Naked-eye, low-cost detection of endotoxin using oil-coated structured surfaces

Overview

This solution offers a low-cost, equipment-free method for detecting endotoxin (lipopolysaccharide, a fever-inducing contaminant from Gram-negative bacteria) using specially engineered surfaces and simple water droplets. The platform concentrates amphiphilic molecules (surfactants and endotoxins) within the contact line of droplets placed on oil-coated, chemically functionalized, topographically structured surfaces. By observing droplet mobility with the naked eye, users can determine amphiphile or endotoxin concentration and even sort droplets by concentration. The approach is designed to translate into a point-of-care detection kit usable by people without laboratory training, addressing a critical need in pharmaceutical manufacturing, medical device testing, and clinical diagnostics where rapid endotoxin screening is essential.

Technical specifications

• Detection principle: Amphiphiles (including endotoxin and its lipid A component) are selectively concentrated within the contact line of water droplets on oil-coated structured surfaces, altering droplet mobility in a concentration-dependent manner
• Sensitivity: Naked-eye detection of synthetic surfactants down to ~100 nM (five orders of magnitude below critical micelle concentration), and endotoxin detection at ~2.5 EU/mL (~0.2–0.5 ng/mL)
• Specificity: Control experiments show response to lipid A at ~0.2 ng/mL but not to polysaccharides at ~10 µg/mL, indicating selective detection of the toxic lipid component
• Sorting capability: Positionally-dependent pinning forces on the chip surface allow aqueous droplets to be physically sorted by amphiphile or endotoxin concentration
• Sample volume: 2 µL droplets
• Substrate flexibility: Ongoing work targets plain glass (e.g., microscope slides), paper, and plastic as low-cost substrates
• No specialized equipment required: Readout is visual droplet mobility assessment

Technology readiness level

The technology has been validated in laboratory experiments demonstrating detection and sorting of both synthetic surfactant (SDS) and endotoxin droplets. Future validation efforts (planned over one year) will focus on improving sensitivity to 0.25 EU/mL through surface chemistry and topography optimization, and on demonstrating the platform on low-cost substrates such as plain glass, paper, and plastic for point-of-care use. The research team is actively seeking industry partnership to provide endotoxin sources, funding for personnel and materials, and pathways toward commercialization.