Fluorescence in situ hybridization (FISH) represents a major step in the analysis of chromosomal aberrations in cancer. It allows the precise detection of specific rearrangements, both for diagnostic and prognostic purposes. Here we present a miniaturized FISH method performed on fresh and fixed hematological samples. This procedure has been developed together with a microfluidic device that integrates cluster-assembled nanostructured TiO2 (ns-TiO2) as a nanomaterial promoting hematopoietic cell immobilization in conditions of shear stress. As a result of miniaturization, FISH can be performed with at least a 10-fold reduction in probe usage and minimal cell requirements, creating the possibility of using FISH in genetic screening applications. We developed the protocol on tumor cells and bone marrow (BM) from a normal donor using commercially sex-specific and onco-hematology probes. The procedure was then validated using either BM or peripheral blood (PB) from six patients with hematological diseases, each associated with different genetic lesions. Miniaturized FISH demonstrated comparable performance to standard FISH, indicating that it is suitable for genetic screenings, in research, and in clinical settings for the diagnosis of samples from onco-hematological malignancies.