Rotational and Translational Diffusion of Peptide-Coated CdSe/CdS/ZnS Nanorods Studied by Fluorescence Correlation Spectroscopy

Abstract

CdSe/CdS/ZnS nanorods (NRs) of three aspect ratios were coated with phytochelatin-related peptides and studied using fluorescence correlation spectroscopy (FCS). Theoretical predictions of the NRs' rotational diffusion contribution to the correlation curves were experimentally confirmed. We monitored rotational and translational diffusion of NRs and extracted hydrodynamic radii from the extracted diffusion constants. Translational and rotational diffusion constants (D trans and D rot ) for NRs were in good agreement with Tirado and Garcia de la Torre's as well as with Broersma's theories, when accounting for the ligand dimensions. NRs fall in the size range where rotational diffusion can be monitored with higher sensitivity than translational diffusion due to a steeper length dependence D rot ~ L −3 versus D trans ~ L −1 . By titrating peptide-coated NRs with Bovine Serum Albumin (BSA) we monitored (nonspecific) binding through rotational diffusion and showed that D rot is an advantageous observable for monitoring binding. Monitoring rotational diffusion of bioconjugated NRs using FCS might prove to be a useful tool for observing binding and conformational dynamics in biological systems.

Self-Directed Growth of AlGaAs Core−Shell Nanowires for Visible Light Applications

“…21 Figure 7 shows the mean square displacement (MSD), <rthe diffusion equation <r 2 > = 4Dt, a linear fit to the data (solid line in Figure 7) gives a diffusion coefficient of D = 0.4 µm 2 /s. To verify that the PL emission in Figure 6 is from a single NW, the diffusion coefficient may be calculated from the hydrodynamic stick theory for rods 22,23 :…”

Diffusion Coefficients of CdSe/CdS Quantum Rods in Water Measured Using Polarized Fluorescence Correlation Spectroscopy

“…Furthermore, the anomalous diffusion exponent α, quantifying the nonlinear diffusion of the Q-rods, decreases from 0.75 to 0.61 with increasing solvent viscosity [21]. This result also may indicate that the difference in diffusion times under high-viscosity conditions is due not to the polarization state but to nonlinear diffusion [22]. Figure 4 illustrates the normalized G() for viscosities of 0.9 and 2.6 cP and the two polarization states studied; as shown in the figure, the rotational fractions were 0.75±0.05 in the XXX state and 0.26±0.03 in the XYY state.…”

“…5(b) 2.2×10 16 m -2 for the XYY state. According to previously published theories on the diffusion coefficient [22], D R /D T has a constant value determined by the particle's aspect ratio and the square of the particle's length. In the results herein, the linear fit with D R =0 and D T =0 gave a better result for the XXX state than for the XYY state.…”

Fluorescence correlation spectroscopy in polymer science

“…74 The theory to analyse rotational diffusion from FCS measurements was developed by Ehrenberg/ Rigler 75 and Aragon/Pecora. 76,77 The drop in correlation due to rotational motion appears around the rotational diffusion time s R which is typically found in the ns to ms range, i.e.…”