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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - SUPERCELL (Single-Use paPER-based fuel CELLs)

Teaser

Summary

Point-of-Care testing (PoCT) devices have risen as a solution to one of the most relevant challenges in healthcare of the past ten years, which is the need of taking diagnostic techniques from specialized labs and hospitals to the place of need. One of the most successful and well-stablished PoC devices are immunocromatographic test strips (also known as lateral flow tests), as they fulfill most of the guidelines set by the World Health Organization (WHO) for the development of diagnostics in resource-poor settings. These tests must be ASSURED (i.e. affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and delivered to those who need it). Today, these products span across a very wide range of industries and analytes. Their output signal is based on colorimetric detection. However, the limited sensitivity of these tests makes it difficult to obtain quantitative results or to perform successful multi-analyte testing, as results are to be read by the naked-eye. Up to date, signal quantification has been assessed by developing dedicated optical electronic readers that translate the visual signal into a digital output. However, this solution is not cost-effective for personalized healthcare â€“ except for chronic diseases such diabetes - or for diagnostics in poor resources-settings.
SUPERCELL proposes to develop single use fuel cells as a key component of smart and single use point-of-care devices. The microfuel cells are inspired in the lateral flow devices in terms of design, manufacturing processes and materials and take advantage of paper capillarity to keep a continuous flow of reactants. At the same time, they are conceived to follow the same life-cycle than the test strips to be powered. These fuel cells generate energy directly from the fluid to be tested in the point-of-care device (namely blood, urine, saliva, sweat...) by oxidizing the molecules present in the samples (glucose, ethanol, ureaâ€¦). This will make possible to deliver power on-board that can be used to enable measuring and communicating functions. As the amount of power generated by the fuel cell depends on the concentration of the molecules to be oxidized, the project also explores the viability of developing self-powered point-of-care sensors, in which the fuel cell acts both as a sensor and a power source. In this way, the paradigm â€œsensor â€“ electronics â€“ power sourceâ€ typically used to develop a PoC device will be extremely simplified, yielding a new generation of intelligent, cost-effective and ASSURED devices.

Work performed

During its first 30-month period, the project has developed a battery-like fuel cell able to produce as much power density as a button cell. This prototype is a stand-alone power source that integrates a paper-based hydrogen fuel cell with a customized chemical heater that produces hydrogen in-situ upon the addition of a liquid. The device operates by capillary action and takes advantage of the hydrogen released as a by-product of an exothermic reaction used in point-of-care diagnostics. The paper-based fuel cell has been able to achieve a maximum power of approximately 25 mW, which is suitable for powering a diversity of electrical devices such as commercially available digital pregnancy tests and glucometers. The heat released in the exothermic reaction can also be used to heat the liquid to be analysed and to enhance the fuel cell catalysis.
Moreover, the project has explored the energy available in a drop of blood in order to evaluate its capability to power a point-of-care device. As any fuel cell, the total energy that can be generated scales down with fuel volume. Unlike other biological sources of energy, blood is limited to a volume of 50ul in finger prick applications, which generates no more than 5-10 mJ (with peak powers of around 50-100 uW). In this sense, the project has explored different strategies to increase the generated power such as creating a capillary flow that enhance convective mass transport or assisting the blood fuel cell with a co-integrated paper battery.
Finally, the project has also opened another unforeseen avenue by presenting a new method for conductivity measurement of biological samples with the use of a liquid-activated paper battery as a sensor. Liquid-activated batteries are devices that consist of at least two electroactive electrodes connected by a hydrophilic material able to hold a fluid and therefore share a lot of features with the fuel cells developed in this project. This kind of battery starts to function upon the addition of a fluid, which acts as the battery electrolyte. For a particular configuration of the battery materials and design, the battery internal resistance will be fully dependent on the conductivity of the liquid sample poured in its paper core. This means that the battery can be used as a conductivity sensor, whose generated power depends on the conductivity of the sample used to activate it. This opens a new paradigm in the world of self-powered sensors, as conductivity is a parameter never tackled before. Taking in advantage the change this new approach, a paper battery as the core of the self-powered device has been optimized to perform a conductivity measurement of sweat samples in order to perform easy screening of Cystic Fibrosis disease in children.
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Final results

Up to now, the project has set the technological basis for optimization of energy generation with body fluids in in-vitro conditions. A battery-like fuel cell that simultaneously provides electrical and heating power to a lateral flow test has been successfully developed and tested. Energy generation with a drop of blood has also been evaluated and optimized. This allows evaluating the capability of the sample to enable functions in an electronic circuit. Finally the concept of â€œself-poweredâ€ conductivity sensor has been demonstrated for the first time and applied to cystic fibrosis screening. The paper has been submitted to a journal and is currently under revision.
For the next 30 months of the project, we plan to prove the concept of self-powered glucose sensor and extend it to other analytes such as ethanol in saliva. We will also explore the possibility of tuning the energy generated by the fuel cell under the presence of antibodies in the biological sample, which will lead to the development of a self-powered immunosensor. Finally, we will extend the applicability of the conductivity battery sensor to selective ion detection, which can have an important impact in wearable portable devices.