Ultrasensitive and unambiguous bacterial pathogen detection through super selective interactions between multivalent supramolecular immuno-nanoparticles (SINs)

Abstract

Unambiguous, rapid, cost-effective and simple methodologies for the detection of microbial pathogens in environmental and medical samples are vital for effectively controlling infectious diseases. Recently, the daunting task of early identification of pathogens has been addressed by using gold nanoparticles coated with antibodies that have shown to increase the sensitivity of detection several fold. However this usually affects the specificity of detection since background responses due to non-specific interactions also get amplified. In this study we have exploited multivalent supramolecular interactions between antibody-coated gold nanoparticles to achieve super selective detection of pathogenic bacteria. We term these as supramolecular immuno-nanoparticles (SINs) and used them to develop a simple, rapid and cost-effective immuno dot-blot detection method to selectively detect pathogenic bacteria even at extremely low densities (LOD: 50 cells per spot). Furthermore, we performed analytical dot-blot and ELISA assays using the antibodies, both in their free form and as SINs, to gain fundamental insights into the reasons behind the remarkable detection characteristics. We found that the combined effects of steric hindrance, signal amplification and surface density of the SINs resulted in the best detection characteristics in an immuno dot-blot format reported so far. These fundamental insights can be widely applied to improve various multivalent nanoparticle based detection methods.