Detection of CXCR4 receptors on cell surface using a fluorescent metal nanoshell.

Fluorescence cell imaging can be used for disease diagnosis and cellular signal transduction. Using a metal nanoshell as molecular imaging agent, we develop a cellular model system to detect CXCR4 chemokine receptor on T-lymphatic cell surface. These metal nanoshells are observed to express enhanced emission intensity and shortened lifetimes due to the near-field interactions. They are covalently bound with anti-CXCR4 monoclonal antibodies for immunoreactions with the target sites of the CXCR4 receptors on the CEM-SS cells. The fluorescence intensity and lifetime cell images are recorded with a time-resolved confocal microscopy. As expected, the emission signals from the metal nanoshells are clearly isolated from the cellular autofluorescence due to strong intensities and distinctive lifetimes. The number of emission spots on the single cell image is estimated by direct count to the emission signals. Analyzing a pool of cell images, a maximal count number is obtained in a range of 200±50. Because there is an average of ̃approximately 6000 binding sites on the cell surface, we estimate that one emission spot from the metal nanoshell may represent ̃approximately 30 CXCR5 receptors. In addition, the CXCR4 receptors are estimated to distribute on ̃approximately 70% area of the cell surface.