Ultrasensitive Biotin Assay of a Noncompetitive Format in a Homogeneous Solution Based on Resonance Energy Transfer Induced by a Protein–Protein Interaction

Competitive binding assay for biotin and biotin derivatives, based on avidin and biotin-4-fluorescein

Biotinylated molecules are extensively employed in bioanalytics and biotechnology. The currently available assays for quantification of biotin groups suffer from low sensitivity, low accuracy, or provide highly variable responses for different biotin derivatives. We developed a competitive binding assay in which avidin was pre-blocked to different extents by the biotinylated analyte and a constant amount of biotin-4-fluorescein (B4F) was added, resulting in strong quenching of the B4F. The assay was robust and the shape of the titration curve immediately revealed whether the data were reliable or perturbed by steric hindrance in case of large biotin derivatives. These advantages justified well the 10× higher sample consumption (~0.6nmol) compared to single point assays. The assay was applied to a representative set of small biotin derivatives and validated by cross-control with the well-established 2-anilinonaphthalene-6-sulfonic acid (2,6-ANS) binding assay. In comparison to the 2,6-ANS binding assay, the lower precision (±10%) was compensated by the 100-fold higher sensitivity and the deviations from the ANS assay were ≤5%. In comparison to the more sensitive biotin group assays, the new assay has the advantage of minimal bias for different biotin derivatives. In case of biotinylated DNA with 30 nucleotides, steric hindrance was found to reduce the accuracy of biotin group determination; this problem was overcome by partial digestion to n≤5 nucleotide residues with a 3'-exonuclease. The newly proposed biotin group assay offers a useful compromise in terms of sensitivity, precision, trueness, and robustness.

Fluorescent Labeling of the Nuclear Envelope Without Relying on Inner Nuclear Membrane Proteins

The nuclear envelope (NE), a double membrane that separates nuclear components from the cytoplasm, undergoes a breakdown and reformation during cell division. To trace NE dynamics, the NE needs to be labeled with a fluorescent marker, and for this purpose, markers based on inner nuclear membrane (INM) proteins are normally used. However, NE labeling with INM proteins has some limitations. Here, we introduce a protocol for fluorescent labeling and imaging of NE that does not rely on INM proteins, along with protocols for simultaneously imaging two nuclear components and for time-lapse imaging of labeled cells.

A G-quadruplex/hemin DNAzyme-based microchip electrophoresis chemiluminescence assay for highly sensitive detection of biotin in flour

Quantitative analysis of biotin in biological fluids, foods, and pharmaceutical is important for diagnosis and treatment of biotin-related diseases and health maintenance. In this work, a novel G-quadruplex/hemin DNAzyme-based microchip electrophoresis chemiluminescence (CL) assay method was established for rapid and highly sensitive detection of biotin. This method is based on the specific binding between biotin and streptavidin, the catalytic CL characteristics of G-quadruplex/hemin DNAzyme to the oxidation-reduction reaction of hydrogen peroxide with luminol, and the on-line separation function of microchip electrophoresis. Under the optimal experimental conditions, on-chip biotin analysis was achieved within 1 min. The CL intensity is linearly proportional to the concentration of biotin in the range of 13-630 nM with a detection limit of 6.4 nM. The proposed method has been applied for the detection of biotin in flour, biotin contents in three flour samples are found in the range of 199-223 ng/g with a mean value of 214 ng/g. The recoveries were in the range of 94-103%. With excellent sensitivity and good selectivity, the proposed method could be applied in a wide range of biological fluids, foods, and pharmaceutical analysis.