When studying the behaviour of a virus, working with viruses requires gentleness. This is often the case with viruses considered to be pathogens. An example is in the case of COVID-19 since the particles do not survive well when making contact with surfaces.
To observe a live virus and move it around, methods that make no physical contact are optimal for keeping the tiny subjects alive longer, allowing more time to study them.
Virginia Tech Assistant Professor Zhenhua Tian has established an approach using two kinds of energy to move microparticles, offering novel applications in diagnosing, treating, and preventing the spread of diseases.
This approach combines acoustic waves with electric fields. For this, researchers developed a microscopic device that can precisely capture and manipulate small particles in a contactless manner.
The scientists combined two forms of energy. The first is acoustic energy using standing waves. These acoustics are outside the range of sound that can be heard by humans, and they are engineered to travel along flat surfaces of small chips equipped with tiny acoustic emitters.
The sound energy is said to move like the energy of an earthquake but at a much smaller scale. Though invisible, ultrasound waves are typically visualized as something like mountains and valleys. How frequently this up-and-down pattern occurs is termed the frequency.
As a demonstration, the scientists emitted two waves of different frequencies, crossing one another. When the waves cross, their overlap creates grid-like energy patterns composed of many energy valleys, called acoustic wells.
When microparticles encounter these wells, they are trapped and settle at the centre. This is where they remain — protected enough to be studied — until another force is introduced.
To control the movements of particles within acoustic wells, another kind of energy is required. These are in the form of electrical fields, generated by using microscopic electrodes.
By overlapping an electrical field with an acoustic well, the scientists were able to precisely move the microparticles trapped in the well. Instead of remaining immobilized at the centre of the well, the force induced by the electric field allows them to move around the well’s centre.
It was also found that the crossing of acoustic waves creates more than one well. The wells are distributed in a grid pattern, allowing multiple particles to be captured at the same time. When electrical fields are used to move the particles within them, each particle can be controlled separately, setting the stage for complex movement.
The applications of this technology are numerous. Researchers working at the microscale will have alternative options for ways to perform their work, and the ability to handle material that is delicate, like virus particles.
The findings have been published in the journal Science Advances. The research paper is titled “Acousto-dielectric tweezers enable independent manipulation of multiple particles.”
