Sub Picogram Detection of Interleukin 6 in Complex Biofluids Using Lubricant Infused Surface Technology

Overexpression of interleukin 6 (IL-6) in human blood could indicate the severity of many medical conditions such as inflammatory diseases, infections, and different types of cancer including lung, colorectal, prostate, and breast cancers. More importantly, in patients with COVID-19, the risk of respiratory failure could be examined via measuring the level of IL-6 expression. Early diagnosis of the aforementioned diseases requires precise detection of IL-6 at very low concentrations (≤5 pg mL-1). While different biosensing approaches such as electrochemical methods, chemiluminescence immunoassays, and immunofluorescence assays (IFA) have shown satisfactory limit of detections (LODs) for IL-6, they could only perform well in buffer or processed serum, and their sensitivities are significantly reduced in more complex biofluids such as human whole plasma or blood. Here, we introduce a novel IFA platform capable of detecting IL-6 in human whole plasma with an LOD of 0.5 pg mL-1 which is significantly lower than the reported LODs in buffer and plasma via IFA methods. The new IFA system comprises IL-6 capture antibodies covalently micropatterned on a lubricant infused matrix. The lubricant infused surface coating that is utilized in our system can effectively supress non-specific adsorption of all biomolecules, thereby diminishing the background noise and enhancing the sensitivity of the biosensor in complex biofluids. The micro-sized islands of the IL-6 capture antibodies throughout the lubricated surface provide a large number of sample analytes to be measured for high throughput purposes. Moreover, we have developed a new type of bioink in which the capture antibodies are conjugated with an epoxy-based silane coupling agent allowing for covalently attachment of the capture antibodies to the fluorosilanized surface via microcontact printing technique. In addition, the assay is performed on low-cost poly(methyl methacrylate) (PMMA) substrate using simple sandwich-based ELISA.