This article reports findings on screen-printed electrodes employed in microfluidic diagnostic devices. The research described includes developing a series of graphene- and other carbon form-based printing pastes compared to their rheological parameters, such as viscosity in static and shear-thinning conditions, yield stress, and shear rate required for thinning. In addition, the morphology, electrical conductivity, and electrochemical properties of the electrodes, printed with the examined pastes, were investigated. Correlation analysis was performed between all measured parameters for six electrode materials, yielding highly significant (p-value between 0.002 and 0.017) correlations between electron transfer resistance (Ret), redox peak separation, and static viscosity and thinning shear-rate threshold. The observed more electrochemically accessible surface was explained according to the fluid mechanics of heterophase suspensions. Under changing shear stress, the agglomeration enhanced by the graphene nanoplatelets’ interparticle affinity led to phase separation. Less viscous pastes were thinned to a lesser degree, allowing non-permanent clusters to de-agglomerate. Thus, the breaking of temporary agglomerates yielded an unblocked electrode surface. Since the mechanism of phase ordering through agglomeration and de-agglomeration is affected by the pastes’ rheology and stress during the printing process and requires no further treatment, it can be appropriately labeled as a self-assembling electrode material.

This study concerns printed, disposable voltammetric electrodes for bioanalytical applications. Sensing electrodes’ electrochemically active surface area was found to relate to the screen-printing pastes’ rheology and manufacturing parameters. The sensors’ response was examined for constant carbon content in the electrode material and varying additions of surfactants and solvents, as well as the forces affecting the printing process. The printing pastes employed graphene nanoplatelets with the addition of carbon black as the functional phase and various polymers (PMMA, TPU, and others) as the composite matrix. Technological parameters examined included: the pressure and movement rate during the printing cycle, screen mesh density, curing, and ozonizing time. The rheological properties determined for each paste were: static viscosity, zero viscosity, and yield stress. To estimate active surface area values, sensors were immersed in redox couple solution and employed for CV measurements at varying scan rates. Finally, the active surface area was calculated according to the transformed Randles–Sevcik equation. The results were compared to electron transfer resistance and surface roughness. Correlation analysis was performed for the above parameters. The obtained statistical relationships will allow fine-tuning of the printed sensors’ performance as well as the faster development of new applications of this technology in analytical devices.

Continuous plantar-pressure monitoring is important for objective gait analysis and early detection of abnormal loading; however, many existing solutions remain laboratory-bound (force plates and instrumented walkways) or rely on costly in-shoe multilayer sensor arrays. Here, we developed and optimized a fully screen-printed pressure-sensing insole based on carbon–polymer nanocomposite layers, with an emphasis on manufacturability and process control to bridge the gap between proof-of-concept force-sensitive resistor (FSR)-based insoles and scalable printed-electronics manufacturing workflows. Composite pastes containing carbon fillers (graphene nanoplatelets, carbon black, and graphite) were formulated to improve sensor repeatability and sensitivity. Sensors were characterized under compression loads from 100 N to 1300 N, showing a sensitivity of 10.5 ± 2.8 Ω per 100 N and a sheet-to-sheet coefficient of variation of 22.1% in resistance response. The effects of paste composition, screen mesh density, electrode layout, and lamination on sensitivity and repeatability were systematically evaluated. In addition, correlation analysis of resistance values from integrated quality-control meanders proved useful for monitoring screen-printing process stability. The final insole integrates printed carbon sensing pads and contacts, a dielectric spacer, and an adhesive layer in a thin, flexible format suitable for integration with wearable electronics. In practical static-load tests, repeated manual placement of weights yielded coefficients of variation as low as 4% at 500 g and a detection limit of ~0.1 N, comparable to a very light finger touch. These results demonstrate that low-cost screen-printed electronics can provide robust pressure sensing for wearable plantar-pressure monitoring.

The growing understanding of the physical mobility impact on human health demands more precise tracking of the objective exertion markers to better tailor training programs. A fully functional, wearable device for sweat analysis is presented, consisting of a flexible sensor array and microfluidic sample collection layer. The potentiometric pH and lactate ion sensors had all materials deposited by means of printing technology, facilitating significant miniaturization, as well as cost and material efficiency. The sensor array for measurements in the microfluidic system was found to exhibit a sensitivity of -49.67 ± 3.64 mV/decade (n=16) towards pH and -77.61 ± 7.24 mV/decade (n=9) towards lactate. The comparison of in vitro calibrations alongside the results collected from sweat during an ergospirometric test highlights the accuracy of the device and its feasibility in physical activity monitoring for medical or athletic purposes. Specifically, a pronounced change in potentiometric signals (56.75 mV for pH and 61.20 mV for lactate) was registered within 52 s of the observed first ventilatory threshold – point of CO₂ equivalent surpassing the O₂ equivalent. These response spikes correspond to changes in pH and lactate ion activity of respectively -1.14 and 0.79 orders of magnitude, consistent with the expected increased acidity and lactate prevalence.