Skin interstitial fluid (ISF) holds great potential as a highly desirable sample resource for point‐of‐care testing (POCT), where the key is to effectively collect target biomarkers from ISF. Hydrogel microneedle patch has great promise for ISF extraction. However, it is challenging to recover target biomarkers from the extracted skin ISF in hydrogel microneedle patches in an easy‐administrated, fast, and bulky instrument‐free manner. Herein, a hydrogel microneedle patch made of polyvinyl alcohol (PVA) and chitosan (CS) for POCT based on the ISF is developed. The phase transition property of PVA/CS hydrogel makes the microneedles stiff when dry, which is beneficial to easily penetrate into skin. Meanwhile, the highly porous microstructure of hydrogel offers good swelling ability for extraction of ISF and the thermal degradation property of PVA makes it convenient to quickly and efficiently recover target biomarkers from microneedle patch. The capability of this platform for POCT applications is further demonstrated by successful detections of typical biomarkers collected from the mimetic skin and monitoring the glucose level in rabbit skins during a day. The developed hydrogel microneedle patch holds the advantages of extraction of skin ISF and recovery of biomarkers, thus presenting as a powerful platform for skin ISF‐based POCT applications.

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Hydrogel‐based electronics have found widespread applications in soft sensing and health monitoring because of their remarkable biocompatibility and mechanical features similar to human skin. However, they are subjected to potential challenges like structural failure, functional degradation, and device delamination in practical applications, especially facing extreme environmental conditions (e.g., abnormal temperature and humidity). To address these, ionically conductive organohydrogel‐based soft electronics are developed, which can perform at subzero and elevated temperatures (thermal compatibility) as well as at dehydrated and hydrated environments (hydration compatibility) for extended applications. More specifically, gelatin/poly(acrylic acid–N‐hydrosuccinimide ester) (PAA–NHS ester)‐based ionic‐conductive organohydrogel is synthesized. By introducing a glycerol–water binary solvent system, the gel can maintain mechanical softness in a wide temperature range (from −80 to 60 °C). Besides, excellent conductivity is achieved under various conditions by soaking the gel into lithium chloride anhydrous (LiCl) solution. Strong adhesion with skin, even under water, can be realized by covalent bonds between NHS ester from gel and amino groups from human skin. The excellent performances of LiCl‐loaded PAA‐based organohydrogel (L‐PAA‐OH)‐based electronics are further demonstrated under freezing and high temperatures as well as underwater conditions, unveiling their promising prospects in wearable health monitoring in various conditions.

Detection of biomarkers associated with body conditions provides in‐depth healthcare information and benefits to disease management, where the key challenge is to develop a minimally invasive platform with the ability to directly detect multiple biomarkers in body fluid. Dermal tattoo biosensor holds the potential to simultaneously detect multiple health‐related biomarkers in skin interstitial fluid because of the features of minimal invasion, easy operation, and equipment‐free result reading. Herein, a colorimetric dermal tattoo biosensor fabricated by a four‐area segmented microneedle patch is developed for multiplexed detection of health‐related biomarkers. The biosensor exhibits color changes in response to the change of biomarker concentration (i.e., pH, glucose, uric acid, and temperature), which can be directly read by naked eyes or captured by a camera for semi‐quantitative measurement. It is demonstrated that the colorimetric dermal tattoo biosensor can simultaneously detect multiple biomarkers in vitro, ex vivo, and in vivo, and monitor the changes of the biomarker concentration for at least 4 days, showing its great potential for long‐term health monitoring.

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