Determination of Mg-Ion concentration in DNA Origami in buffer solutions

DNA-Origami nanostructures (DONs) are an emerging technology with huge potential in research areas such as medicine, single-molecule diagnostics and Lab-on-a-chip devices. The successful preparation of DONs depends on various aspects such as cations, buffers and pH [1]. It was found, that Mg2+ cations are the most important cations for DON stability, as these neutralize the negative charge of the densely packed phosphate backbone of the DNA structures [2]. Different usecases require different buffers, such as phosphate buffered saline (PBS) or Tris buffers. Therefore, it is of high importance to quantify and control the amount of Mg2+ cations in DON solutions. In this paper we describe a method to detect Mg2+ cations from Tris and PBS buffer solutions. This method is based on the thiazole yellow g reaction [3-5]. The detection and quantification of Mg2+ is suited for use with DONs as it works with small sample volumes and is not interfered by commonly used buffers. The method is designed to allow for screening and to be easily adopted in biological laboratories as it only requires a plate-reader. Mg2+ quantification was successful in Tris buffer at various pH values (6, 8.4 and pH 10) while for PBS buffer at pH 9 an estimation was possible for a range of 0.1 – 30 mM Mg2+. This is due to the partial precipitation of Mg2+ after reaction with free hydroxy ions. It was found, that for PBS buffers the amount of free hydroxy ions is higher than for Tris buffers