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

Abstract

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 µM for glutamic acid to 1564 µM 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 µM for aspartic acid and 956 µM for lysine.

Fabrication of mm-Scale Complementary Split Ring Resonators, for Potential Application as Water Pollution Sensors

“…In this context, there have been several recent investigations in which SRRs were used as water quality sensors, distinguishing between different kinds of organic and inorganic materials in aqueous solutions. Although, the main disadvantage of such SRR-like sensors is that the liquids used for sensing should be quite viscous in order to remain in the gap [26][27][28][29][30]. Interestingly, there are reports among these in which complementary SRRs (CSRRs; e.g., Figure 1a,b) are utilized as sensors [18,23,26,[31][32][33].…”

“…Although, the main disadvantage of such SRR-like sensors is that the liquids used for sensing should be quite viscous in order to remain in the gap [26][27][28][29][30]. Interestingly, there are reports among these in which complementary SRRs (CSRRs; e.g., Figure 1a,b) are utilized as sensors [18,23,26,[31][32][33]. Here, it should be noted that CSRRs behave similarly to the corresponding SRRs, although they are essentially the exact inverse counterpart of an SRR (an SRR consists of a metallic loop surrounded by a dielectric material, while the CSRR consists of a dielectric loop surrounded by metal).…”

Analysis and Design of a High Gain Multiband Antenna Based on Metamaterials for RFID Applications

“…This section presents a study of the split-ring resonator (SRR) with its equivalent circuit diagram. This resonator consists of a metal loop with a square shape and a gap on one side (Figure 4) [37]. As shown in Figure 4(c), the splitring resonator is a type of RLC series resonant circuit.…”

Continuous Recording of Resonator Characteristics Using Single-Sideband Modulation

“…Resonators, such as split-ring resonators [1][2][3][4][5][6][7][8][9][10][11][12], are widely used in sensor applications to detect even the slightest changes in ambient conditions. The characteristic parameters of a resonator, namely its resonant frequency, the damping at resonance and its quality factor, can be measured using a vector network analyzer (VNA).…”

“…Using SRRs as detectors in high-performance liquid chromatography (HPLC) and ion chromatography (IC) requires rapid sensor response and thus new concepts capable of fast, accurate and continuous tracking of the resonator's characteristics. In this case, a response time of 1 s or less is required to capture the narrow peaks eluting from the chromatographic column [8,9,17]. The same applies for various other applications, where SRRs are employed as sensing elements, e.g., fast analysis of liquids [2,4,7], the detection of biomarkers [5,6] and the identification of defects and cracks in metal objects [3].…”