Engineering Janus micromotors with WS2 and affinity peptides for turn-on fluorescent sensing of bacterial lipopolysaccharides

Herein we describe an OFF-ON Janus micromotor approach for the fast (5 min) and sensitive determination (limit of detection, 120 pM) of Escherichia coli O111:B4 lipopolysaccharide (LPS) associated with sepsis shock in microliter samples. The OFF-ON strategy relies on the loading of a specifically designed rhodamine-labeled affinity peptide into WS2-Pt-Fe2O3 polycaprolactone Janus micromotors. Specific attachment of the peptide with the WS2 via electrostatic and hydrophobic interactions results in fluorescent quenching, which is subsequently recovered by the detachment of the probe in the presence of the target LPS. Peptide loading into the micmmotor structure increases the overall stability for over 2 months without any change in its properties and excellent analytical performance. No fluorescence recovery is observed in the presence of LPS with a similar structure, illustrating the high selectivity of the protocol, along with quantitative recoveries in human serum and bacteria cultures. The method was validated against the gold standard Limulus Amoebocyte lysate assay in real bacteria culture containing naturally occurring LPS, with similar recoveries in both cases. The micromotors hold great potential to carry out analytical measurements in real-time with small amounts of sample and reagents, allowing for fast detection of deadly toxins with high clinical relevance.