Temperature Correction of Printed Na+, K+, and pH Sensors with PEDOT:PSS‐Based Thermistors toward Wearable Sweat Sensing

Abstract Temperature correction for sensors is a critical aspect of ensuring accurate measurements in wearable devices, because skin and sweat temperatures vary between 20 and 40 °C depending on individual and time. Here, this study reports on the temperature dependence and correction techniques of printed Na+, K+, and pH sensors toward wearable applications. The ion sensor array is fabricated using a cost‐effective printing method. To enable temperature correction, a printed thermistor of crosslinked poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is monolithically integrated with the ion sensor array on a flexible plastic substrate. Temperature dependence of the potential response of the printed ion sensors exhibits a linear behavior with a slope of 1–2 mV °C−1 in the physiological skin temperature range of 20–40 °C. Applying temperature correction to the ion sensors, the maximum relative errors are reduced from 60% to 7.8% for the Na+ sensors and from 76% to 14.6% for the K+ sensors, while the maximum absolute error is reduced from 0.88 to 0.19 for the pH sensors, indicating the critical importance of temperature correction as a technology for wearable printed ion sensors

Investigating the Blocking Effect of Alkanethiol Self-assembled Monolayer on Electrochemical Response of the Split Gq-based DNA-NTs-based Biosensor

The split G-quadruplex-based DNA-nanotweezwers-based electrochemical DNA sensor was characterized by focusing on the blocking ability of the mixed self-assembled monolayer (SAM) against the nonspecific adsorption of hemin and the direct reduction of oxygen on a gold electrode. We found that the mixed SAM composed of MCH and MHA (concentration of each alkanethiol in SAM formation solution was 1.0 mM : 0.1 mM) effectively suppressed the nonspecific adsorption of hemin and the direct reduction of oxygen on the gold electrode

Investigating the Blocking Effect of Alkanethiol Self-assembled Monolayer on Electrochemical Response of the Split Gq-based DNA-NTs-based Biosensor (Supporting Information)

The split G-quadruplex-based DNA-nanotweezwers-based electrochemical DNA sensor was characterized by focusing on the blocking ability of the mixed self-assembled monolayer (SAM) against the nonspecific adsorption of hemin and the direct reduction of oxygen on a gold electrode. We found that the mixed SAM composed of MCH and MHA (concentration of each alkanethiol in SAM formation solution was 1.0 mM : 0.1 mM) effectively suppressed the nonspecific adsorption of hemin and the direct reduction of oxygen on the gold electrode.</p

Detection of 1,5-anhydroglucitol as a Biomarker for Diabetes Using an Organic Field-Effect Transistor-Based Biosensor

Sensor devices that can be fabricated on a flexible plastic film produced at a low cost using inkjet-printing technology are suitable for point-of-care applications. An organic field-effect transistor (OFET)-based biosensor can function as a potentiometric electrochemical sensor. To investigate the usefulness of an OFET-based biosensor, we demonstrated the detection of 1,5-anhydroglucitol (1,5-AG) and glucose, which are monosaccharides used as biomarkers of diabetes. An OFET-based biosensor combined with a Prussian blue (PB) electrode, modified with glucose oxidase (GOx) or pyranose oxidase (POx), was utilized for the detection of the monosaccharides. When the GOx- or POx-PB electrode was immersed in glucose solution at the determined concentration, shifts in the low-voltage direction of transfer characteristic curves of the OFET were observed to be dependent on the glucose concentrations in the range of 0&ndash;10 mM. For 1,5-AG, the curve shifts were observed only with the POx-PB electrode. Detection of glucose and 1,5-AG was achieved in a substrate-specific manner of the enzymes on the printed OFET-biosensor. Although further improvements are required in the detection concentration range, the plastic-filmOFET-biosensors will enable the measurement of not only diabetes biomarkers but also various other biomarkers

Intrinsically Stretchable Electrochromic Display by a Composite Film of Poly(3,4-ethylenedioxythiophene) and Polyurethane

A stretchable, electrochromic film of a uniform composite of poly­(3,4-ethylenedioxythiophene):<i>p</i>-toluene sulfonic acid (PEDOT:PTS) and polyurethane (PU) (PEDOT/PU) was fabricated, and its integration with a hydrogel as a free-standing, stretchable electrochromic (EC) display was demonstrated. The PEDOT/PU composite film was prepared by the spin coating of a solution containing an EDOT monomer and PU, followed by oxidative polymerization using iron­(III) tosylate at elevated temperature. The fabricated film showed reversible electrochromism without an external conductive support. The color change of the film can be used to quantify the progress of the redox reactions by means of digital camera image analysis and a custom mobile phone app

Portable Micropatterns of Neuronal Cells Supported by Thin Hydrogel Films

A grid micropattern of neuronal cells was formed on a free-standing collagen film (35 μm thickness) by directing migration and extension of neurons along a Matrigel pattern previously prepared on the film by the microcontact printing method. The neurons migrated to reach the nodes on the grid pattern and extended neurites to bridge cell bodies at the nodes. The resulting neuronal micropattern on the collagen film containing culture medium can be handled and deformed with tweezers with maintenance of physiological activity of the neurons, as examined by response of cytosolic Ca²⁺ concentration to a dose of bradykinin. This portability is the unique advantage of the present system that will open novel possibility of cellular engineering including the on-demand combination with analytical devices. The repetitive lamination of the film on a microelectrode chip was demonstrated for local electrical stimulation of a specific part of the grid micropattern of neurons, showing Ca²⁺ wave propagation along the neurites. The molecular permeability is the further advantage of the free-standing hydrogel substrate, which allows external supply of nutrients and dosing with chemical stimulants through the film even under rolled and laminated conditions