Multilayer Detachable Microneedles for Therapeutic and Collaborative Digital PCR Monitoring

Microneedle (MN) technology is an appealing route for treating skin cancers, but remains many challenges, such as accommodating multiple theranostic functionalities and configuring personalized sensing, particularly given that MNs typically collect sample volumes from microliters to milliliters, necessitating suitable trace analysis techniques. In this study, we developed a versatile, multilayer, detachable MN administration system capable of simultaneous photocontrolled drug delivery therapy that operated based on real-time in situ conditions monitored by droplet-based PCR (dPCR). The detachable MN consisted of an innermost poly (ethylene glycol) diacrylate extraction layer, an outer gelatin methacryloyl drug-loaded layer containing Vemurafenib and black phosphorus (BP), and a polyvinyl alcohol connection layer designed for thermal detachment. The outer layer enabled light-responsive drug release through BP's photothermal properties, achieving 78% release within 24 h. Subsequently, the significant mechanical strength and swelling characteristics facilitated the effective extraction of approximately 26 µL of interstitial fluid within 10 min. Both in vitro and in vivo studies on melanoma demonstrated the platform's capability to enhance therapeutic efficacy while minimizing systemic toxicity. It enabled dPCR-based monitoring of MCAM and BRAF genes, including the drug-resistant V600E polymorphism, with detection limits of 223 copies/µL, along with digital proximity ligation assay detection of the protein markers IL-6, VEGF, and Ki-67 at 0.64 pg/mL. This well-designed biosystem highlighted its capability to interact with the pathophysiological environment, providing a preclinical proof-of-concept for minimally invasive theranostics in superficial tumors.