Quantum Dots, Efficient Fluorescent Markers for Red Cells.

Semiconductor quantum dots (QDs) are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. In comparison with organic dyes and fluorescent proteins, QDs are emerging as a new class of fluorescent labels with improved brightness, resistance against photobleaching, and multicolor fluorescence emission. These properties could improve the sensitivity of biological detection and imaging by at least 10 to 100 fold. Recent research has shown that QDs can be covalently linked with biorecognition molecules such as peptides, antibodies, nucleic acids and small molecules for use as fluorescent probes. The aim of the present study was to evaluate the application of a Cadmium Sulfide QDs method for the analysis of the expression and distribution of A antigen on living red blood cell surface. Highly luminescent and stable cadmium sulfide colloidal particles were obtained in the nanometer size range. Their surface was functionalized with commercially available monoclonal anti-A antibody via an one-pot glutaraldehyde cross linking procedure, followed by their conjugation to red cells. Samples were obtained from blood bank red cell units, of groups A (n=3), A2 (n=2) and O (n=3). Confocal microscopy (LSM 510 - Carl Zeiss, Jena, Germany) was used and for each cell type, the images were reproduced at least three times. The acquisition confocal image parameters, such as pinhole, filters, beam splitters and photomultiplier gain, were maintained constant to permit a comparative analysis of the luminescence intensity maps. Analyzing the intensity map of group A erythrocytes, a homogeneous emission profile was observed throughout the cell surface, suggesting a homogeneous distribution of A antigen. In contrast, the intensity map analysis of the confocal images showed a lower intensity pattern of the A2 group erythrocytes studied, suggesting different antigen expression on cell surface. The O group cells showed no emission. This result suggests that this new efficient, fast and simple labeling procedure may be employed as a quantitative tool to investigate the expression and distribution of molecules in red blood cells.