Endotoxin or lipopolysaccharide (LPS) is a major constituent of the Gram-negative bacterial cell wall that causes a life-threatening disorder called septicemia resulting from the unregulated activation of the innate immune system. We demonstrate a simple and robust drug-assisted dot blot bioassay for endotoxin detection that can be used right by the critically ill patients' bedside. Target LPS molecules are trapped from serum or water on glass substrates via long-chain alkyls and tagged with reporter gold nanoparticles (NPs) preconjugated to an antibiotic drug called polymyxin B sulfate (PMB). A post-silver-enhancement step enables signal visibility to the bare eye over a wide and clinically relevant concentration range of 50 fg/mL-50 ng/mL, allowing effortless diagnosis of sepsis at various stages, from early sepsis to septic shock.