All fluorescently labeled DNA oligonucleotides were purchased from IBA (Germany) as a HPLC and PAGE purified product (Supplementary Table S1). The G4 forming oligos include a 22 (or 23) nucleotides overhang that was terminally (3′) labeled with Cy3 via amidite coupling. In case of the hTelo-I14 sequence the last guanine of the overhang was labeled with Cy3 via NHS coupling to the amino-C6 dG. The complementary duplex forming oligo was labeled with Cy5 via NHS coupling to the amino-C6 dT. It also contained a biotin at the 3′-end used for surface immobilization.