Skin pH can be used for monitoring infections in a healing wound, the onset of dermatitis, and hydration in sports medicine, but many challenges exist in integrating conventional sensing materials into wearable platforms. We present the development of a flexible, textile-based, screen-printed electrode system for biosensing applications, and demonstrate flexible polyaniline (PANI) composite-based potentiometric sensors on a textile substrate for real-time pH measurement. The pH response of the optimized PANI/dodecylbenzene sulfonic acid/screen-printing ink composite is compared to electropolymerized and drop-cast PANI sensors via open circuit potential measurements. High sensitivity was observed for all sensors between pH 3–10, with a composite based on PANI emeraldine base, demonstrating sufficient response time and a linear sensitivity of −27.9 mV/pH. This exceeded prior flexible screen-printed pH sensors in which all parts of the sensor, including the pH sensing material, are screen-printed. Even better sensitivity was observed for a PANI emeraldine salt composite (−42.6 mV/pH), although the response was less linear. Furthermore, the sensor was integrated into a screen-printed microfluidic channel demonstrating sample isolation during measurement for wearable, micro cloth-based analytical devices. This is the first fully screen-printed flexible PANI composite pH sensor demonstrated on a textile substrate that can additionally be integrated with textile-based microfluidic channels.

This paper presents a new immobilization method for Vapochromic Coordination Polymers (VCPs) for micromachined fluorescence chemical sensors. The method involves creating a sheet of post arrays in polydimethylsiloxane (PDMS) to trap and adhere the VCPs to the sensing surface. The method is simple, robust, and employs inexpensive micro-molding of PDMS polymer. Results suggest that, compared to un-patterned (flat) PDMS surfaces: 1) the VCPs on the patterned surfaces can detect ammonia gas without rendering the VCP inert (unable to fluoresce) or inaccessible; and 2) the technique has improved immobilization (attachment of VCP). We show that as the shapes of the top of the post arrays are changed from simple to mushroom-shaped caps, the sensitivity of the sensing surface is increased. Ammonia detection in the range of 5 ppm is possible with the most pronounced mushroom-shaped posts.

In this article, we present an electro-enzymatic glucose sensor fabricated using a novel self-aligned and hybrid polymer fabrication process. The self-aligned fabrication process was carried out using polydimethylsiloxane (PDMS) as a process substrate material, SU-8 (a negative, epoxy based photoresist) as a sensor substrate material and gold as an electrode material. The electro-enzymatic glucose sensor was assembled from microfabricated components using a self-registration step. The sensor substrate is optically transparent and flexible. Utilizing the process, a wide range of bio-sensors for different constituents (e.g. lactate, pO ₂ etc.) can be fabricated. The glucose sensor was successfully fabricated using our new multilayer SU-8 process on PDMS substrate. The sensor thickness was measured between 117.15 μm and 140.15 μm. The current response of the multi-layer electroenzymatic sensor using different glucose concentrations is also measured. Besides, the current response for long term stability is also presented.

We present a novel self-aligned and hybrid polymer fabrication process for an electro-enzymatic glucose sensor. The self-aligned fabrication process is performed using polydimethylsiloxane (PDMS) as a process substrate material, SU-8 as a sensor structural material, and gold as an electrode material. PDMS has many advantages as a process substrate over conventional substrates such as bare silicon or glass. During the fabrication process, SU-8 has good adhesion to the PDMS. However, after completion of all fabrication steps, the SU-8 based sensors can be easily peeled-off from the PDMS. The PDMS is prepared on a glass handle wafer, and is reusable for many process cycles. Such an SU-8 release technique from a PDMS substrate has never been proposed before. The novel process is employed to realize a glucose sensor with active and reference gold electrodes that are sandwiched between two SU-8 layers with contact pad openings and the active area opening to the top SU-8 layer. The enzyme glucose oxidase is immobilized within the confined active area opening to provide an active electrode sensing surface. After successful fabrication using the hybrid process, the overall thickness of the sensors is measured between 166.15 μm and 210.15 μm. The sensor area and the electrode area are 2mm x 3mm and 2mm x 2mm respectively. The resulting glucose sensors are mechanically flexible. A linear response is observed for the glucose sensors, typically between 50mg/dl and 600mg/dl glucose concentrations.