A tetraphenylethylene-based aggregation-induced emission molecule (BT-5) bearing two positively charged imidazolium pendants and an alkyl chain (C10H20) was designed as a fluorescence turn-on probe for detecting lipopolysaccharide (LPS) in injectable water sample. Upon addition of LPS, the BT-5 aqueous solution showed a concentration-dependent increase in fluorescence spectra. Moreover, BT-5 displayed a high selectivity to LPS in the presence of polysaccharide, surfactants, cations, anions, and several amino acids that may exist in injectable water samples with a low limit of detection of 120 pM, which is much lower than that of previous reports. The sensing procedure was observed by the naked eye under the 365 nm UV light irradiation. The outstanding sensing performance of BT-5 was demonstrated to originate from the combination of electrostatic and hydrophobic interactions between BT-5 and LPS.