Reversible DNA micro-patterning using the fluorous effect† †Electronic supplementary information (ESI) available: Experimental procedures and further data. See DOI: 10.1039/c7cc00288b Click here for additional data file.

We described the use of the fluorous effect as a simple and reversible immobilisation technique for DNA.

Fluorous-tagged DNA Synthesis. Fluorous-tagged oligonucleotides were synthesised using standard solid-phase methods on an Applied Biosystems 392 DNA/RNA synthesiser. DNA synthesis reagents and solutions were purchased from Link Technologies Ltd. Oligonucleotides were purified by RP-HPLC, and characterised by MALDI-MS.

Micro-patterning of Substrates.
Borate wafers (University wafers) were cleaned in toluene, acetone and IPA. They were then oxygen plasma ashered (2 minutes, 100 W) immediately before being transferred to a 1% v/v solution of n-decyltrichlorosilane (DTS) in toluene for 10 minutes. The surfaces were then cured at 100 °C for 30 minutes. Standard photolithography was used to micro-pattern the surfaces. Briefly, wafers were spin coated with S1818 (Shiply, USA) at 4000 rpm for 30 seconds to produce a ~1.8 μm thick layer. Micro-patterns were transferred onto the wafer by exposure to UV radiation (SUSS Microtec MA6, Germany) for 4.5 seconds through a chrome mask. The development of the S1818 resist was performed using a 1:1 ratio of Microposit developer (Shiply, USA) and RO for 1 minute. Samples were then dried under nitrogen. Following development, samples were oxygen plasma ashered for (2 minutes, 100 W) to remove the DTS silane from patterned areas. Samples were then sonicated in acetone for 5 minutes to remove the photoresist, rinsed with IPA and dried under nitrogen where they were then silanised, as described above, using (Heptadecafluoro-1, 1, 2, 2-tetrahydrodecyl) trimethoxysilane) (Gelest). To produce the crests, standard E-beam lithography was used, in place of photolithography, according to the procedure outlined in [1].

Electronic Supplementary Material (ESI) for ChemComm. This journal is © The Royal Society of Chemistry 2017
Immobilization & Hybridization of DNA. Immobilization of fluorous-tagged DNA (FDNA) on the surfaces was carried out in a simple humidity chamber. 1uM (unless otherwise stated) solutions of fluorous-tagged DNA were introduced into the chamber and incubated on FDTS micro-patterned surfaces at RT for 2 hours. Samples were rinsed with TE buffer and the complimentary DNA strand (1 uM unless otherwise stated) was introduced for 2 hours. Samples were then rinsed with DI water, TE buffer, dried under nitrogen then imaged. All experiments were carried out in triplicate.
Removal and Re-immobilization of DNA. Immobilized DNA was removed via the fluorous tag using a 1:1 solution of MeOH:PBS for 30 minutes under gentile agitation (Scheme 1). It was then rinsed with MeOH and dried under nitrogen. Re-immobilization was carried out using the same protocol as described above. Samples were protected from light to minimize photo-bleaching throughout the experiment.
QCM Apparatus. AT-cut quartz crystals with a fundamental resonance frequency of 5 MHz (25 mm) were obtained from Microvacuum Ltd (Hungry). These crystals were supplied with Au/SiO 2 coating that was used to graft silane molecules to using the same method outlined above. Crystals were mounted into an OWLS QCM-I (MicroVacuum, Hungary) attached to a mechanical pump to introduce the samples. DI water was flushed through until a stable baseline was established. The flow rate and temperature (40 μL/minute; 20 °C) remained constant throughout the experiment. Solutions were introduced slowly through an injection loop (total volume was 500 μL).
Fluorescence Microscopy. Surfaces were imaged using an Axio Observer Z1 (Carl Zeiss, Germany) under control of Axiovision software. Images were then analyzed using ImageJ software.