A charge control mechanism of charge control agents （CCAs） has been proposed in the present investigation that assumes an appreciable temperature increase at the "toner/carrier" interface due to triboelectrification. A further assumption is that the CCA is present on the surface of both toner and carrier. Because of local heating, the electrical conductivity of CCAs is increased remarkably to give a conductive channel, through which the carrier flow occurs effectively to charge the toner. These two assumptions have experimentally been verified. Especially, local heating of up to 100℃ has been confirmed by using a pigment marker that changes its color from black to red. Around this temperature, the electrical conductivity of CCAs is also found to increase significantly by one to three orders of magnitude as compared with that at room temperature.

We have focused on a triboelectricity as a surface phenomenon. The frictional action between two polymers should induce the scissions of carbon-carbon bond of polymer main chain on the friction surface. On this point of view, a frictional experiment was designed as a mechanical fracture experiment of polymers in a vacuum in the dark at 77 K. The mechanical fracture induced homogeneous and heterogeneous scissions of carbon-carbon bond of polymer main chain, and produced macro-neutral free radicals （called mechano radicals ; R ● ） and macro-anionic species （called mechano anions ; R^－）.
We proposed that a generation mechanism of triboelectrificity between two polymers A and B was based on an electron transfer reaction from the RA－ having low electron release potential （P_re（R_A）） as an electron donor to the R_B ● having high electron affinity （E_a（R_B ● ）） as an electron acceptor on the friction surface, and resulted in polymer A having positive charge and polymer B having negative charge. A sign and amount of charges can be evaluated from a chemical formula of polymer based on our proposed mechanism.

Semiconductor nanoparticles that are called as quantum dots are a new class of fluorescent materials for use in biolabeling, biosensing, and bioimaging. Compared with traditional organic fluorophores and fluorescent proteins, quantum dots have unique optical properties such as size-dependent emission, high brightness, and high resistance to photobleaching. At 1993, Bawendi group first reported a chemical synthesis of high-quality CdE （E＝S, Se, Te） semiconductor quantum dots. Since then, synthetic methods for preparing highly fluorescent quantum dots that emit at visible to near infrared regions have been extensively developed. In this short review, synthesis and surface modification of quantum dots, and their possible application to biomedical fields are described.