Skin interstitial fluid (ISF) containing a great variety of molecular biomarkers derived from cells and subcutaneous blood capillaries has recently emerged as a clinically potential component for early diagnosis of a wide range of diseases; however, the minimally invasive sampling and detection of cell-free biomarkers in ISF is still a key challenge. Herein, we developed microneedles (MNs) that consist of gelatin methacryloyl (GelMA) and graphene oxide (GO) for the enrichment and sensitive detection of multiple microRNA (miRNA) biomarkers from skin ISF. The GO-GelMA MNs exhibited robust mechanical properties, fast sampling kinetics, and large swelling capacity, which enabled collecting ISF volume high to 21.34 μL in 30 min, facilitating effective miRNA analysis. It preliminarily realized the sensitive detection of three types of psoriasis-related miRNAs biomarkers either on the patch itself or in solution after release from the hydrogel by combining catalytic hairpin assembly signal amplification reaction. The automated and minimally invasive ISF miRNA detection technology of GO-GelMA MNs has great potential to monitor cell-free clinically informative biomarkers for personalized diagnosis and prognosis.

Skin interstitial fluid (ISF) is a biofluid with information-rich biomarkers for disease diagnosis and prognosis. Microneedle (MN) integration of sampling and instant biomarker readout hold great potential in health status monitoring and point-of-care testing (POCT). The present work describes an attractive MN sensor array for minimally invasive monitoring of ISF microRNA (miRNA) and Cu2+. The MN array is made of methacrylated gelatin (GelMA) and methacrylated hyaluronic acid (MeHA), and a further divisionally encapsulated miRNA and Cu2+ detection system, and is cross-linked through blue-light irradiation. The MN patch displays good mechanical properties that enable withstanding more than 0.4 N per needle, and exhibits a high swelling ratio of 700% that facilitates timely extraction of sufficient ISF for biomarker analysis. For proof-of-concept, it realizes detection of miRNAs and Cu2+ efficiently and quantitatively in an agarose skin and fresh porcine cadaver skin model. Given the good sampling and in situ monitoring ability, the MN array holds great promise for skin ISF-based applications.

DNAzyme shows great promise in designing a highly sensitive and specific sensing platform; however, the low cellular uptake efficiency, instability, and especially the insufficient cofactor supply inhibit the intracellular molecule sensor applications. Herein, we demonstrate a novel type of DNAzyme-based self-driven intracellular sensor for microRNA (miRNA) detection in living cells. The sensor consists of a metal–organic framework [zeolite imidazole framework (ZIF-8)] core loaded with a shell consisting of a rationally designed DNAzyme, where the substrate strand is modified with FAM and BHQ-1 nearby both the sides of the restriction site, respectively, while the enzyme strand consists of two separate strands with a complementary fragment to the substrate strand and the targeting miRNA, respectively. The ZIF-8 nanoparticles enable the efficient delivery of DNAzyme into the cell and protect the DNAzyme from degradation. The pH-responsive ZIF-8 degradation is accompanied with the release of the DNAzyme and Zn2+ cofactors, and the intracellular target miRNAs recognize and activate the DNAzyme driven by the Zn2+ cofactors to cleave the substrate strand, resulting in the release of the FAM-labeled shorter product strand and increased fluorescence for miRNA detection. The self-driven approach can be generally applied to various miRNAs’ detection through DNAzyme engineering.