Boosting single-molecule fluorescence enhancement with nanoaperture-nanoantenna hybrid systems

Boosting the sensitivity of single-molecule fluorescence detection (SMFD), a powerful tool in bio- and medical sciences, can be enabled by optical nanoantennas exhibiting hotspots to enhance light-matter interactions. However, precisely delivering molecules into hotspots with nanoscale sizes remains a great challenge for conventional nanoantennas with open interfaces. Here, we integrate carefully designed plasmonic nanoapertures with nanoantennas, and experimentally demonstrate that the hybrid systems can enhance the signal-to-background-ratio of SMFD by nearly an order of magnitude compared to bare nanoantennas. We design and fabricate a series of hybrid systems, and experimentally show that the unique “hotspot-in-a-box” configuration formed in our systems can significantly enhance the probability of molecules accessing the hotspot region and shield low-enhancement events outside the hotspot region, thereby enhancing the single-molecular fluorescence signals with narrower enhancement distributions and diminished background signals. Our strategy can find many applications in bio- and medical sciences, such as high-throughput single-molecule detection, surface-enhanced optical sensing, and so on.