Based on the affinity of lectin with glycosyl complex on cellular surface, a label-free impedimetric biosensor for discrimination and detection of bacteria has been reported. The impedimetric biosensor is fabricated by a simply and reproducibly self-assembled lectin monolayer on the polyelectrolyte modified electrode through electrostatic interaction. Two well-known lectins, concanavalin A (Con A) and ricinus communis agglutinin (RCA), are used to demonstrate proof-of-concept of the recognition interface. The utility of this sensor for selective discrimination of bacterial strain types, e.g., gram-negative bacteria (Escherichia coli DH5 alpha and Enterobacter cloacae), gram-positive bacterium (Bacillus subtilis), fungus (Saccharomyces cerevisiae) and mammalian cell (HeLa cell) with high sensitivity has been achieved. In addition, the Con A-bacteria binding process can be inhibited significantly by the saccharide, mannose, giving further proof of the cytosensing mechanism on lectin interface. (C) 2010 Elsevier B.V. All rights reserved.