Visual aptamer-based capillary assay for ethanolamine using magnetic particles and strand displacement
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ORIGINAL PAPER
Visual aptamer-based capillary assay for ethanolamine using magnetic particles and strand displacement Mostafa Mahmoud 1,2 & Stefan Laufer 2 & Hans-Peter Deigner 1,3 Received: 12 July 2019 / Accepted: 7 September 2019 # Springer-Verlag GmbH Austria, part of Springer Nature 2019
Abstract This work describes an aptamer-based capillary assay for ethanolamine (EA). It is making use of strand displacement format and magnetic particles. The capillary tubes are coated with three layers, viz. (a) first with short oligonucleotides complementary to the aptamer (EA-comp.); (b) then with magnetic particles (Dynabeads) coated with EA-binding aptamer (EA-aptamer), and (c) with short oligonucleotide-coated magnetic particles (EA-comp.). On exposure to a sample containing ethanolamine, the DNA-coated magnetic particles are released and subsequently collected and spatially separated using a permanent magnet. This results in the formation of a characteristic black/brown spots. The assay has a visual limit of detection of 5 nM and only requires 5 min of incubation. Quantification is possible through capture and analysis of digital (RGB) photos in the 5 to 75 nM EA concentration range. Furthermore, results from tap water and serum spiked with EA samples showed that the platform performs well in complex samples and can be applied to real sample analysis. The combined use of plastic capillaries, visual detection and passive flow make the method suited for implementation into a point-of-care device. Keywords Aptamer-assay . Small molecules . Capillary flow . Visual detection . Magnetic particles . RGB images
Introduction The quantification of small molecules remains a considerably challenging task requiring complex setups as well as highly trained personnel e.g. mass spectrometry [1, 2]. Their detection is hampered by their intrinsic properties such as their small size and the availability of only one epitope for binding. Thus, most immunoassays still do not provide a fast turnaround time and lack the sensitivity required for diagnostics [3, 4]. Moreover, the tedious steps included e.g. washing, Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00604-019-3795-9) contains supplementary material, which is available to authorized users. * Hans-Peter Deigner [email protected] 1
Institute of Precision Medicine, Furtwangen University, Jakob-Kienzle-Straße 17, 78054 Villingen-Schwenningen, Germany
2
Department of Pharmaceutical and Medicinal Chemistry, Institute of Pharmaceutical Sciences, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany
3
EXIM Department, Fraunhofer Institute IZI, Leipzig, Schillingallee 68, D-18057 Rostock, Germany
blocking and signal development hinders the transfer of these assays to point of care (POC) devices [5]. On the other hand, aptamers stand out as a promising alternative to antibodies due to their stability, fast binding kinetics and the reversibility of the binding [6, 7]. Aptamers are single stranded DNA/RN
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