Cyclodextrin-modified graphene quantum dots as a novel additive for the selective separation of bioactive compounds by capillary electrophoresis

Highly reliable separation and determination of various biologically active compounds were achieved using capillary electrophoresis (CE) based on β-cyclodextrin-functionalized graphene quantum dots (βcd-GQDs) as the background electrolyte additive. βcd-GQDs improve the separation efficiency between peaks of all analytes. No addition of surfactants or organic solvents was needed in the running buffer containing βcd-GQDs. Up to eight consecutive runs were acquired with high precision for the separation of resveratrol, pyridoxine, riboflavin, catechin, ascorbic acid, quercetin, curcumin, and even of several of their structural analogs. Baseline separation was achieved within just 13 min as a result of the effective mobility of the analytes along the capillary owing to the differential interaction with the additive. The proposed analytical method displayed a good resolution of peaks for all species selecting two absorption wavelengths in the diode array detector. Detection limits lower than 0.28 µg mL^-1 were found for all compounds and precision values were in the range of 2.1-4.0% in terms of the peak area of the analytes. The usefulness of the GQD-assisted selectivity-enhanced CE method was verified by the analysis of food and dietary supplements. The applicability to such complex matrices and the easy and low-cost GQD preparation open the door for routine analyses of food and natural products. The concept of using such a dual approach (macromolecules and nanotechnology) has been explored to tackle the separation of various bioactive compounds in nutritional supplements and food. Schematic illustration of the electrophoretic separation of the bioactive molecules in the capillary which is filled with the running solution without (top) and with βcd-GQDs (bottom). The fused silica capillary with negatively ionizable silanol groups at the wall. The voltage is applied at positive polarity at the outlet. R, riboflavin; r, resveratrol; P, pyridoxine; C, catechin; c, curcumin; A, ascorbic acid; Q, quercetin.

Whey peptide-encapsulated silver nanoparticles as a colorimetric and spectrophotometric probe for palladium(II)

Silver nanoparticles (AgNPs) coated with whey peptides are shown to be a useful optical nanoprobe for the highly sensitive determination of Pd(II). The peptidic surface of the AgNPs works as a molecular receptor for the rapid detection of Pd(II) via a color change from dark yellow to orange/red along with a spectral red-shift with a gap about 120 nm. The effect is caused by the formation of a coordination complex between Pd(II) and the peptide ligands. This results in the aggregation of AgNPs and an absorbance spectral shift from 410 to 530 nm. The absorbance response is linear in the range 0.1 to 1.3 μM Pd(II) with a low detection limit of 115 nM. The nanoprobe responds within a few minutes and is not interfered by other metal ions except for Mg(II). The probe potentially can be applied to the determination of Pd(II) contamination in the products of Pd(II)-catalyzed organic reactions and in pharmaceutical settings. Graphical abstractSchematic representation of the nanoprobe for Pd(II). (a) Synthesis of whey peptide-coated silver nanoparticles (AgNPs), (b) the nanoprobe design for Pd(II) detection, (c) HR-TEM imaging and elemental mapping, (d) quantitative determination of Pd(II) (Inset shows colorimetric results).