Spectral multiplexing using quantum dot tagged microspheres with diffusing colloidal probe microscopy

This work involves the development of a new technique that integrates Diffusing Colloidal Probe Microscopy (DCPM) and luminescence to simultaneously measure multiple particle-wall interactions. DCPM can be used to map potential energy profiles of multiple particle-surface interactions simultaneously and accurately. Colloidal semiconductor quantum dots were used for spectral multiplexing to enable monitoring of multiple analytes at the same time. DCPM combines Total Internal Reflection Microscopy (TIRM) and Video Microscopy to simultaneously measure multiple particle-surface interactions with nanometer resolution in particle-surface separation. By acquiring the scattered intensity emitted by the particles, the separation distance can be calculated and subsequently the forces of interactions between the particle and the surface. This work demonstrates the use of luminescence instead of scattering as the mode of detection in DCPM. The luminescence is provided by quantum dots which are incorporated into polystyrene microspheres. The unique optical properties of quantum dots enable the creation of an optically multiplexed system where microspheres are tagged by quantum dots of different emission wavelengths. Scattering in DCPM may result in erroneous calculation of the potential energy profiles because of particle polydispersity. Since scattering is dependent on particle size, luminescence is introduced into the system and some interesting results are obtained. These results illustrate that the effect of particle polydispersity is significantly reduced when luminescence is used as the mode of detection. This combined with the DCPM system?s sensitivity would enable the monitoring of multiple functionalized particlesurface interactions simultaneously and accurately.