The invention discloses a near-
infrared silver sulphide 
quantum dot as well as a preparation method and application thereof. The silver sulphide 
quantum dot has a monoclinic phase structure, the particle 
diameter of the silver sulphide 
quantum dot is below 8nm, and the surface of the silver sulphide 
quantum dot can be connected and modified with a hydrophilic group of hydrophilic 
reagent containing sulfydryl. The preparation method comprises the following steps: fully reacting a mixed 
reaction system containing silver source and long-chain mercaptan in a sealed environment; cooling the mixed 
reaction system, and then adding a polar 
solvent; carrying out 
centrifugation and wshing to obtain a hydrophobic near-
infrared silver sulphide 
quantum dot; fully mixing the hydrophobic near-
infrared silver sulphide 
quantum dot and hydrophilic 
reagent containing sulfydryl in 
organic solvent to react; and carrying out 
centrifugation and washing the reacting mixture to obtain the 
biocompatibility near-infrared silver sulphide quantum dot. The quantum dot disclosed by the invention has the advantages of high 
fluorescence yield, good 
fluorescence stability, good 
biocompatibility and even size, and can be used for 
biological tissue imaging; and the preparation technology has moderate condition, short period and good 
repeatability, is simple to operate and is easy to control.