A fundamental difficulty of working with nanoparticles is that your objects of study are too small for an optical microscope to resolve, and thus measuring their size can be quite a challenge. Of course, if you have a scanning electron microscope, measuring particle size is straightforward. But for less well-equipped labs, a dynamic light scattering system, such as [Etienne]’s OpenDLS, fits the bill.
Dynamic light scattering works by shining a laser beam into a suspension of fine particles, then using a light sensor to measure the intensity of light scattered onto a certain point. As the particles undergo Brownian motion, the intensity of the scattered light changes. Based on the speed with which the scattered light varies, it’s possible to calculate the speed of the moving particles, and thus their size.
The OpenDLS uses a 3D printed and laser-cut frame to hold a small laser diode, which shines into a cuvette, on the side of which is the light sensor. [Etienne] tried a few different options, including a photoresistor and a light sensor designed for Arduino, but eventually chose a photodiode with a two-stage transimpedance amplifier. An Arduino samples the data at 67 kHz, then sends it over serial to a host computer, which uses SciPy and NumPy to analyse the data. Unfortunately, we were about six years late in getting to this story, and the Python program is a bit out of date by now (it was written in Python 2). It shouldn’t, however, be too hard for a motivated hacker to update.
With a standard 188 nm polystyrene dispersion, the OpenDLS calculated a size of 167 nm. Such underestimation seemed to be a persistent issue, probably caused by light being scattered multiple times. More dilution of the suspension would help, but it would also make the signal harder to measure, and the system’s already running near the limits of the hardware.
This isn’t the only creative way to measure the size of small particles, nor even the only way to investigate small particles optically. Of course, if you do have an electron microscope, nanoparticles make a good test target.
Measuring Nanoparticles By Scattering A Laser
… by scattering a LASER?
by scattering a laser BEAM!
A simple link to the original article would have be sufficient. The quality of this digest is abysmal. Almost word for word but consistently worse and truncated. Am I the only one to think that the quality of write-ups here is sinking at fast speed ? It is suite sad to witness that, and I hope it’s just a temporary low before the editor in chief comes back from summer holidays and sets on a goal of improving quality and accuracy. In comparison, hackster.io does way better !
Wait… What? What the relation between speed and size ? Speed and mass, I would have understood if they was a way to limit deviation of the particle’s energy but size ? Are all particles the same size and and mass ? The same volume ?
Check the much better, original article because this write-ups is terrible.