The design of the coordination shell of an Os-complex and its integration within an electrodeposition polymer enables fast electron transfer between an electrode and a polymer entrapped high-potential laccase from the basidiomycete Trametes hirsuta. The redox potential of the Os3+/2+-centre tethered to the polymer backbone (+720 mV vs. NHE) is perfectly matching the potential of the enzyme (+780 mV vs. NHE at pH 6.5). The laccase and the Os-complex modified anodic electrodeposition polymer were simultaneously precipitated on the surface of a glassy carbon electrode by means of a pH-shift to 2.5. The modified electrode was investigated with respect to biocatalytic oxygen reduction to water. The proposed modified electrode has potential applications as biofuel cell cathode.

Electrochemical characterization of the GreeDo variant of a high redox potential fungal laccase obtained by laboratory evolution together with computer-guided mutagenesis, in comparison to its parental variety (the OB-1 mutant), is presented. Both laccases, when immobilized on graphite electrodes either by direct physical adsorption or covalently attached via gold nanoparticles, were capable of both non-mediated and mediator-based bioelectroreduction of molecular oxygen at low overpotentials. GreeDo exhibited higher open circuit potential values and onset potentials for oxygen bioelectroreduction compared to OB-1. However, even though in homogeneous catalysis GreeDo outperforms OB-1 in terms of turnover numbers and catalytic efficiency, when exposed to high redox potential substrates, direct electron transfer based bioelectrocatalytic currents of GreeDo and OB-1 modified electrodes were similar. High operational stability of freely diffusing GreeDo and also the immobilized enzyme in the acidic electrolyte was registered, in agreement with high storage stability of GreeDo in acidic solutions.

Direct transformation of solar energy into electrical energy by means of biological photosynthesis is considered as an attractive option for sustainable electrical energy production. Thylakoid membranes, the site of photosynthesis, are regarded as a promising biological material for the development of photoelectric biodevices, which produce electrical power consuming only light energy as oxygen evolves at photobioanode upon irradiation and biocathode converts it back to water. Therefore, in this work dual-feature photobioanode based on nanoimprinted gold substrates modified with thylakoids in combination with a capacitive part made of a planar gold substrate coated with a conductive polymer was designed and evaluated, providing open-circuit potential of -0.21 V vs. Ag vertical bar AgCl vertical bar KClsat and a capacitance of ca. 60 F m(-2) both at ambient light and artificial illumination of 400 W m(-2). Combination of thylakoid based dual-feature photobioanode with bilirubin oxidase modified transparent and capacitive indium tin oxide biocathode resulted in a photoelectric biosupercapacitor with remarkable characteristics at ambient light, viz. an open-circuit voltage as high as 0.74 V, which was stable upon charge-discharge cycles during ca. 2 h.

As the global energy demand continues to increase, the interest in photosynthetic energy conversion is growing accordingly. Chloroplasts, photosynthetic organelles present in plants and algae, are attractive candidates for construction of bio solar cells; however, they have been less studied because of their complex membrane system, which restricts electrochemical communication with an electrode surface. Nevertheless, in this work photobioanodes based on planar and nanoimprinted gold substrates modified with chloroplasts were designed and evaluated. Apparently, nanoimprint lithography contributed to higher photocurrent densities, not only owing to the enlarged real surface area, but also due to boosting electrochemical communication between the photosynthetic organelles and the electrode. Combining chloroplast-modified nanoimprinted gold electrodes with a capacitive part made of a planar gold substrate, coated with a conductive polymer, resulted in a dual-feature photobioanode providing a lower open-circuit potential, i. e., -0.11 V vs. Ag|AgCl|KClsat, and an enhanced capacitance of ca. 37 F m(-2) upon illumination of 400 W m(-2).

High-performance autotolerant bioelectrodes should be ideally suited to design implantable bioelectronic devices. Because of its high redox potential and ability to reduce oxygen directly to water, human ceruloplasmin, HCp, the only blue multicopper oxidase present in human plasma, appears to be the ultimate biocatalyst for oxygen biosensors and also biocathodes in biological power sources. In comparison to fungal and plant blue multicopper oxidases, e.g. Myrothecium verrucaria bilirubin oxidase and Rhus vernicifera laccase, respectively, the inflammatory response to HCp in human blood is significantly reduced. Partial purification of HCp allowed to preserve the native conformation of the enzyme and its biocatalytic activity. Therefore, electrochemical studies were carried out with the partially purified enzyme immobilised on nanostructured graphite electrodes at physiological pH and temperature. Amperometric investigations revealed low reductive current densities, i.e. about 1.65 µA cm−2 in oxygenated electrolyte and in the absence of any mediator, demonstrating nevertheless direct electron transfer based O2 bioelectroreduction by HCp for the first time. The reductive current density obtained in the mediated system was about 12 µA cm−2. Even though the inflammatory response of HCp is diminished in human blood, inadequate bioelectrocatalytic performance hinders its use as a cathodic bioelement in a biofuel cell.

