The present invention provides a trialkoxysilanes having structure I wherein R1 and R2 are independently at each occurrence a C1-C3 alkyl group; R3 is independently at each occurrence a hydrogen or a C1-C3 alkyl group; R4 is a C1-C5 aliphatic radical, a C7-C12 aromatic radical, or a C5-C10 cycloaliphatic group; n is 0, 1, 2 or 3; q is 1, 2 or 3; and X− represents a charge balancing counterion. The trialkoxysilanes are useful for the preparation of nanoparticulate diagnostic imaging agent compositions.