A flexible and wearable epidermal ethanol biofuel cell for on-body and real-time bioenergy harvesting from human sweat (2023)

A sustainable power source is essential for soft artificial muscle to achieve untethered actuation, typically driven by rigid and bulky batteries that severely restrict their applications. Herein, a wearable sweat-based energy generator (SEG) is designed to directly power up a soft artificial muscle for establishing a self-powered conjunct system. The generator generates electricity from sweat based on the redox reaction, which shows a maximum power density of 18.3 μw cm⁻² at a resistance of 0.3kΩ with a small amount of sweat (0.2mL). It is sufficient to activate the artificial muscles. Next, the sweat generator is integrated with artificial muscle to present an autonomously powered actuator, resulting in a bending motion based on converting electricity into movement by the electroactive polymer poly(vinylidene fluoride-hexafluoropropylene) (PVDF(HFP)) containing LiCl liquid. This autonomously powered artificial muscle can imitate finger motion, bionic flowers, and a self-powered gripper to manipulate tiny objects. Moreover, integrating artificial muscle and electromyogram sensors with sweat-based energy generators may have potential application values in repairing damaged muscle with closed-loop sensing and treatment. Thus, this autonomously powered artificial muscle can be of great interest for soft robotics, the biomedical field, and biomimetic devices.

Recent advances in enzymatic biofuel cells (EBFCs) have resulted in great progress in health monitoring and supplying power to medical applications, such as drug delivery. On the other hand, to enhance the electric field-assisted transdermal permeation for facial mask application, an external power source is usually required. Herein, we attempted to combine an EBFC with a facial mask so that the microcurrent generated can boost the transdermal permeability of target molecules in the facial mask essence. When screen-printed onto a polypropylene-based non-woven fabric, the three-layered flexible EBFC could produce a voltage of ∼0.4V and a maximum power density of 23.3μWcm⁻², leading to an approximately 2–3-fold increase in permeated nicotinamide, arbutin, and aspirin levels within 15min compared to non-iontophoretic transdermal drug delivery. Both cell viability and animal experiments further demonstrated that the EBFC-powered iontophoresis worked well in living animals with good biocompatibility. These results suggest that the EBFC-powered iontophoretic facial mask can effectively improve the permeation of drugs and holds a promise for the possible cosmetic application.

Soft, conformal and wearable epidermal fuel cells may offer promising energy solutions to power next-generation on-skin electronics on-demand anytime anywhere. However, it is non-trivial to design intrinsically stretchable electrode in order to maintain the fuel cell performance under real-world and dynamic mechanical deformations. Here, we present a tattoo-like epidermal fuel cell based on Pd conformally-coated, one-end-embedded percolation gold nanowire (EP-AuNW/EP-AuPdNW) networks, which are in essence the combination of in-plane percolation conductivity and out-plane anisotropic conductivity. Both EP-AuNW and EP-AuPdNW are intrinsically stretchable conductors for anode and cathode in fuel cell. Compared to non-conformal counterparts, a 6-times greater power density was achieved for conformal system. Importantly, EP-NW based fuel cell can function under various mechanical deformations including stretching, compression, bending, and twisting; the power density showed negligible changes to the tensile strain up to ∼50% and could maintain its 75% performance even under 80% strain. Furthermore, a dragon-tattoo epidermal fuel cell was fabricated, demonstrating on-demand power generation with real-world ethanol sources.

Developing wearable flexible biosensors with excellent electrical conductivity and outstanding flexibility simultaneously for disease diagnosis and health monitoring is a current hot topic in the field of sensor research. In this study, nitrogen-doped graphene (N-Gr) and gold nanoparticles (AuNPs) were successively deposited onto ITO-PET flexible conductive films by chemical deposition, and then a flexible electrochemical immunosensor with high sensitivity and selectivity was constructed for detecting depression markers by exploiting the high affinity between AuNPs and the sulfhydryl groups of depression marker (DM) antibody. Due to the composite of N-Gr, AuNPs and ITO-PET, the prepared flexible sensor can maintain a relatively stable electrical signal response regardless of the deformation such as spiral, rolling, and bending, without shedding or fracture of the N-Gr and AuNPs, and can also significantly amplify the electrochemical response signal of the immunosensor. Under optimized experimental conditions, the fabricated immunosensor showed good linearity over a wide range of 0.023–300.00ng/mL with a low detection limit of 0.010ng/mL (3σ, n=5), when it was used for the determination of depression markers-human Apo-A4 in 100% whole serum samples. The flexibility of the constructed immunosensor and the stability and sensitivity of biomolecular analysis are expected to be further made into implantable depression marker in-situ monitoring probe with the help of micro-machining technology, which will develop a promising method for objective, efficient and accurate clinical diagnosis of depression.