An intrinsic self-charging biosupercapacitor built on a unique concept for the fabrication of biodevices based on redox polymers is presented. The biosupercapacitor consists of a high-potential redox polymer based bioanode and a low-potential redox polymer based biocathode in which the potentials of the electrodes in the discharged state show an apparent potential mismatch E-anode > E-cathode and prevent the use of the device as a conventional biofuel cell. Upon charging, the potentials of the electrodes are shifted to more positive (cathode) and more negative (anode) values because of a change in the a(ox-)to-a(red) ratio within the redox polymer matrix. Hence, a potential inversion occurs in the charged state (E-anode < E-cathode) and an open circuit voltage of >0.4 V is achieved and the bio-device acts as a true biosupercapacitor. The bioanode consists of a novel specifically designed high-potential Os complex modified polymer for the efficient immobilization and electrical wiring of glucose converting enzymes, such as glucose oxidase and flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase. The cathodic side is constructed from a low-potential Os complex modified polymer integrating the O-2 reducing enzyme, bilirubin oxidase. The large potential differences between the redox polymers and the prosthetic groups of the biocatalysts ensure fast and efficient charging of the biodevice.

Detailed impedance and voltammetric studies of hexameric octaheme nitrite reductase immobilized on carbon-based nanomaterials, specifically nanotubes and nanoparticles, were performed. Well-pronounced bioelectrocatalytic reduction of nitrite on enzyme-modified electrodes was obtained. Analysis of the impedance data indicated the absence of long-lived intermediates involved in the nitrite reduction. Cyclic voltammograms of biomodified electrodes had a bi-sigmoidal shape, which pointed to the presence of two enzyme orientations on carbon supports. The maximum (limiting) catalytic currents were determined and, by applying the correction by the mixed kinetics equation, the Tafel dependences were plotted for each catalytic wave/each enzyme orientation. Finally, two schemes for the rate-limiting processes during bioelectrocatalysis were proposed, viz. for low- and high-potential orientations.

A flexible electrochemical micro(bio)sensor has been designed for determination of several biological compounds, specifically, ascorbate, dopamine, and glucose, in human lachrymal liquid (tears). The microsensor for simultaneous determination of ascorbate and dopamine concentrations was based on a gold microwire modified with the tetrathiafulvalen–7,7,8,8-tetracyanoquinodimethane complex as a catalyst. To monitor glucose concentration in tears, glucose dehydrogenase was immobilized on a gold microwire modified with carbon nanotubes and an osmium redox polymer. A capillary microcell was constructed for sampling tears. The cell had a working volume of 60–100 nL with a sampling deviation of 6.7 %. To check if the microcell was properly filled with buffer or tear sample, a control electrode was introduced into the construction. The electrode was used to measure the electrical resistance of a fully filled nanovolume cell. The mechanical flexibility is one of the most important features of the prototype and allowed direct collection of tears with minimized risk of damage to the eye.

When compared to the general population, socioeconomically disadvantaged communitiesfrequently experience compromised health. Monitoring the divide is challenging since standardizedbiomedical tests are linguistically and culturally inappropriate. The aim of this study was to developand test a unique mobile biomedical testbed based on non-invasive analysis, as well as to explorethe relationships between the objective health measures and subjective health outcomes, asevaluated with the World Health Organization Quality of Life survey. The testbed was evaluated in asocioeconomically disadvantaged neighborhood in Malmö, which has been listed as one of the twelvemost vulnerable districts in Sweden. The study revealed that compared to conventional protocolsthe less intrusive biomedical approach was highly appreciated by the participants. Surprisingly, thecollected biomedical data illustrated that the apparent health of the participants from the ethnicallydiverse low-income neighborhood was comparable to the general Swedish population. Statisticallysignificant correlations between perceived health and biomedical data were disclosed, even thoughthe dependences found were complex, and recognition of the manifest complexity needs to beincluded in further research. Our results validate the potential of non-invasive technologies incombination with advanced statistical analysis, especially when combined with linguistically andculturally appropriate healthcare methodologies, allowing participants to appreciate the significanceof the different parameters to evaluate and monitor aspects of health.

A chloride-resistant high-potential biocathode based on Trametes hirsuta laccase incorporated into an optimized Os-complex modified redox hydrogel (80 mV potential difference to the T1 Cu) is described. The bioelectrocatalytic activity towards O2 reduction is due to an intimate access of the polymer-bound Os-complex to the T1 Cu site. The chloride resistance of the biocathode is due to the tight binding of the polymer-bound Os-complex to the T1 Cu site.

The recent media hoopla regarding ‘smart’, ‘bionic’, or more appropriately, electronically augmented contact lenses is analyzed in terms of real achievements coupled to the critically important issue of power management. Not depending on the availability, currently or in the near future, of to-the-purpose discrete or integrated electronic devices, power management, including delivery/supply and temporal sustainability, will be an outstanding issue if present-day technology should remain the only option. Radically different approaches have been taken to deliver electric power to electronically augmented contact lenses, that is, ranging from quite simplistic wire-based delivery assemblies, grossly inappropriate for end users, to various elaborate wireless designs drawing on over-the-air power delivery, as well as solar and electrochemical cells. Nonetheless, given the complex restrictions offered by a contact lens, conventional, even state-of-the-art, power management technology is at an impasse, and to ensure a bright future for smart lenses, radical technological measures need to be taken. Bridging the conceptual gap between fuel cells and supercapacitors, an ingenious novel approach to on-lens power management is presented: a charge-storing fuel cell, or alternatively, a self-charging capacitor, that is, a hybrid electric power device.

