Microneedle-Coupled Epidermal Sensors for In-Situ-Multiplexed Ion Detection in Interstitial Fluids

Smart Wearable Sensor Fuels Noninvasive Body Fluid Analysis

The advancements in wearable sensor technology have revolutionized noninvasive body fluid monitoring, offering new possibilities for continuous and real-time health assessment. By analyzing body fluids such as sweat, saliva, tears, and interstitial fluid, these technologies provide painless diagnostic alternatives for detecting biomarkers such as glucose, electrolytes, and metabolites. These sensors play a crucial role in early disease detection, chronic condition management, and personalized healthcare. Recent innovations in flexible electronics, microfluidic systems, and biosensing materials have significantly improved the accuracy, reliability, and integration of sensors into everyday textiles. Moreover, the convergence of artificial intelligence and big data analytics has enhanced the precision and personalization of health monitoring systems, transforming wearable sensors into powerful tools for health holographic inspection. Despite significant progress, challenges remain, including improving sensor stability in dynamic environments, achieving real-time data transmission, and covering a broader range of biomarkers. Future research directions focus on enhancing material sustainability through green synthesis, optimizing sampling techniques, and leveraging machine learning to further improve sensor performance. This Review highlights the transformative potential of wearable sensors in medical applications, aiming to bridge gaps in healthcare accessibility and elevate the standards of patient care through noninvasive continuous monitoring technologies.

Lab-on-the-Needles: A Microneedle Patch-Based Mobile Unit for Highly Sensitive Ex Vivo and In Vivo Detection of Protein Biomarkers

Detection of biomarkers associated with physiological conditions provides critical insights into healthcare and disease management. However, challenges in sampling and analysis complicate the detection and quantification of protein biomarkers within the epidermal layer of the skin and in viscous liquid biopsy samples. Here, we present the "Lab-on-the-Needles" concept, utilizing a microneedle patch-based sensing box (MNP-based SenBox) for mobile healthcare applications. This system facilitates the rapid capture of protein biomarkers directly from the in situ epidermal layer of skin or liquid biopsies, followed by on-needle analysis for immediate assessment. The integration of horseradish peroxidase-incorporated zeolitic imidazolate framework-8 (HRP@ZIF-8) as a sensitive and stable signal probe, the detection limit for anti-SARS-CoV-2 NP IgA antibodies and various SARS-CoV-2 S1P mutant strains improves by at least 1,000-fold compared to FDA-approved commercial saliva lateral flow immune rapid tests. Additionally, the MNP-based SenBox demonstrated minimally invasive monitoring and rapid quantification of inflammatory cytokine levels (TNF-α and IL-1β) in rats within 30 min using a portable ColorReader. This study highlights the potential of the MNP-based SenBox for the minimally invasive collection and analysis of protein biomarkers directly from in situ epidermal layers of skin or liquid biopsies that might facilitate mobile healthcare diagnostics and longitudinal monitoring.

Lateral Flow-Based Skin Patch for Rapid Detection of Protein Biomarkers in Human Dermal Interstitial Fluid

Rapid diagnostic tests (RDTs) offer valuable diagnostic information in a quick, easy-to-use and low-cost format. While RDTs are one of the most commonly used tools for in vitro diagnostic testing, they require the collection of a blood sample, which is painful, poses risks of infection and can lead to complications. We introduce a blood-free point-of-care diagnostic test for the rapid detection of protein biomarkers in dermal interstitial fluid (ISF). This device consists of a lateral flow immunochromatographic assay (LFIA) integrated within a microfluidic skin patch. ISF is collected from the skin using a microneedle array and vacuum-assisted extraction system integrated in the patch, and transported through the lateral flow strip via surface tension. Using this skin patch platform, we demonstrate in situ detection of anti-tetanus toxoid IgG and SARS-CoV-2 neutralizing antibodies, which could be accurately detected in human ISF in <20 min. We envision that this device can be readily modified to detect other protein biomarkers in dermal ISF, making it a promising tool for rapid diagnostic testing.

Simultaneous Detection of Biomarkers in Urine Using a Multicalibration Potentiometric Sensing Array Combined with a Portable Analyzer

Domestic monitoring devices make real-time and long-term health monitoring possible, allowing people to track their health status regularly. Uric acid (UA), creatinine, and urea in urine are three important biomarkers for various diseases, especially kidney diseases. This work proposed a 10-channel potentiometric sensing array containing a UA electrode group, a creatinine electrode group, a urea electrode group, a pH electrode group, and one pair of reference channels, which could be connected with a portable potentiometric analyzer, realizing the simultaneous detection of UA, creatinine, urea, and pH in urine. The prepared Pt/carbon nanotubes (CNTs)-uricase, creatinine deiminase, Au@urease, and polyaniline were employed as the sensing materials, showing responses to four targets with high sensitivity and selectivity. To improve the accuracy of domestic monitoring, a calibration channel was integrated into each electrode group to calibrate the basic potential of the sensing channels, and the influences of pH and temperature on the responses were investigated through the pH electrode group and an external temperature probe to calibrate the slope and intercept. With the preset of the deduced calibration parameters and computational formula for the four targets in the analyzer in Lab Mode, the concentrations of UA, creatinine, and urea and the pH of the human urine samples were directly displayed on the screen of the analyzer in Practical Mode. The agreement of these results with those obtained from commercial kits and pH meters reveals the high potential of these methods for developing domestic devices to facilitate health monitoring.

