within 50 minutes, thereby reducing antimicrobial misuse.

Furthermore, we did isothermal amplification on Dx-FS to identify the bacterial strain and performed a rapid antimicrobial susceptibility test (AST) for two antimicrobial drugs on 30 clinical isolates from 30 patients with a UTI using Dx-FS in South Korea, where we could deliver 100% accurate results within 2 hours. Compared with conventional AST methods, a Fidget-AST can be performed instrument free by someone with minimal training.

Overall, this simple, hand-powered, portable device with estimated material cost of < 50 cent allows rapid enrichment of pathogens from human urine samples, showing high potential for future low-cost POCT diagnostic applications.

Movie 2. UTI test procedure using Dx-FS.

The full paper discussed in this post can be accessed here: https://www.nature.com/articles/s41551-020-0557-2

Prof. Yoon-Kyoung Cho’s group website: http://fruits.unist.ac.kr/

References:

1. Michael, I.J., Kim, T.H., Sunkara, V. & Cho, Y.K. Challenges and Opportunities of Centrifugal Microfluidics for Extreme Point-of-Care Testing. Micromachines 7 (2016).

2. Bhamla, M.S. et al. Hand-powered ultralow-cost paper centrifuge. Nature Biomedical Engineering 1, 0009 (2017).

3. Cho, Y. et al. One-step pathogen specific DNA extraction from whole blood on a centrifugal microfluidic device. Lab on a Chip 7, 565-573 (2007). 

4. Park, J., Sunkara, V., Kim, T.-H., Hwang, H. & Cho, Y.-K. Lab-on-a-Disc for Fully Integrated Multiplex Immunoassays. Analytical Chemistry 84, 2133-2140 (2012).

5. Kim, T.-H. et al. FAST: Size-Selective, Clog-Free Isolation of Rare Cancer Cells from Whole Blood at a Liquid–Liquid Interface. Analytical Chemistry 89, 1155-1162 (2017).

6. Woo, H.-K. et al. Exodisc for Rapid, Size-Selective, and Efficient Isolation and Analysis of Nanoscale Extracellular Vesicles from Biological Samples. ACS Nano 11, 1360-1370 (2017).

7. Woo, H.K. et al. Urine-based liquid biopsy: non-invasive and sensitive AR-V7 detection in urinary EVs from patients with prostate cancer. Lab on a Chip 19, 87-97 (2019).

8.  Sunkara, V. et al. Fully Automated, Label-Free Isolation of Extracellular Vesicles from Whole Blood for Cancer Diagnosis and Monitoring. Theranostics 9, 1851-1863 (2019).