We present a transparent and flexible self-charging biosupercapacitor based on an optimised mediator- and membrane-free enzymatic glucose/oxygen biofuel cell. Indium tin oxide (ITO) nanoparticles were spray-coated on transparent conducting ITO supports resulting in a flocculent, porous and nanostructured electrode surface. By this, high capacitive currents caused by an increased electrochemical double layer as well as enhanced catalytic currents due to a higher number of immobilised enzyme molecules were obtained. After a chemical pretreatment with a silane derivative, bilirubin oxidase from Myrothecium verrucaria was immobilized onto the ITO nanostructured electrode surface under formation of a biocathode, while bioanodes were obtained by either immobilisation of cellobiose dehydrogenase from Corynascus thermophilus or soluble PQQ-dependent glucose dehydrogenase from Acinetobacter calcoaceticus. The latter showed a lower apparent K-M value for glucose conversion and higher catalytic currents at mu M glucose concentrations. Applying the optimised device as a biosupercapacitor in a discontinuous charge/discharge mode led to a generated power output of 0.030 mW/cm(2) at 50 mu M glucose, simulating the glucose concentration in human tears. This represents an enhancement by a factor of 350 compared to the power density obtained from the continuously operating biofuel cell with a maximum power output of 0.086 mu W/cm(2) under the same conditions. After 17 h of charging/discharging cycles a remarkable current enhancement was still measured. The entire device was transferred to flexible materials and applied for powering a flexible display showing its potential applicability as an intermittent power source in smart contact lenses.

The development of miniature autonomous bioelectronic devices that function in the human or animal internal environments is one of the most popular areas of bioelectronics. In recent works, a concept was developed for the creation of charge-storing fuel cells, or in other words self-charging supercapacitors based on (bio)electrodes with a dual function of generation and accumulation of electric charge and operating in both continuous and pulse modes. The main purpose of this work is to create a potentially implantable biodevice with a dual function of generation and accumulation of electrical charge on the basis of a membraneless nanobiocomposite biocathode with CNT/PANI/MvBOx composite material and a bioanode with GOx/AuNPs composite material, as well as investigation of their stability and efficiency in solutions close to the human blood. Nanobiocomposite materials are widely used as components of electronic devices for biomedical applications (biosensors, bio-fuel cells, biobataries, etc.) Modern bioelectronic devices based on nanocomposite materials can be used to influence organs and tissues, as well as for point delivery of drugs. Electrically conductive polymers are usually synthesized by chemical methods in an acid medium by oxidative polymerization of the monomer. This approach has a number of disadvantages, in particular, contamination of the final product with residual monomers and oxidant degradation products. Therefore, in this paper, electrochemical and enzymatic methods for the synthesis of electrically conducting polymers have been tested, which may be an alternative to chemical polymerization.

Capacitive humidity sensors typically consist of interdigitated electrodes coated with a dielectric layer sensitive to varying relative humidity levels. Previous studies have investigated different polymeric materials that exhibit changes in conductivity in response to water vapor to design capacitive humidity sensors. However, lipid films like monoolein have not yet been integrated with humidity sensors, nor has the potential use of capacitive sensors for skin hydration measurements been fully explored. This study explores the application of monoolein-coated wireless capacitive sensors for assessing relative humidity and skin hydration, utilizing the sensitive dielectric properties of the monoolein-water system. This sensitivity hinges on the water absorption and release from the surrounding environment. Tested across various humidity levels and temperatures, these novel double functional sensors feature interdigitated electrodes covered with monoolein and show promising potential for wireless detection of skin hydration. The water uptake and rheological behavior of monoolein in response to humidity were evaluated using a quartz crystal microbalance with dissipation monitoring. The findings from these experiments suggest that the capacitance of the system is primarily influenced by the amount of water in the monoolein system, with the lyotropic or physical state of monoolein playing a secondary role. A proof-of-principle demonstration compared the sensor's performance under varying conditions to that of other commercially available skin hydration meters, affirming its effectiveness, reliability, and commercial viability.

A new conceptual approach to improve the performance of a laccase-based cathode at neutral pH is presented. The working pH of Trametes hirsuta laccase, typically acidic, can be achieved by oxidn. of biol. compds. such as glucose catalyzed by a second enzyme immobilized in the vicinity of the laccase electrode.

We report on the fabrication and characterisation of the very first direct electron transfer-based glucose/oxygen biofuel cell (BFC) operating in neutral glucose-containing buffer and human serum. Corynascus thermophilus cellobiose ehydrogenase and Myrothecium verrucaria bilirubin oxidase were used as anodic and cathodic bioelements, respectively. The following characteristics of the mediator-, separator- and membrane-less, a priori, non-toxic and simple miniature BFC, was obtained: an open-circuit voltage of 0.62 and 0.58 V, a maximum power density of ca. 3 and 4 lW cm–2 at 0.37 and 0.19 V of cell voltage, in phosphate buffer and human serum, respectively.

We report the fabrication and characterisation of a non-compartmentalised, mediator and cofactor free glucose–oxygen biofuel cell based on adsorbed enzymes exhibiting direct bioelectrocatalysis, viz. cellobiose dehydrogenase from Dichomera saubinetii and laccase from Trametes hirsuta as the anodic and cathodic bioelements, respectively, with the following characteristics: an open-circuit voltage of 0.73 V; a maximum power density of 5 μW cm−2 at 0.5 V of the cell voltage and an estimated half-life of >38 h in air-saturated 0.1 M citrate–phosphate buffer, pH 4.5 containing 5 mM glucose.

