Self-Powered and Sensitive DNA Detection in a Three-Dimensional Origami-Based Biofuel Cell Based on a Porous Pt-Paper Cathode

Paper-based electrodes as a tool for detecting ligninolytic enzymatic activities

Lignin is the most important natural source of aromatic compounds. The valorisation of lignin into aromatics requires fractionation steps that can be catalysed by ligninolytic enzymes. However, one of the main limitations of biological lignin fractionation is the low efficiency of biocatalysts; it is therefore crucial to enhance or to identify new ligninolytic enzymes. Currently, the screening of ligninolytic activities on lignin polymers represents a technological bottenleck and hinders the characterization and the discovery of efficient ligninolytic biocatalysts. An efficient and fast method for the measurement of such enzymatic activities is therefore required. In this work, we present a new electrochemical tool based on lignin-coated paper electrodes for the detection and the characterization of ligninolytic activity. The suitability of this method is demonstrated using a catalase-peroxidase isolated from Thermobacillus xylanilyticus.

Research Progress in Enzyme Biofuel Cells Modified Using Nanomaterials and Their Implementation as Self-Powered Sensors

Enzyme biofuel cells (EBFCs) can convert chemical or biochemical energy in fuel into electrical energy, and therefore have received widespread attention. EBFCs have advantages that traditional fuel cells cannot match, such as a wide range of fuel sources, environmental friendliness, and mild reaction conditions. At present, research on EBFCs mainly focuses on two aspects: one is the use of nanomaterials with excellent properties to construct high-performance EBFCs, and the other is self-powered sensors based on EBFCs. This article reviews the applied nanomaterials based on the working principle of EBFCs, analyzes the design ideas of self-powered sensors based on enzyme biofuel cells, and looks forward to their future research directions and application prospects. This article also points out the key properties of nanomaterials in EBFCs, such as electronic conductivity, biocompatibility, and catalytic activity. And the research on EBFCs is classified according to different research goals, such as improving battery efficiency, expanding the fuel range, and achieving self-powered sensors.

Tuneable Plasmonic Resonances Of A Dynamic Thin Film Of Ultrasmall Nanocrystals Modified In the Anti-Galvanic Reduction Process

Ultrasmall gold nanoparticles (NPs) have revolutionized nanotechnology as they are an excellent starting substrate for the synthesis of organic-inorganic hybrid materials with photonic or energy conversion applications, often with a responsive nature. However, ultrasmall NPs do not sustain plasmonic resonances, preventing their use in plasmon-related applications. In the presented work, we show a method of chemical modification of ultrasmall gold nanoparticles in order to fabricate dynamically controlled plasmonic thin films. For this purpose, we used the Anti-Galvanic Reduction process (AGR) to modify the surface of small gold nanoparticles, inducing plasmonic properties without notable size increases. Au@Ag NPs are then modified with liquid crystal-like organic ligands. The obtained NPs can assemble into densely packed films with long-range order and temperature-dependent structural properties. Namely, we detect two, fully reversible phase transitions between the hexagonal and cubic symmetries. The combination of AGR and organic surface modifications enabled us to demonstrate the possibility of managing plasmonic properties in the thin film of ~2 nm diameter metallic NPs.

Hollow-Channel Paper Analytical Devices Supported Biofuel Cell-Based Self-Powered Molecularly Imprinted Polymer Sensor for Pesticide Detection

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.

Engineering Self-Powered Electrochemical Sensors Using Analyzed Liquid Sample as the Sole Energy Source

Many healthcare and environmental monitoring devices use electrochemical techniques to detect and quantify analytes. With sensors progressively becoming smaller-particularly in point-of-care (POC) devices and wearable platforms-it creates the opportunity to operate them using less energy than their predecessors. In fact, they may require so little power that can be extracted from the analyzed fluids themselves, for example, blood or sweat in case of physiological sensors and sources like river water in the case of environmental monitoring. Self-powered electrochemical sensors (SPES) can generate a response by utilizing the available chemical species in the analyzed liquid sample. Though SPESs generate relatively low power, capable devices can be engineered by combining suitable reactions, miniaturized cell designs, and effective sensing approaches for deciphering analyte information. This review details various such sensing and engineering approaches adopted in different categories of SPES systems that solely use the power available in liquid sample for their operation. Specifically, the categories discussed in this review cover enzyme-based systems, battery-based systems, and ion-selective electrode-based systems. The review details the benefits and drawbacks with these approaches, as well as prospects of and challenges to accomplishing them.

