Resonance-Induced Capacitively Coupled Contactless Conductivity Detection (ReC4D) Unit for Nucleic Acid Amplification Testing

Nucleic acid amplification (NAA) is a technique that increases the number of copies of a gene, making it possible to detect microorganisms. This technique is often used in clinical tests, biochemical analysis, and environmental assays, to mention only a few. However, developing portable, robust, and low-cost measurement platforms to evaluate NAA products remains a technological challenge. Therefore, in this work, we introduce an attractive unit for detecting and quantifying nucleic acids based on the capacitively coupled contactless conductivity detection (C4D) principle. The proposed unit, ReC4D, combines electrical resonance with C4D to enhance sensitivity when evaluating an NAA reaction. The ReC4D units advantages are twofold: (i) the transducer is electrically isolated to allow its reuse, and (ii) the induced electrical resonance in the ReC4D unit minimizes the stray capacitances of the conventional C4D assays, which enhances sensitivity, increases the linear operating range, and improves the limit of detection (LoD). Furthermore, we evaluated the proposed device for quantifying different concentrations of SARS-CoV-2 genetic material and compared it with measurements from a conventional C4D unit. Thus, we demonstrate that the ReC4D unit can measure concentrations of NAA products with an LoD of 0.24 copyμL and a sensitivity of 5.618 kHzlog(copyμL). These results position the ReC4D unit close to the state-of-the-art NAA testing platforms, with the added value of a low cost, robustness, reusability, and affordability.