It was found that homogeneous activity of Trametes hirsuta laccase is considerably diminished in the presence of gold nanoparticles (Au-NPs). Heterogeneous electron transfer studies revealed that Au-NPs facilitate direct electron transfer (DET) between the T1 copper site of the laccase and the surface of Au-NP modified electrodes. DET was characterized by the standard heterogeneous ET constant of 0.5 +/- 0.6 s(-1) at Au-NPs with an average diameter of 50 nm. As a consequence of this a well pronounced DET based bioelectrocatalytic oxygen reduction with current densities of 5-30 mu A cm(-2) has been achieved at the laccase-Au-NP modified electrodes.

Bioelectrocatalytic reduction of oxygen to water at electrodes modified with gold nanoparticles and a new laccase from Trichaptum abietinum (TaLc) was studied. The bioelectrocatalytic current was found to be much higher at TaLc modified electrodes than at similarly prepared electrodes modified with a broadly used laccase from Trametes hirsuta (ThLc). To explain this difference the bioelectrocatalysis was described in terms of kinetic rate constants based on simultaneous cyclic voltammetry and quartz crystal microbalance measurements. From analysis of the rate constants both laccases appeared to possess similar rates (k(0)) of direct electron transfer. However, the enzyme turnover (k(cat)) was about three-fold higher for gold nanoparticle bound TaLc than for ThLc, calculated using surface concentration of enzyme established by QCM-D. Near reversible potential-induced reorientation of adsorbed proteins was observed by surface enhanced Raman spectroscopy. (C) 2014 Elsevier Ltd. All rights reserved.

Specific wiring of biocatalysts par excellence, viz. redox enzymes, to an electrode can be exploited in the fabrication of high-performance bioelectronic devices. Here we report oxygen electroreduction catalysed by Didymocrea sp. J6 laccase wired to gold nanoparticles via the trinuclear copper cluster. Bypassing the intramolecular electron transfer, which under certain conditions is the rate-limiting step of oxygen bioelectroreduction, has resulted in the fabrication of a high current density biocathode based on high-redox-potential laccase, which is able to operate in electrolytes with a broad pH range in the presence of high fluoride concentrations.

High surface area graphene electrodes were prepd. by simultaneous electrodeposition and electroredn. of graphene oxide. The electrodeposition process was optimized in terms of pH and cond. of the soln. and the obtained graphene electrodes were characterized by XPS, FTIR spectroscopy, SEM and electrochem. methods (cyclic voltammetry and impedance spectroscopy)​. Electrodeposited electrodes were further functionalized to carry out covalent immobilization of two O-​reducing multicopper oxidases: laccase and bilirubin oxidase. The enzymic electrodes were tested as direct electron transfer based biocathodes and catalytic currents ≤1 mA​/cm2 were obtained. Finally, the mechanism of the enzymic O redn. reaction was studied for both enzymes calcg. the Tafel slopes and transfer coeffs.

An IR spectroelectrochem. study of Trametes hirsuta laccase and Magnaporthe oryzae bilirubin oxidase has been performed using azide, an inhibitor of multicopper oxidases, as an active IR probe incorporated into the T2​/T3 copper cluster of the enzymes. The redox potential-​controlled measurements indicate that N3-​ stretching IR bands of azide ion bound to the T2​/T3 cluster are only detected for the oxidized enzymes, confirming that azide only binds to Cu2+. Moreover, the process of binding​/dissocn. of azide ion is shown to be reversible. The interaction of halide anions, which also inhibit multicopper oxidases, with the active site of the enzymes was studied by measuring the changes in the azide FTIR bands. Enzymes inhibited by azide respond differently upon addn. of fluoride or chloride ions to the sample soln. inhibited by azide. Fluoride ions compete with azide for binding at one of the T2​/T3 Cu ions, whereas competition from chloride ions is much less evident.

The multicopper oxidase Trametes hirsuta laccase (ThLc) served as a bioelectrocatalyst on nanostructured cathodes. Nanostructuring was provided by gold nanorods (AuNRs)​, which were characterized and covalently attached to electrodes made of low-​d. graphite. The nanostructured electrode was the scaffold for covalent and oriented attachment of ThLc. The bioelectrocatalytic currents measured for oxygen redn. were as high as 0.5 mA​/cm2 and 0.7 mA​/cm2, which were recorded under direct and mediated electron transfer regimes, resp. The exptl. data were fitted to math. models showing that when the O2 is bioelectroreduced at high rotation speed of the electrode the heterogeneous electron transfer step is the rate-​liming stage. The electrochem. measurement hints a wider population of non-​optimally wired laccases than previously reported for 5-​8 nm size Au nanoparticle-​modified electrode, which could be due to a larger size of the AuNRs when compared to the laccases as well as their different crystal facets.

This study was aimed to create a practical supervision model, in which three levels of academic work are weaved together: undergraduate studies, PhD stidies and research programs. The research methods used in development of the supervision model include literature studies, seminars connected to the subject and abductive reasoning. This work resulted in development of a multipart model called TRIAD SUPERVISION. This TRIAD model of supervising is meant to be used at bachelor-level in nursing education where the supervision may become a didactically conducted process of learning. It is concluded that the TRIAD way of crating learning environment may be a smooth introduction to empiric concepts of students.

