Conjugated Polyelectrolyte and Aptamer Based Potassium Assay via Single‐ and Two‐Step Fluorescence Energy Transfer with a Tunable Dynamic Detection Range

Abstract

A new potassium ion detection assay was developed using a dye‐labeled aptamer and conjugated polyelectrolyte (CPE) as a signaling platform via 1‐step and 2‐step fluorescence resonance energy transfer. Guanine‐rich K+‐specific aptamers were designed as K+ ion recognition species with 6‐carboxyfluorescein (6‐FAM) and 6‐carboxytetramethylrhodamine (6‐TAMRA) at both termini. In the presence of K+ ions, the aptamers undergo a conformational change from an unfolded to folded form by forming a G‐quadruplex with K+, bringing two dyes in proximity. FRET‐induced 6‐TAMRA emission was proportional to [K+] in a range of 22.5 μm–100 mm in water without interference by the presence of excess Na+ ions (100 mm). Upon the addition of CPE, a two‐step FRET process from CPE to 6‐TAMRA via 6‐FAM was enabled, showing an intensified 6‐TAMRA signal with K+ ions. The dynamic detection range and limit of detection (LOD) was fine‐tuned from ∼millimolar to ∼nanomolar concentrations of K+ by modulating the signal amplification effect of CPE. The LOD was determined to be ≈3.0 nm. This detection assay also showed high selectivity against other metal ions. This sensing scheme can be extended to the detection of a wide range of target materials by simply modifying the recognition aptamer sequence.

Sodium and Potassium Ion Selective Conjugated Polymers for Optical Ion Detection in Solution and Solid State

“…We found that the sensitivity increases in a polymeric structure and outperforms an equivalent small molecule structure. Compared to other approaches [ 29 ] for selective alkali metal ion detection in solution, the presented optical sensor consists only of a one compound polymer system. The advantage of the optical sensor materials is that in addition to PL spectroscopy, [ 29,30 ] simple UV-vis spectroscopy can also be used to detect alkali metal ions in solution.…”

“…Compared to other approaches [ 29 ] for selective alkali metal ion detection in solution, the presented optical sensor consists only of a one compound polymer system. The advantage of the optical sensor materials is that in addition to PL spectroscopy, [ 29,30 ] simple UV-vis spectroscopy can also be used to detect alkali metal ions in solution. The selectivity toward different alkali metal ions can be adjusted by varying the ring size of the crown ether ring and selectivity is also retrained in the background of other alkali metal ions.…”

Recent advances in M13 bacteriophage-based optical sensing applications

“…Furthermore, due to their unique electrical and optical properties, conjugated polymers have also received more attention as probe materials in the investigation of the FRET mechanism. Conjugated polymers have a unique structure characterized by a π-orbital enabling exciton hopping along their backbone [ 65 , 72 – 82 ]. In addition to the use of organic molecules, recent research has suggested that colloidal semiconductor nanocrystals or QDs are also useful for FRET applications [ 83 – 91 ], because they have many advantages as compared to conventional organic fluorophores, such as high extinction coefficient and size tenability [ 9 , 14 , 92 – 96 ].…”

Intermolecular distance measurement with TNT suppressor on the M13 bacteriophage-based Förster resonance energy transfer system

“…FRET-based sensing facilitates the visualization of receptor-analyte interactions through the detection of color change and provides clues regarding relative intermolecular distances between reacting molecules through time-integrated or time-resolved analysis. Consequently, the FRET-based approach has been widely utilized in various applications such as medical diagnostics 28 , biomarkers 29,30 , cell imaging 31,32 , DNA sequence analysis 33,34 , molecular interaction in DNA or proteins 35–41 , and chemosensors 25,42,43 .…”