Polyelectrolyte-Carbon Dot Complex Coacervation

Abstract

This Letter presents complex coacervation between the biopolymer diethylaminoethyl dextran hydrochloride (DEAE-Dex) and carbon dots. The formation of these coacervates was dependent on both DEAE-Dex concentration and solution ionic strength. Fluorescence spectroscopy revealed that the blue fluorescence of the carbon dots was unaffected by coacervation. Additionally, microrheological studies were conducted to determine the viscosity of these coacervates. These complex coacervates, formed through the interaction of nanoparticles and polyelectrolytes, hold a promising role for future applications where the combination of optical properties from the carbon dots and encapsulation via coacervation can be leveraged.

Figure 1

(a) UV absorbance spectrum for a suspension of carbon dots in water. (b) Fluorescence emission spectra of carbon dots at different excitation wavelengths. Photograph of a suspension of carbon dots in water alongside a vial of water, and the carbon dot solution painted onto paper in (c) normal light and (d) when exposed to UV light.

Figure 2

(a) TEM image of carbon dots. The inset shows the interplanar spacing within the carbon dot and (b) the corresponding size histogram for the observed nanoparticles fitted by a Gaussian (where y₀ is the baseline of the Gaussian curve, A is an area under the Gaussian curve, B is a constant that determines the peak shape, x_c is the peak center, w is full width at half-maximum (fwhm), the exponential term shows the shape of Gaussian curve, and C is a normalization factor to relate A to the area under the curve).

Figure 3

(a) Turbidity as a function of the weight fraction of DEAE-Dex. The inset micrograph shows the formation of liquid droplets. (b) Zeta potential for complex coacervates of DEAE-Dex and carbon dots as a function of increasing weight fraction of DEAE-Dex. (c) Turbidity as a function of increasing NaCl concentration for samples containing a 0.33 weight fraction of DEAE-Dex. The inset micrographs are shown for three different salt concentrations, highlighting the loss of phase separation with increasing salt.

Figure 4

(a) Fluorescence emission spectra for coacervate, supernatant, and a carbon dot solution excited at 370 nm. (b) Brightfield and fluorescent micrographs for DEAE-Dex-carbon dot coacervates, along with a photograph of a microcentrifuge tube containing sedimented, fluorescent coacervates and a weakly emissive supernatant.

Figure 5

(a) Brightfield optical micrograph, and the corresponding (b) fluorescence micrograph. (c) The merged image demonstrates the incorporation of fluorescent beads into the coacervate. (d) Mean of mean squared displacement (MSD) vs lag time for bead trajectories in coacervates. The dotted line shows the power-law fit. Inset shows an example trace of bead motion in the coacervate. (e) Probability distribution of displacement with time.