Polydiacetylene (PDA) liposomes have been widely applied for detection due to their distinctive optical properties. However, the liquid phase in which PDA liposomes are dispersed generates several drawbacks, for instance, instability, compromise of detection sensitivity induced by dilution, and separation of target sampling and detection, making it inconvenient for application. In this paper, various functionalized PDA liposomes for detecting target were prepared, which were also immobilized into swelling microneedles to construct a solid-phase detection system. The PDA liposomes-complexed microneedles (PDA/MNs) enable the integration of target sampling and detection in one platform. The effects of the dispersing matrix phase on the detection sensitivity of PDA liposomes were systematically investigated from both environmental and chemical perspectives. PDA/MNs exhibited higher sensitivity than their counterparts in liquid phase. PDA/MNs were optimized and validated for lead ion (Pb²⁺) and sialic acid (SA) detections. For Pb²⁺ detection, the limit of detection (LOD) of the PDA/MNs was 13.7 μM and 2.5 times lower than the liquid phase. For SA detection, the LOD of the PDA/MNs was 0.83 μM and 1.7 times lower than the liquid phase. The results suggested that such PDA/MNs were validated to provide a label-free, stable, sensitive, and convenient tool in an all-in-one manner for physiologic target detection.

The maturation of dendritic cells (DCs) and infiltration effector T cells in tumor-draining lymph node (tdLN) and tumor tissue are crucial for immunotherapy. Despite constructive progresses have been made with anti-programmed death-1 (anti-PD1) checkpoint blockade for immunotherapy, the efficacy of PD1/PD-L1 therapy deserves to be improved. Here, we constructed a novel transfersomes based nanovaccine complexed microneedles to enhance anti-PD1 immunotherapy via transdermal immunization for skin tumor therapy. Transfersomes were functionalized with DCs targeting moiety αCD40, co-encapsulated with antigens and adjuvant poly I:C. Moreover, transdermal administration promoted accumulation in tumor-draining lymph nodes (tdLN), which could facilitate cellular uptake, activate DCs maturation and enhance Th1 immune responses. Using a mouse melanoma model, combined therapy of such nanovaccine complexed microneedles with pembrolizumab (αPD1) was able to enhance cytotoxic T lymphocytes activation, promote infiltration and reduce regulatory T cells frequency in tdLN and tumor tissues, which achieved reversion of the immunosuppressive microenvironment into immune activation. This study highlighted the potential of transfersomes based nanovaccines complexed microneedles as an attractive platform for tumor immunotherapy.