Modification of thread-based microfluidic device with polysiloxanes for the development of a sensitive and selective immunoassay

© 2018 Elsevier B.V. We demonstrate that polysiloxanes can be tuned to be partially hydrophilic for manipulating the fluidic flow in the pores of cotton thread-based microfluidic devices. A mixture of methanol and isopropanol was used as a diluent for siloxane precursor, which was included into the thread to enable rapid curing of polysiloxanes for fluidic control and enhance detection sensitivity. Interestingly, twelve-fold diluted polysiloxanes enabled desirable fluidic delay and optimum interaction between the targeted antigen and detection antibody-gold nanoparticles (dAb-AuNPs) in the thread-based immunoassay, generating more antigen-dAb-AuNP complexes that bound to the capture antibody (cAb) at the test zone and achieved signal enhancement (∼10-fold over unmodified device). The phenomenon of fluidic delay was evaluated by mathematical simulation, through which the fluidic movement on the polysiloxanes-coated region was observed and the simulation data was in agreement with the experimental data. This polysiloxanes-modified device could detect Salmonella enterica serotype Enteritidis (as a model analyte) in phosphate buffered saline, spiked whole milk, juice and lettuce with the detection limit of 500, 1000, 1000 and 5000 CFU/mL, respectively, which was comparable to or even more sensitive than the existing immunoassays. This work expands the application of polysiloxanes in the microfluidic devices for biomedical diagnosis, water quality monitoring, and food safety surveillance.