Hyperspectral stray light imaging of chromosomes: a novel concept for label-free karyotyping

Abstract

We describe the design and performance of a Hyperspectral Imaging System (HSI) for label-free characterization of human metaphase chromosomes. Chromosomes consist of a DNA-protein complex that is organized in sub-structures and can be described by an array of "particles" with different size and refractive indices. This locally resolved stray light pattern can be used to visualize and characterize unstained chromosomes. The paper describes an imaging system where stray light spectra of chromosomes are detected using a Pushbroom Imaging device attached to a standard microscope in combination with multivariate data analysis. To proof the concept, single particle spectra as well as particle array spectra are analyzed and explained by means of Mie scattering theory and the results are confirmed with FDTD (Finite Difference Time Domain) simulations. This label free signature is due to the superposition of the interference pattern of the different layer thicknesses, the spectral interference of the band pattern, changes in refractive indices along the chromosome axis as well as the absorption of chromophores in different spectral regions of the chromatin condensation. This complex spectral signature can be analyzed by means of a principal component analysis (PCA) and classified in a multidimensional PCA space.