Magnetic labelling

Sitharaman B, Tran LA, Pham QP, Bolskar RD, Muthupillai R, Flamm SD, Mikos AG, Wilson LJ (2007) Gadofullerenes as nanoscale magnetic labels for cellular MRI. Contrast Media Mol. Imag. 2 139-146. 

Figure 4. Accumulation of iron-labeled MSC in the renal cortex. Animals were anesthetized and coronal T 2-weighted gradient echo in vivo magnetic resonance images (MRl) were obtained before (A) and immediately (B) or 3 days (C) after injection of magnetically labeled (iron-dextran) syngeneic mesenchymal stem cells.

Apart from attaching MRI contrast agents to the cell surface, cell labeling may also be achieved by using cell uptake processes. Endocytosis, whether receptor mediated or not, and phagocytosis are mechanisms that maybe considered and that could lead to accumulation of a magnetic label inside the cell. Provided the... 

Figure 5. 31P NMR magnetization transfer measurements of ATP turnover in immobilized yeast cells. A control spectrum is shown in (a). Saturation of the y-phosphate resonance of ATP and transfer of this magnetic label through chemical exchange results in a decrease in the intensity of the P, and sugar phosphate resonances (b). This is most clearly seen in the difference spectrum (a-b). The magnitude of the decrease in the P, resonance can be used to calculate the flux between P, and ATP and, hence, the rate of ATP turnover (see Brindle, 1988a,b).

The idea behind a spintronic biochip or biosensor is to replace traditionally used fluorescent markers by magnetic labels. Instead of detecting biomolecular recognition using expensive optical or laser-based... 

Figure 26. Schematic of the post hybridization detection method. A DNA target solution labeled with biotin is first incubated with the DNA probe functionalized chip. Targets diffuse passively from the solution to the surface where they hybridized with the probes if complementary. A solution containing streptavidin-functionalized magnetic labels is then incubated with the chip. Labels bind through the biotin-streptavidin interaction to where hybridization occurred. DNA hybridization is detected with spintronic transducers.

The increase of the sensor size comes with a decrease in sensor label sensitivity, that is, the sensor response for a single magnetic label is smaller. On the other hand, the sensor dynamic range is larger as the sensor is able to detect a larger number of particles. In order to be sensitive to single labels 106 the sensor size can be reduced to match the label size [121], but in this case the assay biological sensitivity is smaller. 

Figure 3. Process of detecting DNA via a magnetoresistive device. (After [97]) The probe DNA is fixed to a polymer layer on the chip (1), the analyte DNA tagged with a molecule such as biotin in introduced and allowed to bind (2). The excess analyte is removed and a molecule that binds to the biotin (streptavidin) is attached to the magnetic label and introduced (3).

Make sure to have enough cells. Cell density (50-100) x 10 cells per ml is sufficient to perform FACS analysis. Perform FACS analysis as quickly as possible to avoid cell aggregation and aging in the FACS buffer. Cells are magnetically labeled post-magnetofection due to association with magnetic transfection complexes vortex cells before FACS analysis. 

Wilhelm C, Gazeau F, Bacri JC (2002) Magnetophoresis and ferromagnetic resonance of magnetically labeled cells. Eur Biophys J 31 118-125... 

Cellular imaging with MRM using T2 and T2 contrast magnetic labeling... 

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