Cellulose Structures as a Support or Template for Inorganic Nanostructures and Their Assemblies

Cellulose is the most abundant natural polymer and deserves the special attention of the scientific community because it represents a sustainable source of carbon and plays an important role as a sustainable energent for replacing crude oil, coal, and natural gas in the future. Intense research and studies over the past few decades on cellulose structures have mainly focused on cellulose as a biomass for exploitation as an alternative energent or as a reinforcing material in polymer matrices. However, studies on cellulose structures have revealed more diverse potential applications by exploiting the functionalities of cellulose such as biomedical materials, biomimetic optical materials, bio-inspired mechanically adaptive materials, selective nanostructured membranes, and as a growth template for inorganic nanostructures. This article comprehensively reviews the potential of cellulose structures as a support, biotemplate, and growing vector in the formation of various complex hybrid hierarchical inorganic nanostructures with a wide scope of applications. We focus on the preparation of inorganic nanostructures by exploiting the unique properties and performances of cellulose structures. The advantages, physicochemical properties, and chemical modifications of the cellulose structures are comparatively discussed from the aspect of materials development and processing. Finally, the perspective and potential applications of cellulose-based bioinspired hierarchical functional nanomaterials in the future are outlined.

A glucose/O2 biofuel cell integrated with an exonuclease-powered DNA walker for self-powered sensing of microRNA

With the aid of an exonuclease-powered DNA walker, the amount of glucose oxidase immobilized on the bioanode can be facilely tailored by varying the concentration of microRNA-141, so a glucose/O₂ biofuel cell is employed as a self-powered sensor for sensitive and selective detection of microRNA-141.

A portable signal-on self-powered aptasensor for ultrasensitive detection of sulfadimethoxine based on dual amplification of a capacitor and biphotoelectrodes

A one-compartment photofuel cell with two photoelectrodes was combined with a capacitor to develop a portable self-powered sensor for sulfadimethoxine (SDM) detection. The developed sensor was applied to the assay of SDM in veterinary drug samples with desirable accuracy and precision.

Origami paper-based sample preconcentration using sequentially driven ion concentration polarization

Ion concentration polarization (ICP) is one of the preconcentration techniques which can acquire a high preconcentration factor. Still, the main hurdles of ICP are its instability and low efficiency under physiological conditions with high ionic strength and abundant biomolecules. Here, we suggested a sequentially driven ICP process, which enhanced the electrokinetic force required for preconcentration, enabling enrichment of highly ionic raw samples without increasing the electric field. We acquired a 13-fold preconcentration factor (PF) in human serum using a paper-based origami structure consisting of multiple layers for three-dimensional sequential ICP (3D seq-ICP). Moreover, we demonstrated a paper-based enzyme-linked immunosorbent assay (ELISA) by 3D seq-ICP using tau protein, showing a 6-fold increase in ELISA signals.

Flexible Electrochemical Bioelectronics: The Rise of In Situ Bioanalysis

The amalgamation of flexible electronics in biological systems has shaped the way health and medicine are administered. The growing field of flexible electrochemical bioelectronics enables the in situ quantification of a variety of chemical constituents present in the human body and holds great promise for personalized health monitoring owing to its unique advantages such as inherent wearability, high sensitivity, high selectivity, and low cost. It represents a promising alternative to probe biomarkers in the human body in a simpler method compared to conventional instrumental analytical techniques. Various bioanalytical technologies are employed in flexible electrochemical bioelectronics, including ion-selective potentiometry, enzymatic amperometry, potential sweep voltammetry, field-effect transistors, affinity-based biosensing, as well as biofuel cells. Recent key innovations in flexible electrochemical bioelectronics from electrochemical sensing modalities, materials, systems, fabrication, to applications are summarized and highlighted. The challenges and opportunities in this field moving forward toward future preventive and personalized medicine devices are also discussed.

Nanomaterial-Modified Conducting Paper: Fabrication, Properties, and Emerging Biomedical Applications

The emerging demand for wearable, lightweight portable devices has led to the development of new materials for flexible electronics using non-rigid substrates. In this context, nanomaterial-modified conducting paper (CP) represents a new concept that utilizes paper as a functional part in various devices. Paper has drawn significant interest among the research community because it is ubiquitous, cheap, and environmentally friendly. This review provides information on the basic characteristics of paper and its functionalization with nanomaterials, methodology for device fabrication, and their various applications. It also highlights some of the exciting applications of CP in point-of-care diagnostics for biomedical applications. Furthermore, recent challenges and opportunities in paper-based devices are summarized.

