Broadband excitable NIR-II luminescent nano-bioprobes based on CuInSe2 quantum dots for the detection of circulating tumor cells

•A new family of NIR-II semiconductor nano-bioprobes based on CuInSe2 QDs is proposed.•The excitation band of these CuInSe2 QDs spans from ultraviolet to NIR regions.•A record-high absolute NIR-II photoluminescence quantum yield (21.8%) for CuInSe2@ZnS QDs is achieved.•These CuInSe2@ZnS nanoprobes are employed for autofluorescence-free bioassay of circulating tumor cells spiked in whole blood samples with the limit of detection down to 12 cell/well of a 96-well plate.•The CuInSe2@ZnS nanoprobes are exploited for real-time tumor-targeted bioimaging in live mice with a signal-to-noise ratio of 5.8.