Microbead 'lasers' engulfed by cells, artistic impression

Plastic microbead 'lasers' engulfed by astrocyte cells, artistic impression. This image shows astrocytes which have engulfed (by a process called phagocytosis) plastic microbeads stained with a fluorescent dye. These plastic beads trap light, and when the fluorescent dye in the bead is excited with a short pulse of blue light, this trapped light gets amplified, leading to the emission of laser light. The spectrum of the laser light consists of multiple narrow lines and the spectral position of these lines depends very strongly on the size of the bead. As all beads have slightly different size, each bead has a different spectrum and therefore the spectrum can be used as a barcode for each cell. The spectrum is measured and displayed in real-time and indeed looks somewhat like the barcodes we know from the supermarket. This method enables reliable non-contact optical tracking of a large number of cells over prolonged periods of time.