Scientists at Purdue University have developed a self-contained point-of-care diagnostic device that is made completely from paper, is powered by the user’s touch, and provides easy-to-read color-coded results. The self-powered, paper-based electrochemical device (SPED) has been developed for use in remote or resource-limited settings, explains Ramses V. Martinez, Ph.D., who is assistant professor of industrial and biomedical engineering at Purdue University. “SPEDs are inexpensive, lightweight, flexible, and easy to use.…We hope these devices will serve untrained people located in remote villages or military bases to test for a variety of diseases without requiring any source of electricity, clean water, or additional equipment.”
The SPED format is based on microfluidic channels in which electrochemically detected colorimetric assays are carried out. The SPED structure is created in two layers. The top layer is composed of untreated cellulose paper with patterned hydrophobic domains in which the microfluidic channels wick up the sample for testing. The sample can be a fingerprick of blood spotted directly onto a circular feature on the surface of the device. Alternatively, the SPED contains a self-pipetting test zone that can be dipped into a sample.
The assay generates a visible color change result, and the Purdue team has also developed a machine-vision diagnostic application that can automatically identify and quantify each of the colorimetric tests, using a digital image of the SPED, which could be taken by a mobile phone camera, for example. The researchers suggest that the machine-vision application will aid faster diagnosis and could also be used for remote consultation with expert clinicians.
The bottom layer of the SPED is a triboelectric generator, or TEG, fabricated on hydrophobic paper. Rubbing or pressing on the TEG layer effectively generates the electric current needed to power the electrochemical detection. The researchers have in parallel developed a low-cost, hand-held potentiostat that can be attached to the SPED to automate accurate, quantitative electrochemical detection of the biological markers, such as glucose, uric acid, or L-lactate, which they say makes the tests more suitable for untrained users. The battery that powers the potentiostat can even be recharged using the SPED’s on board TEG.
The SPED diagnostics could feasibly be produced cost-effectively using mass printing methods, such as roll-to-roll printing or spray deposition. And because SPEDS are made from paper, they can be disposed of by incineration. “To our knowledge, this work reports the first self-powered, paper-based devices capable of performing rapid, accurate, and sensitive electrochemical assays in combination with a low-cost, portable potentiostat that can be recharged using a paper-based TEG,” Martinez said.
The Purdue team reports on development of the SPED diagnostic the portable potentiostat and the machine-vision algorithm in Advanced Materials Technologies, in a paper entitled “Self-Powered, Paper-Based Electrochemical Devices for Sensitive Point-of-Care Testing.”
The developers say they have used the SPED technology to accurately test for biological markers that can help to detect liver and kidney disorders, malnutrition, and anemia. However, they suggest that producing SPEDs with additional layers will enable the design of more complex assays capable of diagnosing a range of infectious diseases including dengue fever, yellow fever, malaria, HIV, and hepatitis.