Simple fabrication of electrochemical sensor based on integration of dual signal amplification by the supporting electrode and modified nanochannel array for direct and sensitive detection of vitamin B2

Development of simple and reliable sensor for detecting vitamin content is of great significance for guiding human nutrition metabolism, overseeing the quality of food or drugs, and advancing the treatment of related diseases. In this work, a simple electrochemical sensor was conveniently fabricated by modification a carbon electrode with vertically-ordered mesoporous silica film (VMSF), enabling highly sensitive electrochemical detection of vitamin B2 (VB2) based on the dual enrichment of the analyte by the supporting electrode and nanochannels. The widely used glassy carbon electrode (GCE), was preactivated using simple electrochemical polarization, The resulting preactivated GCE (p-GCE) exhibited improved potential resolution ability and enhanced peak current of VB2. Stable modification of VMSF on p-GCE (VMSF/p-GCE) was achieved without introducing another binding layer. The dual enrichment effect of the supporting p-GCE and nanochannels facilitated sensitive detection of VB2, with a linear concentration ranged from 20 nM to 7 μM and from 7 μM to 20 μM. The limit of detection (LOD), determined based on a signal-to-noise ratio of three (S/N = 3), was found to be 11 nM. The modification of ultra-small nanochannels of VMSF endowed VMSF/p-GCE with excellent anti-interference and anti-fouling performance, along with high stability. The constructed sensor demonstrated the capability to achieve direct electrochemical detection of VB2 in turbid samples including milk and leachate of compound vitamin B tablet without the need for complex sample pretreatment. The fabricated electrochemical can be easily regenerated and has high reusability. The advantages of simple preparation, high detection performance, and good regeneration endow the constructed electrochemical sensor with great potential for direct detection of small molecule in complex samples.

Microneedle Assays for Continuous Health Monitoring: Challenges and Solutions

Continuous health monitoring aims to reduce hospitalization and the need for constant supervision of the patients. For an outpatient monitoring device to be effective, it must meet certain criteria: it should demand minimal patient involvement, be reliable, be connected, remain stable with infrequent replacements, be cost-efficient, be compatible with humans, and ultimately be self-powered. Microneedle (MN) technology, designed for transdermal biosensing, offers a promising solution for meeting a wide range of these demands in the field of continuous health monitoring. A variety of MN platforms have been developed to facilitate this crucial function. Our focus in this Perspective is on the significant challenges linked to MN-based biosensors. These challenges include ensuring skin compatibility, the effective integration of biorecognition elements into the MN systems, and the durability concerns of these sensors in enabling extended periods of continuous monitoring. Tackling these hurdles could pave the way for more effective and reliable MN-based health monitoring solutions in the future.

Implantable Electrochemical Microsensors for In Vivo Monitoring of Animal Physiological Information

In vivo monitoring of animal physiological information plays a crucial role in promptly alerting humans to potential diseases in animals and aiding in the exploration of mechanisms underlying human diseases. Currently, implantable electrochemical microsensors have emerged as a prominent area of research. These microsensors not only fulfill the technical requirements for monitoring animal physiological information but also offer an ideal platform for integration. They have been extensively studied for their ability to monitor animal physiological information in a minimally invasive manner, characterized by their bloodless, painless features, and exceptional performance. The development of implantable electrochemical microsensors for in vivo monitoring of animal physiological information has witnessed significant scientific and technological advancements through dedicated efforts. This review commenced with a comprehensive discussion of the construction of microsensors, including the materials utilized and the methods employed for fabrication. Following this, we proceeded to explore the various implantation technologies employed for electrochemical microsensors. In addition, a comprehensive overview was provided of the various applications of implantable electrochemical microsensors, specifically in the monitoring of diseases and the investigation of disease mechanisms. Lastly, a concise conclusion was conducted on the recent advancements and significant obstacles pertaining to the practical implementation of implantable electrochemical microsensors.

