Bioconjugation of 32-macrocyclic polyammonium cations-functionalized gold nanoparticles with BSA

• Published in: Journal of colloid and interface science Vol. 344; no. 1; pp. 137 - 143
• Main Authors: Misra, Tarun Kumar, Huang, Kuan-Pin, Liu, Chuen-Ying
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.04.2010
• Subjects: Animals; Bioconjugation; Cations; Cattle; Chlorides; Conjugation; Fluorescence; Gold; Gold - chemistry; Gold nanoparticles; Macrocyclic compounds; Macrocyclic Compounds - chemistry; Macrocyclic polyammonium chlorides; Nanoparticles - chemistry; Nanoparticles - ultrastructure; Protein; Proteins; Quaternary Ammonium Compounds - chemistry; Serum Albumin, Bovine - chemistry; Spectrometry, Fluorescence; Spectrophotometry; Spectrum Analysis, Raman; Tryptophan; Water dispersion; Bioconjugation; Water dispersion; Gold nanoparticles; Protein; Macrocyclic polyammonium chlorides
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2009.12.031

32-macrocyclic polyammonium chloride, [32]ane- ( NH 2 + ) 8 · 8 Cl - (32-MCPAC) stabilized water dispersed Au-NPs conjugate with biomolecule, BSA. BSA strongly binds Au-NPs at the isoelectric point (p I = 4.6). Water-dispersed, spherical, underivatized Au-NPs with particle size less than 5 nm were synthesized from an aqueous solution of 32-macrocyclic polyammonium chloride, [32]ane- ( NH 2 + ) 8 · 8 Cl - (32-MCPAC) using sodium borohydride (NaBH 4) as the reducing agent. The bioconjugation of the synthesized Au-NPs at different pHs (3.6–5.6) with bovine serum albumin (BSA) protein was studied using UV–Vis, fluorescence, and Raman spectroscopy. These studies support that the Au-NPs were incorporated into the protein moiety and bound to it chemically. The binding constants ( K b ) and stoichiometries ( n) (i.e., the number of Au-NPs bound by the proteins) of BSA protein to the Au-NPs at different pHs were determined by measuring the quenching of the fluorescence intensity of the tryptophan residues of the protein molecules after conjugation. The values for K b ( n) were found to be 1.05 × 10 10 M −1 (1.66), 2.09 × 10 10 M −1 (2.30), and 1.86 × 10 10 M −1 (1.75) at pH 3.60, 4.60, and 5.60 for BSA–Au-NPs conjugations, respectively. The results show that BSA binds to the Au-NPs strongly at pH 4.60, which is equivalent to its isoelectric point (p I 4.6).