Thin-film Platinum Electrodes Research Articles

An evaluation of the electrochemical characteristics of 2-nitrobenzene-1,4-diamine organic monomer on gold or platinum thin film electrodes with a full-block random design in acidic environments

The randomized all-design statistical method utilized to elaborate and optimize an experimental model of the electropolymerization of 2-nitrobenzene-1,4-diamine organic monomer. Thin film synthesis was performed using electrochemical cyclic voltammetry (CV) on Micrux® single electrodes made of platinum and gold (A = 0.008 cm2) in 0.1 mol dm–3 H2SO4 at 1.2 pH. The Micrux® electrode chips proved to be reusable with a single sample size of only 10 µL. The electrode material, sampling rate, and monomer concentration were investigated using the phenomenon of electropolymerization. The interaction between these factors was analyzed. The first anodic and second current peaks were selected as the response results. In the first module, a new chip was used for each run, while a previously refurbished chip was used in the second module. The morphological features of the polymers were observed using scanning electron microscopy. A reduction of the spherical particle size was observed when an increase in the sweep scan rate occurred. The importance of the block design, the interaction between the factors, the advantages of the used techniques, and the electropolymerization process of the new polymer were assessed. In comparison with the classical sputtering process, it was demonstrated that an electropolymerization coating using a Micrux® single electrode combined with a block design can be an effective approach to coat materials in optimum conditions.

A Direct-Reading MEMS Conductivity Sensor with a Parallel-Symmetric Four-Electrode Configuration.

This work proposes a design for a direct-reading conductivity sensor with a parallel symmetrical four-electrode structure, which integrates a silicon-based platinum thin-film strip electrode and a serpentine temperature compensation electrode. The optimal structural parameters of the electrode were determined by finite element simulations performed via COMSOL Multiphysics. Next, the designed conductivity sensor chip was fabricated using MEMS technology, and subsequently, the conductivity measurement circuit was designed to test the fabricated sensor’s performance. In laboratory tests, the optimal AC excitation frequency was observed to be 1.067 kHz, while the maximum measurement range was 0–107.41 mS/cm and the measurement precision in low concentration range (0–76.422 mS/cm) was ±0.1 mS/cm. Furthermore, the maximum measurement error of the sensor evaluated using the National Center of Ocean Standards and Metrology was ±0.073 mS/cm. The designed sensor possesses the characteristics of high accuracy, high range, and miniaturization, and enables real-time reading of conductivity value and temperature compensation, which is of great significance for the on-site observation of the physical parameters of marine environment.

In situ stability monitoring of platinum thin-film electrodes for neural interfaces in the presence of proteins.

The long-term stability of platinum electrodes is a key factor that determines the life-time of biomedical devices, such as implanted neural interfaces like brain stimulation or recording electrodes, cochlear implants, and biosensors. The downsizing of such devices relies on the usage of microfabricated thin-film electrodes. In order to determine and investigate the causal degradation processes for platinum electrodes, it is essential to use potential-controlled experiments, which allow selectable polarization of the electrode without exceeding the water stability window boundaries. Therefore, the surface processes and redox reactions occurring at the electrode are known at all times. In this study, we present the continuous in situ monitoring of platinum-based thin-film electrodes along their complete life cycle in neutral pH with and without the presence of proteins. The usage of chronoamperometry for electrode aging, monitoring of surface processes and the tracking of analyte redox processes, together with cyclic voltammetry to determine the complete amount of surface charge, allows a reliable quantification of fundamental degradation processes. We found that platinum dissolution is primarily driven by the formation and removal of Pt oxide. Despite the significantly lowered charge transfer, the presence of proteins did not prevent material loss or increase electrode lifetime. These results should be considered when interpreting results from current-controlled methods as typically used for neural interfaces. Clinical Relevance- All clinically relevant applications of microelectrodes, ranging from cell culture over diagnostics to in vivo use, involve the presence of proteins. Detailed and fundamental insight into electrode stability in the presence of proteins is therefore essential for successful clinical translation of neural interface technologies.

