(Invited) Microneedle Arrays Featuring Microcavities for Electrochemical Biosensing in Sweat and Interstitial Fluid

Microneedle arrays are a promising tool in the development of transdermal biosensing devices, and considerable research effort is being devoted to the development, microfabrication, optimization, and testing of different microneedle-based sensing platforms.[1] To date, microneedles have been fabricated from various materials in different shapes, sizes, and densities, with the aim of enhancing the performance of biosensors and developing user-friendly microneedle devices.[1] And we have demonstrated sensing of small molecules and macromolecules using both silicon and polymer based microneedle arrays [2-4]. However, one of the main challenges yet to be addressed is devices remaining fully functional and providing an accurate electrochemical response after skin insertion.[5] Such failure can mainly occur due to delamination or damage of the sensing layer during skin insertion. To address the above-mentioned challenges, we developed a microneedle array featuring recessed microcavities or 3D polymer lattices.[6-8] Those features are conductive microscale pockets located at the tip of the microneedles which can i) accommodate a biosensing layer and conduct electrochemical measurements, ii) protect the sensing layer from delamination during insertion and removal from the skin, and iii) position the sensing layer deep in the skin enabling proper access to the interstitial fluid. In our work, we illustrated that microcavities protect against delamination of the sensing layer during multiple skin applications, unlike microneedles without microcavities. The retained functionality of the sensing platform in glucose, urea and insulin sensing has been successfully demonstrated via ex vivo and in vivo tests. The aim of this work is to set the foundation for a new kind of microneedle design, involving the engineering of the microneedle surface to develop transdermal sensing devices suitable for practical application. This will not just help to advance transdermal sensing technology by overcoming challenges but also reduce the cost and duration of wearable sensor fabrication, and improve the reliability of microneedle-based diagnostics and health monitoring. References: [1] Nano Today 30 (2020) 100828. [2] Advanced Functional Materials 32 (2022) 200985. [3] Biosensors and Bioelectronics 222 (2023) 114955. [4] Biosensors & Bioelectronics, 192 (2021), 113496. [5] Nature Biomedical Engineering 5 (2021) 64-76. [6] ACS Materials Letters 5 (2023) 1851-1858 [7] ACS Sensors 9 (2024), 932–941. [8] Advanced Materials, 36 (2024), 2412999.