Antioxidant activity assay based on the inhibition of oxidation and photobleaching of l-cysteine-capped CdTe quantum dots

Abstract

Quantum dots (QDs) have recently been the focus of attention of many investigators for development of diagnostic tools in many research areas. In this work, we established a new QD-based assay to evaluate the antioxidant/polyphenolic activity. This assay is based on measurement of the inhibitory effect of the antioxidant/polyphenolic compounds on the UV-induced bleaching of CdTe QDs with L-cysteine capping. QDs exhibited excellent photostability without any UV exposure, while they bleached rapidly under UV irradiation. Generation of reactive oxygen species (ROS) under UV irradiation is probably the main cause of the photobleaching of QDs. By comparing the photostability of QDs in buffer solution in the absence and presence of sodium azide, as a known (1)O(2) quencher, the involvement of (1)O(2) in photobleaching of QDs was confirmed. The photobleaching effect induced by ROS could be reduced in the presence of antioxidant/polyphenolic compounds. We tested several antioxidant/polyphenolic compounds as well as known antioxidants such as trolox and 4 different types of tea. The results obtained by the QD-based assay revealed a very good correlation with the data acquired by Folin-Ciocalteu assay. Furthermore, a deeper understanding of the mechanism and the solution for photobleaching of QDs under UV irradiation might be very meaningful in promoting their clinical applications.

Self-Assembly Fabrication of Honeycomb-like Magnetic–Fluorescent Fe3O4–QDs Nanocomposites for Bimodal Imaging

“…The CdTe QDs were prepared by a method described in a previous publication. 36 In this typical synthesis approach, 3-mercaptopropionic acid (MPA, Sigma-Aldrich (Shanghai) Trading Co., Ltd.) was chosen as capping agent while cadmium chloride hydrate (CdCl 2 •2.5H 2 O, Shanghai Tingxin Chemical Reagent Co., Ltd.) was used as the Cd source and fresh NaHTe was served as the Te source. Briefly, 1 mmol of CdCl 2 and 100 mL of ultrapure water were added into a three-necked flask and nitrogen was let in to deoxidize for 30 min before 2.4 mmol of MPA was dissolved in.…”

“…The CdTe QDs were prepared by a method described in a previous publication . In this typical synthesis approach, 3-mercaptopropionic acid (MPA, Sigma-Aldrich (Shanghai) Trading Co., Ltd.) was chosen as capping agent while cadmium chloride hydrate (CdCl 2 ·2.5H 2 O, Shanghai Tingxin Chemical Reagent Co., Ltd.) was used as the Cd source and fresh NaHTe was served as the Te source.…”

Nanomaterial-Based Sensing and Biosensing of Phenolic Compounds and Related Antioxidant Capacity in Food

“…An antioxidant activity assay based on L-cysteine-capped CdTe QDs was proposed by Hemmateenejad et al [ 58 ]. Measurement of the inhibitory effect of antioxidant/PCs (due to their scavenging activity) on the UV-induced bleaching of CdTe QDs was used.…”

Antioxidant capacity automatic assay based on inline photogenerated radical species from l-glutathione-capped CdTe quantum dots

“…Additionally, the QDs are capable of generating free radical species upon irradiation in aqueous media [3], through the absorption of photons with energy equal to or greater than the energy of the band gap by a process of photoactivation [4]. This means that when the QD is exposed to an electromagnetic radiation in the ultraviolet [3,5,6] or visible region [4,7] of the spectrum, this can promote a displacement of an electron from the valence band to the conduction band forming a particle called exciton. The exciton formed is endowed with redox properties dependent on the values of the two surrounding energy bands being perfectly capable of reducing the molecular oxygen to ROS [3].…”

“…A bibliographic survey in the scientific literature revealed only two works dealing with the photogeneration of radical species from quantum dots, for the determination of substances with antioxidant properties, namely, epinephrine [4] and ascorbic acid [7] in pharmaceutical formulations, both methodologies implemented in an automatic flow system. Additionally, it can be found one work involving the photobleaching of Lcysteine-capped CdTe QDs with radical species photogenerated by UV irradiation of the nanoparticles, for the fluorometric determination of the antioxidant capacity of tea samples, in batch assays [6].…”