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Herein, a paper-based glucose/air biofuel cell (BFC) was constructed and implemented for self-powered pesticide detection. Our developed paper-based chip relies on a hollow-channel to transport fluids rather than capillarity, which reduces analysis times as well as physical absorption. The gold nanoparticles (Au NPs) and carbon nanotubes (CNTs) were adapted to modify the paper fibers to fabricate the flexible conductive paper anode/cathode electrode (Au-PAE/CNT-PCE). Molecularly imprinted polymers (MIPs) using 2,4-dichlorophenoxyacetic acid (2,4-D) as a template were synthesized on Au-PAE for signal control. In the cathode, bilirubin oxidase (BOD) was used for the oxygen reduction reaction. Based on a competitive reaction between 2,4-D and glucose-oxidase-labeled 2,4-D (GOx-2,4-D), the amount of GOx immobilized on the bioanode can be simply tailored, thus a signal-off self-powered sensing platform was achieved for 2,4-D determination. Meanwhile, the coupling of the paper supercapacitor (PS) with the paper-based chip provides a simple route for signal amplification. Combined with a portable digital multi-meter detector, the amplified signal can be sensitively readout. Through rational design of the paper analytical device, the combination of BFC and PS provides a new prototype for constructing a low-cost, simple, portable, and sensitive self-powered biosensor lab-on-paper, which could be easily expanded in the field of clinical analysis and drug delivery.

Biofuel cells (BFCs) based on anodic oxidation and cathodic oxygen reduction represent an attractive alternative to self-powered devices. A glucose/oxygen BFC is described for monitoring glucose. It is making use of a piece of paper carrying a glucose oxidase (GOx) based bioanode, and a bilirubin oxidase (BilOx) based biocathode. The performance of the BFC is affected by the generation of H 2 O 2 , a byproduct of enzymatic glucose oxidation. Therefore, the removal of H 2 O 2 is a crucial step in terms of BFC performance and stability. In addition, direct, unambiguous visual read-out is an ideal way to provide quantitative information. The colorimetric readout system described here is based on the consumption of undesired H 2 O 2 and to convert the extent of energy generation into recognizable variations in color. As the H 2 O 2 travels along the hydrophilic channel by capillary action, the formation of red gold nanoparticles from AuCl 4 - leads to the appearance of a red bar that provides distance-based information that can be read visually. The multiply readable information (maximum power density of BFC or visible distance) provides further choices for quantification. It also enhances reliability. The self-powered system based on the BFC exhibits excellent performance. Glucose can be determined by this method in the 1 to 50 mM concentration range. Graphical abstract Schematic presentation of a paper-supported biofuel cell equipped with a visual distance readout to display the level of energy generation in biofuel cells, and its application in sensing of glucose.

The exploitation of self-powered devices that get rid of the power source restriction represents the development tendency of sensing systems. Herein, a paper-supported glucose/O 2 biofuel cell (BFC)-based self-powered sensing platform for visual analysis was developed. The BFC device utilized gold nanoparticle-modified paper fibers as the electrode to wire glucose oxidase (GOx) and bilirubin oxidase for the fabrication of bioanodes and biocathodes. To implement an assay protocol, a target-responsive cargo release system based on mesoporous silica nanocarriers controlled by microRNA-21 (miRNA-21) was designed. During the BFC operation, undesired H 2 O 2 , the side product of glucose oxidation which would be deleterious for GOx, was generated, leading to inevitable degeneration of BFC performance. On the basis of the H 2 O 2 -mediated iodide oxidation reaction to form iodine that further modulated the starch chromogenic reaction, undesired H 2 O 2 could be effectively removed, resulting in remarkably improved BFC performance as well as providing a means for visual signal readout. Thanks to the dual output signals (maximum power output density or length of blue bar), enhanced analysis reliability and sensitive detection of miRNA-21 over a range of 5 fM to 100 pM were achieved. Moreover, this study demonstrates a proof of concept in visualized BFC-based self-powered systems for sensing applications and provides a blueprint to advance future sensors and analysis devices powered by BFCs in a wide variety of in vitro applications.

