Self-Assembly of Gold Nanoparticles with Oppositely Charged, Long, Linear Chains of Periodic Copolymers

Abstract

We studied the assembly of nanoparticles with oppositely charged linear and periodic copolymers (CPs), alternating ionic and polar sequences, in the dilute range of polymer concentration. For the first time, we considered CPs displaying a contour length much higher than the AuNP perimeter. We assumed that such CPs will enable to collect a finite number of NPs into linear nanostructures with a gain of colloidal stability and a better structural control compared to electrostatic complexes obtained with homo polyelectrolytes. As a case study, we synthesized anionic gold nanoparticles (AuNPs) and CPs consisting of alternated cationic poly-L-lysine (PLL) blocks and polar sequences of poly(ethyleneglycol) (PEG). We showed that complexation of AuNPs with CPs is quite similar to that observed with homo PLL. In that respect, finite size nanometric clusters, of less than 30 NPs, outside the electro neutrality domain and a fast phase separation occurs at the electro neutrality. Nevertheless, the presence of PEG blocks allowed us to highlight some specific effects. First, the global charge of the positively charged clusters was found to be always lower for CP based clusters than for homo PLL with a dependence of the charge with the number and the mass of the PEG blocks. Second, in spite of this effect which should have promoted the formation of dense structure, the fractal dimension characterizing the structure of the clusters in bulk was found to be always below 1.8. Finally, we showed that PEG blocks influence the interparticle distance by disfavoring plasmon delocalization when the clusters are dispersed in water and collapse around the nanoparticles when the clusters are deposited on substrate.

Tumor-Selective Immune-Active Mild Hyperthermia Associated with Chemotherapy in Colon Peritoneal Metastasis by Photoactivation of Fluorouracil–Gold Nanoparticle Complexes

“…This resulted in a plasmon shift toward NIR according to the appearance of a second absorbance peak around 635 nm (Figure B). The direct visualization of the complexes with cryo-TEM imaging (Figure S2) further emphasizes the temporal enhancement of the AuNP–5-FU complex size and fractal dimension, as previously observed for AuNP complexes obtained by polyethylenimine-mediated gold reduction or preformed AuNP complexation with polyelectrolytes: , the particles appear to be in contact, showing 29 ± 10 particles/cluster and a cluster diameter of 110 ± 11 nm at 24 h.…”

“…This resulted in a plasmon shift toward NIR according to the appearance of a second absorbance peak around 635 nm (Figure 1B). The direct visualization of the complexes with cryo-TEM imaging (Figure S2) further emphasizes the temporal enhancement of the AuNP−5-FU complex size and fractal dimension, as previously observed for AuNP complexes obtained by polyethylenimine-mediated gold reduction 43 or preformed AuNP complexation with polyelectrolytes: 44,45 the particles appear to be in contact, showing 29 ± 10 particles/cluster and a cluster diameter of 110 ± 11 nm at 24 h. 5-FU can bind with AuNPs by hydrogen bonding between the 5-FU nitrogen and fluorine atoms and the carboxyl residues on AuNPs according to the theoretical modeling of relaxed structures for 5-FU. It suggests the equilibrium among three structural forms (diketo, keto−enol, and dienol) through orbital delocalizations and proton exchanges, thus supporting the formation of H-bonds.…”