To test the viability of the designed system, we have designed a number of experiments. These experiments are conducted to verify whether the individual elements of our device work. An overview of the experiments is given below.

A vital aspect of our device is clicking the aptamers to the membrane proteins. For this click, we madeuse of the exact same click chemistry used by iGEM TU Eindhoven 2014. iGEM TU Eindhoven 2014 has used the click reaction N-terminally. To analyze whether the localization of the azide-functionalized amino acid within the loops of OmpX impedes the click reaction, we clicked a DBCO-functionalized fluorophore (TAMRA) to the outer membrane proteins. After some washing steps and spinning down, we expected the cells to remain fluorescent. To analyze the fluorescence at the single-cell level, we measured cells using the Fluorescence-Activated Cell Sorter (FACS) <img src="https://static.igem.org/mediawiki/2015/8/87/TU_Eindhoven_Ingeklapt.png" id="spoilerbutton1" class="spoilerbutton">.<div class="spoiler" id="spoiler1">

As we have already touched upon lightly, it has long been thought that nucleic acids had only a single role: carrying hereditary information. As discussed, the discovery that DNA could fold into higher-order structures gave way to SELEX, an evolutionary method of discovering aptamers. The construction of DNA nanostructures, however, was not only carried out through a combinatorial approach: the specificity and predictability of Watson-Crick basepairing enabled rational design for engineering at the nanoscale [1]. Initially, the designed DNA nanostructures were mostly static, but dynamic nanostructures have become available over the years. Most of these dynamic nanostructures share a common feature: they exploit a biophysical phenomenon known as DNA strand-displacement.

DNA strand-displacement is a very robust technology: the sequences of the used strands often go unreported as they play a minor role. The robustness of the technology enabled rational design of numerous nanostructures. These nanostructures include DNA walkers, strand displacement cascades and self-assembling dendrimers <a href="#ref1" name="reft1">[1]</a>.

In our project, we want to bring two membrane proteins in close proximity through aptamers. To test whether a close proximity indeed triggers an intracellular signal, we used DNA to bring the membrane proteins in close proximity. DNA is the ideal probe for this purpose, as its high specificity and predictability allowed us to bring the membrane proteins in vicinity. To make the system with DNA reversible, we designed a simple system exploiting the strand displacement (see Figure X).

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<a href="#reft1" name="ref1">[1]</a> D. Y. Zhang and G. Seelig, “Dynamic DNA nanotechnology using strand-displacement reactions.,” Nat. Chem., vol. 3, no. 2, pp. 103–13, Mar. 2011. <br />

<!--<a href="#reft2" name="ref2">[2]</a> W. Zhou, P.-J. J. Huang, J. Ding, and J. Liu, “Aptamer-based biosensors for biomedical diagnostics.,” Analyst, vol. 139, no. 11, pp. 2627–40, 2014.<br />

<a href="#reft15" name="ref15">[15]</a> I. Medintz and N. Hildebrandt, Eds., FRET - Förster Resonance Energy Transfer. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2013. <br /> -->