Magnetic microspheres encoded with photoluminescent quantum dots for multiplexed detection

A combination of layer- by- layer ( LBL) self- assembly and magnetic separation has been used to encode magnetic microspheres with multiple colours of photoluminescent semiconductor quantum dots ( QDs). Magnetic separation increased the speed of the LBL process and led to high yields of encoded microspheres. This is important because it allows the full potential of QDs to be harnessed for optically encoded microspheres. The assembly process was investigated using fluorescence microscopy, transmission electron microscopy ( TEM) and microelectrophoresis. The same assembly process was repeated on planar surfaces and investigated using atomic force microscopy ( AFM) and UV/ vis spectroscopy. Three sets of microspheres with different spectral codes were combined to form a suspension array that was used to screen for three different types of explosive in the same sample. Results were analyzed with a fluorescence microscope that decoded the microspheres and detected fluorescent reporter molecules bound to their surface. The results allowed individual explosives and mixtures of explosives to be detected in multiplexed immunoassays.