A self-powered origami paper analytical device with a pop-up structure for dual-mode electrochemical sensing of ATP assisted by glucose oxidase-triggered reaction

A self-powered origami paper-based analytical device (oPAD), being with a pop-up structure as mechanical valve to first realize dual-mode of differential pulse voltammery (DPV)/supercapacitor amplified signal read out systems, was designed for detecting adenosine 5'-triphosphate (ATP) assisted by glucose oxidase (GOx)-triggered reaction. In order to accommodate the alternative step for dual-mode detection, a pop-up structure inspired by pop-up greeting cards was developed, making it possible to change the fluidic path with good registration and repeatability. To realize supercapacitor detection mode, a sandwich structure of a DNA sequence (DNA1), aptamer and a DNA sequence modified with GOx (GOx-DNA2) was formed on detection zone by hybridization reaction. With the addition of ATP, the GOx-DNA2 could be released with the specific binding between ATP and aptamer, and flowed into the reaction zone to catalyze the oxidation of glucose. Due to the difference in concentrations of [Fe(CN)₆]^3- and [Fe(CN)₆]^4- caused by the GOx-triggered reaction, a voltage could be produced to charge a paper supercapacitor which could provide a high instantaneous current with a digital multimeter to transduce the result of the assay, and realize the self-generation of an amplified electrical signal. By simply varying the direction of pop-up structure, the electrochemical signal from DPV read out mode could be achieved through catalytic oxidation of glucose by the remaining GOx-DNA2 on the detection zone. The proposed self-powered oPAD enabled the sensitive diagnosis of ATP in a linear range of 10-5000 nM with a limit of detection of 3 nM and 1.4 nM, respectively.

Paper-Supported Self-Powered System Based on a Glucose/O2 Biofuel Cell for Visual MicroRNA-21 Sensing

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/O₂ 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 H₂O₂, 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 H₂O₂-mediated iodide oxidation reaction to form iodine that further modulated the starch chromogenic reaction, undesired H₂O₂ 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.

Flexible Electronics Based on Micro/Nanostructured Paper

Over the past several years, a new surge of interest in paper electronics has arisen due to the numerous merits of simple micro/nanostructured substrates. Herein, the latest advances and principal issues in the design and fabrication of paper-based flexible electronics are highlighted. Following an introduction of the fascinating properties of paper matrixes, the construction of paper substrates from diverse functional materials for flexible electronics and their underlying principles are described. Then, notable progress related to the development of versatile electronic devices is discussed. Finally, future opportunities and the remaining challenges are examined. It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based electronic devices.

Flexible plastic, paper and textile lab-on-a chip platforms for electrochemical biosensing

Flexible biosensors represent an increasingly important and rapidly developing field of research. Flexible materials offer several advantages as supports of biosensing platforms in terms of flexibility, weight, conformability, portability, cost, disposability and scope for integration. On the other hand, electrochemical detection is perfectly suited to flexible biosensing devices. The present paper reviews the field of integrated electrochemical bionsensors fabricated on flexible materials (plastic, paper and textiles) which are used as functional base substrates. The vast majority of electrochemical flexible lab-on-a-chip (LOC) biosensing devices are based on plastic supports in a single or layered configuration. Among these, wearable devices are perhaps the ones that most vividly demonstrate the utility of the concept of flexible biosensors while diagnostic cards represent the state-of-the art in terms of integration and functionality. Another important type of flexible biosensors utilize paper as a functional support material enabling the fabrication of low-cost and disposable paper-based devices operating on the lateral flow, drop-casting or folding (origami) principles. Finally, textile-based biosensors are beginning to emerge enabling real-time measurements in the working environment or in wound care applications. This review is timely due to the significant advances that have taken place over the last few years in the area of LOC biosensors and aims to direct the readers to emerging trends in this field.

Self-Powered Biosensors

Self-powered electrochemical biosensors utilize biofuel cells as a simultaneous power source and biosensor, which simplifies the biosensor system, because it no longer requires a potentiostat, power for the potentiostat, and/or power for the signaling device. This review article is focused on detailing the advances in the field of self-powered biosensors and discussing their advantages and limitations compared to other types of electrochemical biosensors. The review will discuss self-powered biosensors formed from enzymatic biofuel cells, organelle-based biofuel cells, and microbial fuel cells. It also discusses the different mechanisms of sensing, including utilizing the analyte being the substrate/fuel for the biocatalyst, the analyte binding the biocatalyst to the electrode surface, the analyte being an inhibitor of the biocatalyst, the analyte resulting in the blocking of the bioelectrocatalytic response, the analyte reactivating the biocatalyst, Boolean logic gates, and combining affinity-based biorecognition elements with bioelectrocatalytic power generation. The final section of this review details areas of future investigation that are needed in the field, as well as problems that still need to be addressed by the field.