Here for the first time, we detail self-​contained (wireless and self-​powered) biodevices with wireless signal transmission. Specifically, we demonstrate the operation of self-​sustained carbohydrate and oxygen sensitive biodevices, consisting of a wireless electronic unit, radio transmitter and sep. sensing bioelectrodes, supplied with elec. energy from a combined multi-​enzyme fuel cell generating sufficient current at required voltage to power the electronics. A carbohydrate​/oxygen enzymic fuel cell was assembled by comparing the performance of a range of different bioelectrodes followed by selection of the most suitable, stable combination. Carbohydrates (viz. lactose for the demonstration) and oxygen were also chosen as bioanalytes, being important biomarkers, to demonstrate the operation of the self-​contained biosensing device, employing enzyme-​modified bioelectrodes to enable the actual sensing. A wireless electronic unit, consisting of a micropotentiostat, an energy harvesting module (voltage amplifier together with a capacitor) and a radio microchip, were designed to enable the biofuel cell to be used as a power supply for managing the sensing devices and for wireless data transmission. The electronic system used required current and voltages greater than 44 μA and 0.57 V, resp. to operate; which the biofuel cell was capable of providing, when placed in a carbohydrate and oxygen contg. buffer. In addn., a USB based receiver and computer software were employed for proof-​of concept tests of the developed biodevices. Operation of bench-​top prototypes was demonstrated in buffers contg. different concns. of the analytes, showcasing that the variation in response of both carbohydrate and oxygen biosensors could be monitored wirelessly in real-​time as analyte concns. in buffers were changed, using only an enzymic fuel cell as a power supply.

Here we present unequivocal exptl. proof that microscale cofactor- and membrane-less, direct electron transfer based enzymic fuel cells do produce significant amts. of elec. energy in human lachrymal liq. (tears). 100 μm diam. gold wires, covered with 17 nm gold nanoparticles, were used to fashion three-dimensional nanostructured microelectrodes, which were biomodified with Corynascus thermophilus cellobiose dehydrogenase and Myrothecium verrucaria bilirubin oxidase as anodic and cathodic bioelements, resp. The following characteristics of miniature glucose/oxygen biodevices operating in human tears were registered: 0.57 V open-circuit voltage, about 1 μW cm-2 max. power d. at a cell voltage of 0.5 V, and more than 20 h operational half-life. Theor. calcns. regarding the max. recoverable elec. energy can be extd. from the biofuel and the biooxidant, glucose and mol. oxygen, each readily available in human lachrymal liq., fully support our belief that biofuel cells can be used as elec. power sources for so called smart contact lenses.

To elucidate the mechanism of bilirubin oxidase (BOx)function in order to design efficient and stablebiocathodes working at different conditions, the enzymewas studied thoroughly. BOx is a copper-containing redoxenzyme that catalyzes the oxidation of a variety ofdifferent organic and inorganic compounds withconcomitant reduction of O2 directly to H2O.

A microscale membrane-​less biofuel cell, capable of generating elec. energy from human lachrymal liq., was developed by using the ascorbate and oxygen naturally present in tears as fuel and oxidant. The biodevice is based on three-​dimensional nanostructured gold electrodes covered with abiotic (conductive org. complex) and biol. (redox enzyme) materials functioning as efficient anodic and cathodic catalysts, resp. Three-​dimensional nanostructured electrodes were fabricated by modifying 100 μm gold wires with 17 nm gold nanoparticles, which were further modified with tetrathiafulvalene-​tetracyanoquinodimethane conducting complex to create the anode and with Myrothecium verrucaria bilirubin oxidase to create the biocathode. When operated in human tears, the biodevice exhibited the following characteristics: an open circuit voltage of 0.54 V, a maximal power d. of 3.1 μW cm-​2 at 0.25 V and 0.72 μW cm-​2 at 0.4 V, with a stable c.d. output of over 0.55 μA cm-​2 at 0.4 V for 6 h of continuous operation. These findings support the authors' proposition that an ascorbate​/oxygen biofuel cell could be a suitable power source for glucose-​sensing contact lenses to be used for continuous health monitoring by diabetes patients.

A review of some historical developments made in the field of enzymic fuel cells, discussing important design considerations taken when constructing mediator-, cofactor-, and membrane-less biol. fuel cells. Since the topic is rather extensive, only biol. fuel cells utilizing direct electron transfer reactions on both the anodic and cathodic sides are considered. Moreover, the performance of mostly glucose/oxygen biodevices is analyzed and compared. We also present some unpublished results on mediator-, cofactor-, and membrane-less glucose/oxygen biol. fuel cells recently designed in our group and tested in different human physiol. fluids, such as blood, plasma, saliva, and tears. Finally, further perspectives for biol. fuel cell applications are highlighted.

A review. Interdisciplinary research has combined the efforts of many scientists and engineers to gain an understanding of biotic and abiotic electrochem. processes, materials properties, biomedical, and engineering approaches for the development of alternative power-​generating and​/or energy-​harvesting devices, aiming to solve health-​related issues and to improve the quality of human life. This review intends to recapitulate the principles of biofuel cell development and the progress over the years, thanks to the contribution of cross-​disciplinary researchers that have combined knowledge and innovative ideas to the field. The emergence of biofuel cells, as a response to the demand of elec. power devices that can operate under physiol. conditions, are reviewed. Implantable biofuel cells operating inside living organisms have been envisioned for over fifty years, but few reports of implanted devices have existed up until very recently. The very first report of an implanted biofuel cell (implanted in a grape) was published only in 2003 by Adam Heller and his coworkers. This work was a result of earlier scientific efforts of this group to "wire" enzymes to the electrode surface. The last couple of years have, however, seen a multitude of biofuel cells being implanted and operating in different living organisms, including mammals. Herein, the evolution of the biofuel concept, the understanding and employment of catalyst and biocatalyst processes to mimic biol. processes, are explored. These potentially green technol. biodevices are designed to be applied for biomedical applications to power nano- and microelectronic devices, drug delivery systems, biosensors, and many more.

