Aptamer-functionalized Near-infrared Quantum Dots Combined with Flow Cytometry for Rapid Detection of Leukemia Cells

As a haematological malignancy, leukemia poses a great threat to human health and life. Its early and rapid diagnosis is crucial for the improvement of the cure and survival rate of patients. In this paper, a novel leukemia cell assay strategy has been proposed based on aptamer-functionalized quantum dots (QDs) combined with flow cytometry. In this strategy, a biotin-labeled cancer-specific aptamer was adopted as the recognition molecule, and avidin-modified QDs with near-infrared fluorescence emission were utilized as the signal generator. Through the "biotin-avidin" interaction, QDs could be functionalized with aptamers to construct a novel aptamer-QDs fluorescent nano-probe. This probe could specifically bind to target cell surface via the interaction between aptamers and receptors on cell membrane, thus indicating the presence of the target after analysis with a flow cytometer. As proof of concept, the detection of human acute lymphoblastic leukemia CCRF-CEM cells was performed using the specific aptamer, Sgc8c, as a demonstration. Results showed that the modification with Sgc8c did not markedly influence the fluorescence emission and size of QDs. With a simple incubation with cell samples for just 30 min, this Sgc8c-QDs nano-probe could successfully achieve the highly selective detection of CCRF-CEM cancer cells both in buffer and in serum. By comparison with the traditional fluorescent dye labeling method, this Sgc8c-QDs-based strategy exhibited a substantial enhancement in analysis sensitivity for CCRF-CEM cells in buffer, which realized about 4.3 folds signal-to-background ratio of the FAM-labeled Sgc8c ( FAM-Sgc8c) strategy. In particular, when used for serum sample analysis, the Sgc8c-QDs nano-probe still reserved a perfect applicability and displayed a relatively high signal-to-background ratio of about 9, while FAM-Sgc8c nearly lost the detection efficiency at the same concentration. It has been clearly verified that this aptamer-QDs strategy is facile, fast, washing-free, specific and sensitive, which might hold a great potential as a versatile technique for diagnosis and prognosis applications in cancer researches.