Earlier this year, IBM Zurich demonstrated, for the first time, the ability to image the charge distribution of a molecule. Now researchers at the University of Zurich, led by Prof. Madhavi Krishnan, have developed a method that makes possible the measurement of the electrostatic charge of nanoparticles for the first time.
The research, which was published in the journal Nature Nanotechnology ("Measuring the size and charge of single nanoscale objects in solution using an electrostatic fluidic trap") developed a method by which “single nanoscale objects can be directly measured with high throughput by analyzing their thermal motion in an array of electrostatic traps.”
Krishnan and her colleagues set up the “electrostatic traps” by using glass plates the size of computer chips and creating energy holes between the two plates of glass. Each hole contains a weak electrostatic charge, so when a solution is dropped on the glass plates, particles get trapped there. Because molecules from the solution continue to bounce off the trapped particles, the particles are forced into a circular motion within the traps. It is this motion that enables the measurement of the charge of each particle.
Those of you familiar with the work of the 1923 Nobel Prize winner in physics—Robert A. Millikan—might be thinking that this sounds remarkably similar to the traps he created to measure the velocity of oil drops. “But he examined the drops in a vacuum,” Prof. Krishnan explains in a press release. “We on the other hand are examining nano particles in a solution which itself influences the properties of the particles.”
The ability to measure charge in solution is critical. It is in fact the electrical charge of the particles within the solution that determines the consistency of various solutions ranging from blood to pharmaceuticals. “With our new method, we get a picture of the entire suspension along with all of the particles contained in it,” Krishnan says. “The charge of the particles plays a major role in this.”
The scientists believe that the ability to make these measurements of a single nanoparticle in real time will alter the way research is conducted for nanoparticles used in drug delivery. Any change in charge to a nanoparticle due to its reactions to various proteins and other large molecules can dramatically affect how the nanoparticle interacts in the body when carrying out a function like delivering a drug.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.