In this paper we describe the double nanohole laser tweezer system used to trap single nanoparticles. We cover the basic theory behind the DNH and what makes it more powerful than traditional laser tweezers commonly used for larger particles. We outline the basic setup used to reliably trap several different types of particles ranging in size from 1 nm to 40 nm. Data from several experiments is shown which displays exactly how a particle is confirmed to be trapped. We will discuss the use of autocorrelation as well as other information that can be extracted from the optical transmission in our setup and how it has been applied to the identification of protein small molecule interactions and protein binding. Other uses of the data collected from our setup will be discussed including the observation of protein folding. Finally we discuss the current developments of the process and its possible uses as a drug discovery tool, a new type of single particle nanopipette and new bio-sensors.
Optical trapping is a promising technique which involves holding and manipulating small particles in a non-destructive
way. Conventional trapping methods are able to trap dielectric particles with size greater than 100 nm. Using a double-nanohole
in a metal film (with sharp tips where the holes meet) has enabled us to trap dielectric particles such as
quantum dots and single proteins. This has been achieved even while using low laser power. Since the refractive index of
the particle is larger than the surrounding environment, the aperture appears larger when the particle enters the aperture.
This allows for more light transmitted through the aperture. The change in transmission changes the light momentum,
and by Newton’s third law, there will be a force which will push back the particle to the equilibrium position. The
change in light transmission also allows for facile detection of the trapping event. In this work, we use the double-nanohole
to trap encapsulated quantum dots. Quantum dots are practically useful for several purposes including
computing, biology and electronic devices. The ability to manipulate these particles with precision is critical to
development of quantum dots usage in these fields. The CdS quantum dots, which are used in this work, are coated with
a polymer shell, with a total size between 20 nm to 22 nm. The trapping and manipulation of quantum dots is promising
for nanofabrication technologies that seek to place a quantum dot at a specific location in a plasmonic or nanophotonic
structure. The next step in this research will be imaging of quantum dots using their fluorescence while trapping is
occurring, so that a clear indication of trapping event will be available.