Immuno-battery: A single use self-powered immunosensor for REASSURED diagnostics.

In this work, we present a novel self-powered approach totally independent from any external energy source. We have developed a self-powered paper-based immunosensor that generates energy in the presence of the biomarker in the sample. In particular, the device - which has been labeled as Immuno-Battery - makes use of magnesium as anode and the widely employed HRP-labeled antibody as cathodic catalyst to detect C-reactive protein (CRP) presence in artificial samples. Feasibility of self-powered sensing is proved by submitting the immuno-battery to a resistive load. In this regime, the sensor provides operation voltages above 1.55 V and maximum power densities from 40 to 571 µW cm-2 that allow for future implementation of an electronic readout circuit. We have demonstrated that sensitivity of the system is not compromised by the self-powered mode operation, as the LOD value delivered by our battery (20 ± 2 ng mL-1) is compliant with LOD values reported for protein detection in paper-based electrochemical immunoassays with chronoamperometric methods. Moreover, as a case study, a LOD of 269 ± 39 ng mL-1 is obtained for CRP detection, in accordance with available commercial high-sensitivity CRP detection kits. This proof-of-concept opens the path towards the development of digital diagnostic devices in a sustainable and affordable manner.

Nanoceria dissolution at acidic pH by breaking off the catalytic loop.

This manuscript proves the reproducibility and robustness of cerium oxide nanoparticles, nanoceria, employed as a chemical reagent with oxidizing capacity (as an electron sink) at acidic pH. Unlike nanoceria multi-enzyme-mimetic capabilities at neutral or high pH, nanoceria can behave as a stoichiometric reagent at low pH where insoluble Ce4+ ions transform into soluble Ce3+ in the nanocrystal that finally dissolves. This behaviour can be interpreted as enzyme-like when nanoceria is in excess with respect to the substrate. Under these conditions, the Ce3+/Ce4+ ratio in the NPs can easily be estimated by titration with ferrocyanide. This procedure could become a rapid assessment tool for evaluating nanoceria capacity in liquid environments.

A plant-like battery: a biodegradable power source ecodesigned for precision agriculture.

The natural environment has always been a source of inspiration for the research community. Nature has evolved over thousands of years to create the most complex living systems, with the ability to leverage inner and outside energetic interactions in the most efficient way. This work presents a flow battery profoundly inspired by nature, which mimics the fluid transport in plants to generate electric power. The battery was ecodesigned to meet a life cycle for precision agriculture (PA) applications; from raw material selection to disposability considerations, the battery is conceived to minimize its environmental impact while meeting PA power requirements. The paper-based fluidic system relies on evaporation as the main pumping force to pull the reactants through a pair of porous carbon electrodes where the electrochemical reaction takes place. This naturally occurring transpiration effect enables to significantly expand the operational lifespan of the battery, overcoming the time-limitation of current capillary-based power sources. Most relevant parameters affecting the battery performance, such as evaporation flow and redox species degradation, are thoroughly studied to carry out device optimization. Flow rates and power outputs comparable to those of capillary-based power sources are achieved. The prototype practicality has been demonstrated by powering a wireless plant-caring device. Standardized biodegradability and phytotoxicity assessments show that the battery is harmless to the environment at the end of its operational lifetime. Placing sustainability as the main driver leads to the generation of a disruptive battery concept that aims to address societal needs within the planetary environmental boundaries.

Microfluidics for Electrochemical Energy Conversion.

Electrochemical energy conversion is an important supplement for storage and on-demand use of renewable energy. In this regard, microfluidics offers prospects to raise the efficiency and rate of electrochemical energy conversion through enhanced mass transport, flexible cell design, and ability to eliminate the physical ion-exchange membrane, an essential yet costly element in conventional electrochemical cells. Since the 2002 invention of the microfluidic fuel cell, the research field of microfluidics for electrochemical energy conversion has expanded into a great variety of cell designs, fabrication techniques, and device functions with a wide range of utility and applications. The present review aims to comprehensively synthesize the best practices in this field over the past 20 years. The underlying fundamentals and research methods are first summarized, followed by a complete assessment of all research contributions wherein microfluidics was proactively utilized to facilitate energy conversion in conjunction with electrochemical cells, such as fuel cells, flow batteries, electrolysis cells, hybrid cells, and photoelectrochemical cells. Moreover, emerging technologies and analytical tools enabled by microfluidics are also discussed. Lastly, opportunities for future research directions and technology advances are proposed.

Self-Powered Potentiometric Sensors with Memory.

