Poly-L-Lysine is widely used in cell culture applications to promote cell adhesion to solid surfaces such as glass or plastic. It forms a positively charged layer on surfaces, which enhances the attachment of negatively charged cell membranes, making it especially useful for culturing neurons and other sensitive or weakly adherent cell types.

It is also employed in molecular biology and biotechnology to precipitate nucleic acids, particularly in transfection protocols where it helps in the delivery of DNA or RNA into cells. Its ability to condense genetic material improves cellular uptake and transfection efficiency.

In biomaterials and tissue engineering, Poly-L-Lysine is used to modify scaffold surfaces, improving biocompatibility and supporting cell growth and differentiation. Additionally, it finds use in biosensors and protein immobilization due to its stable binding properties.

Due to its biodegradability and low toxicity, it is suitable for certain drug delivery systems and has been explored in controlled release formulations and gene therapy applications.