Enhancing Single-Molecule Fluorescence Spectroscopy with Simple and Robust Hybrid Nanoapertures

Abstract

Plasmonic nanoapertures have found exciting applications in optical sensing, spectroscopy, imaging, and nanomanipulation. The subdiffraction optical field localization, reduced detection volume (∼attoliters), and background-free operation make them particularly attractive for single-particle and single-molecule studies. However, in contrast to the high field enhancements by traditional "nanoantenna"-based structures, small field enhancement in conventional nanoapertures results in weak light−matter interactions and thus small enhancement of spectroscopic signals (such as fluorescence and Raman signals) of the analytes interacting with the nanoapertures. In this work, we propose a hybrid nanoaperture design termed "gold-nanoislandsembedded nanoaperture" (AuNIs-e-NA), which provides multiple electromagnetic "hotspots" within the nanoaperture to achieve field enhancements of up to 4000. The AuNIs-e-NA was able to improve the fluorescence signals by more than 2 orders of magnitude with respect to a conventional nanoaperture. With simple design and easy fabrication, along with strong signal enhancements and operability over variable light wavelengths and polarizations, the AuNIs-e-NA will serve as a robust platform for surface-enhanced optical sensing, imaging, and spectroscopy.

Optothermal rotation of micro-/nano-objects

“…She is working alongside Dr Yuebing Zheng and his research group, and her research interests lie in optical manipulation and the manipulation of micro/nanoparticles. nanofabrication, [53][54][55][56][57][58] chemical and biological sensing, [59][60][61] and cargo delivery. 62,63 Based on this, optothermal rotation has been further developed recently for precise and versatile rotations of colloidal particles and living cells with striking advantages such as low operation power, high applicability, and long working distance.…”

“…Over the past two decades, researchers have established multiple theories to describe the translational migration of colloids and living objects under temperature gradient fields. [31][32][33][34][35][36] Consequently, different optothermal manipulation techniques have been developed, [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] leading to applications in nanofabrication, [53][54][55][56][57][58] chemical and biological sensing, [59][60][61] and cargo delivery. 62,63 Based on this, optothermal rotation has been further developed recently for precise and versatile rotations of colloidal particles and living cells with striking advantages such as low operation power, high applicability, and long working distance.…”

Optical Manipulation Heats up: Present and Future of Optothermal Manipulation

“…Plasmonic tweezers 93 offer the right combination of site specificity and controlled heat generation, which enables plasmon-enhanced optical or optothermal trapping along with optothermal delivery of target particles. 94 Using plasmonic nanostructures as substrates, target particles are attracted from long-range distances and trapped locally and stably at the nanostructures due to the enhanced electromagnetic and temperature hot spots. 97,99 The highly localized electric field enhancements lead to a high trapping stiffness of different entities such as DNA, proteins, nanoparticles, and quantum dots.…”

“…Although optothermal tweezers on solid substrates arose as a promising solution, other techniques are essential to overcome the problem in liquid media. Plasmonic tweezers offer the right combination of site specificity and controlled heat generation, which enables plasmon-enhanced optical or optothermal trapping along with optothermal delivery of target particles. − Using plasmonic nanostructures as substrates, target particles are attracted from long-range distances and trapped locally and stably at the nanostructures due to the enhanced electromagnetic and temperature hot spots. , The highly localized electric field enhancements lead to a high trapping stiffness of different entities such as DNA, proteins, nanoparticles, and quantum dots. Initial studies did not include the effects of thermophoretic force on particle trapping, mainly due to negligible thermophoretic force at the singularity.…”

Fluorescence Brightness, Photostability, and Energy Transfer Enhancement of Immobilized Single Molecules in Zero-Mode Waveguide Nanoapertures

“…Regarding the fluorescence brightness, several studies have reported fluorescence enhancement of the photon count rate for diffusing molecules. ,− On the contrary, for immobilized single molecules, the results are less documented and appear sometimes to be contradictory. Aluminum ZMWs were shown to enhance the fluorescence brightness of green dyes Atto 550 and Atto 565 by 2.2- and 2.5-fold, respectively. , However, for the red dye Atto 647N, either 2.5-fold enhancement, no enhancement, or 10-fold lower brightness , was reported.…”