Highly sensitive electrochemical immunosensor based on electrodeposited platinum nanostructures confined in silica nanochannels for the detection of the carcinoembryonic antigen

In this study, we report a highly sensitive electrochemical immunosensor for carcinoembryonic antigen (CEA) detection based on the electrodeposited platinum nanoparticles (Pt NPs) confined in the ultrasmall nanochannels of vertically ordered mesoporous silica film (VMSF). VMSF bearing amine groups (NH2-VMSF) can be prepared on the indium tin oxide electrode surface via a one-step co-condensation route using an electrochemically assisted self-assembly method, which renders a strong electrostatic effect for [PtCl6]2- and leads to the spatial confinement of Pt NPs inside the silica nanochannels after electrodeposition. The external surface of NH2-VMSF is functionalized with CEA antibodies using glutaraldehyde as a coupling agent, resulting in an electrochemical immunosensing interface with good specificity for CEA detection. Under optimal experimental conditions, high affinity between the CEA antibody and CEA produces a steric hindrance effect for the accessibility of the electrochemical probe ([Fe(CN)6]3-) in the bulk solution to the underlying indium tin oxide surface, eventually resulting in the attenuated electrochemical signal and enabling the detection of the CEA with a wide linear range of 0.01 pg/mL∼10 ng/mL and a pretty low limit of detection of 0.30 fg/mL. Owing to the signal amplification ability of Pt NPs and the anti-biofouling property of NH2-VMSF, the as-prepared electrochemical immunosensor based on the Pt NPs@NH2-VMSF displays an accurate analysis of the CEA in human serum samples, holding significant promise for health monitoring and clinical diagnosis.

A highly sensitive immunosensor based on nanochannel-confined nano-gold enhanced electrochemiluminescence for procalcitonin detection

Sensitive detection of procalcitonin (PCT) in serum is crucial for the timely diagnosis and treatment of rheumatoid arthritis. In this work, an electrochemiluminescence (ECL) detection platform is developed based on in-situ growth of Au nanoparticles (AuNPs) in nanochannels and an analyte-gated detection signal, which can realize ECL determination of PCT with high sensitivity. Vertically ordered mesoporous silica films with amine groups and uniform nanochannel array (NH2-VMSF) is easily grown on the supporting indium tin oxide (ITO) electrode through electrochemical assisted self-assembly method (EASA). Anchored by the amino groups, AuNPs were grown in-situ within the nanochannels to catalyze the generation of reactive oxygen species (ROS) and amplify the ECL signal of luminol. An immuno-recognitive interface is constructed on the outer surface of NH2-VMSF, through covalent immobilization of PCT antibodies. In the presence of PCT, the immunocomplex will hinder the diffusion of luminol and co-reactants, leading to a gating effect and decreased ECL signals. Based on this principle, the immunosensor can detect PCT in the range from 10 pg/mL to 100 ng mL-1 with a limit of detection (LOD) of 7 pg mL-1. The constructed immunosensor can also be used for detecting PCT in serum. The constructed sensor has advantages of simple fabrication and sensitive detection, demonstrating great potential in real sample analysis.

Influence of the Composition of Plasticizer-Free Silicone-Based Ion-Selective Membranes on Signal Stability in Aqueous and Blood Plasma Samples

Solid-contact ion-selective electrodes (SC-ISEs) in direct long-term contact with physiological samples must be biocompatible and resistant to biofouling, but most wearable SC-ISEs proposed to date contain plasticized poly(vinyl chloride) (PVC) membranes, which have poor biocompatibility. Silicones are a promising alternative to plasticized PVC because of their excellent biocompatibility, but little work has been done to study the relationship between silicone composition and ISE performance. To address this, we prepared and tested K+ SC-ISEs with colloid-imprinted mesoporous (CIM) carbon as the solid contact and three different condensation-cured silicones: a custom silicone prepared in-house (Silicone 1), a commercial silicone (Dow 3140, Silicone 2), and a commercial fluorosilicone (Dow 730, Fluorosilicone 1). SC-ISEs prepared with each of these polymers and the ionophore valinomycin and added ionic sites exhibited Nernstian responses, excellent selectivities, and signal drifts as low as 3 μV/h in 1 mM KCl solution. All ISEs maintained Nernstian response slopes and had only very slightly worsened selectivities after 41 h exposure to porcine plasma (log KK,Na values of -4.56, -4.58, and -4.49, to -4.04, -4.00, and -3.90 for Silicone 1, Silicone 2, and Fluorosilicone 1, respectively), confirming that these sensors retain the high selectivity that makes them suitable for use in physiological samples. When immersed in porcine plasma, the SC-ISEs exhibited emf drifts that were still fairly low but notably larger than when measurements were performed in pure water. Interestingly, despite the very similar structures of these matrix polymers, SC-ISEs prepared with Silicone 2 showed lower drift in porcine blood plasma (-55 μV/h, over 41 h) compared to Silicone 1 (-495 μV/h) or Fluorosilicone 1 (-297 μV/h).