Gold-Nanoparticle Based Turn-on Fluorometric Sensor for Quantification of Sulfhydryl and Disulfide Forms of Biothiols: Measurement of Thiol/Disulfide Homeostasis

A simple and sensitive method was developed to determine biothiols in both sulfhydryl (-SH) and disulfide (S-S) forms using a fluorometric sensor composed of citrate-stabilized gold nanoparticles (AuNPs) prepared by electrostatic adsorption of water-soluble fluorophore Rhodamine-6G (Rh-6G) dye onto citrate-stabilized AuNPs resulting in the fluorescence resonance energy transfer in the turn-off mode. Due to the high surface affinities of biothiols to AuNPs, the fluorescence increment at 552 nm (turn-on mode) accompanying the release of Rh-6G indicated the thiol content. This assay also enables the differentiation of oxidized and reduced thiols and the measurement of thiol/disulfide homeostasis as a vital oxidative stress indicator using thiol-alkylating agent N-ethylmaleimide (NEM). After pretreatment with NEM, disulfides were measured in the presence of reduced thiols. The overall biothiol levels and thiol/disulfide ratios were measured using the proposed assay. This method was shown to be selective over various potential interfering compounds (e.g., polyphenols and plasma antioxidants) known to adversely affect redox-based assays. The proposed assay also enabled the naked-eye detection of biothiols by NP agglomeration and may be successfully applied to pharmaceutical samples containing thiols

Screening Method for Argan Oil Adulteration with Vegetable Oils: An Online HPLC Assay with Postcolumn Detection Utilizing Chemometric Multidata Analysis

This study is focused on examining the tocopherol isomers (alpha-, gamma-, and delta-) fingerprinting by online RP-HPLC analysis with post column detection using CUPRAC (cupric reducing antioxidant capacity) methodology for argan oil authenticity. The proposed online assay was validated with good precision, reproducibility, and linearity. Sixteen argan oil samples (100% pure-certified and other commercial argan oils), possible adulterating vegetable oils (i.e., olive, sunflower, corn, and soya oils), and virgin argan oil blended with olive, sunflower, corn, and soya oils at levels of 5%, 10%, 15%, and 20% were analyzed. Spectrophotometric CUPRAC, DPPH, and ABTS assays were applied. Discrimination of fraudulent argan oils from virgin samples was performed by utilizing orthogonal partial least-squares discriminant analysis (OPLS-DA) regression modeling with good sensitivity and specificity. We suggested [gamma-toc/alpha-toc] value as a new first screening adulteration factor (AF) that could be used to assess fraudulent argan oil samples. The distinct decrement in AF value was observed by the increase of adulteration rate. The AF values for virgin argan oils were ranged from 11.8 (lower limit) to 18.6 (upper limit). The presence of beta-sitosterol detected in commercial argan oils (with AF values out of limit values) was evaluated as fraudulent which was in accordance with the proposed assay. Our method enabled the detection of argan oil samples at adulteration levels of >5% in the case of sunflower, olive, and soya oils, >15% in the case of corn oil. This method may be an alternative and specific assay for the authentication and quality detection of commercial argan oils