A Cascade FRET‐Mediated Ratiometric Sensor for Cu²⁺Ions Based on Dual Fluorescent Ligand‐Coated Polymer Nanoparticles

Abstract

Core-shell type dual fluorescent nanoparticles (NPs) in the 16 nm diameter range with a selective ligand (cyclam) attached to the surface and two fluorophores--9,10-diphenyl-anthracene (donor, D) and pyrromethene PM 567 (acceptor, A)--embedded within the polymer core were synthesized and their fluorescent and copper-sensing properties were studied and compared to single D-doped and A-doped NPs. The acceptor (A) and donor (D) dyes were chosen to allow two sequential Förster resonance energy transfer (FRET) processes from D to A and from the encapsulated dyes to copper complexes that form at the surface and act as quenchers. NPs with different D/A loads were readily obtained by two consecutive entrapments of the dyes. Dual NPs present tunable fluorescence emission that is dependent on the doping ratio. FRET from D to A results in sensitized emission from A upon excitation of D, with FRET efficiencies reaching 80 % at high acceptor loads. A 9-fold amplification of the signal of A is observed at high D-to-A ratios. Single- and dual-dye-doped NPs were used to detect the presence of cupric ions in water by using the quenching of fluorescence as a transduction signal. In accordance with the spectral overlaps and the values of the critical distance (R0) of D- and A-copper complex pairs, the acceptor is much more sensitive than the donor. In dual fluorescent NPs, the sensitized emission of A is efficiently attenuated whereas the remaining emission of D is much less affected, allowing the detection of copper in a ratiometric manner upon excitation at a single (D) wavelength. Dual-dye-doped NPs with the highest acceptor loads (23 A-per-NP) were found to be the most sensitive for the detection of copper over a wide range of concentrations (20 nM to 8.5 microM). Owing to its great convenience and modularity, the cascade FRET strategy based on dual fluorescent NPs holds great promise for the design of various sensing nanodevices.

Study on the Fluorescence Characteristics of CdTe and Charged Coumarin-Contained Polymer Blending System

“…6), the quantum yields of CdTe QDs varied little before C-CPA adding into the blending system. This phenomenon conform the theory that the concentration will have little affect to the quantum yields of the fluorescent substance as the concentration of the fluorescent substance is low enough 24 . After C-CPA added into the blending system, the quantum yields of CdTe QDs with different concentrations all increased more than 50 %.…”

Polymeric nanoparticles for optical sensing

“…For different nanosystems the fluorescence is either quenched or enhanced upon addition of the target analyte (Hu et al, 2011a(Hu et al, , 2011bPeng et al, 2010). Other nanoparticles have been prepared which show on/off behaviour of the FRET process, dependent on the presence or absence of the substance to be detected (Chen et al, 2009b;Frigoli et al, 2009;Liu et al, 2012;Ma et al, 2010;Zhu et al, 2007). FRET-based polymeric NPs have been used to detect ionic species, demonstrating good sensitivity.…”

“…FRET-based polymeric NPs have been used to detect ionic species, demonstrating good sensitivity. For instance, Frigoli and colleagues used a copper-selective ligand, tetraazacyclotetradecane (cyclam) capable of quenching the fluorescence emission of the embedded acceptor dye (pyrromethene 567) upon interaction with copper, achieving a LOD in the nanomolar range (Frigoli, 2009). By exploiting a similar quenching mechanism, Chen and colleagues prepared core-shell polymeric NPs for the detection of Cu 2+ .…”

Optical Chemical Sensors:Design and Applications

“…For example, the ratio of two fluorescent peaks is used instead of the absolute intensity of one peak. The sensors therefore typically contain a reference dye; the advantage of this approach is that factors such as excitation source fluctuations and sensor concentration will not affect the ratio between the fluorescence intensities of the indicator and the reference dye Buck et al, 2004;Cywinski et al, 2009;Doussineau et al, 2009;Frigoli et al, 2009;Sun et al, 2006).…”

“…The rate of energy transfer from donor to acceptor is highly dependent on many factors, such as the extent of the spectral overlap, the relative orientation on the transition dipoles, and, most importantly, the distance between the donor and the acceptor. Due to its sensitivity to distance, FRET has been used to investigate molecular interactions (Demchenko, 2009;Frigoli et al, 2009;Kikuchi et al, 2004;Lakowicz, 2006).…”