Nanomaterials-modified cellulose paper as a platform for biosensing applications

Recently, paper substrates have attracted tremendous interest from both academia and industry. Not only is paper highly abundant and portable, it is lightweight, disposable, easy-to-use, and can be rolled or folded into 3D configurations. More importantly, with a unique porous bulk structure and rough and absorptive surface properties, the construction of nanomaterials-functionalized cellulose has enabled cellulose paper to be applied for point-of-care (POC) paper devices with reasonably good performance at low cost. In this review, the latest advances in the modification of nanomaterials on paper cellulose are summed up. To begin with, the attractive properties of paper-based analytical devices are described. Then, fabricating methods for the functionalization of cellulose with diverse materials, including noble metals, bimetals, metal oxides, carbon nanomaterials, and molecular imprinting polymer nanoparticles, as well as their applications, are introduced in detail. Finally, the current critical issues, challenges, and future prospectives for exploring a paper-based analytical system based on nanomaterials-modified cellulose are discussed. It is believed that more strategies will be developed in the future to construct nanomaterials-functionalized cellulose, paving the way for the mass production of POC paper devices with a satisfactory performance.

Fabrication of Surface Protein-Imprinted Biofuel Cell for Sensitive Self-Powered Glycoprotein Detection

Glycoproteins are important biomarkers and therapeutic targets in clinical diagnostics. The conventional analytical methods for glycoprotein are usually faced with some challenges, such as the complex pretreatment of samples, poor availability, and limited stability of antibody, making them not suitable for point-of-care and on-site application. Herein, we demonstrate a novel miniaturized biofuel cells (BFCs)-based self-powered nanosensor for the specific and sensitive determination of glycoproteins in complex samples through the combination of boronate-affinity molecularly imprinted polymer (MIP) and the boronate affinity functionalized biliroxidase-carbon nanotube nanocomposites. The above MIP and the nanocomposites act as both signal probe and biocatalyst at the cathode. The as-obtained self-powered MIP-BFC-based biosensor can detect horseradish peroxidase (a type of glycoprotein) with a wide linear range of 1 ng/mL to 10 μg/mL and a very low detection limit of 1 ng/mL. Especially, it shows high tolerance for different interferences (e.g., sugars and other glycoproteins) and can even measure the α-fetoprotein level in serum samples. Moreover, it exhibits significant advantages over the conventional assays in terms of cost efficiency, stability, and speed, especially inexpensive instrument needed. Our novel approach for construction of the sensor paves a simple and economical way to fabricate portable devices for point-of-care and on-site application.

Enzymatic Biofuel Cells on Porous Nanostructures

Biofuel cells (BFCs) that utilize enzymes as catalysts represent a new sustainable and renewable energy technology. Numerous efforts have been directed to improve the performance of the enzymatic BFCs (EBFCs) with respect to power output and operational stability for further applications in portable power sources, self-powered electrochemical sensing, implantable medical devices, etc. The latest advances in EBFCs based on porous nanoarchitectures over the past 5 years are detailed here. Porous matrices from carbon, noble metals, and polymers promote the development of EBFCs through the electron transfer and mass transport benefits. Some key issues regarding how these nanostructured porous media improve the performance of EBFCs are also discussed.

A miniature origami biofuel cell based on a consumed cathode

A miniature origami BFC has been fabricated from a MnO₂–graphite flake consumed solid-state cathode.

Paper-Based Analytical Devices Relying on Visible-Light-Enhanced Glucose/Air Biofuel Cells

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.

Instant power generation from an air-breathing paper and pencil based bacterial bio-fuel cell

We present a low-cost, disposable microbial fuel cell fabricated on a paper based platform, having a start-up time of 10 s. The platform deploys ordinary pencil strokes for graphite electrode deposition. The device uses a membrane-less design in a one-time injection (OTI) mode or a continuous capillary driven flow mode (CPF), where oxygen from the atmosphere is used up at the cathode for water formation, leading to the generation of bioelectricity. The performance of the fuel cell is evaluated using two bacterial strains, namely, Pseudomonas aeruginosa IIT BT SS1 and Shewanella putrefaciens. This flexible device is shown to retain bacteria for a period of at least one hour, resulting in the generation of almost 0.4 V using P. aeruginosa and a maximum current of 18 μA using S. putrefaciens without the use of any additional catalysts.