Potentiometric sensors induce a spontaneous voltage that indicates ion activity in real time. We present here an advanced self-powered potentiometric sensor with memory. Specifically, the approach allows for one to record a deviation from the analyte's original concentration or determine whether the analyte concentration has surpassed a threshold in a predefined time interval. The sensor achieves this by harvesting energy in a capacitor and preserving it with the help of a diode. While the analyte concentration is allowed to return to an original value following a perturbation over time, this may not influence the sensor readout. To achieve the diode function, the sensor utilizes an additional pair of driving electrodes to move the potentiometric signal to a sufficiently high base voltage that is required for operating the diode placed in series with the capacitor and between the sensing probes. A single voltage measurement across the capacitor at the end of a chosen time interval is sufficient to reveal any altered ion activity occurring during that period. We demonstrate the applicability of the sensor to identify incurred pH changes in a river water sample during an interval of 2 h. This approach is promising for achieving deployable sensors to monitor ion activity relative to a defined threshold during a time interval with minimal electronic components in a self-powered design.

Self-Powered Potentiometric Sensor Transduction to a Capacitive Electronic Component for Later Readout.

Potentiometric sensors operate as galvanic cells where the voltage is spontaneously generated as a function of the sample composition. We show here that energy can be harvested, stored during the sensing process without external power, and physically isolated from the sensor circuit for later readout. This is accomplished by placing an electronic capacitor as a portable transduction component between the indicator and the reference electrode at the point where one would ordinarily connect the high-input-impedance voltmeter. The voltage across this isolated capacitor indicates the originally measured ion activity and can be read out conveniently, for example, using a simple handheld multimeter. The capacitor is shown to maintain the transferred charge for hours after its complete disconnection from the sensor. The concept is demonstrated to detect the physiological concentrations of K+ in artificial sweat samples. The methodology provides a readout principle that could become very useful in portable form factors and opens possibilities for potentiometric detection in point-of-care applications and inexpensive sensing devices where an external power source is not desired.

Paper-Based Batteries as Conductivity Sensors for Single-Use Applications.

We present a novel approach to measure ionic conductivity with a self-powered strategy. In particular, we propose the use of a paper-based battery as a sensor. The battery sensor unit consists of two electrodes placed side-by-side and covered by a piece of hydrophilic paper strip. The electrodes are externally connected to a resistive element. The addition of the fluid to be sensed-which acts as the electrolyte-activates the battery, which generates an output voltage that is dependent on the conductivity of the liquid sample. The device, which is conceived as a single-use disposable sensor, has been tested with different synthetic and biological liquid samples. The battery sensor effectiveness has been assessed by comparing its performance with a commercial laboratory conductometer. The device opens new avenues for conductivity monitoring in small portable and wearable devices, as it simplifies the number of electronic components and the need of additional power sources.

Standalone operation of an EGOFET for ultra-sensitive detection of HIV.

A point-of-care (POC) device to enable de-centralized diagnostics can effectively reduce the time to treatment, especially in case of infectious diseases. However, many of the POC solutions presented so far do not comply with the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment free, and deliverable to users) guidelines that are needed to ensure their on-field deployment. Herein, we present the proof of concept of a self-powered platform that operates using the analysed fluid, mimicking a blood sample, for early stage detection of HIV-1 infection. The platform contains a smart interfacing circuit to operate an ultra-sensitive electrolyte-gated field-effect transistor (EGOFET) as a sensor and facilitates an easy and affordable readout mechanism. The sensor transduces the bio-recognition event taking place at the gate electrode functionalized with the antibody against the HIV-1 p24 capsid protein, while it is powered via paper-based biofuel cell (BFC) that extracts the energy from the analysed sample itself. The self-powered platform is demonstrated to achieve detection of HIV-1 p24 antigens in fM range, suitable for early diagnosis. From these developments, a cost-effective digital POC device able to detect the transition from "healthy" to "infected" state at single-molecule precision, with no dependency on external power sources while using minimal components and simpler approach, is foreseen.

An Organic Redox Flow Cell-Inspired Paper-Based Primary Battery.

A portable paper-based organic redox flow primary battery using sustainable quinone chemistry is presented. The compact prototype relies on the capillary forces of the paper matrix to develop a quasi-steady flow of the reactants through a pair of porous carbon electrodes without the need of external pumps. Co-laminar capillary flow allows operation Under mixed-media conditions, in which an alkaline anolyte and an acidic catholyte are employed. This feature enables higher electrochemical cell voltages during discharge operation and the utilization of a wider range of available species and electrolytes and provides the advantage to form a neutral or near-neutral pH as the electrolytes neutralize at the absorbent pad, which allows a safe disposal after use. The effects of the device design parameters have been studied to enhance battery features such as power output, operational time, and fuel utilization. The device achieves a faradaic efficiency of up to 98 %, which is the highest reported in a capillary-based electrochemical power source, as well as a cell capacity of up to 11.4 Ah L-1 cm-2 , comparable to state-of-the-art large-scale redox flow cells.

