Tackling the challenges of developing microneedle-based electrochemical sensors

Microneedles provide unique advantages in biomedical areas, particularly biosensing, because of their opportunities for minimally invasive and convenient detection. This review introduces concepts of electrochemical microneedle-based sensors for minimally invasive analysis together with insights into skin compartments for designing successful microneedles. We discuss requirements for developing microneedle-based biosensors, including electrical and electrochemical behaviors of materials (such as metals, nanomaterials, and conducting polymers) which are the key factors for sensitive biosensors. We further emphasize immobilization strategies to attach biorecognition elements to electrode materials. Moreover, we detail advanced techniques that require state-of-the-art fabrications and materials to realize porous, biodegradable, and antifouling materials to enhance biosensing performances. We also emphasize studies of cytotoxicity and damage to the skin to elucidate biocompatible potentials. Furthermore, we highlight the latest advances in microneedles published from 2019 to 2022. This review also includes an overview of key remaining obstacles and opportunities where developments will push the advances continuously. The conclusion and outlook on the status of laboratory and commercial availability are added. We prospect that microneedle sensors will be integrated into a closed-loop system biodevice for diverse applications, e.g., detection and therapy. This review discusses concepts of electrochemical microneedle-based sensors for minimally invasive monitoring. We discuss requirements including geometry, mechanical, electrical, electrochemical properties, and immobilization strategy. We illustrate advanced techniques and materials to enrich biosensor features, e.g., porosity, dissolvable ability, and anti-fouling capability. Concern of toxicity is highlighted. We also illustrate recent applications and outlooks of recently published study that exploits microneedle-based biosensors.