Sustainable conversion of renewable biomass into high-performance electrode materials has attracted extensive scientific and technological attention. However, to our knowledge, the potential of biomass derived carbon in biosensors and biofuel cells (BFCs) developments remains to be explored. Herein, the carbon nanorods assembled coral-like hierarchical meso-macroporous carbon (CN-CHMC) was synthesized as a sustainable electrode material to construct biosensor and lactate/air BFC. The CN-CHMC from cucumber (Cucumis sativus) possesses porous structure and plentiful defects, which not only facilitate the effective immobilization of enzymes but also accelerate electron transfer on the bioelectrode surfaces. As an electrochemical lactate biosensor, the CN-CHMC-based biosensor exhibits a wider linear range with lower detection limit (3.6μM) and higher sensitivities (57.18 and 30.99μAmM⁻¹cm⁻²) compared to carbon nanotube (CNT)-based biosensor. The feasibility of CN-CHMC-based biosensor in practical analysis is demonstrated by detecting lactate contents in real samples. By coupling with bilirubin oxidase-based biocathode, the lactate/air BFC equipped with CN-CHMC reveals a higher output power (112.7μWcm⁻²) than that of CNT-based BFC. More interestingly, the lactate/air BFC demonstrates the ability to harvest energy from multi-component samples. The application of CN-CHMC may provide a new avenue to synthesize electrode materials with economical cost and excellent electrochemical activity.

The chemistry of the metal-organic frameworks (MOFs) coating may affect the biological functionality of the encapsulated biomacromolecules in harsh environment. Enzymes encapsulated in hydrophilic MAF-7 can retain high activity in harsh environment. We conducted this study to prepare a non-invasive wearable [emailprotected] electrochemical sensor that can achieve accurate and sensitive detection of UA levels in sweat by integrating a flexible microfluidic chip and wireless electronic readout device. The flexible microfluidic chip enabled an easy and effective collection of sweat samples. MAF-7 protected enzyme activity by encapsulating uricase. The [emailprotected] electrochemical sensor enabled the highly sensitive detection of UA in the concentration range of 2μM–70 μM with a detection limit of as low as 0.34μM. Additionally, we evaluated the utility of the sensor for monitoring UA levels in real sweat samples by means of a high purine dietary challenge. This personalized wearable sweat sensing device has a potential to be used for monitoring disease-related metabolites in daily life.

Nano Energy, Volume 59, 2019, pp. 754-761

A novel self-powered wearable sweat-lactate analyzer for building sports big data has been realized basing on sweat-evaporation-biosensing coupling effect. The self-powered biosensor in analyzer is fabricated from porous carbon film (modified with lactate oxidase). The hydrophilic carbon can soak up sweat, and harvest environmental thermal energy to generate electricity through nature sweat-evaporation. The outputting voltage increases with increasing sweat-lactate concentration, which can be regarded as biosensing signal. The surface enzymatic reaction can change the zeta potential of carbon and thus influence the outputting voltage. On the flexible substrate, the biosensor can be integrated with wireless transmitter and capacitor, constructing a self-powered wearable sweat-lactate analyzer. The analyzer can detect sweat-lactate concentration on athlete's skin, wirelessly transmit the exercise physiological information to terminal, and build sports big data. This work can provoke a new research direction for realizing self-powered wearable exercise-analyzing system, and can also promote the development of sports big data.

Nano Energy, Volume 68, 2020, Article 104308

Self-powered biosensor, as a new sensing platform, utilizes biofuel cells as synchronous power source and biosensor system, with the advantages of no external power source, simple instrumentation and easy miniaturization. Meanwhile, inspired by biomimics for the encapsulation of soft tissue within protective exteriors in nature, encapsulation of biological macromolecules by metal organic-frameworks (MOFs) have been proved to be an effective strategy for enhancing the biocatalytic activity in maintaining biological functions. Herein, we successfully encapsulated laccase (LAC) in zeolitic imidazolate framework-8 (ZIF-8) and combined it with bacterial cellulose (BC)/carboxylated multi-walled carbon nanotubes (c-MWCNTs) skeleton to prepare highly flexible BC/c-MWCNTs/[emailprotected] electrode. Subsequently, we ingeniously designed an highly flexible self-powered sensing platform based on biofuel-cell driven by single-enzyme, harvesting bisphenol A (BPA) as a model analyte. The maximum power density (P_max) of single-enzymatic biofuel cell (EBFC) exhibited an excellent linear dynamic range from 0.01 to 0.4mM with a lower detection limit of 1.95×10⁻³mM for BPA concentrations. Therefore, the designed single-EBFC-based self-powered sensor is feasible in BPA detection and has a broad application prospect in the field of water pollutants detection.

