[en] Highlights: • Thin film of DNA:PbS nanocomposite are prepared for bistable memristors. • Uniform (few cm²) films are deposited by a simple electrografting on ITO surface. • The negative differential resistance memory effect with high on/off ratio and good endurance is observed. • Results are explained using reduction/oxidation of Pb^0/2+ and energy band diagram. - Abstract: Composite films of deoxyribonucleic acid (DNA) and lead sulfide (PbS) nanoparticles are prepared to fabricate biological memory devices. A simple solution based electrografting is developed to deposit large (few cm²) uniform films of DNA:PbS on conducting substrates. The films are studied by X-ray photoelectron spectroscopy, field emission SEM, FTIR and optical spectroscopy to understand their properties. Charge transport measurements are carried out on ITO-DNA:PbS-metal junctions by cyclic voltage scans, electrical bi-stability is observed with ON/OFF ratio more than ∼10⁴ times with good stability and endurance, such performance being rarely reported. The observed results are interpreted in the light of strong electrostatic binding of nanoparticles and DNA stands, which leads doping of Pb atoms into DNA. As a result, these devices exhibit negative differential resistance (NDR) effect due to oxidation of doped metal atoms. These composites can be the potential materials in the development of new generation non-volatile memory devices.