Was created a colloidal nanotweezer to capture and manipulate nanoparticles.
Source: Technology.org
A major problem faced with optical tweezers and other conventional trapping techniques is their inability to hold extremely small sized objects, also called cargo. Imagine picking up grains of salt using only a pair of needles! What makes it tough is that the force required to capture a particle reduces as it’s size decreases.
What is a optic tweezer? It is a tool which gets particles in micrometer and nanometer sizes with two laser beans in opposite directions. The lasers pass through microscope objective lens to focus in micrometer object. On the particle, a force in picoNewtons (10^{-12}) is exerted. Is an important tool in nanotechnology, quantum optics, molecular biology, etc.
The key technological breakthrough for enabling these optical tweezers to reach deeper into the nanoscale and become so-called “nanotweezers” has been plasmonics. When illuminated by light, noble metallic nanostructures create a strong electromagnetic field around themselves that can attract and trap nanoparticles that are close.
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However, plasmonic tweezers also have limitations. With a limited range of influence and being fixed in space, these tweezers can only capture nanoparticles in their vicinity. This makes the entire trapping process inherently slow and inefficient for transport. So, it is important to design a technique that has the efficiency of a traditional plasmonic tweezer but, at the same time, is manoeuvrable like conventional optical tweezers.
In this work, to be published in the journal Nature Communications, we demonstrate an advanced nanomanipulation technique that works on optical forces alone and therefore versatile in nature. In our experiment, we have integrated a plasmonic nanodisk (made of silver) to a dielectric microrod (made of glass) and maneuvered the hybrid structure with a focused laser beam. This is a unique manifestation of “tweezer in a tweezer” concept where trapping and manuevering is achieved with a single laser beam.
These all-optical nanotweezers can be driven to any target objects in any fluidic environment with precise control to capture, transport and release nanoscale cargos as small as 40 nm (typical length scale of virus, DNA and various macromolecules) with high speed and efficiency. We also showed parallel and independent control in manipulation with various nanoobjects including fluorescent nanodiamonds, magnetic nanoparticles with ultra-low laser power which is lower than the typical damage threshold of soft biological objects.
The schematics of colloidal nanotweezer (a), static (b) and dynamic manipulations (c).
This demonstrated technology may enable isolation, manipulation and chip-level assembly of nanomaterials such as nanocrystals, fluorescent nanodiamonds and quantum dots, and allow non-invasive manipulation of fragile bio-specimens, such as bacteria, virus and various macromolecules. Apart from carrying small objects to various spots of a microfluidic device, we can also localize them with high spatial resolution and then take them away if necessary. This capability may open up new avenues in nanoscale assembly and sensing.
