Poly-D-lysine hydrobromide is widely used as a coating agent to enhance cell adhesion on surfaces, particularly in cell culture applications. Its positive charge promotes the attachment of cells, especially neurons, to negatively charged substrates like glass or plastic. This makes it invaluable in neuroscience research for studying neuronal behavior, growth, and differentiation. It is also employed in tissue engineering to create environments that mimic natural extracellular matrices, facilitating cell growth and proliferation. Additionally, it is used in diagnostic assays and microscopy to ensure cells remain firmly attached during experimental procedures. Its effectiveness in improving cell adhesion makes it a critical tool in various biological and medical research fields.