Towards a flexible electrochemical biosensor fabricated from biocompatible Bombyx mori silk

In modern days, there is an increasing relevance of and demand for flexible and biocompatible sensors for in-vivo and epidermal applications. One promising strategy is the implementation of biological (natural) polymers, which offer new opportunities for flexible biosensor devices due to their high biocompatibility and adjustable biodegradability. As a proof-of-concept experiment, a biosensor was fabricated by combining thin- (for Pt working- and counter electrode) and thick-film (for Ag/AgCl quasi-reference electrode) technologies: The biosensor consists of a fully bio-based and biodegradable fibroin substrate derived from silk fibroin of the silkworm Bombyx mori combined with immobilized enzyme glucose oxidase. The flexible glucose biosensor is encapsulated by a biocompatible silicon rubber which is certificated for a safe use onto human skin. Characterization of the sensor set-up is exemplarily demonstrated by glucose measurements in buffer and Ringer's solution, while the stability of the quasi-reference electrode has been investigated versus a commercial Ag/AgCl reference electrode. Repeated bending studies validated the mechanical properties of the electrode structures. The cross-sensitivity of the biosensor against ascorbic acid, noradrenaline and adrenaline was investigated, too. Additionally, biocompatibility and degradation tests of the silk fibroin with and without thin-film platinum electrodes were carried out.

Voltammetry of 7-dehydrocholesterol as a new and useful tool for Smith-Lemli-Opitz syndrome diagnosis

7-Dehydrocholesterol is an essential biomarker of Smith-Lemli-Opitz syndrome, a congenital autosomal recessive disorder. This study shows for the first time that electrochemical oxidation of 7-dehydrocholesterol can be used for its voltammetric determination. Two classes of supporting electrolytes in acetonitrile and a mixture of acetonitrile-water were used: inorganic acids known to promote structural changes of steroids and indifferent electrolytes. Oxidation of 7-dehydrocholesterol at ca +0.8 V (vs. Ag/AgNO3 in acetonitrile) in 0.1 mol L−1 NaClO4 in acetonitrile is useful for its voltammetric detection using common bare electrode materials. Detection limits for 7-dehydrocholesterol lie in the low micromolar range for all the working electrodes, including boron-doped diamond (0.4 μmol L−1) and disposable thin-film platinum electrodes (0.5 μmol L−1), which are advantageous because of the low volumes of studied solutions. After Bligh-Dyer extraction, quantification of 7-dehydrocholesterol concentration (boron-doped diamond) or concentration range (thin-film platinum) is easily attainable in artificial serum. The mere knowledge of the concentration range provides clinically valuable information, as 7-dehydrocholesterol levels are employed for SLOS diagnosis as a binary criterion (elevated, tens to hundreds μmol L−1 in symptomatic/non-elevated, typically bellow 1 μmol L−1 in healthy individuals in plasma). Moreover, it is shown that 7-dehydrocholesterol (provitamin D3) and cholecalciferol (vitamin D3) can be oxidized in 0.1 mol L−1 HClO4 in acetonitrile. Under these conditions, their voltammetric response changes dramatically, and their oxidation potential difference transiently increases from 0.08 V to 0.25 V, which should facilitate their simultaneous voltammetric determination. This work constitutes a foundation for a reliable and straightforward method for Smith-Lemli-Opitz syndrome diagnosis and monitoring 7-dehydrocholesterol’s biotransformation to cholecalciferol.

The Role of Local Heating and Phosphate Poisoning during the Oxygen Reduction Reaction in Solid Acid Fuel Cells

