Strictly sparse surface modification and its application for endowing nanoparticles with an exact "valency"

Sparsely modified surfaces can be used as a general platform for precisely modifying small nanoparticles. However, strictly, rather than statistically, sparse surface modification remains a big challenge. Herein, we report a new and general method for strictly sparse modification of the surface of relatively large nanoparticles. The method is analogous to planting big trees and then removing the big crowns, leaving the stumps on the ground; due to the large exclusive size of the crowns, the stumps are strictly sparsely distributed. As a proof of concept, strictly sparse modification of surfaces was demonstrated by the successful preparation of "monovalent" and "divalent" golden nanoparticles (AuNPs) with different sizes. Starting from the "monovalent" and "divalent" AuNPs, AuNP dimers and chain-like AuNP assemblies were prepared, respectively.