title: Gold Nanoparticles-based Extraction-Free Colorimetric Assay in Organic Media: An Optical Index for Determination of Total Polyphenols in Fat-Rich Samples.
abstract: In this work, a rapid and simple gold nanoparticle (AuNPs)-based colorimetric assay meets a new type of synthesis of AuNPs in organic medium requiring no sample extraction. The AuNPs synthesis extraction-free approach strategically involves the use of dimethyl sulfoxide (DMSO) acting as an organic solvent for simultaneous sample analyte solubilization and AuNPs stabilization. Moreover, DMSO works as a cryogenic protector avoiding solidification at the temperatures used to block the synthesis. In addition, the chemical function as AuNPs stabilizers of the sample endogenous fatty acids is also exploited, avoiding the use of common surfactant AuNPs stabilizers, which, in an organic/aqueous medium, rise to the formation of undesirable emulsions. This is controlled by adding a fat analyte free sample (sample blank). The method was exhaustively applied for the determination of total polyphenols in two selected kinds of fat-rich liquid and solid samples with high antioxidant activity and economic impact: olive oil (n = 28) and chocolate (n = 16) samples. Fatty sample absorbance is easily followed by the absorption band of localized surface plasmon resonance (LSPR) at 540 nm and quantitation is refereed to gallic acid equivalents. A rigorous evaluation of the method was performed by comparison with the well and traditionally established Folin-Ciocalteu (FC) method, obtaining an excellent correlation for olive oil samples (R = 0.990, n = 28) and for chocolate samples (R = 0.905, n = 16). Additionally, it was also found that the proposed approach was selective (vs other endogenous sample tocopherols and pigments), fast (15-20 min), cheap and simple (does not require expensive/complex equipment), with a very limited amount of sample (30 μL) needed and a significant lower solvent consumption (250 μL in 500 μL total reaction volume) compared to classical methods.
authors.affiliation: †Faculty of Bioscience and Technology for Food, Agriculture and Environment, University of Teramo, 64023 Teramo, Italy.|‡Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, Faculty of Biology, Environmental Sciences and Chemistry, University of Alcalá, E-28871 Alcalá de Henares, Madrid, Spain.
authors.forename: Flavio
authors.initials: F
authors.lastname: Della Pelle
authors.affiliation: ‡Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, Faculty of Biology, Environmental Sciences and Chemistry, University of Alcalá, E-28871 Alcalá de Henares, Madrid, Spain.
authors.forename: María Cristina
authors.initials: MC
authors.lastname: González
authors.affiliation: †Faculty of Bioscience and Technology for Food, Agriculture and Environment, University of Teramo, 64023 Teramo, Italy.
authors.forename: Manuel
authors.initials: M
authors.lastname: Sergi
authors.affiliation: †Faculty of Bioscience and Technology for Food, Agriculture and Environment, University of Teramo, 64023 Teramo, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Del Carlo
authors.affiliation: †Faculty of Bioscience and Technology for Food, Agriculture and Environment, University of Teramo, 64023 Teramo, Italy.
authors.forename: Dario
authors.initials: D
authors.lastname: Compagnone
authors.affiliation: ‡Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, Faculty of Biology, Environmental Sciences and Chemistry, University of Alcalá, E-28871 Alcalá de Henares, Madrid, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Escarpa
mesh_terms: D003124:Colorimetry / Q000379:methods*; D005223:Fats / Q000032:analysis*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles; D046529:Microscopy, Electron, Transmission; D059808:Polyphenols / Q000032:analysis*
chemical_list: D005223:Fats; D059808:Polyphenols; D006046:Gold