Nanotechnologies and nanomaterials have gained much success in the fields of biological applications. In particular,
quantum dots (QDs) are emerging as a revolutionary means for imaging and optical detection in opposition to
conventional organic dyes. For their robust photostability, large extinction coefficients, and relatively small size, QDs
present superior advantages in single molecules monitoring over long time period in living cell. The interaction between
functionalized QDs and living cell is the primary problem of the QDs application in living cell. In this work, carboxyl
and transferrin conjugated CdS QDs were evaluated using total internal reflect fluorescence (TIRF) microscopy and
single particle tracking (SPT) techniques at living cell surface. The diffusion and binding were quantitively measured by
mean square displacement (MSD) versus time plotting. To study the influence of different QDs surface on interaction
between QDs and cell, dynamic characters of carboxyl and transferrin conjugated QDs were calculated respectively. The
photonic characters of QDs were also investigated, considering that functionalized surface can lead to behavior altering
of QDs under illuminating. Simultaneous imaging of several QDs with frame rates of up to 30 frames/s and localization
accuracy of ~10 nm was present.
We have developed a practical method to control the number of attaching biomolecules to an AFM tip. Monolayer of OEG that has little interaction with some biomolecules was self-assembled on tips. Electric pulses were used to oxidize a patch of OEG monolayer on tip and generate COOH groups for further linking at the activated area. The surface groups were detected by chemical force titration. The total numbers of molecule bound on the tip was examined by the studies of biotin/streptavidin system.