Molecular imaging is powerful tool to explore the distribution or the function of a given target,thus has drawn significant attention in the fields of chemical biology and disease diagnosis.CD22 is a 140kDa transmembrane sialo-adhesion protein highly expressed on mature B cells and B cells lymphomas,which is also an important target for the treatment of lymphomas.Molecular imaging of CD22 in living cells is very crucial to investigate the distribution of this key protein in various cells and to explore its biological functions in physiological and pathological conditions.Herein,a novel salic acid functionalized quantum dots was synthesized and used for highly selective detection of this key protein in human cancer cells.N-Acetylneuraminic acid(Neu5Ac)was selected as the recognition part of the nanoprobe,which was coupled to amino groups in the surface of CdSe/ZnS quantum dots(QDs)to prepare SA-QDs through acetylation reaction with EDC as cross linker.The obtained nanocrystals with a photoluminescence quantum yield of 70%were purified via ultrafiltration.The average size of SA-QD nanoparticle was about 25 nm,and its fluorescent emission wavelength was 560 nm.The low cytotoxicity of both bare and SA-functionalized QDs was verified through CCK8 assays.The ability of SA-QDs targeting to cancerous cells was then investigated by comparing the uptake of nanoparticles by CD22+cells(Daudi)and CD22-cells(HepG2)by CLSM.Specificity of the SA-QDs fluorescent nanoprobes targeting CD22 was verified with cellular uptake inhibition assay,in which Daudi cells were incubated with both SA-QDs and free salic acid.In addition,the specificity was also confirmed by the collocation of the immunofluorescence staining of anti-CD22 and the cellular uptake of SA-QDs.All these findings suggested that this practical fluorescent nanoprobe can serve as a powerful tool for molecular imaging of CD22 in living cells,and thus hold great promise in CD22-associated basic researches and disease diagnosis.