Sweat is a promising biofluid in allowing for non-invasive sampling. Here, we investigate the use of a voltammetric electronic tongue, combining different metal electrodes, for the purpose of non-invasive sample assessment, specifically focusing on sweat. A wearable electronic tongue is presented by incorporating metal electrodes on a flexible circuit board and used to non-invasively monitor sweat on the body. The data obtained from the measurements were treated by multivariate data processing. Using principal component analysis to analyze the data collected by the wearable electronic tongue enabled differentiation of sweat samples of different chemical composition, and when combined with 1H-NMR sample differentiation could be attributed to changing analyte concentrations.

We present data on operation of a miniature membrane-less, direct electron transfer based enzymatic fuel cell in human sweat and saliva. The enzymatic fuel cell was fabricated following our previous reports on miniature biofuel cells, utilizing gold nanoparticle modified gold microwires with immobilized cellobiose dehydrogenase and bilirubin oxidase. The following average characteristics of miniature glucose/oxygen biodevices operating in human sweat and saliva, respectively, were registered: 580 and 560 mV open-circuit voltage, 0.26 and 0.1 μW cm–2 power density at a cell voltage of 0.5 V, with up to ten times higher power output at 0.2 V. When saliva collected after meal ingestion was used, roughly a two-fold increase in power output was obtained, with a further two-fold increase by addition of 500 μM glucose. Likewise, the power generated in sweat at 0.5 V increased two-fold by addition of 500 μM glucose.

An electronic tongue is a powerful analytical instrument based on an array of non-selective chemical sensors with a partial specificity for data gathering and advanced pattern recognition methods for data analysis. Connecting electronic tongues with electrochemical techniques for data collection has led to various applications, mostly within sensing for food quality and environmental monitoring, but also in biomedical research for the analyses of different bioanalytes in human physiological fluids. In this paper, an electronic tongue consisting of six electrodes (viz., gold, platinum, palladium, titanium, iridium, and glassy carbon) was designed and tested in authentic (undiluted, unpretreated) human saliva samples from eight volunteers, collected before and during the COVID-19 pandemic. Investigations of 11 samples using differential pulse voltammetry and a principal component analysis allowed us to distinguish between SARS-CoV-2-free and infected authentic human saliva. This work, as a proof-of-principle demonstration, provides a new perspective for the use of electronic tongues in the field of enzyme-free electrochemical biosensing, highlighting their potential for future applications in non-invasive biomedical analyses.

Non-invasive healthcare technologies are an important part of research and development nowadays due to the low cost and convenience offered to both healthcare receivers and providers. This work overviews the recent advances in the field of non-invasive electrochemical biosensors operating in secreted human physiological fluids, viz. tears, sweat, saliva, and urine. Described electrochemical devices are based on different electrochemical techniques, viz. amperometry, coulometry, cyclic voltammetry, and impedance spectroscopy. Challenges that confront researchers in this exciting area and key requirements for biodevices are discussed. It is concluded that the field of non-invasive sensing of biomarkers in bodily fluid is highly convoluted. Nonetheless, if the drawbacks are appropriately addressed, and the pitfalls are adroitly circumvented, the approach will most certainly disrupt current clinical and self-monitoring practices.

In the last few years, there have been an increasing number of reports where different energy harvesters are directly combined with charge storing devices, based on dual-function electrodes able to convert and store electrical energy in the same volume. This includes (bio)fuel cells harvesting chemical energy, (bio)solar cells harvesting solar energy, tribo- and piezoelectric devices harvesting mechanical energy, and thermoelectrics harvesting thermal energy, which now have been intimately combined with batteries and electrochemical capacitors. These new types of hybrid electric devices show great promise especially for the design of self-powered electronics where an integrated hybrid power system is preferable to separated ones, capable of scavenging ambient energy and simultaneously store it and in this way increasing the efficiency and enabling further miniaturization. This paper details the recent emergence of hybrid energy systems, reviewing the progress made using widely different energy harvesting techniques, which have so-far not been described in a single body of work.

Galactose monitoring in individuals allows the prevention of harsh health conditions related to hereditary metabolic diseases like galactosemia. Current methods of galactose detection need development to obtain cheaper, more reliable, and more specific sensors. Enzyme-containing amperometric sensors based on galactose oxidase activity are a promising approach, which can be enhanced by means of their inclusion in a redox polymer coating. This strategy simultaneously allows the immobilization of the biocatalyst to the electroactive surface and hosts the electron shuttling units. An additional deposition of capping polymers prevents external interferences like ascorbic or uric acid as well as biofouling when measuring in physiological fuels. This work studies the protection effect of poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate (MPC) and polyvinylimidazole-polysulfostyrene (P(VI-SS)) when incorporated in the biosensor design for the detection of galactose in human plasma.

