Rapid colorimetric lactoferrin-based sandwich immunoassay on cotton swabs for the detection of foodborne pathogenic bacteria

Cotton swab is the conventional swabbing tool that is usually applied for collecting pathogens from contaminated surfaces, followed by cells lysis and DNA extraction before subjecting to genetic analysis. However, such an approach is time consuming as it involves several steps and requires highly trained personnel to perform the experiment. In this study, we developed a new cotton swab-based detection system that involved integrating bacterial collection, preconcentration and detection on Q-tips. The platform is based on a sandwich assay that can detect different pathogens visually by color changes. Lactoferrin-immobilized cotton is used as a general capturing tool to collect various pathogens from surfaces. The presence of particular bacteria is then detected by immersing the cotton in antibodies attached to different colored nanobeads. The target cell is captured between the lactoferrin and specific antibody-conjugated beads which results in certain color development. The effectiveness of this simply fabricated sensor was demonstrated using Salmonella typhimurium, Salmonella enteritidis, Staphylococcus aureus and Campylobacter jejuni. The intensity of the color on the cotton surfaces increased with increasing the concentration of the pathogenic bacteria. The detection limit was as low as 10 cfu/ml for Salmonella typhimurium and Campylobacter jejuni, 100 cfu/ml for Salmonella enteritidis and 100 cfu/ml for Staphylococcus aureus on chicken meat surface. Moreover, this method showed high selectivity and was further confirmed by loop-mediated isothermal amplification (LAMP). The simplicity and the low cost of this colorimetric sensor renders it applicable to a wide range of other pathogens on different surfaces.