Photophysics and Dynamics of Dye-Doped Conjugated Polymer Nanoparticles by Time-Resolved and Fluorescence Correlation Spectroscopy

Abstract

Fluorescent dye encapsulated conjugated polymer nanoparticles have been paid significant attention for potential applications in photonics and biophotonics due to their high brightness and better photostability. Bright, photostable, and monodispersed Nile Red (NR) dye encapsulated poly-Nvinylcarbazole (PVK) fluorescent polymer nanoparticles have been prepared to understand the influence of size of particles and the concentration of dye inside the particles on the photophysical properties by using steady-state, timeresolved fluorescence spectroscopy and fluorescence correlation spectroscopy (FCS). Here, we have quantitatively analyzed the hydrodynamic diameter, particle brightness, and population of NR molecules inside the particle with varying the particle size and NR concentration by using fluorescence correlation spectroscopy (FCS). The average fluorescence intensity of a single nanoparticle, i.e., per particle brightness (PPB) value, increases from 80 to 500 kHz, and the number of NR molecules per nanoparticle increases from 5 to 22 by increasing the concentration of NR from 0.5 to 1.8 wt % at the time of nanoparticle preparation. Fluorescence anisotropy study has been undertaken to understand the rotational dynamics of encapsulated NR molecules with varying particle size and NR concentration inside the nanoparticle. The particle brightness and quantum yield are enhanced due to increasing the radiative decay rate. Higher brightness (almost one order of magnitude higher with respect to free dye) and better photostability (15-fold enhancement) of these polymer nanoparticles are found to be efficient for bioimaging purposes.

Multichromophoric Organic Molecules Encapsulated in Polymer Nanoparticles for Artificial Light Harvesting

“…QTH (0.04×10 −6 M ) encapsulated in PMMA NPs were prepared by using a simple solution‐based reprecipitation method described previously (the detailed procedure is given in the Supporting Information) 36. 44, 50 Furthermore, the reprecipitation technique was employed for the fabrication of both QTH and NR encapsulated in PMMA NPs.…”

“…Furthermore, the photophysics and rotational motions of encapsulated dye molecules inside the semiconducting polymer nanoparticles have been discussed 35. The influence of particle size and the concentration of dye inside the particles on the photophysical properties has been investigated by using steady‐state, time‐resolved fluorescence spectroscopy, and fluorescence correlation spectroscopy (FCS) 36. Thus, dye‐doped polymer nanoparticles were recently found to be a suitable candidate for photonic, biophotonic, bioimaging, and sensing devices 29.…”

Perspective of dye-encapsulated conjugated polymer nanoparticles for potential applications

“…The inner environment of PNPs is heterogeneous with different polarities, while silica matrix is commonly homogeneous. The FCS study on Nile red (NR) dye-doped different-sized PVK PNPs using a 532-nm laser source (for the direct excitation of NR dye molecules) is reported [21] and it is found that the hydrodynamic radius is increased from 20 to 55 nm (shown in figure 3C) on increasing the size of the PNPs from 40 to 100 nm. We have calculated the particle concentration of as-prepared aliquots, which is on the order of ∼50-80 nM.…”

“…Pecher and Mecking [19] have described the fundamental photophysics of conjugated PNPs. Furthermore, the colour tunability and brightness of fluorescent PNPs can be enhanced by encapsulating organic fluorophores inside the PNPs [20][21][22]. Photophysics of encapsulated dye molecules in PNPs and the confined motion of dye molecules were reported recently [20][21][22][23].…”

Pdots, a new type of nanoparticle, bind to mTHPC via their lipid modified surface and exhibit very high FRET efficiency between the core and the sensitizer

“…Among the important nanostructures that have found use in biology and medicine one can list quantum dots (QDs Nanoparticles have attracted great interest due to their promising potential for applications in biological sciences and other biomedical 1,2 , nanoparticles of gold, silicon, silica, metal oxides and several forms of carbon and the recently advanced semiconducting polymer dots (Pdots). Nanoparticles are used as drug-delivery vehicles, biosensors, imaging tools and markers, where their special chemical and optical properties are employed for analytical and diagnostic purposes 3 . Quantum dots (QDs), especially, found the most wide-spread uses in scientific applications.…”