Quartz Whispering-Gallery-Mode Resonator with Microfluidic Chip as Sensor for Permittivity Measurement of Liquids

TL;DR

This paper introduces a quartz whispering-gallery-mode resonator integrated with a microfluidic chip for highly sensitive permittivity measurements of liquids, enabling detection of low-concentration biological solutions with improved accuracy over sapphire-based sensors.

Contribution

The study presents an advanced quartz resonator technique that significantly lowers detection limits for biological liquids compared to existing sapphire-based methods.

Findings

Detection limit for glucose in water is an order of magnitude lower with quartz resonator.

The technique can detect glucose concentrations comparable to human blood levels.

Successful measurement of glucose, lactalbumin, and bovine serum albumin in the Ka-band.

Abstract

Studies of biological solutions require high measurement accuracy, the ability to detect low changes in substance concentration, and small amounts of the liquid under test. A microwave complex permittivity measurement technique based on a high-quality-factor whispering-gallery-mode resonator with a microfluidic chip allows small amounts of dielectric liquids to be investigated with high accuracy. An existing technique based on a sapphire resonator does not provide for a low-concentration detection limit for substances with low molecular weight. Here, we present an advanced technique based on a quartz dielectric resonator. The detection limit obtained for glucose in water solution was found to be about one order of magnitude lower for the quartz resonator cell than for the sapphire-resonator-based measurement cell. The limit is about or lower than the concentration of glucose in human blood. This fact means that the technique can be used as the sensor for investigations of biological solutions in the microwave range. A study of glucose, lactalbumin, and bovine serum albumin was successfully performed in the Ka -band using the developed sensor.