With the ongoing effort to decarbonize and decentralize the electricity infrastructure by shifting to renewable energy sources, fuel cells and in particular intermediate temperature fuel cells receive a growing interest as a promising technology for a highly efficient, on demand transformation of chemical into electrical energy. Since the 2000s, fuel cells have cycled from high expectations to disillusion, caused by the high production cost an insufficient stability. High temperature polymer electrolyte membrane fuel cells (HT PEM FC) are a prominent and well investigated candidate for the intermediate temperature range. However, the usage of concentrated, highly corrosive phosphorous acid as membrane dopant required expensive production materials and causes deterioration of the catalyst over time. Changing from a liquid to a solid electrolyte can simultaneously improve the long term stability and reduce the construction price. A suitable solid acid is CsH2PO4. It is a non-toxic and less corrosive electrolyte with a proton conductivity of 2*10-2 S/cm at 240°C.[1] Since first demonstrated for fuel cell fabrication in 2003,[2] the platinum utilization and power densities have been improved ever since.[3,4] Solid acid fuel cells (SAFC) are already used in industry in a small scale, but the development has been hampered by the poor stability of the cathode electrode. The rate limiting reaction step is the complex oxygen reduction reaction (ORR) at the cathode side. During operation, it is the largest source of overpotential and hence waste heat generation.[5] For an active site, the current collector, electrolyte and gas phase need to be in direct contact with each other to provide all necessary reactants, thereby the interface resistance between the current collector and the catalyst is crucial for the performance.In the work we are going to present, we investigated electrodes based on a platinum thin film catalyst layer.[6,7] These electrodes enable us to investigate degradation effects on a reasonable time scale. We will show that only a few areas close to the current collectors meet the requirements for active sites and consequently generating most of the measured current, leading to a localized heating. We observed a current density depended morphology chance of CsH2PO4 during operation at these active sites, located close to the current collector. While a variety of degradation processes can result from this process, we determined a phosphate adsorption on the catalyst as the most pronounced one. Similar to HT PEM FC, phosphate species from the electrolyte can adsorb at the platinum surface and act as catalyst poison.[8–10] We will present, that these poisoning effects can be reversed but not prevented by cyclic voltammetry (CV) measurements. After reactivating the cell by CV measurements, the cell performance increased to the initial value before degrading again. The reversibility of the process was shown for five reactivations over a period of 50 h. Overall, we identified the cause and nature of the main degradation mechanism in solid acid fuel cells with platinum thin film electrodes and will present different design optimizations for a stable, high performance fuel cell which arise from our findings.

Detection of sulfur dioxide at low parts-per-million concentrations using low-cost planar electrodes with ionic liquid electrolytes

Sulfur dioxide (SO2) is a toxic gas at low parts-per-million (ppm) concentrations, with a permissible exposure limit (PEL) of 2 ppm. Its detection is mandatory, particularly in the fields of occupational health and safety, and environmental pollution. In this work, ppm concentration detection of sulfur dioxide was performed in six room temperature ionic liquids (RTILs), as well as on two different electrode materials – platinum and gold – and with two different electrode geometries, i.e. macro thin-film electrodes (TFEs) and microarray thin-film electrodes (MATFEs). Calibration curves were established for 10–200 ppm SO2 using cyclic voltammetry to determine the optimum combination of RTIL, electrode surface and geometry for the sensing. The RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonium)imide ([C4mpyrr][NTf2]) with a platinum thin-film electrode was found to give the best response due to the relatively low viscosity of the RTIL combined with the high sensitivity and a clean blank response. On MATFEs, deposited sulfur particles – confirmed using scanning electron microscopy (SEM) coupled to an energy dispersive spectrometer – were found to passivate and block some of the microholes, leading to unstable long-term chronoamperometric responses. To the best of our knowledge, this is the first observation of sulfur deposition from SO2 reduction in aprotic ionic liquids. Consecutive additions of 2 ppm SO2 were studied in [C4mpyrr][NTf2] on a TFE using long-term chronoamperometry, showing excellent reproducibility upon successive additions. This demonstrates that small volumes of RTILs can be combined with miniaturized, low-cost TFEs and applied for the reliable and continuous monitoring of sulfur dioxide gas at concentrations lower than the permissible exposure limit of 2 ppm.

Electrochemical Properties of a Verdazyl Radical in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) have been widely investigated as alternative electrochemical solvents for a range of dissolved species over the past two decades. However, the behaviour of neutral radicals dissolved in RTILs is relatively unexplored. In this work, the electrochemistry of a stable verdazyl radical – 1,5-dimethyl-3-phenyl-6-oxoverdazyl (MPV) – has been studied on a platinum thin-film electrode using cyclic voltammetry and chronoamperometry in 10 different RTILs. The organic solvent propylene carbonate is also employed as a comparison. The nature of the solvent system was found to have a large effect on the electrochemical behaviour, particularly on the reduction reaction of the verdazyl radical. Chronoamperometry on a microdisk electrode was used to calculate diffusion coefficients (D), and plots of D versus the inverse of viscosity were linear, suggesting typical hydrodynamic diffusional characteristics of the radical, in line with the behaviour of dissolved neutral and charged compounds (e.g. ferrocene and cobaltocenium) in RTILs. Overall, this study demonstrates that different RTILs have a significant influence on the electrochemistry of MPV, and therefore careful selection of the solvent system for electrochemical applications is advised.

