An electrochemical lipopolysaccharide sensor based on an immobilized Toll-Like Receptor-4

Infections affect millions of people each year and yet methods to ascertain their cause can take more than 24h to be effective. This delay between the presentation with symptoms and the ability to make an informed decision about treatment can have adverse consequences, including death in severe cases. Additionally, pathogen identification is a concern for public safety amid the growing threat of bioterrorism. Developing a detection system based on the immune system offers the advantage of broad specificity, while still remaining pertinent to human health. In this work, human Toll-Like Receptor-4 (TLR-4), a protein responsible for detecting lipopolysaccharide (LPS) of Gram-negative bacteria, was immobilized on both a large area and micro gold electrode via the tethering interaction of a modified Self-Assembled Monolayer (mSAM). In response to varying concentrations of its target, the protein-electrode combination showed a logarithmically proportional increased resistance to charge transfer from a solution-based redox probe, due to the formation of TLR-4 protein dimers. It also demonstrated excellent sensitivity to trace levels of Gram-negative bacteria, while remaining insensitive to both Gram-positive and viral challenges. Further characterization of our mSAM revealed that maintaining the appropriate receptor orientation on the electrode surface, mimicking TLR-4's role in a cellular context, was essential in producing a responsive sensor.