In this work, a novel sensing platform based on visible light driven biofuel cell (BFC) has been facilely designed for sensitive detection of prostate-specific antigen (PSA) with the photo-response bioanode, realizing the dual route energy conversion of light energy and chemical energy to electricity. The hierarchical branched TiO2 nanorods (B-TiO2 NRs) decorated with CdS quantum dots (QDs) act as the substrate to confine glucose dehydrogenase (GDH) for the visible light driven glucose oxidation at the bioanode. Three dimensional flowers like hierarchical carbon/gold nanoparticles/bilirubin oxidase (3D FCM/AuNPs/BOD) bioconjugate served as biocatalyst for O2 reduction at the biocathode. With an increase in the concentration of PSA, the amount of BOD labels on biocathode increases, thus leading to the higher current output of the as-proposed visible light driven BFC. Based on this, this sensing platform provide great performance in sensitivity and specificity, increasing linear detection range from 0.3pgmL(-1) to 7μgmL(-1) with a detection limit of 0.1pgmL(-1). Most importantly, our new sensing strategy provided a simple and inexpensive sensing platform for tumor markers detection, suggesting its wide potential applications for clinical diagnostics., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A strategy that combines visible-light-enhanced biofuel cells (BFCs) and electrochemical immunosensor into paper-based analytical devices was proposed for sensitive detection of the carbohydrate antigen 15-3 (CA15-3). The gold nanoparticle modified paper electrode with large surface area and good conductibility was applied as an effective matrix for primary antibodies. The glucose dehydrogenase (GDH) modified gold-silver bimetallic nanoparticles were used as bioanodic biocatalyst and signal magnification label. Poly(terthiophene) (pTTh), a photoresponsive conducting polymer, served as catalyst in cathode for the reduction of oxygen upon illumination by visible light. In the bioanode, electrons were generated through the oxidation of glucose catalyzed by GDH. The amount of electrons is determined by the amount of GDH, which finally depended on the amount of CA15-3. In the cathode, electrons from the bioanode could combine with the generated holes in the HOMO energy level of cathode catalysts pTTh. Meanwhile, the high energy level photoexcited electrons were generated in the LUMO energy level and involved in the oxygen reduction reaction, finally resulting in an increasing current and a decreasing overpotential. According to the current signal, simple and efficient detection of CA15-3 was achieved.

A mediator-less and compartment-less glucose/O2 enzymatic biofuel cell (BFC) was introduced into microfluidic paper-based analytical devices (μ-PADs) that relies on flow in hollow channels with silver nanoparticles/graphene modified paper electrode as the anodic and cathodic substrate, to implement self-powered sensitive carcinoembryonic antigen (CEA) detection. Glucose dehydrogenase (GDH)-gold nanoparticles bioconjugate modified with CEA acted as a biocatalyst for enhancing glucose oxidation in the bioanode, as well as the transducing enzyme for signaling magnification. Similarly, nanoporous PtNi/bilirubin oxidase (BOD) acted as a biocatalyst for enhancing O2 reduction in the biocathode. With an increase in the concentration of CEA, the amount of CEA-Au-GDH bioconjugate on bioanode decreases, thus leading to the lower output of the as-prepared BFC. This proposed BFC-based self-powered immunosensor for CEA possessed largely increased linear detection range from 1 pg mL(-1) to 0.5 μg mL(-)(1) with a detection limit of 0.7 pg mL(-)(1). The proposed BFC-based self-powered immunosensor shows high sensitivity, stability, and reproducibility and can become a promising platform for other protein detection., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A dual functional analytical device performing both energy conversion and electric energy storage based on biofuel cells to implement self-powered point-of-care testing was developed based on a piece of Ti foil.

In this work, a mediator-less and compartment-less glucose/air enzymatic biofuel cell (BFC) was introduced into microfluidic paper-based analytical devices (μ-PADs) with gold nanoparticles (AuNPs) and platinum nanoparticles (PtNPs)-modified paper electrode as the anodic and cathodic substrate, respectively, to implement self-powered, sensitive, low-cost and simple DNA detection. As a further development of the analytical equipment, an all-solid-state paper supercapacitor (PS) was designed and integrated into the BFC for current amplification, and a terminal digital multi-meter detector (DMM) was introduced for the current detection. A highly sensitive DNA sensor was fabricated by covalently immobilizing the capture DNA in the AuNPs-modified anode. The nanoporous gold conjugated with bienzymes, glucose oxidase and horseradish peroxidase, which were used as electrochemical labels. The electrons generated at the anode flow through an external circuit to the PtNPs-modified cathode that catalyzed the reduction of oxygen with the participation of protons. In addition, the generated current could be collected and stored by the PS. After that, the PS was automatically shorted under the control of a switch to output an instantaneously amplified current, which could be sensitively detected by the terminal DMM. At the optimal conditions, the paper-based analytical platform can detect DNA at the femtomole level. This approach also shows excellent specificity toward single nucleotide mismatches., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A three-dimensional microfluidic origami glucose-air immuno-biofuel cell has been successfully demonstrated for the first time to implement self-powered, sensitive, and low-cost sandwich immunoassay for cancer markers based on the signal amplifications of a porous Au-paper electrode and Au nanoparticles attached to carbon nanotubes.