Quantitative determination of H2O2 for detection of alanine aminotransferase using thin film electrodes

The abnormal concentrations or absence of biomolecules (e.g., proteins) in blood can further be used in diagnosis of a particular pathology at an early stage. Current studies are intensely focusing on the analysis of interaction and detection of biomolecules via point-of-care systems (POCs), allowing miniaturized and parallelized reactions, simultaneously. Recent developments have shown that the collaboration of electrochemical sensing techniques and POCs to overcome challenging problems in health-care settings provides new approaches in diagnosis and treatment of diseases. The aim of this study was to adapt the alanine aminotransferase (ALT) enzyme to the platinum (Pt) thin film electrode system and quantitatively determine the enzyme levels via enzymatically generated H2O2 with differential pulse voltammetry (DPV). A simple potentiostat architecture with expanded sweep range utilizing dual LMP91000 devices was developed and adapted to the needs of the biosensor. In order to calibrate the system, known concentrations of H2O2 were also tested. Moreover, signals associated with the other electroactive species coming from the ALT reaction were eliminated. Resulted potential range has been achieved between +500 mV and +900 mV and the linear range was found to be 0.05 M–0.5 M for H2O2, whereas 5 UL−1 to 120 UL−1 for ALT enzyme.

Fluid Temperature Measurement in Aqueous Solution via Electrochemical Impedance

A novel temperature transduction method using the high-frequency electrochemical impedance between a pair of microelectrodes exposed to aqueous solution is reported. The solution resistance of an aqueous ionic solution is highly temperature dependent, and the electrochemical impedance between two microelectrodes is dominated by solution resistance when measured at the appropriate frequency. Therefore, precise measurements of electrochemical impedance at the proper frequency in a two-electrode system can be used to transduce solution temperature. To demonstrate this method, a temperature sensor composed of two thin-film platinum electrodes on a freestanding Parylene C substrate was designed and fabricated. A platinum resistance temperature detector was co-fabricated to provide a simple means of benchmarking against an existing standard. Transduction via electrochemical impedance was achieved by measuring the real part of impedance at the frequency where phase was minimized. Fluid temperature was transduced between 15°C and 50°C with high sensitivity (−1.21%/°C) and resolution (0.02°C). A $4\times $ improvement in sensitivity and resolution over the conventional platinum resistance temperature detector was achieved. The sensor design described here features flexible construction with inert materials which facilitates future use in biomedical or microfluidic applications. [2019-0190]

Reliability of platinum contacts in a cold operated MEMS switch

Lifetime testing results of an electrostatically actuated microelectromechanical systems (MEMS) switch with Pt-Pt contact are presented. Moveable electrode of the switch is an aluminium beam with platinum contact bumps, which comes in contact with platinum thin-film electrodes. The switch operates in a cold DC mode. Testing is performed at several levels of the input current. Dependence of the switch resistance in the “on” state on the number of actuation cycles is measured. Lifetime of the device is limited by the sharp increase of the on-resistance up to 100 MΩ and depends on the switch design and the input current. Morphology and chemical composition of the contacting surfaces are investigated and mechanisms of the contact degradation are determined.

Electrochemical Stability of Thin-Film Platinum as Suitable Material for Neural Stimulation Electrodes.

Only thin-film technology can satisfy the requirements of high spatial selectivity at high-channel-count electrode array designs by simultaneously good conformability to the targeted tissue through mechanical flexibility enriching future applications of functional neural stimulation. However, caused by the high impact of the microstructure on the mechanical and electrochemical film properties, varying fabrication processes of the same thin-film makes the difference between acute and chronic long-term stable electrodes. The influence of standard clinical electrical pulsing on flexible polyimide-based thin-film platinum electrodes for neuroprostheses, either sputter deposited or evaporated, and different diameters was assessed and compared. The electrochemical and morphological analysis showed a higher corrosion susceptibility and electrochemical degradation for the sputter deposited platinum electrodes with even total failures of smaller diameters. In contrast, the evaporated thin-films provided itself as more stable and reliable metallization with also smaller electrodes keeping their film integrity intact over the experimental period, -appearing to be the preferable material for improving thin-film electrodes' longevity.

