Spatial engineering of nanocomposite microneedle arrays for interstitial fluid sampling, detection, and stable readout

Nanocomposite microneedle arrays are promising platforms for minimally invasive interstitial fluid (ISF) monitoring, integrating skin-accessible microscale structures with functional nanomaterials. Nevertheless, inefficient microsample utilization, limited target enrichment, unstable signal transduction, wet-state mechanical failure, biofouling, and long-term readout drift continue to limit reliable ISF monitoring. These problems are determined not only by the choice of nanomaterials, but also by the fact whether functional components are located in places corresponding to bottlenecks at the device level. In this Review, we employ a spatial engineering method to evaluate nanocomposite microneedle arrays and categorise representative strategies into three groups: bulk incorporation, surface functionalization, and channel functionalization. We explore the significance of these spatial arrangements for three related functional aspects: sampling, detection, and readout stability. Matrix strength, swelling and microsample retention are primarily governed by bulk incorporation. Recognition and transduction interfaces are reconstructed by surface functionalization while sample transport, local enrichment and continuous supply to sensor regions are controlled by channel functionalization. We discuss design trade-offs concerning mechanical reinforcement versus mass transfer, signal amplification versus stability, and antifouling protection versus diffusion resistance, and translational criteria including biosafety, batch consistency, storage stability and scalable manufacturing. This spatially resolved approach could enable the rational design of reliable nanocomposite microneedle systems for ISF-based biochemical monitoring.