High sensitivity gram-negative bacteria biosensor based on a small-molecule modified surface plasmon resonance chip studied using a laser scanning confocal imaging-surface plasmon resonance system

•A new highly selective and sensitive method for detecting gram-negative bacteria was investigated.•Gram-negative bacteria can be distinguished from gram-positive bacteria and fungi based on polymyxin B modified SPR sensor chip.•A LOD of 1.0 × 102 CFU/mL was reached for E. coli and bacteria concentrations have a good linear relationship with SPR signal.•The results indicated that sensor has potential further application in sensitive and rapid detection gram-negative bacteria in real-time.