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 µm diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

Sputtered Platinum Thin-films for Oxygen Reduction in Gas Diffusion Electrodes: A Model System for Studies under Realistic Reaction Conditions

The development of catalysts for the oxygen reduction reaction in low-temperature fuel cells depends on efficient and accurate electrochemical characterization methods. Currently, two primary techniques exist: rotating disk electrode (RDE) measurements in half-cells with liquid electrolyte and single cell tests with membrane electrode assemblies (MEAs). While the RDE technique allows for rapid catalyst benchmarking, it is limited to electrode potentials far from operating fuel cells. On the other hand, MEAs can provide direct performance data at realistic conditions but require specialized equipment and large quantities of catalyst, making them less ideal for early-stage development. Using sputtered platinum thin-film electrodes, we show that gas diffusion electrode (GDE) half-cells can be used as an intermediate platform for rapid benchmarking at fuel-cell relevant current densities (~1 A cm−2). Furthermore, we demonstrate how different parameters (loading, electrolyte concentration, humidification, and Nafion membrane) influence the performance of unsupported platinum catalysts. The specific activity could be measured independent of the applied loading at potentials down to 0.80 VRHE reaching a value of 0.72 mA cm−2 at 0.9 VRHE in the GDE. By comparison with RDE measurements and Pt/C measurements, we establish the importance of catalyst characterization under realistic reaction conditions.

Lifetime testing of a MEMS switch with Pt-Pt contact

This paper presents the lifetime testing results of an electrostatically actuated microelectromechanical systems (MEMS) switch with the resistive contact and the active contact breaking mechanism. Moveable electrode of the switch is an aluminium beam with platinum contact bumps located on its bottom surface, which comes in contact with platinum thin-film electrodes. The switch operates in a cold DC mode in a standard laboratory environment. Testing is performed at three levels of the input current: 0.05, 0.5 and 5 mA. The dependence of the resistance in the “on” state on the number of actuation cycles is measured. Resistance of the “fresh” samples is in the range from 150 to 350 Ω. Instability of the resistance is observed during cycling, that is probably related to contamination of the contacts. Lifetime of the switch is limited by the sharp increase of the on-resistance up to 100 MΩ and varies from 2×103 to 5×104 cycles depending on the switch design and the input current.

Evaluation of the thermal conductance of flip-chip bonding structure utilizing the measurement based on Fourier’s law of heat conduction at steady-state

Fourier’s law of heat conduction at steady-state was adopted to establish a measurement method utilizing platinum (Pt) thin-film electrodes as the heater and the temperature sensor. The thermal conductivities (κ’s) of Pyrex glass, an epoxy resin and a commercial underfill for flip-chip devices were measured and a good agreement with previously reported values was obtained. The thermal boundary resistances (RTBR’s) of Pt/sample interfaces were also extracted for discussing their influence on the thermal conduction of samples. Afterward, the flip-chip samples with 2×2 solder joint array utilizing Si wafers as the die and the substrate, without and with the underfills, were prepared and their thermal conductance were measured. For the sample without underfill, the air presenting in the gap of die and the substrate led to the poor thermal conductance of sample. With the insertion of underfills, the thermal conductance of flip-chip samples improved. The resistance to heat transfer across Si/underfill interfaces was also suppressed and to promote the thermal conductance of samples. The thermal properties of underfill and RTBR at Si/underfill interface were further implanted in the calculation of thermal conductance of flip-chip samples containing various solder joint arrays. The increasing number of solder joints diminished the influence of thermal conduction of underfill and RTBR of Si/underfill interface on the thermal conductance of samples. The insertion of underfill with high-κ value might promote the heat conductance of samples containing low-density solder joint arrays; however, it became insignificant in improving the heat conductance of samples containing high-density solder joint arrays.

