This paper describes three findings. The first is a method for producing colloidal solutions of quantum dot (QD) nanoparticles with silica shells (QD/SiO2). QD nanoparticles averaging 10.3 +/- 2.1 nm in size were coated with silica via a sol-gel reaction with tetraethyl orthosilicate using NaOH as a catalyst. The QD/SiO2 particle size could be varied by varying the QD concentration. The average particle sizes were 19.1 +/- 3.0 (S-QD/SiO2) and 47.0 +/- 6.1 nm (L-QD/SiO2) for QD concentrations of 6.4 x 10(-9) M (4.6 x 10(11) particles/L) and 6.4 x 10(-10) M (4.6 x 10(10) particles/L), respectively. The second finding is a method to modify the particle surface with poly(ethylene glycol), which is called PEGylation (QD/SiO2/PEG). S-QD/SiO2 and L-QD/SiO2 were PEGylated using methoxy polyethylene glycol silane (S-QD/SiO2/PEG and L-QD/SiO2/PEG, respectively). The third finding is an in-vivo fluorescence imaging technique using the QD/SiO2/PEG particle colloid solutions. Both QD/SiO2/PEG particle colloid solutions fluoresced with intensities comparable with that of the QD colloid solution. Mouse tissues could be imaged by injecting the QD/SiO2/PEG colloid solution into them and measuring the emitted fluorescence intensity. The L-QD/SiO2/PEG particles did not form aggregates in blood, which allowed the particles to reach the tissues more efficiently than the S-QD/SiO2/PEG particles.