Split-Ring Resonator Based Sensor for the Detection of Amino Acids in Liquids

Amino acids belong to the most important compounds for life. They are structural components of proteins and required for growth and maintenance of cells. Essential amino acids cannot be produced by the organism and must be ingested through the nutrition. Therefore, the detection of amino acids is of great interest when analyzing cell culture media and nutrition. In this work, we present a split-ring resonator as a simple but sensitive detector for amino acids. Split-ring resonators are RLC resonant circuits with a split capacitance and thus a resonance frequency that depends on the electromagnetic properties of a liquid sample at the split capacitance. Here, the split capacitance is an interdigital structure for highest sensitivity and covered with a fluidic channel for flow through experiments. First measurements with a vector network analyzer show detection limits in the range from 105 mu M for glutamic acid to 1564 mu M for isoleucine, depending on the electromagnetic properties of the tested amino acids. With an envelope detector for continuous recording of the resonance frequency, the split-ring resonator can be used in ion chromatography. At a flow rate of 0.5 mL/min, it reaches limits of detection of 485 mu M for aspartic acid and 956 mu M for lysine.

Automated summary

Amino acids play a vital role in life as they are essential components of proteins and necessary for cell growth and maintenance. This study introduces a split-ring resonator as a sensitive and simple detector for amino acids. The split-ring resonator uses the electromagnetic properties of a liquid sample to determine the resonance frequency, and initial measurements show detection limits for tested amino acids ranging from 105 μM to 1564 μM. With an envelope detector, the split-ring resonator can be used in ion chromatography and achieve detection limits of 485 μM for aspartic acid and 956 μM for lysine at a flow rate of 0.5 mL/min.