Magnetic and pneumatic actuation of polymeric microneedles for plasmonic hot-spot engineering and molecular sensing

Soft actuators offer dynamic control of plasmonic particle gaps for hot-spot engineering, yet their potential remains underexplored. Here, we demonstrate two polymeric microneedle platforms designed for precise hot-spot generation and molecular sensing. The first employs magnetic actuation, embedding Fe particles into microneedles to enable reversible deformation under magnetic fields, with stable performance over 1000 cycles. Decorating these structures with silver nanoparticles yields strong surface-enhanced Raman scattering amplification. The second utilizes pneumatic actuation with polydimethylsiloxane microneedles, providing greater flexibility and tip contact area under negative pressure. When functionalized with gold nanoparticles, the microneedles achieve ~3.0-fold higher Raman signals than magnetic counterparts. To demonstrate multifunctionality, we integrate independent vacuum sources and a robotic arm for cargo transport and selective molecular detection. These dynamic microneedle platforms overcome limitations of conventional approaches and offer programmable, tunable, and scalable solutions for plasmon-enhanced sensing in diverse real-world applications.