ABSTRACT Liquid‐gated transistor biosensors, fabricated using complementary metal‐oxide‐semiconductor (CMOS)‐compatible technology, face significant challenges relating to their long‐term stability when utilized in complex bio‐liquid environments. In this study, we use diamond‐like carbon (DLC) layers of nanometer‐scale thicknesses, ranging from 1 to 14 nm, to modify the surface properties of a low‐defect‐density SiO2 layer. By analyzing the capacitance–voltage characteristics and stability time traces of DLC‐covered silicon‐based structures, we registered three well‐separated regions of the flat‐band voltage values. The DLC layers demonstrate advanced properties: enhanced stability compared to the bare SiO2 layer and good sensitivity. X‐ray photoemission and Raman spectroscopy results enable an analysis of DLC material and the estimation of sp2 graphitic and sp3 diamond components. Measurements of different pH and biological C‐reactive protein solutions show that DLC‐modified structures, including nanowire field‐effect transistors (FET), have great potential for bio‐signal monitoring. The mechanism of long‐term stability is established using impedance spectroscopy and modeling data analysis. This study opens up prospects for the design of dielectric layer‐covered structures and their surface modification at the liquid–solid interface of biosensors, providing valuable insights into DLC interface engineering for the development of highly sensitive and reliable FET biosensors.
ABSTRACT Alcohol‐impaired driving highlights the need for reliable pre‐driving alcohol screening technologies. We present a portable wireless electrochemical sensing system for non‐invasive ethanol monitoring in human saliva. The system integrates a disposable Au/self‐assembled monolayer (SAM)/ferrocene‐cored poly(amidoamine) dendrimer (Fc‐PAMAM)/alcohol oxidase (AOx) sensing electrode with a portable wireless potentiostat. Fc‐PAMAM functions as both a redox mediator and an enzyme immobilization matrix, facilitating interfacial electron transfer and stable AOx immobilization. The developed system exhibited concentration‐dependent chronoamperometric responses to ethanol over 0–80 mM in artificial saliva with high linearity (R2 > 0.99). Furthermore, the portable system detected time‐dependent changes in electrochemical responses from human saliva following alcohol consumption, demonstrating its applicability to real‐sample monitoring. These results demonstrate the feasibility of the proposed platform as a portable and non‐invasive approach for salivary ethanol monitoring and as a complementary tool to conventional breath‐based alcohol screening.
ABSTRACT Cortisol is a dynamic endocrine biomarker regulated by hypothalamic–pituitary–adrenal (HPA) axis activity, and plays a central role in circadian regulation and physiological stress responsiveness. This review summarizes key aspects of cortisol dynamics, including circadian rhythms, modulatory factors, dysregulation, and acute and chronic stress responses. We further examine commonly used laboratory stress‐induction paradigms, such as the Trier Social Stress Test, Cold Pressor Test, Maastricht Acute Stress Test, cognitive stressors, and multicomponent stress protocols, with an emphasis on their applicability to wearable cortisol sensor development. Particular attention is given to experimental design considerations, including the choice of sampling matrix, sensor‐influenced temporal resolution, and acquisition frequency, as these parameters critically influence the interpretation of cortisol fluctuations and define the performance requirements of sensing platforms. To complement the literature review, we additionally report preliminary observations from a pilot study involving three healthy adult participants. The pilot experiments explore the feasibility of selected stress‐induction protocols for eliciting measurable stress responses using a dense temporal sampling protocol. By integrating insights from prior studies with our pilot observations, we highlight methodological considerations for capturing physiologically meaningful cortisol responses to stress, with a specific focus on stress‐induced dynamics and the temporal resolution necessary for continuous or near‐continuous monitoring.
ABSTRACT In this work, by exploiting in situ electropolymerization of molecularly imprinted polymer (eMIP) layers over surface plasmon resonance (SPR) optical fiber probes, the capability to extend the analyte detection concentration range by tuning eMIP layer thickness is demonstrated. More specifically, in this proof‐of‐concept sensing strategy, the caffeine was used as a template in order to evaluate the responses of the sensors in the detection of a small molecule. Two sensor configurations are designed, developed, and tested exploiting two eMIP layers with different thicknesses combined with the same SPR plastic optical fiber (POF) platform. The experimental results demonstrated that two detection ranges, in the femtomolar and picomolar ranges, were achieved using the developed sensor configurations. Moreover, the developed SPR‐POF‐eMIP sensors offer several advantages, including high selectivity, a fast response time (about 10 min), the intrinsic versatility of eMIP coding, small‐size and low‐cost sensor chips, and a portable and simple setup (reader).
ABSTRACT Non‐invasive lactate monitoring in saliva holds considerable potential for disease diagnostics and personalized oral healthcare. However, the complex salivary matrix, characterized by high protein content, pellicle formation, and elevated viscosity, poses major challenges for electrochemical biosensors, including biofouling, signal interference, and limited stability. Here, we present an electrochemical lactate biosensor rationally engineered for reliable operation in untreated human saliva. A multilayer surface architecture comprising Prussian Blue, lactate oxidase, bovine serum albumin (BSA), and a zwitterionic polydopamine–MPC (pDA/MPC) coating minimizes nonspecific adsorption while preserving substrate accessibility. The optimized sensor exhibits a sensitivity of −0.48 µA/ mM−1 and a linear range up to 2.5 mM in phosphate buffer at an operating potential of +0.055 V. In untreated human saliva, the sensor accurately quantified endogenous lactate and detected up to an additional 1 mM lactate before reaching saturation, covering the physiologically relevant concentration range. The multilayer architecture further provided stable and reproducible responses with negligible interference from glucose, uric acid, and ascorbic acid. Cytotoxicity studies using human gingival fibroblasts confirmed the biocompatibility of the modified sensor surface. These results demonstrate that rational multilayer surface engineering enables robust electrochemical lactate sensing in saliva and represents a promising strategy for future intraoral biosensing applications.