Self-powered smart patch for sweat conductivity monitoring.

A self-powered skin patch for the measurement of sweat conductivity is presented. The key component of the patch consists of a paper battery that is activated upon absorption of sweat. This body fluid acts as the battery electrolyte, the conductivity of which has a direct impact on the battery-generated output power and voltage. This particular behaviour enables the operation of a very simple and robust conductivity sensor in direct current mode without needing an external power source. The device presented in this paper takes advantage of this new measurement method to develop a sweat patch for screening cystic fibrosis that operates with an extremely simple electronic circuit that minimizes its cost and environmental impact. The patch provides an unambiguous digital result that can be read in an electrochromic display and yields 95% sensitivity and 100% specificity when tested with artificial eccrine perspiration samples.

'Plug-and-Power' Point-of-Care diagnostics: A novel approach for self-powered electronic reader-based portable analytical devices.

This paper presents an innovative approach in the portable Point-of-Care diagnostics field, the Plug-and-Power concept. In this new disposable sensor and plug-and-play reader paradigm, the energy required to perform a measurement is always available within the disposable test component. The reader unit contains all the required electronic modules to run the test, process data and display the result, but does not include any battery or power source. Instead, the disposable part acts as both the sensor and the power source. Additionally, this approach provides environmental benefits related to battery usage and disposal, as the paper-based power source has non-toxic redox chemistry that makes it eco-friendly and safe to follow the same waste stream as disposable test strips. The feasibility of this Plug-and-Power approach is demonstrated in this work with the development of a self-powered portable glucometer consisting of two parts: a test strip including a paper-based power source and a paper-based biofuel cell as a glucose sensor; and an application-specific battery-less electronic reader designed to extract the energy from the test strip, process the signal provided and show the glucose concentration on a display. The device was tested with human serum samples with glucose concentrations between 5 and 30 mM, providing quantitative results in good agreement with commercial measuring instruments. The advantages of the present approach can be extended to any kind of biosensors measuring different analytes and biological matrices, and in this way, strengthen the goals of Point-of-Care diagnostics towards laboratory decentralization, personalized medicine and improving patient compliance.

Paper-based microfluidic biofuel cell operating under glucose concentrations within physiological range.

This work addresses the development of a compact paper-based enzymatic microfluidic glucose/O2 fuel cell that can operate using a very limited sample volume (≈35µl) and explores the energy generated by glucose at concentrations typically found in blood samples at physiological conditions (pH 7.4). Carbon paper electrodes combined with a paper sample absorption substrate all contained within a plastic microfluidic casing are used to construct the paper-based fuel cell. The anode catalysts consist of glucose dehydrogenase and [Os(4,4'-dimethoxy-2,2'-bipyridine)2(poly-vinylimidazole)10Cl]+ as mediator, while the cathode catalysts were bilirubin oxidase and [Os(2,2'-bipyridine)2(poly-vinylimidazole)10Cl]+ as mediator. The fuel cell delivered a linear power output response to glucose over the range of 2.5-30mM, with power densities ranging from 20 to 90µWcm-2. The quantification of the available electrical power as well as the energy density extracted from small synthetic samples allows planning potential uses of this energy to power different sensors and analysis devices in a wide variety of in-vitro applications.

Comprehensive characterization and understanding of micro-fuel cells operating at high methanol concentrations.

We report on the analysis of the performance of each electrode of an air-breathing passive micro-direct methanol fuel cell (µDMFC) during polarization, stabilization and discharge, with CH3OH (2-20 M). A reference electrode with a microcapillary was used for separately measuring the anode the cathode potential. Information about the open circuit potential (OCP), the voltage and the mass transport related phenomena are available. Using 2 M CH3OH, the anode showed mass transport problems. With 4 and 6 M CH3OH both electrodes experience this situation, whereas with 10 and 20 M CH3OH the issue is attributed to the cathode. The stabilization and fuel consumption time depends mainly on the cathode performance, which is very sensitive to fuel crossover. The exposure to 20 M CH3OH produced a loss in performance of more than 75% of the highest power density (16.3 mW·cm(-2)).

Membraneless glucose/O2 microfluidic enzymatic biofuel cell using pyrolyzed photoresist film electrodes.

