Methods for qPCR gene expression profiling applied to 1440 lymphoblastoid single cells.

The stochastic nature of generating eukaryotic transcripts challenges conventional methods for obtaining and analyzing single-cell gene expression data. In order to address the inherent noise, detailed methods are described on how to collect data on multiple genes in a large number of single cells using microfluidic arrays. As part of a study exploring the effect of genotype on Wnt pathway activation, data were collected for 96 qPCR assays on 1440 lymphoblastoid cells. The description of methods includes preliminary data processing steps. The methods used in the collection and analysis of single-cell qPCR data are contrasted with those used in conventional qPCR.

Biotin-4-fluorescein based fluorescence quenching assay for determination of biotin binding capacity of streptavidin conjugated quantum dots.

The valency of quantum dot nanoparticles conjugated with biomolecules is closely related to their performance in cell tagging, tracking, and imaging experiments. Commercially available streptavidin conjugates (SAv QDs) are the most commonly used tool for preparing QD-biomolecule conjugates. The fluorescence quenching of biotin-4-fluorscein (B4F) provides a straightforward assay to quantify the number of biotin binding sites per SAv QD. The utility of this method was demonstrated by quantitatively characterizing the biotin binding capacity of commercially available amphiphilic poly(acrylic acid) Qdot ITK SAv conjugates and poly(ethylene glycol) modified Qdot PEG SAv conjugates with emission wavelengths of 525, 545, 565, 585, 605, 625, 655, 705, and 800 nm. Results showed that 5- to 30-fold more biotin binding sites are available on ITK SAv QDs compared to PEG SAv QDs of the same color with no systematic variation of biotin binding capacity with size.

Calibration of Flow Cytometry for Quantitative Quantum Dot Measurements.

Observations of quantum dot (QD) labeled cells in biomedical research are mainly qualitative in nature, which limits the ability of researchers to compare results experiment-to-experiment and lab-to-lab to improve the state-of-the-art. Labeled cells are useful in a range of in vitro and in vivo assays where tracking behavior of administered cells is integral for answering research questions in areas such as tissue engineering and stem cell therapy. Before the full potential of QD based toolsets can be realized in the clinic, uptake of QDs by cells must be quantified and standardized. This unit describes a novel, simple method to assess the number of QDs per cell using flow cytometry and commercially available standards. This quick and easy method can be used by all researchers to calibrate their flow cytometry instruments and settings, and quantify QD uptake by cells for in vitro and in vivo experimentation for comparable results across QD conjugate types, cell types, research groups, lots of commercial QDs, and homemade QDs.