Fluorescence energy transfer probes based on the guanine quadruplex formation for the fluorometric detection of potassium ion

Dual-labeled oligonucleotide derivative, FAT-0, carrying 6-carboxyfluorescein (FAM) and 6-carboxy-tetramethylrhodamine (TAMRA) labels at 5'- and 3'-termini of thrombin-binding aptamer (TBA) sequence 5-GGTTGGTGTGGTTGG-3' and its derivatives, FAT-n (n = 3, 5, and 7) were designed and synthesized. FAT-n derivatives contained a T(m)A spacer (m = 2, 4, and 6, respectively) at 5-end of TBA sequence. The probes were developed to estimate the spacer effect on FRET efficiency and to identify the best probe for sensing of K+. Circular dichroism (CD), UV-vis absorption, and fluorescence studies revealed that all FAT-n probes could form the intramolecular tetraplex structures after binding K+. Association constants of particular K+/FAT-n complexes were determined using different experimental approaches. Suitability of particular probes for sensitive monitoring of K+ in intra- and extracellular conditions was examined and discussed. Calibration graphs of fluorescence ratio were linear in the K+ concentration range of 2-10 mM for extracellular conditions showing sensitivity of 1.2% mM(-1) K+ and for intracellular conditions in the range of 100-200 mM with sensitivity of 0.49% mM(-1) K+. (c) 2006 Elsevier B.V. All rights reserved.