Biofuel cells typically yield lower power and are more difficult to fabricate than conventional fuel cells using inorganic catalysts. This work presents a glucose/O2 microfluidic biofuel cell (MBFC) featuring pyrolyzed photoresist film (PPF) electrodes made on silicon wafers using a rapid thermal process, and subsequently encapsulated by rapid prototyping techniques into a double-Y-shaped microchannel made entirely of plastic. A ferrocenium-based polyethyleneimine polymer linked to glucose oxidase (GOx/Fc-C6-LPEI) was used in the anode, while the cathode contained a mixture of laccase, anthracene-modified multi-walled carbon nanotubes, and tetrabutylammonium bromide-modified Nafion (MWCNTs/laccase/TBAB-Nafion). The cell performance was studied under different flow-rates, obtaining a maximum open circuit voltage of 0.54 ± 0.04 V and a maximum current density of 290 ± 28 µA cm(-2) at room temperature under a flow rate of 70 µL min(-1) representing a maximum power density of 64 ± 5 µW cm(-2). Although there is room for improvement, this is the best performance reported to date for a bioelectrode-based microfluidic enzymatic biofuel cell, and its materials and fabrication are amenable to mass production.

Tolerant chalcogenide cathodes of membraneless micro fuel cells.

The most critical issues to overcome in micro direct methanol fuel cells (µDMFCs) are the lack of tolerance of the platinum cathode and fuel crossover through the polymer membrane. Thus, two novel tolerant cathodes of a membraneless microlaminar-flow fuel cell (µLFFC), Pt(x)S(y) and CoSe(2), were developed. The multichannel structure of the system was microfabricated in SU-8 polymer. A commercial platinum cathode served for comparison. When using 5 M CH(3)OH as the fuel, maximum power densities of 6.5, 4, and 0.23 mW cm(-2) were achieved for the µLFFC with Pt, Pt(x)S(y), and CoSe(2) cathodes, respectively. The Pt(x)S(y) cathode outperformed Pt in the same fuel cell when using CH(3)OH at concentrations above 10 M. In a situation where fuel crossover is 100 %, that is, mixing the fuel with the reactant, the maximum power density of the micro fuel cell with Pt decreased by 80 %. However, for Pt(x)S(y) this decrease corresponded to 35 % and for CoSe(2) there was no change in performance. This result is the consequence of the high tolerance of the chalcogenide-based cathodes. When using 10 M HCOOH and a palladium-based anode, the µLFFC with a CoSe(2) cathode achieved a maxiumum power density of 1.04 mW cm(-2). This micro fuel cell does not contain either Nafion membrane or platinum. We report, for the first time, the evaluation of Pt(x)S(y)- and CoSe(2)-based cathodes in membraneless micro fuel cells. The results suggest the development of a novel system that is not size restricted and its operation is mainly based on the selectivity of its electrodes.

Fuel cell-powered microfluidic platform for lab-on-a-chip applications.

The achievement of a higher degree of integration of components--especially micropumps and power sources--is a challenge currently being pursued to obtain portable and totally autonomous microfluidic devices. This paper presents the integration of a micro direct methanol fuel cell (µDMFC) in a microfluidic platform as a smart solution to provide both electrical and pumping power to a Lab-on-a-Chip system. In this system the electric power produced by the fuel cell is available to enable most of the functionalites required by the microfluidic chip, while the generated CO(2) from the electrochemical reaction produces a pressure capable of pumping a liquid volume through a microchannel. The control of the fuel cell operating conditions allows regulation of the flow rate of a liquid sample through a microfluidic network. The relation between sample flow rate and the current generated by the fuel cell is practically linear, achieving values in the range of 4-18 µL min(-1) while having an available power between 1-4 mW. This permits adjusting the desired flow rate for a given application by controlling the fuel cell output conditions and foresees a fully autonomous analytical Lab-on-a-Chip in which the same device would provide the electrical power to a detection module and at the same time use the CO(2) pumping action to flow the required analytes through a particular microfluidic design.

Residual stress of free-standing membranes of yttria-stabilized zirconia for micro solid oxide fuel cell applications.

The present study is devoted to analyze the compatibility of yttria-stabilized zirconia thin films prepared by pulsed laser deposition and metalorganic chemical vapor deposition techniques, with microfabrication processes based on silicon technologies for micro solid oxide fuel cells applications. Deposition of yttria-stabilized zirconia on Si/SiO2/Si3N4 substrates was optimized for both techniques in order to obtain high density and homogeneity, as well as a good crystallinity for film thicknesses ranging from 60 to 240 nm. In addition, stabilized zirconia free-standing membranes were fabricated from the deposited films with surface areas between 50 x 50 microm2 and 820 x 820 microm2. Particular emphasis was made on the analysis of the effect of the nature of the deposition technique and the different design and fabrication parameters (membrane area, thickness and substrate deposition temperature) on the residual stress of the membranes in order to control their thermomechanical stability for application as electrolyte in micro solid oxide fuel cells.