Novel Platform for Droplet Detection and Size Measurement Using Microstrip Transmission Lines

Abstract

We propose a novel platform for detecting as well as measuring the size of individual droplets in microfluidic channels using microstrip transmission lines. The most outstanding feature of our platform is that, as opposed to previous related works, its design allows for the droplet to flow in a microfluidic channel fabricated between the top strip and the ground plane of a microstrip transmission line. This provides enhanced interaction of the electromagnetic field with the detected droplets. The proposed design allows us to measure droplet size directly from the phase of the microwave signal, without the need for a resonator. The platform is based on low temperature co-fired ceramic (LTCC), which makes it more compatible with Radiofrequency (RF) and microwave technology than platforms used in previous works. With this platform, we are able to measure droplets as small as 150 µm in radius. It is worth pointing out that our device could also be used for detection, counting and measurement of other microscopic objects.

Microfluidic Modules Integrated with Microwave Components—Overview of Applications from the Perspective of Different Manufacturing Technologies

“…Another example is the LTCC microfluidic-microwave device for detecting the droplets in test emulsion placed in the microchannel [ 102 ]. The microwave circuit was designed to observe the presence and specific dimensions of droplets.…”

“… The scheme of a microfluidic-microwave device for measurements of droplets; the view of layers consisted of the module ( a ), the top view of the device ( b ), and the picture of the fabricated device ( c ) [ 102 ]. …”

Real Time Water-In-Oil Emulsion Size Measurement in Optofluidic Channels

“…Be it for PCR and DNA analysis, or for other applications such as drug delivery, the ability to have means for real-time measurement and even control over droplet size is a very desirable feature. Different techniques have been proposed for real-time droplet detection and size measurement, such as: methods that rely on the change of capacitance [15] or impedance [16] of the liquids flowing through the microchannels; radiofrequency (RF) based methods, in which a variation of the permittivity of the liquids induces a change in the phase [17] or amplitude (typically using resonators) [18] of electromagnetic wave flowing through the liquids; image analysis methods, in which the images captured with a high-speed camera are analyzed in real-time [19]; optical methods using light reflected or transmitted through the sample [20].…”

Real-time precise microfluidic droplets label-sequencing combined in a velocity detection sensor

“…The latter detects the thermal variation caused by a droplet flowing inside a microchannel 14 . Electrical-based methods rely on the contrast between the two phases in the electrical properties, measuring the impedance 15 , 16 or capacitance 17 – 20 or current 21 or exploiting microwave-based sensing 22 . However, these solutions require calibrations and are limited by the electrical properties of liquids.…”