[INVITED] Raman microscopy based sensing of leukemia cells: A review

Leukemia diagnosis and classification requires the use and combination of several technologies usually involving staining and morphology examining of cells in a blood sample, or selective detection of specific cell membrane antigens. Standard morphological protocols often lack the specificity and sensitivity required for an accurate and early diagnosis. Fluorescence based analyses of the cell surface receptors, although providing specific information, are limited by photobleaching and number of surface proteins that can be imaged simultaneously. In this review, we consider our recent efforts towards the development of a Raman spectroscopy-based protocol for a complete biochemical and morphological analysis of leukemia cells. Indeed, Raman spectroscopy is an optical technique based on inelastic scattering of light by vibrating molecules and can provide high specific biochemical information with minimal or no sample pretreatment. We discuss single-point Raman analysis for the identification, classification and follow-up of acute lymphoblastic leukemia type B (B-ALL). Normal B cells and three B-ALL cell lines (RS4;11, REH and MN60) were analyzed, and several intrinsic Raman markers associated with proteins, nucleic acids and lipids were used for cells sensing and follow-up after the low-dose chemotherapy treatment. Multivariate statistical analyses allowed us confirming the significance of the Raman data for identifying and classifying the leukemia cells in their maturation/differentiation stages. False color Raman imaging was additionally used to visualize the leukemia cell morphology, as the standard May Grunwald-Giemsa histochemical staining protocol, but without the use of any label. Finally, the selective probing of leukemia cell membrane by surface enhanced Raman scattering (SERS) is reported. The SERS substrate was a 3D diatom frustule covered with a gold layer (40 nm in thickness). These observations are promising for the development of a Raman-based protocol for the diagnosis and the complete morpho-functional assessment of leukemias.