The demand for a versatile and portable point-of-use (POU) sensor platform has surged due to the pandemic, especially in countries with limited medical laboratory facilities. We recently unveiled a portable, non-planar, interdigitated, flow-through, porous electrode platform that automatically measures electrochemical impedance spectroscopy (EIS) signals from various biomarkers. However, the packed powder exhibited a loss of performance over time due to displacement, leaching, and poor stability. Herein, we modified the packing strategy by synthesizing the sensing material within the channel, thereby improving adhesion, structural integrity, and stability. Leveraging the exceptional thermal stability, mechanical strength, and chemical resistance of polyimide (PI), we developed a novel fabrication approach that combines liquid-phase inversion and breath-figure techniques to create a porous PI manifold with single-walled carbon nanotubes (SWCNTs) under varying humidity conditions. Scanning electron microscope (SEM) analysis revealed that lower relative humidity (RH) conditions yield larger but less uniformly distributed pores, leading to increased channel pressure. The manifold demonstrated exceptional stability under rigorous flow conditions, withstanding a high flow rate of 30 µL/min while maintaining consistent pressure-EIS responses. The device produced a measurable proof-of-concept impedance response following exposure to a femtomolar concentration of complementary target ssDNA in 1× PBS within 15 min. A formal limit of detection was not determined in the present study. We developed a mechanically stable sensor design with improved durability under repeated flow conditions by systematically optimizing synthesis conditions and manifold configuration. This innovative fabrication strategy demonstrates the importance of packing methodology in sensor design and paves the way for robust, scalable, and efficient diagnostic solutions in resource-limited settings.
The transition toward decentralized environmental monitoring demands the development of integrated, portable platforms capable of combining sampling, pre-concentration, and electrochemical detection into a single device. This study introduces a proof of concept for a novel semisolid-state electrochemical platform driven by low-cost poly(sodium acrylate) hydrogels integrated with unmodified 3D-printed miniaturized sensors. The devices were fabricated via 3D pen technology using conductive polylactic acid/graphite filaments and extensively characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Considering the advantage of the hydrogel's swelling dynamics, the proposed approach facilitates direct analyte uptake and provides a stable, highly controlled environment for the electrochemical process, significantly simplifying sample handling. To demonstrate the analytical feasibility of this semisolid system, sulfanilamide was selected as a representative model of veterinary antibiotic residues. Under optimized square wave voltammetry conditions (15 Hz frequency, 8 mV step potential, and 55 mV amplitude in 0.1 mol L-1 BR buffer, pH 10.0), the platform delivered a linear response from 10 to 50 µmol L-1 and a limit of detection of 5.55 µmol L-1. The architecture's robustness was validated through successful recovery trials (99% to 108%) in complex aquaculture water and pharmaceutical formulations. This hydrogel-based, 3D-printed platform establishes a baseline for a simple and low-cost alternative sampling strategy, representing a significant development in field-deployable tools for smart environmental monitoring.
Wallace Burger Veríssimo de Oliveira, Matheus Comastri de Oliveira Leite, Gabriela Couto da Silva et al.· Analytical Methods· 0 citations
Carbon microelectrodes are attractive for microfluidic biosensing due to their wide potential window, low overpotentials, chemical stability, and compatibility with low-cost microfabrication. Pyrolysis of photopatterned SU-8 offers a scalable route to carbon electrode fabrication; however, conventional two-step pyrolysis often leads to adhesion issues, geometric distortion, and limited surface area in low-aspect-ratio planar designs. These constraints restrict performance and broader adoption in analytical microdevices. Hematocrit determination, a clinically essential diagnostic measurement, requires electrodes with high reproducibility and robust electrochemical response. A simplified fabrication strategy that improves electrode surface area and performance while maintaining low-aspect-ratio planar geometries remains unresolved. We developed a three-step pyrolysis protocol that enables fabrication of low-aspect-ratio planar SU-8–derived carbon electrodes with both micro- and millimeter-scale features while improving structural integrity and surface morphology. The electrodes were integrated into a PDMS-based microfluidic device for hematocrit detection by measuring current responses of red blood cells suspended in phosphate-buffered saline at 100 V for 30 s. A linear correlation was observed between current and red blood cell concentration. The device achieved 3.6% precision and 3.8% accuracy for hematocrit determination, comparable to previously reported platinum-based systems (2.8% precision, 2.6% accuracy). Surface characterization via field-emission scanning electron microscopy and atomic force microscopy revealed a 25% increase in surface area relative to platinum electrodes, resulting from 2.7 times greater roughness and 58 times greater thickness. These structural enhancements reduced charge-transfer and concentration overpotentials, improving electrochemical performance. This work introduces a reproducible three-step pyrolysis method that overcomes long-standing limitations in the fabrication of low-aspect-ratio pyrolytic carbon electrodes. By increasing electroactive surface area without complex coatings or noble metals, the approach enables high-performance, low-cost microelectrodes suitable for integrated biosensing. The demonstrated equivalence to platinum electrodes in hematocrit detection highlights its translational potential for scalable diagnostic microdevices.
