Enantioselective recognition mechanism of ofloxacin via Cu(II)-modulated DNA

A novel copper ion enhanced electrochemical DNA biosensor for the determination of epinephrine

A novel electrochemical biosensor was developed for the detection of epinephrine (EP) by immobilizing double-strand DNA (dsDNA) bound with copper ions on a gold electrode (Cu2+/dsDNA/MCH/AuE). The electrochemical behavior of EP at Cu2+/dsDNA/MCH/AuE was examined, and the results demonstrated a significant enhancement in the electrocatalytic oxidation peak current of EP due to the formation of a stable G-Cu(II)-G sandwich structure between Cu2+ and guanine at the modified electrode. The modification process of the electrode was characterized by scanning electron microscopy, infrared spectroscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. A study on the effect of pH in phosphate buffer solution on the electrochemical oxidation of EP indicated that the catalytic oxidation process was pH-dependent. A plot of catalytic current versus EP concentration exhibited a dual-linear relationship within two ranges: 1.0-12.5 μM and 12.5-1000.0 μM, with correlation coefficients of 0.995 and 0.997, respectively. The limit of detection was determined to be 47 nM (S/N = 3). According to the calculated Hill coefficient (0.99), it can be concluded that the electrocatalytic process followed the Michaelis-Menten kinetic mechanism. The maximum catalytic current Im was 25 μA, while the apparent Michaelis-Menten constant Km was 1.425 mM. These findings indicated excellent electrocatalytic activity of the modified electrode towards oxidation of EP. The developed biosensor successfully detected EP in spiked mouse serum as well as epinephrine hydrochloride injection with high selectivity, sensitivity, stability, and accuracy.

Label-Free Fluorescent Turn-On Glyphosate Sensing Based on DNA-Templated Silver Nanoclusters

In this work, a label-free fluorescent detection method for glyphosate, based on DNA-templated silver nanoclusters (DNA-Ag NCs) and a Cu²⁺-ion-modulated strategy, was developed. In the presence of Cu²⁺, the fluorescence of the DNA-Ag NCs was quenched. Glyphosate can restore the fluorescence of DNA-Ag NCs. By analyzing the storage stability of the obtained DNA-Ag NCs using different DNA templates, specific DNA-Ag NCs were selected for the construction of the glyphosate sensor. The ultrasensitive detection of glyphosate was achieved by optimizing the buffer pH and Cu²⁺ concentration. The sensing of glyphosate demonstrated a linear response in the range of 1.0-50 ng/mL. The limit of detection (LOD) was 0.2 ng/mL. The proposed method was successfully applied in the detection of glyphosate in a real sample, indicating its high application potential for glyphosate detection.

Sequence requirements of oligonucleotide chiral selectors for the capillary electrophoresis resolution of low-affinity DNA binders

We recently reported that a great variety of DNA oligonucleotides (ONs) used as chiral selectors in partial-filling capillary electrophoresis (CE) exhibited interesting enantioresolution properties toward low-affinity DNA binders. Herein, the sequence prerequisites of ONs for the CE enantioseparation process were studied. First, the chiral resolution properties of a series of homopolymeric sequences (Poly-dT) of different lengths (from 5 to 60-mer) were investigated. It was shown that the size increase-dependent random coil-like conformation of Poly-dT favorably acted on the apparent selectivity and resolution. The base-unpairing state constituted also an important factor in the chiral resolution ability of ONs as the switch from the single-stranded to double-stranded structure was responsible for a significant decrease in the analyte selectivity range. Finally, the chemical diversity enhanced the enantioresolution ability of single-stranded ONs. The present work could lay the foundation for the design of performant ON chiral selectors for the CE separation of weak DNA binder enantiomers.

Chiral resolution capabilities of DNA oligonucleotides

Herein, we studied the chiral resolution properties of a repertoire of arbitrarily chosen DNA oligonucleotides (ON). Ten oligonucleotidic sequences characterized by diverse base compositions, sizes, and structural features, ranging from secondary structure-free homo-oligonucleotides to duplex, hairpin, and three-way junction architectures, were investigated as potential chiral selectors. Their enantioselective features were assessed by using ONs as running buffer additives in partial-filling capillary electrophoresis. It was shown that all the screened sequences displayed enantiodiscrimination capabilities toward small aromatic compounds. Under (sub)millimolar DNA concentration conditions, the combination of only three oligonucleotidic sequences provided the chiral resolution of around 20 racemates, including drugs, illegal drugs, amino-acids, and nucleosides. This work represents the first demonstration of such analyte selectivity spectrum for nucleic acid-based chiral separation tools.