Biosensing　of　circulating　tumor　cells　(CTCs)　is　of　vital　significance　in　cancer　theranostics.　Thus,　the　development　of　highly　efficient　luminescent　nano-bioprobes　is　imperative　to　meet　the　growing　demand　of　CTCs-related　clinical　diagnosis　and　biomedical　research.　Herein,　we　exquisitely　manipulate　the　stoichiometry　of　Se/In　to　synthesize　CuInSe2　(CISe)　quantum　dots　(QDs)　with　near-infrared　(NIR)　emission　peak　tunable　from　920　to　1224　nm.　Meanwhile,　the　excitation　band　of　these　CISe　QDs　spans　from　ultraviolet　to　NIR　regions,　which　is　highly　desired　for　various　bioapplications.　Through　surface　coating　of　thin　ZnS　shell,　an　absolute　NIR-II　photoluminescence　quantum　yield　of　21.8%　can　be　achieve,　which　is　the　highest　among　Pb/Cd-free　QDs　reported　so　far.　By　virtue　of　their　intense　NIR-II　emission,　we　demonstrate　the　application　of　CISe　nanoprobes　for　autofluorescence-free　bioassay　of　CTCs　(e.g.,　human　breast　cancer　MCF-7　cells)　spiked　in　whole　blood　samples,　with　the　limit　of　detection　down　to　12　cell/well　of　a　96-well　plate.　Furthermore,　the　CISe@ZnS　nanoprobes　are　exploited　for　tumor-targeted　bioimaging　in　live　mice　with　a　signal-to-noise　ratio　of　5.8.　These　findings　reveal　the　great　potentials　of　the　novel　NIR-II　luminescent　CuInSe2　nanoprobes　in　the　field　of　cancer　diagnosis　and　imaging-guided　surgery.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.