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

Maintaining the concentrations of various ions in body fluids is critical to all living organisms. In this contribution, we designed a flexible microneedle patch coupled electrode array (MNP-EA) for the in situ multiplexed detection of ion species (Na+, K+, Ca2+, and H+) in tissue interstitial fluid (ISF). The microneedles (MNs) are mechanically robust for skin or cuticle penetration (0.21 N/needle) and highly swellable to quickly extract sufficient ISF onto the ion-selective electrochemical electrodes (∼6.87 µL/needle in 5 min). The potentiometric sensor can simultaneously detect these ion species with nearly Nernstian response in the ranges wider enough for diagnosis purposes (Na+: 0.75-200 mM, K+: 1-128 mM, Ca2+: 0.25-4.25 mM, pH: 5.5-8.5). The in vivo experiments on mice, humans, and plants demonstrate the feasibility of MNP-EA for timely and convenient diagnosis of ion imbalances with minimal invasiveness. This transdermal sensing platform shall be instrumental to home-based diagnosis and health monitoring of chronic diseases and is also promising for smart agriculture and the study of plant biology.

Colorimetric microneedle patches for multiplexed transdermal detection of metabolites.

Skin Interstitial Fluid (ISF) is an alternative source for biomarkers. Herein, a highly swellable microneedle patch (MNP) to rapidly extract ISF painlessly and bloodlessly is presented. The MNP is made of crosslinked methacrylated hyaluronic acid (MeHA) and dissolvable hyaluronic acid (HA) with the optimal balance of mechanical strength (0.6 N/MN) and absorption capability (16.22 µL in 20 min). Incorporated with wax-patterned and sensing-reagent-decorated test paper (TP) for multiplexed colorimetric detection of metabolites (glucose, lactate, cholesterol, and pH), this TP-MNP biosensor gives rapid color change in biomarker concentration-dependent manner based on specific enzymatic reactions, whereby allowing diagnosis by the naked eye or quantitative RGB analysis. Both the in vitro and in vivo experiments demonstrate the feasibility of TP-MNPs to detect multiple biomarkers in skin interstitial fluid within minutes. Such convenient and self-administrable profiling of metabolites shall be instrumental for home-based long-term monitoring and management of metabolic diseases.