Here we report on an entirely new kind of bioelectronic device - a solar biosupercapacitor, which is built from a dual-​feature photobioanode combined with a double-​function enzymic cathode. The self-​charging biodevice, based on transparent nanostructured indium tin oxide electrodes modified with biol. catalysts, i.e. thylakoid membranes and bilirubin oxidase, is able to capacitively store electricity produced by direct conversion of radiant energy into elec. energy. When self-​charged during 10 min, using ambient light only, the biosupercapacitor provided a max. of 6 mW m-​ 2 at 0.20 V.

We detail a mediator- and membrane-free enzymatic glucose/oxygen biofuel cell based on transparent and nanostructured conducting supports. Chemically modified indium tin oxide nanoparticle modified electrodes were used to substantially increase the active surface area without significantly compromising transparency. Two different procedures for surface nanostructuring were employed, viz. spray-coating and drop-coating. The spray-coated biodevice showed superior characteristics as compared to the drop-coated enzymatic fuel cell, as a result of the higher nanostructured surface area as confirmed by electrochemical characterisation, as well as scanning electron and atomic force microscopy. Subsequent chemical modification with silanes, followed by the immobilisation of either cellobiose dehydrogenase from Corynascus thermophiles or bilirubin oxidase from Myrothecium verrucaria, were performed to obtain the bioanodes and biocathodes, respectively. The optimised biodevice exhibited an OCV of 0.67 V and power output of up to 1.4 mu W/cm(2) at an operating voltage of 0.35 V. This is considered a significant step forward in the field of glucose/oxygen membrane- and mediator-free, transparent enzymatic fuel cells.

Here we report on an entirely new kind of bioelectronic device - a conventional biosupercapacitor, which is built from copper containing redox proteins. Prior to biodevice fabrication, detailed spectroelectrochemical studies of the protein, viz. Acidithiobacillus ferrooxidcats rusticyanin, in solution and in adsorbed state, were performed, including estimation of the redox potential of the T1 site (0.62 V vs. NHE), protein midpoint potential when adsorbed on a self-assembled monolayer (0.34 V vs. NHE), as well as biocapacitance of rusticyanin modified gold electrodes (115 mu F cm(-2)). The symmetrical biosupercapacitor based on two identical gold electrodes modified with rusticyanin is able to capacitively store electricity and deliver electric power accumulated mostly in the form of biopseudocapacitance, when charged and discharged externally. When charged during Just 5 s, the biosupercapacitor with a total capacitance of about 73 mu F cm(-2) provided a maximum of 4 mu A cm(-2) peak current at 0.40 V. The biodevice, which can be charged and discharged at least 50 times without a significant loss of ability to store electric energy, had a low leakage current below 50 nA cm(-2).

Here the authors detail an optimized transparent capacitive glucose oxidizing bioanode, capable of supplying current densities of 10 μA cm-​2 at applied potentials of 0.1 V-​0.2 V vs. SCE, when continuously performing in a simple phosphate buffer, pH 7.4 and artificial human tears, both with a glucose concn. of 0.05 mM only. When operating in pulse mode, the bioanode was able to deliver current densities ≤21 μA cm-​2 at the beginning of the pulse with 571 μC cm-​2 total charges stored. The biogenic part of the enzymic device was a recombinant glucose oxidase mutant from Penicillium amagasakiense with high catalytic efficiency towards glucose, up to 14.5x104 M-​1 s-​1. The nonbiogenic part of the anodic system was based on a poly(3,​4-​ethylenedioxythiophene)​-​graphene nanocomposite, as a highly capacitive component with a capacitance d. in the 1 mF cm-​2 range, multi-​walled carbon nanotubes, as an addnl. nanostructuring element, and a conductive org. complex, as an electron shuttle between the redox enzyme and the electrode surface. The bioanode could potentially serve as a prototype of a double-​function enzymic anode for hybrid elec. power biodevices, energizing smart contact lenses.

Direct electron transfer (DET) reactions between redox enzymes and electrodes can be maximized by oriented immobilization of the enzyme mols. onto an electroactive surface modified with functionalized Au nanoparticles (AuNPs). Here, the authors present such strategy for obtaining a DET-based laccase (Lc) cathode for O2 electroredn. at low overpotentials. The stable nanostructured enzymic electrode is based on the step-by-step covalent attachment of AuNPs and Lc mols. to porous graphite electrodes using the diazonium salt redn. strategy. Oriented immobilization of the enzyme mols. on adequately functionalized AuNPs allows establishing very fast DET with the electrode via their Cu T1 site. The measured electrocatalytic waves of O2 redn. can be deconvoluted into two contributions. The one at lower overpotentials corresponds to immobilized Lc mols. that are efficiently wired by the AuNPs with a heterogeneous electron transfer rate const. k0 » 400 s-1.

The response of low-density graphite electrodes hosting Trametes hirsuta laccase in a direct electron transfer regime is presented for real-time analysis of O2 concentrations. The use of contrasting immobilisation methods developed for biocathodes affords good reproducibility and reliability of the amperometric biosensor, which shows a limit of detection below 1 µM and a sensitivity slightly higher than 60 nA cm−2 M.

Lactoperoxidase (LPO) is an enzyme, which is used as an antimicrobial agent in a number of applications, e.g., food technology. In the majority of applications LPO is added to a homogeneous product phase or immobilised on product surface. In the latter case, however, the measurements of LPO activity are seldom reported. In this paper we have assessed LPO enzymatic activity on bare and protein modified gold surfaces by means of electrochemistry. It was found that LPO rapidly adsorbs to bare gold surfaces resulting in an amount of LPO adsorbed of 2.9 mg/m2. A lower amount of adsorbed LPO is obtained if the gold surface is exposed to bovine serum albumin, bovine or human mucin prior to LPO adsorption. The enzymatic activity of the adsorbed enzyme is in general preserved at the experimental conditions and varies only moderately when comparing bare gold and gold surface pretreated with the selected proteins. The measurement of LPO specific activity, however, indicate that it is about 1.5 times higher if LPO is adsorbed on gold surfaces containing a small amount of preadsorbed mucin in comparison to the LPO directly adsorbed on bare gold.

