title: Gold-nanosphere formation using food sample endogenous polyphenols for in-vitro assessment of antioxidant capacity.
abstract: In this work it was demonstrated that sample endogenous polyphenols are selectively driving the gold-nanoparticle (AuNPs)-formation process when representative food samples were used as natural sources of reducing compounds. The process of AuNPs formation was characterized by UV-visible spectroscopy and was described by a sigmoidal curve (R                         (2) ≥ 0.990) which gave information about the polyphenol concentration at which the localized surface plasmon resonance (LSPR) absorption reached its half-value, X                                                     (c)                                      (50)                         , and about AuNPs production per polyphenol concentration unit, K                         (AuNPs). The behavior of phenolic acids was different, with lower X                                                     (c)                                      (50)                          and higher K                         (AuNPs) values than flavonoids. For the food samples tea, apple, pear, wine, and honey X                                                     (c)                                      (50)                          values were 0.22, 7.3, 11.5, 20.4, 30.3, and 53.5 (mg mL(-1)) and K                         (AuNPs) values were 28.7, 0.70, 0.60, 0.20, 0.14, and 0.10 (mg(-1) mL), respectively. Excellent correlation between K                         (AuNPs) and total phenolics (TP) was obtained (r = 0.98, p-value < 0.05), implying K                         (AuNPs) is a novel marker for evaluation of food sample antioxidant capacity in vitro. The K                         (AuNPs) values of samples indicated their antioxidant capacity was in the order: tea > apple > pear > wine > honey. The reproducibility of the AuNPs formation approach was excellent, not only for polyphenol standards (RSD < 6 % for X                                                     (c)                                      (50)                          and RSD < 11 % for K                         (AuNPs)) but also for food samples (RSD < 9 % for X                                                     (c)                                      (50)                          and RSD < 15 % for K                         (AuNPs)). Transmission electronic microscopy (TEM) enabled confirmation of the formation of stabilized Au-nanospheres from endogenous polyphenols with very well-defined sizes under 20 nm diameter for all the food samples investigated.
authors.affiliation: Department of Analytical Chemistry and Chemical Engineering, University of Alcalá, 28871, Alcalá de Henares, Madrid, Spain.
authors.forename: Diana
authors.initials: D
authors.lastname: Vilela
authors.forename: María Cristina
authors.initials: MC
authors.lastname: González
authors.forename: Alberto
authors.initials: A
authors.lastname: Escarpa
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D066298:In Vitro Techniques; D053768:Metal Nanoparticles; D013056:Spectrophotometry, Ultraviolet; D020349:Surface Plasmon Resonance
chemical_list: D000975:Antioxidants; D006046:Gold