Chip-based biosensor for the detection of low adrenaline concentrations to support adrenal venous sampling

A chip-based amperometric biosensor referring on using the bioelectrocatalytical amplification principle for the detection of low adrenaline concentrations is presented. The adrenaline biosensor has been prepared by modification of a platinum thin-film electrode with an enzyme membrane containing the pyrroloquinoline quinone-dependent glucose dehydrogenase and glutaraldehyde. Measuring conditions such as temperature, pH value, and glucose concentration have been optimized to achieve a high sensitivity and a low detection limit of about 1 nM adrenaline measured in phosphate buffer at neutral pH value. The response of the biosensor to different catecholamines has also been proven. Long-term stability of the adrenaline biosensor has been studied over 10 days. In addition, the biosensor has been successfully applied for adrenaline detection in human blood plasma for future biomedical applications. Furthermore, preliminary experiments have been carried to detect the adrenaline-concentration difference measured in peripheral blood and adrenal venous blood, representing the adrenal vein sampling procedure of a physician.

Portable microfluidic chip electrophoresis device with integrated Pt electrodes for the analysis of AgNPs

A portable electrophoresis device based on the SU-8/Pyrex microfluidic chip with integrated three 100 μm platinum (Pt) thin-film electrodes (working, reference, and auxiliary) was adapted for the analysis of silver nanoparticles (AgNPs). The microfluidic platform includes the main electrophoresis instrument, reusable holder, and microfluidic chip with integrated Pt electrodes. The electrochemical oxidation behaviours of AgNPs on Pt thin-film electrode were investigated by using cyclic voltammetry, while the electrophoresis behaviours of AgNPs were studied on the `Lab-on-a-chip' platform. The influences of parameters including running buffer, separation voltage, and detection potential on the electrophoresis behaviours of AgNPs were all investigated. The results showed that AgNPs could be oxidised at 0.2-0.4 V [phosphate buffer solution buffer, pH 7.0] on the Pt thin-film electrode. The peak current enhanced with the increase of separation voltage, while the retention time decreased. The peak current varied with the detection potential and reached the highest value at 0.4 V. This microfluidic platform could be a fast and portable detection system for the analysis of total AgNPs.

Electrochemical Roughening of Thin-Film Platinum for Neural Probe Arrays and Biosensing Applications

We report a method for electrochemical roughening of thin-film platinum (Pt) electrodes that increases active surface area, decreases electrode impedance, increases charge injection capacity, increases sensitivity of biosensors and improves adhesion of electrochemically deposited films. First, a well-established technique for electrochemical roughening of thick Pt electrodes (wires and foils) by oxidation-reduction pulses was modified for use on thin-film Pt. Optimal roughening of thin-film Pt electrodes with this established protocol in a sulfuric acid solution was found to occur at about four times lower frequency than that typically used for thick Pt. This modification in established procedure created a 21x surface area increase but showed nanoscale cracks from inter-grain Pt dissolution that compromised film integrity. A crack free surface with Pt nanocrystal re-deposition (20–30 nm in size) and higher enhancement in surface area (44x) was obtained when the electrolyte was switched to a non-adsorbing perchloric acid solution. These electrochemically roughened electrodes have charge injection limits comparable to titanium nitride and just below carbon nanotube-based materials. Roughened microelectrodes showed a 2.8x increase in sensitivity to hydrogen peroxide detection, indicative of improved enzymatic biosensor performance. Platinum iridium and iridium oxide coatings on these roughened surfaces showed an improvement in adhesion.

Optimization of an amperometric biosensor array for simultaneous measurement of ethanol, formate, d- and l-lactate

The immobilization of NAD+-dependent dehydrogenases, in combination with a diaphorase, enables the facile development of multiparametric sensing devices. In this work, an amperometric biosensor array for simultaneous determination of ethanol, formate, d- and l-lactate is presented. Enzyme immobilization on platinum thin-film electrodes was realized by chemical cross-linking with glutaraldehyde. The optimization of the sensor performance was investigated with regard to enzyme loading, glutaraldehyde concentration, pH, cofactor concentration and temperature. Under optimal working conditions (potassium phosphate buffer with pH 7.5, 2.5 mmol L-1 NAD+, 2.0 mmol L-1 ferricyanide, 25 °C and 0.4% glutaraldehyde) the linear working range and sensitivity of the four sensor elements was improved. Simultaneous and cross-talk free measurements of four different metabolic parameters were performed successfully. The reliable analytical performance of the biosensor array was demonstrated by application in a clarified sample of inoculum sludge. Thereby, a promising approach for on-site monitoring of fermentation processes is provided.