Hwi-yong Lee, Jessika A. Rogers, C. Kendrick et al.· Biomedical microdevices· 0 citations
Polymeric ionic liquids (i.e., PILs) have diverse sensing capabilities due to their potentially high ionic conductivity and tunable chemical response. However, integrating them into miniaturized sensor components often requires harsh nonaqueous developers, limiting eco-friendly microfabrication. To overcome this challenge, we designed a system that utilizes a UV-active thiol–ene click reaction to cross-link a photopatternable PIL, PAGE-TFSI–EMIm+, that enables device patterning under 365 nm exposure. This specific design leverages the material’s ionic nature to enable fully aqueous development, bridging the gap between precise microfabrication and processing with a lower environmental footprint in the development stage. The resulting films were successfully patterned with 12.8 μm resolution. As an independent proof-of-concept for the functional application of these materials, an impedance-type humidity sensor was fabricated by integrating interdigitated electrodes with patterned 3 mm-diameter PAGE-TFSI–EMIm+ films. The sensor demonstrated excellent sensitivity with low hysteresis (2.5% relative humidity (RH)) across a broad humidity range of 0–78% RH. Equivalent circuit fitting of electrochemical impedance spectroscopy (EIS) results suggest that the sensing mechanism is primarily governed by the variable ionic conductivity with humidity within the film. This approach underscores the potential of photopatterned PILs for advanced sensor architectures.
Tokio Mimura, Liam Warlick, Alexandra Zele et al.· ACS Macro Letters· 0 citations
Electrochemical gas sensing is a low-cost and rapid way to detect gases in the atmosphere, with various devices including amperometric gas sensors (AGSs) being developed for this purpose. However, it is challenging to achieve miniaturization and fast response times with the traditional AGS design because of the use of a membrane. Room temperature ionic liquids (RTILs) have been proposed to overcome these challenges because of their nonvolatility, allowing for the removal of the membrane; however, there are still limitations with the use of liquid electrolytes due to stability and robustness when the sensor is employed in different electrode orientations. In this work, we have combined platinum wicking membrane interdigitated electrodes (WM-IDEs) with RTILs to produce thin films of solvent with uniform thickness (30 μm) over the whole electrode. Three gases—oxygen, ammonia, and sulfur dioxide—were successfully detected at analytically relevant levels using cyclic voltammetry and chronoamperometry on these devices, with stable and reproducible responses observed over long periods of time. In particular, the best responses were observed for oxygen using long-term chronoamperometry with very fast response times of <4 s, faster than other miniaturized designs. This platform may be further modified and adapted to detect other air pollutants or volatile organic compounds in breath for health monitoring.
S. Doblinger, Junqiao Lee, Marta K. Orlowska et al.· ACS Electrochemistry· 0 citations
Porous silicon (PSi) biosensors offer significant potential for point-of-care diagnostics, yet their analytical performance is constrained by slow analyte diffusion into the porous matrix. To address this issue, we developed a lab-on-a-chip (LOC) device that combines a PSi immunosensor with a surface acoustic wave (SAW)-driven mixer, housed in a 3D-printed microfluidic flow cell. The platform was evaluated for the optical detection of lactoferrin (LF), a protein biomarker relevant to inflammatory bowel disease and chronic pancreatitis. Acoustic streaming generated by the SAW mixer enhanced convective mixing at the microscale and increased mass transfer of the target analyte towards the sensor surface. SAW-driven mixing achieved a 3-fold increase in the signal-to-noise ratio and a 5-fold reduction in the limit of detection compared to unmixed conditions, advancing the analytical range towards clinically significant concentrations.
Jonathan Nyenhuis, Josef Zürn, A. Lazanas et al.· RSC Advances· 0 citations
Despite the rapid development of flexible piezoresistive pressure sensors in medical monitoring and human–computer interaction, traditional sensors fabricated with dense materials (e.g., elastomers) generally suffer from inadequate permeability and sweat trapping. This not only impairs wearing comfort but also may cause skin inflammation during long-term use. Moreover, most such sensors lack effective degradation pathways, exacerbating electronic-waste concerns, which are against the trends of sustainable development. To this end, we propose a co-electrospun approach for two precursor solutions, i.e., polydimethylsiloxane/polyamide (PDMS/PA) solution with/without carboxylated multi-walled carbon nanotube (c-MWCNT) additive. This approach produces a permeable and fully degradable nanofiber composite membrane, in which the PDMS/PA nanofibers form a nonconductive scaffold to support the conductive PDMS/PA/c-MWCNTs nanofibers with pressure-sensitive functionality. In addition to excellent and adjustable pressure-sensor performance, this device further possesses high air and moisture permeabilities (59.61 mm/s and 434.24 g·m–2·day–1) and waterproof capability, which maintains its sensing performance in the situation of human motion. The device is also fully degradable (in alcohol within 300 s) and recyclable, ensuring that the sensor conforms to the principles of sustainability-oriented process from production to disposal. Finally, we demonstrate the wide applications of this sensor in various scenarios, including human health monitoring, motion detection, and Morse code recognition.
Weiyi Ouyang, Xiaodong Zhao, Gongtao Yao et al.· ACS Applied Electronic Mater...· 0 citations