More sustainable ways to produce and store energy are urgently needed to reduce our dependence on fossil fuels, which are the principal drivers of global warming and pollution. Hydrogen may become the energy vector needed for this purpose if its production through water splitting can become competitive against steam methane reforming. Even after decades of research, the proposed strategies for water splitting are not efficient enough to overcome the high overpotential of the water oxidation reaction. In a quest for new approaches to this problem, recent studies have attempted to combine inorganic catalysts with biocatalysts, aiming to open new possibilities towards a definitive solution. In the present work we have tested a chalcogenide semiconductor, SnS2, characterized by a deep valence band and a visible-light band gap of approximately 2.2eV (lambda=550nm). Preparation of a fluorine-doped tin oxide electrode modified with SnS2 and laccase allowed water oxidation at a lower overpotential, taking better advantage of light energy. Additionally, indium tin oxide nanoparticles were added to increase the contact area between SnS2 and the electrode surface and thereby improve charge separation for photobioelectrocatalytic water oxidation. We tested the nanostructured anode electrodes under different applied potentials and irradiance intensities from a solar simulator to find the optimal photonic and faradaic efficiencies.

An effect of permeabilisation and lyophilisation of the yeast cells Hansenula polymorpha on their electrochemical behaviour in the presence of mediators, substrates (formaldehyde, glucose, methanol, ethanol), and cofactors (NAD+, NADP+, NADH, NADPH, glutathione) has been studied. Two amperometric techniques differing in the cell immobilisation methods were applied. The cells of a wild strain (356) and mutant strains (C-105 and KCA 33) of the yeast, grown in the presence of glucose or methanol, were used in the experiments. The intact cells revealed the highest reduction rates of mediators, 2,6-dichlorphenolindophenol (DCIP) and 2,4-benzoquinone (BQ), as measured by amperometry. The addition of formaldehyde significantly enhanced the response, if the cells were grown in the presence of glucose. The permeabilised cells showed the lowest current level in the presence of DCIP and BQ and no response to the addition of formaldehyde and NAD+. However, the addition of NADH gave significant current surge. All these phenomena imply that the permeabilised cells lost cofactors and the activity of dehydrogenases producing NADH, but they remained the activity of NADH-ubiquinone oxidoreductase and of some components of the electron transport chain. The electrochemical behaviour of the lyophilised cells shows they are heterogeneous. The partial degradation of the outer membrane of the cells after their lyophilisation was electrochemically confirmed.

To characterise bioelectrocatalytic oxygen reduction at gold nanoparticles (AuNPs) modified with Trametes hirsuta laccase (ThLc) combined electrochemical and quartz crystal microbalance measurements have been used. The electrodes with different degrees of AuNP-monolayer coverage, theta, have been studied. In every case of theta close to theoretically possible 44 ThLc molecules adsorbed at 22 nm diameter AuNP. The bioelectrocatalytic current was recalculated down to the current at a single AuNR Unexpectedly, the current at a single AuNP was higher when theta was higher. The maximum current reached at a single AuNP was 31.10(-18) A which corresponds to the enzyme turnover (k(cat)) 13 s(-1). This rate is lower than the homogeneous ThLc turnover (190 s(-1)) suggesting partial denaturation of ThLc upon adsorption or that some ThLc are not in DET contact with the electrode surface

Direct electron transfer (DET) between cellobiose dehydrogenase from Humicola insolens ascomycete (HiCDH) and gold nanoparticles (AuNPs) was achieved by modifying AuNPs with a novel, pos. charged thiol N-​(6-​mercapto)​hexylpyridinium (MHP)​. The DET enabled the use of the HiCDH enzyme as an anodic biocatalyst in the design of a mediatorless carbohydrate​/oxygen enzymic fuel cell (EFC)​. A biocathode of the EFC was based on bilirubin oxidase from Myrothecium verrucaria (MvBOx) directly immobilized on the surface of AuNPs. The following parameters of the EFC based on Au​/AuNP​/MHP​/HiCDH bioanode and Au​/AuNP​/MvBOx biocathode were obtained in quiescent air satd. PBS, pH 7.4, contg.: (i) 5 mM glucose-​open-​circuit voltage (OCV) of 0.65 ± 0.011 V and the maximal power d. of 4.77 ± 1.34 μW cm-​2 at operating voltage of 0.50 V; or (ii) 10 mM lactose-​OCV of 0.67 ± 0.006 V and the maximal power d. of 8.64 ± 1.91 μW cm-​2 at operating voltage of 0.50 V. The half-​life operation times of the EFC were estd. to be at least 13 and 44 h in air satd. PBS contg. 5 mM glucose and 10 mM lactose, resp. Among advantages of HiCDH​/MvBOx FCs are (i) simplified construction, (ii) relatively high power output with glucose as biofuel, and (iii) the absence of the inhibition of the HiCDH based bioanode by lactose, when compared with the best previously reported CDH based bioanode.