The invention provides methods of controlled release of an agent into an intracellular environment of a biological cell using a needle nanoelectrode. The agent may be attached to an outer surface of the needle nanoelectrode through a linking molecule, wherein the attachment comprises an electroactive chemical bond. After penetrating a cellular membrane with the needle nanoelectrode to position at least a portion of the nanoelectrode in the intracellular environment, an electric potential may be applied to the needle nanoelectrode to break the electroactive chemical bond, thereby releasing the agent to the intracellular environment. The linking molecule may be a surface active organosulfur compound capable of forming a self-assembled monolayer on a metal surface of the nanoelectrode