International Journal of Hydrogen Energy, Volume 46, Issue 4, 2021, pp. 3183-3192

The present work establishes a simple, customized, and economical laser-induced graphene (LIG) material produced using a CO₂ laser. The one-step LIG bioelectrodes have been further validated for Enzymatic Biofuel Cell (EBFC) application by integrating them into a microfluidic device, fabricated by the conventional soft-lithography on Polydimethylsiloxane (PDMS). This electrode and device manufacturing technology delivers a simple and quick fabrication method, which eliminates the necessity of any further amendment and post-processing. LIG electrodes were created at optimized CO₂ laser (5.1W power and 0.625cms⁻¹ speed) irradiation which has been further modified by Multi-walled carbon nanotubes (CNT), called C-LIG electrodes, which offers improved performance and enzyme stability. In this novel study, CNT functionalized LIG electrodes have been incorporated into a microfluidic device for biofuel cell applications. LIG and C-LIG bioelectrodes have been integrated into a microfluidic device under the laminar fluid flow regime and the electrochemical and polarization study of the platform have been carried out. This C-LIG bioelectrodes integrated microfluidic device, without any metal catalyst, generated 2.2μW/cm² power density with an optimized 200μl/min flow rate which is 1.37 times higher than the LIG bioelectrodes. Such novel and simple EBFC platform is amenable to further improvement for generating even more power output by optimizing the LIG formation, alternate nano-functionalisation and mediator based electrochemical analysis.

Journal of Power Sources, Volume 427, 2019, pp. 49-55

We report enzymatic biofuel cells (EBFCs) based on MgO-templated carbon (MgOC)-carbon textile composite electrodes, which are lightweight, flexible, and used as liquid containers. MgOC particles with a pore size of 40 nm were modified on a carbon cloth substrate using poly(vinylidenedifluoride) as an anodic binder and polytetrafluoroethylene as a cathodic binder. Flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from Aspergillus terreus was used for the anode, with 1,4-naphthoquinone chosen as the redox mediator. The O₂-reducing cathode contains bilirubin oxidase (BOD) from Myrocecium verucaria and 2,2′-azinobis(3-ethylbenzothiazolin-6-sulfonate) (ABTS), which facilitates electron transfer between the active site of BOD and the electrode. The hydrophobicity of the gas diffusion layer in the textile composite cathode is tuned with the aid of a PTFE binder, to increase the amount of O₂ supplied from the air. The open circuit potential is 0.75 V and maximum output power density is 2 mW cm⁻² at 0.4 V (room temperature, without O₂ gas flow). Our results clearly indicate that MgOC-textile materials are very promising for the development of high-performance, wearable EBFCs.

Materials Today Energy, Volume 22, 2021, Article 100886

The rise of energy harvesting textiles opens up an emerging path to prospective energy solutions for the next generation of wearable electronics. Flexible electrodes as the core link in enzymatic biofuel cell (EBFC) should be stretchable while using enzyme molecules to transfer the energy from chemical of green fuels into electricity, which is beneficial to meet the key requirements of practical applications and shows considerable potential in wearable electronics. As a result, we develop a single EBFC based on intramolecular electron transfer using a stretchable electrode made of polyurethane/zeolitic imidazolate [emailprotected]/carbon nanotubes (PU/[emailprotected]/CNTs), which encapsulates LAC into ZIF-8 crystals during ZIF-8 in-situ growth on PU nanofibers. The maximal power density output of single-EBFC reached 1.33Wm⁻³. More importantly, after multiple deformations of 75 stretching cycles, continuously stretching and holding and 180° twisting cycles, the single-EBFC retains an E^OCV of more than 50%, which exhibits stable energy output, thus the stretchability of PU/[emailprotected]/CNTs are proved. This stretchable electrode can establish a stable platform of power devices and will be potentially integrated into wearable electronics.

Biosensors and Bioelectronics, Volume 101, 2018, pp. 60-65

A novel three-dimensional (3D) carbon composite of PANI₁₆₀₀@CNTs with rhizobium-like structure is prepared by in-situ polymerization of aniline monomers around and along the functionalized carbon nanotubes (CNTs) and then carbonized at 1600°C for enzymatic biofuel cells (EBFCs). The SEM and TEM images clearly show that the carbonized PANI grew seamlessly on the surface of CNTs and presented the rhizobium-like structure. The carbonized PANI acts like conductive “glue” and connects the adjacent tubes together, which can assemble the CNTs into a 3D network. The PANI₁₆₀₀@CNTs composite modified glassy carbon electrodes based on glucose oxidase (GOx) and laccase (Lac) exhibit high electrochemical performance. A glucose//O₂ EBFC constitutes of the fabricated anode and cathode performs a maximum power density of 1.12mWcm⁻² at 0.45V. Furthermore, three of the fabricated EBFCs in series are able to lightening up a yellow light-emitting diode (LED) whose turn-on voltage is about at 1.8V. This work may be helpful for exploiting novel substrates by carbonizing the composites of conducting polymer with nano materials at high-temperature for immobilization of enzymes in the EBFCs or biosensor fields.