Semiconducting polymer dots(Pdots)have emerged as a new type of fluorescent nanomaterials and rational functionalization of Pdots remains a challenge to expand their applications in chemo/biosening and biomedicine.Herein,functionalized Pdots modified with β-Cyclodextrin(CD),CD-Pdots,has been designed to construct a ratiometric sensor for cholesterol(Cho).Using CD-Pdots as energy donors while rhodamine B(RB)as energy acceptors,a fluorescence resonance energy transfer(FRET)pair has been built,which leads to the fluorescence quenching of CD-Pdots via FRET because the host-guest interaction between RB and β-Cyclodextrin attached to Pdots brings donors-acceptors pair into close proximity.In the presence of Cho,the acceptors departs from the donors due to competitive inclusion interaction between Cho and RB with CD attached to Pdots,resulting in the hindering of FRET process between CD-Pdots and RB and therefore a drastic fluorescence recovery of CD-Pdots and fluorescence quenching of RB.Based on the turn-on fluorescence of CD-Pdots and turn-off fluorescence of RB,a sensitive ratiometric method for the determination of Cho in concentration range from 25 nM to 350 nM with a detection limit of 4.9 nM was achieved.The proposed method was also used to determine Cho in human serum samples with satisfactory results.