Boosting Single‐Molecule Fluorescence Enhancement With Nanoaperture‐Nanoantenna Hybrid Systems

ABSTRACT Boosting the sensitivity of single‐molecule fluorescence detection (SMFD), an unique 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 PMMA‐substrated titanium nanoapertures with nanoantennas, and experimentally demonstrate that the hybrid systems can enhance the signal‐to‐background ratio of SMFD by up to 16 times compared to bare nanoantennas, although requiring higher molecular concentrations to achieve comparable detection efficiency. We design and fabricate a series of hybrid systems, and experimentally show that the unique “nanoaperture‐confined hotspot” 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 single‐molecule sequencing, surface‐enhanced optical sensing, and so on.