Counterion effects on fluorescence energy transfer in conjugated polyelectrolyte-based DNA detection.
Cationic poly[9,9'-bis[6''-(N,N,N-trimethylammonium)hexyl]fluorene-co-alt-phenylene]s with five different counterions (CIs) were synthesized and studied as fluorescence resonance energy transfer (FRET) donors (D) to dye-labeled DNA (FRET acceptor, A). The polymers with different CIs show the same pi-conjugated electronic structure with similar absorption (lambda(abs) = approximately 380 nm) and photoluminescence (lambda(PL) = approximately 420 nm) emission spectra in water. The CIs accompanying the polymer chain are expected to affect the D/A complexation and modify the D-A intermolecular separation by acting as a spacer. Polymers with different CIs function differently as FRET excitation donors to fluorescein (Fl)-labeled single-stranded DNA (ssDNA-Fl). The FRET-induced Fl emission was enhanced significantly by the larger CI-exchanged polymers. The polymers with the CIs of tetrakis(1-imidazolyl)borate (FPQ-IB) and tetraphenylborate (FPQ-PB) showed a 2-4-fold enhancement in the FRET-induced signal compared with the polymer with bromide (FPQ-BR). The delayed FRET signal saturation and low association constants (K(a)) with ssDNA-Fl (3.53 x 10(6) M(-1) for FPQ-BR and 1.80 x 10(6) M(-1) for FPQ-PB) were measured for the polymers with larger CIs. The delayed acceptor saturation strengthens the antenna effect and reduces self-quenching of Fl by increasing the polymer concentration near Fl. The weak polymer/ssDNA-Fl association reduces the amount of energy-wasting charge transfer by increasing D-A intermolecular separation. The combined effects lead to increase the overall FRET-induced signal.
Department of Nanofusion Technology (BK21), Pusan National University, Miryang 627-706, Republic of Korea.
Okhil Kumar
OK
Nag
Mijeong
M
Kang
Sungu
S
Hwang
Hongsuk
H
Suh
Han Young
HY
Woo
D004247:DNA / Q000032:analysis*; D004573:Electrolytes / Q000737:chemistry; D005449:Fluorenes / Q000138:chemical synthesis / Q000737:chemistry*; D031541:Fluorescence Resonance Energy Transfer; D015394:Molecular Structure; D000644:Quaternary Ammonium Compounds / Q000138:chemical synthesis / Q000737:chemistry*
D004573:Electrolytes; D005449:Fluorenes; D000644:Quaternary Ammonium Compounds; C541373:poly(9,9'-bis(6''-(N,N,N-trimethylammonium)hexyl)fluorene-co-alt-phenylene); D004247:DNA