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.

Antioxidant capacity index based on gold nanoparticles formation. Application to extra virgin olive oil samples

“…AuNPs were formed following the protocol described by Vilela et al (2014Vilela et al ( , 2012b based on a controlled reduction of HAuCl 4 . CTAC (8.0 Â 10 À1 mol L À1 ), HAuCl 4 solution (2.0 Â 10 À2 mol L À1 ), and finally different volumes of the standards or sample extract were added in the reported order in phosphate buffer solution was used (pH 8.0; 1.0 Â 10 À2 mol L À1 ), up to final volume of 500 lL.…”

“…In this work, the ability of the polyphenols to reduce HAuCl 4 (III) to AuNPs(0) in aqueous solvent was demonstrated and the AuNPs optical absorption peak due to the localized surface plasmon resonance (LSPR) detected. More recently, Escarpa (2014, 2012b) have associated the AuNP formation driven by endogenous polyphenols (Vilela et al, 2014(Vilela et al, , 2012b in food samples to a sigmoidal function. The aim of this work was to demonstrate the performances of the AuNPs based antioxidant capacity index as an alternative method to evaluate the antioxidant power in olive oils.…”

Voltammetric analysis of Pinus needles with physiological, phylogenetic, and forensic applications

“…This approach was based on the voltammetry of immobilized particles (VIMP), a methodology which provides the electrochemical response of sparingly soluble solids attached to inert electrodes in contact with suitable electrolytes [23][24][25]. Conventional solutionphase [26][27][28][29][30] and solid-state [31,32] electrochemical techniques have been applied for testing the antioxidative capacity of samples from fruits and vegetables.…”

Novel Method for the Identification of the Variety of Grape Using Their Capability to Form Gold Nanoparticles

“…Different anions can be used to modulate the size and the color of the AuNPs. Size and shape dependent electrochemical and optical properties can be used for a wide range of applications, including chemical sensors for the assessment of the antioxidant capacity of foods [16][17][18][19][20][21][22]. According to these previous experiments, the optical properties of gold nanoparticles could be used to develop novel tools for the characterization of foods based on their antioxidant characteristics.…”