Patent of the Month

Materials World magazine
31 Jan 2019
Credit: Withers & Rogers

Patent Attorney Gemma McGeough at Withers & Rogers discusses a patent for analysing fluid flow on a nanoscopic scale. 

Analytical devices capable of measuring and manipulating minute quantities of fluid are commonly used to detect the presence of specific particles, such as antibodies in biological immunoassays.
Velocimetry, which is the measurement of fluid velocity, can be used to provide information about the fluid flow. For example, magnetic nanoparticles can be used as tracers for velocimetric techniques. However, due to their size and their relatively weak magnetic field, detection of single nanoparticles in moving fluids can be problematic.
IBM was recently granted a UK patent, GB 2558154, relating to a new sensor for the characterisation and analysis of fluid flow on a micro or nanoscale. According to the patent, this new, graphene-based, magnetic sensor is capable of detecting a single nanoparticle, with a diameter as small as 1nm, in a flowing fluid. It can also accurately determine the speed of flow.
Figure 15, taken from GB 2558154, illustrates the new sensor, which has a two-dimensional lattice structure (130) made from graphene and biased with a voltage (Vsource) to promote the flow of current. A series of contacts placed at various points around the lattice measure the voltage across the graphene lattice.
The sensor (100) also includes an AC coil (105) and a DC coil (120), to which an AC voltage (VAC) and a DC voltage (VDC) are respectively applied.
To detect the characteristics of a channel of fluid on a micro or nanoscale, magnetic particles are introduced. An AC magnetic field is generated by applying an AC voltage across the AC coil, which magnetises the particle. The magnetised particle generates an AC field in the graphene lattice structure. A DC voltage is also applied across the DC coil to provide a DC magnetic field, which is superimposed on the generated AC field in the sensing device.
In the patented sensor, an AC Hall voltage measured across the graphene is greatly increased by the presence of the magnetised particle, providing a means of detection. By placing a series of sensors along a microfluidic channel, the speed of flow through the channel can also be calculated. 
Two-dimensional information regarding the fluid flow can also be achieved by measuring the AC Hall voltage of the graphene, at different locations, perpendicular to the direction of flow. This enables the position of the nanoparticle to be determined. In addition, the voltage signal will vary according to the strength of the AC-magnetic field strength. Therefore, the distance of the magnetic particle from the sensor and its depth in the channel can be measured. In this way, the precise location of the magnetic nanoparticle can be established, helping to determine the three-dimensional flow velocity field of the surrounding fluid.
By obtaining a granted British patent for its invention, IBM has secured a 20-year period of exclusivity to exploit its commercial potential by bringing the technology to market or securing licensing deals.