Researchers are interested in measuring mental stress because it is linked to a variety of diseases. Real-time stress monitoring via wearable sensor systems can aid in the prevention of stress-related diseases by allowing stressors to be controlled immediately. Physical tests, such as heart rate or skin conductance, have recently been used to assess stress; however, these methods are easily influenced by daily life activities. As a result, for more accurate stress monitoring, validations requiring two or more stress-related biomarkers are demanded. In this review, the combinations of various types of sensors (hereafter referred to as multiplexed sensor systems) that can be applied to monitor stress are discussed, referring to physical and chemical biomarkers. Multiplexed sensor systems are classified as multiplexed physical sensors, multiplexed physical–chemical sensors, and multiplexed chemical sensors, with the effect of measuring multiple biomarkers and the ability to measure stress being the most important. The working principles of multiplexed sensor systems are subdivided, with advantages in measuring multiple biomarkers. Furthermore, stress-related chemical biomarkers are still limited to cortisol; however, we believe that by developing multiplexed sensor systems, it will be possible to explore new stress-related chemical biomarkers by confirming their correlations to cortisol. As a result, the potential for further development of multiplexed sensor systems, such as the development of wearable electronics for mental health management, is highlighted in this review.

Solution-based direct patterning on an elastomer substrate with meniscus-dragging deposition (MDD) enables fabrication of very thin carbon nanotube (CNT) layers in the nanometer scale (80–330 nm). To fabricate the CNT pattern with CNT solution, contact angle, electrical variation, mechanical stress, and surface cracks of elastomer substrate were analyzed to identify the optimal conditions of O₂ treatment (treatment for 30 s with RF power of 50 W in O₂ atmosphere of 50 sccm) and mixture ratio between Ecoflex and polydimethylsiloxane (PDMS) (Ecoflex:PDMS = 5:1). The type of mask for patterning of the CNT layer was determined through quantitative analysis for sharpness and uniformity of the fabricated CNT pattern. Through these optimization processes, the CNT pattern was produced on the elastomer substrate with selected mask (30 μm thick oriented polypropylene). The thickness of CNT pattern was also controlled to have hundreds nanometer and 500 μm wide rectangular and circular shapes were demonstrated. Furthermore, the change in the current and resistance of the CNT layer according to the applied strain on the elastomer substrate was analyzed. Our results demonstrated the potential of the MDD method for direct CNT patterning with high uniformity and the possibility to fabricate a stretchable sensor.

Since separation of target biomolecules is a crucial step for highly sensitive and selective detection of biomolecules, hence, various technologies have been applied to separate biomolecules, such as deoxyribonucleic acid (DNA), protein, exosome, virus, etc. Among the various technologies, dielectrophoresis (DEP) has the significant advantage that the force can provide two different types of forces, attractive and repulsive DEP force, through simple adjustment in frequency or structure of microfluidic chips. Therefore, in this review, we focused on separation technologies based on DEP force and classified various separation technologies. First, the importance of biomolecules, general separation methods and various forces including DEP, electrophoresis (EP), electrothermal flow (ETF), electroosmosis (EO), magnetophoresis, acoustophoresis (ACP), hydrodynamic, etc., was described. Then, separating technologies applying only a single DEP force and dual force, moreover, applying other forces simultaneously with DEP force were categorized. In addition, advanced technologies applying more than two different kinds of forces, namely complex force, were introduced. Overall, we critically reviewed the state-of-the-art of converged various forces for detection of biomolecules with novelty of DEP.

Three-dimensional (3D) organoids provide physiologically relevant models for studying human neural development and disease; however, stable bioelectronic interfacing with curved and dynamic organoid surfaces remains challenging. Here, we present a thermally actuated, shape-memory polymer (SMP)-based foldable bioelectronic interface for simultaneous electrophysiological recording and electrochemical cytokine sensing in human spinal cord organoids (hSCOs). Near physiological temperature (36-37 °C), the SMP substrate undergoes pronounced mechanical softening, enabling conformal 3D wrapping around organoids without external mechanical compression. The platform integrates gold microelectrodes for extracellular neural recording and antibody-functionalized sensing electrodes for label-free cytokine detection. Finite element simulations and experimental mechanical analyses confirmed temperature-dependent bending, enhanced conformal contact, low interfacial stress, and mechanically stable biointerfacing. Electrochemical characterization demonstrated linear cytokine sensing responses over 1-100 ng/ml, with calculated limits of detection (LOD) of 0.44 ng/ml for TNF-α and 0.41 ng/ml for IL-8. Using this multimodal platform, stable electrophysiological recordings and cytokine monitoring were simultaneously obtained from hSCOs under inflammatory stimulation. TNF-α treatment induced dose-dependent increases in neural firing activity together with corresponding electrochemical cytokine responses. Collectively, this thermally adaptive bioelectronic interface provides a minimally invasive platform for integrated electrical and biochemical profiling of intact organoids and offers a promising tool for neuroinflammatory organoid studies.