Ion-selective electrodes, which detect activity of specific substances, are one of main analytical techniques in many fields e.g. medical and environmental analysis or process control in industries. This article describes manufacturing of screen-printed electrode for potassium determination, which can be used in potentiometric measurements. Electrode was made with usage of two conductive pastes. The first consists of silver nanoplatelets and thermoplastic polyurethane (TPU). The second contained PMMA matrix and graphene nanoplatelets as intermediate material. Two membranes for electrode coating, which differ in composition, were prepared and compared. For both membranes polyvinyl chloride (PVC) was used as a matrix and valinomycin was used as ionophore which binds potassium ions. Moreover, some of the prepared electrodes had an additional intermediate layer made of a conductive polymer - poly(3,4-ethylene-1,4- dioxythiophene) (PEDOT). Received calibration curves were linear. The curve slope for electrode with PEDOT intermediate layer in the physiological range (3,8-5,5 mM) was 62 mV/dec which exceed the Nernstian value.
Numerous biosensing configurations have been researched for detection of organophosphorus pesticides in agricultural and household applications. Selectivity for the specific insecticide, sensitivity and low detection limit being the main challenges gives a great potential to targeted enzymatic biosensors. Acetylcholinesterase is being employed in receptors, because organophosphorus pesticides, such as malathion, display inhibitory effect towards it. Proteins within other structures can have decreased activity, be contaminated, denatured or have a diffusion barrier resulting in reduced interaction with the analyte. Choice of the immobilization method for the enzyme may be the most important aspect in the development of electrochemical biosensor. Numerous acetylcholinesterase based biosensing solutions for the detection of organophosphorus pesticides have been reviewed.
The paper includes description of a novel approach for producing stretchable, conductive interconnects for wearable electronics. At first the current state-of-the-art and market solutions were reviewed, and then we described our optimization of the composition of conductive pastes used in the screen printing technology. Namely, the ratios of TPU (Thermoplastic Polyurethane) dissolved in DMF (Dimethylformamide) as a carrier were empirically optimized, followed by adding silver flakes as a filler. To test the quality of the final paste, a number of tracks were printed on 100% cotton fabric substrate. Changes in the electrical resistance were measured while the samples were stretched, twisted, soaked, and washed. Despite being pushed to the limits of the substrate physical capabilities, printed interconnects still retained their conductive properties, with electrical resistance increasing by no more than 10x relative to initial, very low resistances of a few ohms, and then decreasing over time. We have also discovered that ironing the samples did not destroy the tracks. Instead, the ironing process regenerated them, and their electrical resistances returned to initial values or even decreased. The method described in this paper is innovative because it enables printing directly onto textiles and the usage of a non-synthetic textile substrate while still retaining robustness in electrical conductivity.
Electrodes for measuring pH of the solution were fabricated by the means of screen-printing technology. Potentiometric sensors’ layers comprised of composite with polymer matrix and graphene nanoplatelets/ruthenium (IV) oxide nanopowder as functional phase. Transceivers were printed on the elastic PMMA foil. Regarding potential application of the sensors in the wearable devices, dynamic response of the electrodes to changing ultraviolet radiation levels was assessed, since RuO<sub>2</sub> is reported to be UV-sensitive. Observed changes of the electrodes’ potential were of sub-millivolt magnitude, being comparable to simultaneously observed signal drift. Given this stability under varying UV conditions and previously verified good flexibility, fabricated sensors meet the requirements for wearable applications.
System of wireless energy supply for a electrochemical sensor is presented. As a first step, various theoretical models of the sensor were considered and a new model, proper for the application studied, was proposed to enable further design stages. In the experiment conducted, it was verified, that the sensor, working in an amperometric mode and in the presence of constant or quasi-constant voltage supply, could be electrically approximated as element of the constant impedance value. Given this, power-consumption was calculated for the sensor using Ohm’s law and the proof of concept device was fabricated to evaluate performance of the sensor under theoretically calculated conditions. The results obtained were comparable to the data previously recorded using conventional laboratory potentiostat. For verification of the resistive character of the sensor, chronoamperometric method was employed, with sensor’s response complying with the theoretical prediction for quasi-constant powering signal and being influenced only by major voltage changes. Calculated power consumption of the sensor was P<sub>max.</sub> = 18.23<i>μW</i>. Concerning sensor’s requirement for quasiconstant voltage, simple half-wave rectifier was designed that was connected to the antenna used for powering signal reception. In the second experiment, calibration of the sensor was performed, yielding sensitivity<i> s = 2.03</i> <i>μA/μmol/L</i> and linear correlation coefficient <i>ρ = 0.986</i> and thus confirming proper operation of the device in the conditions considered.
Screen-printed sensor for measuring human pulse was designed and first tests using a demonstrator device were conducted. Various materials and sensors’ set ups were compared and the results are presented as the starting point for fabrication of fully functional device. As a screen printing substrate, commercially available temporary tattoo paper was used. Using previously developed nanomaterials-based pastes design of a pressure sensor was printed on the paper and attached to the epidermis. Measurements were aimed at determining sensors impedance constant component and its variability due to pressure wave caused by the human pulse. The constant component was ranging from 2kΩ to 6kΩ and the variations of the impedance were ranging from ±200Ω to ±2.5kΩ, depending on the materials used and the sensor’s configuration. Calculated signal-to-noise ratio was 3.56:1 for the configuration yielding the highest signal level. As the device’s net impedance influences the effectiveness of the wireless communication, the results presented allow for proper design of the sensor for future health-monitoring devices.
Various methods and materials for enzyme stabilization within screen-printed graphene sensor were analyzed. Main goal was to develop technology allowing immediate printing of the biosensors in single printing process. Factors being considered were: toxicity of the materials used, ability of the material to be screen-printed (squeezed through the printing mesh) and temperatures required in the fabrication process. Performance of the examined sensors was measured using chemical amperometry method, then appropriate analysis of the measurements was conducted. The analysis results were then compared with the medical requirements. Parameters calculated were: correlation coefficient between concentration of the analyte and the measured electrical current (0.986) and variation coefficient for the particular concentrations of the analyte used as the calibration points. Variation of the measured values was significant only in ranges close to 0, decreasing for the concentrations of clinical importance. These outcomes justify further development of the graphene-based biosensors fabricated through printing techniques.