Colorimetric determination of polyphenols via a gold nanoseeds-decorated polydopamine film

A polystyrene ELISA plate (EP) modified with a thin film based on gold nanoseeds (AuSDs) assembled onto polydopamine (PDA) is proposed. The nanodecorated film (PDA@AuSD) allows to evaluate the polyphenols antioxidant capacity (AOC) through a colorimetric approach based on a seed-mediated growth strategy. Polyphenols, in the presence of the nanodecorated (PDA@AuSD) surfaces are able to drive an increase in size of the AuSDs according to their AOC; this produces an increase of the localized surface plasmon resonance (LSPR; maximum at λ ~ 550 nm) that is taken as analytical signal. The PDA@AuSD EP manufacturing shows good intraplates repeatability (RSD ≤ 6.6%, n = 96 wells) and interplates reproducibility (RSD ≤ 7.4%, n = 748 wells), resulting stable for 1 year. The AuSDs growth kinetic has been studied using 11 polyphenols belonging to different chemical classes and 4 different food samples. The PDA@AuSD film is able to return quantitative information on the AOC of food polyphenols. Good repeatability (RSD ≤ 5.7%, n = 12 EP wells) and reproducibility (RSD ≤ 8.1%, n = 12 EP wells) was achieved, with acceptable linear correlation coefficients (R² ≥ 0.990) and useful limits of detection (LODs ≤ 2.5 10^-5 mol L^-1). The samples analyzed with the PDA@AuSD device have been successfully ordered according to their AOC in agreement with conventional optical methods. The PDA@AuSD plate allows multiple measurements (96 wells per EP) with a one-step strategy, overcoming the limitations related to the use of colloidal nanoparticles; in addition, since absorbance is measured after washing, it is not affected by sample color or turbidity. Graphical abstract Schematic representation of ELISA plate (EP) modified with polydopamine (PDA) film decorated with gold nanoseeds (AuSD). The colorimetric assay, to evaluate the antioxidant capacity, is based on the AuSD growth mediated by polyphenols, resulting in absorbance increase at 550 nm (ΔAbs₅₅₀), which is employed as analytical signal.