Label-Free Optical Detection of DNA Translocations through Plasmonic Nanopores

Abstract

Solid-state nanopores are single-molecule sensors that hold great potential for rapid protein and nucleic-acid analysis. Despite their many opportunities, the conventional ionic current detection scheme that is at the heart of the sensor suffers inherent limitations. This scheme intrinsically couples signal strength to the driving voltage, requires the use of high-concentration electrolytes, suffers from capacitive noise, and impairs high-density sensor integration. Here, we propose a fundamentally different detection scheme based on the enhanced light transmission through a plasmonic nanopore. We demonstrate that translocations of single DNA molecules can be optically detected, without the need of any labeling, in the transmitted light intensity through an inverted-bowtie plasmonic nanopore. Characterization and the cross-correlation of the optical signals with their electrical counterparts verify the plasmonic basis of the optical signal. We demonstrate DNA translocation event detection in a regime of driving voltages and buffer conditions where traditional ionic current sensing fails. This label-free optical detection scheme offers opportunities to probe native DNA–protein interactions at physiological conditions.

Temperature Measurement in Plasmonic Nanoapertures Used for Optical Trapping

“…4b) and other independent measurements on bowtie nanoapertures. 37 We also probe two different gap sizes and find again similar temperature increases (Fig. 4g).…”

“…37 This value is lower than the one that we measure experimentally, we ascribe this difference to the presence of the titanium adhesion layer in our case, while no adhesion layer was used in ref. 37 Interestingly, this observation suggests new routes to tune the local temperature increase, which we are currently exploring. It should still be noted that the temperature increase in the presence of a continuous metal film 29 remains always significantly lower than for isolated structures such as nanoparticles 25 or nanoantennas.…”

Plasmonic optical tweezers based on nanostructures: fundamentals, advances and prospects

“…Ploschner et al theoretically studied the optical forces exerted on glass nanobeads in the proximity of a gold nanoantenna and noted that the localization of the particles is due to heating effects, which probably dominate over optical forces [63]. Verschueren et al demonstrated a temperature increase of 3.6°C at metallic nanopore when illuminated with an incident power of 7.5 mW [64]. Xu et al predicted a maximum temperature increase of 6°C for double nanoaperture at an incident laser intensity of 6.67 mW/μm 2 [65].…”

Nano‐Optical Tweezing of Single Proteins in Plasmonic Nanopores

“…Near‐field focusing by the antenna of the incident optical field to a nanosized hotspot permits optical nanotweezing of small nano‐objects like single proteins, whereupon changes in the light transmitted through the antenna report on the presence of the object. The advantages that this all‐optical readout offers over traditional ionic‐current sensing are outlined elsewhere . Notably, the plasmonic nanopore chip separates two fluidic reservoirs in a custom‐made flow cell, which allows for a variable bias voltage to be applied across the membrane and an electrophoretic force to be acted on the object (see Experimental Section for details).…”

“…The advantages that this all-optical readout offers over traditional ionic-current sensing are outlined elsewhere. [29,30] Notably, the plasmonic nanopore chip separates two fluidic reservoirs in a custom-made flow cell, which allows for a variable bias voltage to be applied across the membrane and an electrophoretic force to be acted on the object (see Experimental Section for details). Figure 1B shows a schematic of the optical nanoantenna, with the definition of various geometrical parameters indicated in the figure.…”