AuNP surfaces

In principle, there are two factors that will influence the catalytic activity First, the collapsed PNIPA layer probably presents a higher steric barrier for benzyl alcohol molecules to diffuse from bulk aqueous dispersion to the surface of AuNPs, causing the reaction to slow down (as shown in Fig. 8). Second, with the increase of temperature, water-soluble hydrophilic PNIPA networks become oil-soluble and hydrophobic, which is favorable for the diffusion of hydrophobic benzyl alcohol onto the AuNP surface (as shown in Fig. 14). Thus, the catalytic activity of Au composite particles should increase with increasing temperature. Figure 15 demonstrates that the second effect prevails over most of the temperature range the TOF value at 40°C... 

Figure 8. AFM images of (A) bare Au substrate and the different AuNPs surfaces after incubation of AChE-CS/Au in growth solution containing (B) 1.2, (C) 3.0 and (D) 4.8mM ATC1. (Reproduced with permission from Dua et al. A. Sens. Actuators B 2007, 127, 317-322).

Fourier transform infrared (FTIR) spectra were carried out using an OPUS/IR spectrometer (Vector 22, Bruker Corporation, MA, USA) in the interval 4000-600 cm at a resolution of 4cm . Control AuNPs and those exposed to culture media were removed from their suspensions by centrifugation at 14,000 rpm and dried at 80 °C into a powder. Figme 5.12b displays the IR spectra of sodium citrate-capped AuNPs and AuNPs in DMEMF-12 culture media with 1% FBS. The major stretching frequencies in the presence of the protein corona on AuNPs surface (Une (ii) of Figure 5.12b) were observed at 3272, 2921, 1734, 1626, 1530, 1244, and 1052 cm, which represents the O—H stretching modes. 

In order to confirm the GSH mediation of protein corona-capped AuNPs, the IR spectrum of the protein corona-capped AuNPs in the presence of GSH showed a new weak absorption signal at 2356 cm (line (ii) of Figure 5.20b), which was assigned to S-H vibration (Ding et al., 2009) indicating the thiol conjugation with the AuNPs surface. This peak was not present in protein corona-capped AuNPs not reacted with GSH (line (i) of Figure 5.20b). 

---