<p>Lipopolysaccharide (LPS), also known as an endotoxin, poses serious health risks, such as sepsis, shock, and fever. Detecting LPS is important for hemodiafiltration therapy. In this study, an electrochemical LPS sensor with carbon nanotubes (CNTs) and polymyxin B (PmB) was developed for the first time. Layer-by-layer fabrication was done using dispersed CNTs and a PmB solution. LPS selectively bound to sensing elements and hindered redox reaction of markers, causing the peak current to decrease. As the LPS concentration increased, the number of LPS molecules bound to sensing elements increased, and fewer markers could approach the electrode surface. Consequently, the peak current decreased with increasing LPS concentration. The CNTs contribute to enhance the electrochemical current due to marker ion because of theirs high conductivity and catalytic ability. PmB discriminates LPS, and the CNTs enhance the signal arising from this response. The measurement range was 10&#xa0;fg/mL–10&#xa0;ng/mL. This sensor did not respond to other chemicals, such as human serum albumin, glucose, and bicarbonate, present in biological samples. This performance makes it suitable for water quality management of dialysis fluids, helping reduce the workload of clinical engineers. The CNT-based platform can be expanded to detect other targets and has the potential for widespread application in various areas.</p> Graphic abstract <p></p>