Binding affinity of surface functionalized gold nanoparticles to hydroxyapatite

Department of Aerospace and Mechanical Engineering, Bioengineering Graduate Program, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Journal of Biomedical Materials Research Part A (Impact Factor: 3.37). 10/2011; 99(1):58-66. DOI: 10.1002/jbm.a.33165
Source: PubMed


Gold nanoparticles (Au NPs) have been investigated for a number of biomedical applications, including drug and gene delivery vehicles, thermal ablation therapy, diagnostic sensors, and imaging contrast agents. Surface functionalization with molecular groups exhibiting calcium affinity can enable targeted delivery of Au NPs to calcified tissue, including damaged bone tissue. Therefore, the objective of this study was to investigate the binding affinity of functionalized Au NPs for targeted delivery to bone mineral, using hydroxyapatite (HA) crystals as a synthetic analog in vitro. Au NPs were synthesized to a mean particle size of 10-15 nm and surface functionalized with either L-glutamic acid, 2-aminoethylphosphonic acid, or alendronate, which exhibit a primary amine for binding gold opposite carboxylate, phosphonate, or bisphosphonate groups, respectively, for targeting calcium. Bisphosphonate functionalized Au NPs exhibited the most rapid binding kinetics and greatest binding affinity to HA, followed by glutamic acid and phosphonic acid. All functional groups reached complete binding after 24 h. Equilibrium binding constants in de-ionized water, determined by nonlinear regression of Langmuir isotherms, were 3.40, 0.69, and 0.25 mg/L for bisphosphonate, carboxylate, and phosphonate functionalized Au NPs, respectively. Functionalized Au NPs exhibited lower overall binding in fetal bovine serum compared to de-ionized water, but relative differences between functional groups were similar.

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Available from: Ryan D Ross, Dec 26, 2013
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    • "The mean (AEstandard deviation) hydrodynamic diameter was 45.8 (1.5) nm, as measured by DLS (Fig. 1c), which was consistent with previously published results for 13 nm BP-Au NPs [29]. The characteristic SPR peak was observed at w527 nm in UVeVis spectroscopy (Fig. 1d), which was also consistent with previously published results for 13 nm BP-Au NPs [28] [29]. The hydrodynamic diameter and characteristic SPR peak were characterized for each batch of BP-Au NPs synthesized and over time to ensure that BP-Au NPs remained well-dispersed and stable. "
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    • "The absorption of amines onto gold surfaces occurs due to the formation of a weak covalent bond, as well as an electrostatic complex between the positively charged amine groups and chloroaurate ions on Au NP surfaces (Leff et al. 1996; Kumar et al. 2003; Selvakannan et al. 2003; Aslam et al. 2004). The mean (±standard deviation) surface density of glutamic acid, phosphonic acid, and bisphosphonate was 5.01 (0.02), 4.96 (0.02), and 3.25 (0.14) lmol/mg Au, respectively, as measured by mass spectroscopy (Ross and Roeder 2011). The lower surface density of bisphosphonate was most likely due to steric interactions of the larger bisphosphonate molecules. "
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