Lab-on-a-Bubble Surface Enhanced Raman Indirect Immunoassay for Cholera

Abstract

We describe a novel sandwich assay based on surface enhanced Raman scattering (SERS) comprised of buoyant silica microspheres coated with antibodies against the β subunit of the cholera toxin (CT), and gold nanoparticles tagged with a Raman reporter, shelled with silica and coated with antibodies against the β subunit of the CT. Together these components couple to form a sandwich which, after incubation, floats on the surface of the sample. The buoyant silica microparticle/nanoparticle reporter combination has been coined a lab on a bubble (LoB). LoB materials may provide a platform for rapid detection of antigen in solution and offers advantages over lateral flow or magnetic pull-down assays. The Raman reporter provides a unique and intense signal to indicate a positive analysis. Our limit of detection for the β subunit of the CT in a buffer based system is 1100 ng.

Novel One-pot Fabrication of Lab-on-a-Bubble@Ag Substrate without Coupling-agent for Surface Enhanced Raman Scattering

“…LoBs@APTES@Ag: LoBs@APTES@Ag was prepared by the method reported by Schmit et al19. LoBs were first activated by APTES.…”

“…The LoB material is prepared by coating Au or Ag NPs on hollow buoyant SiO 2 microspheres by using a silane coupling agent such as aminopropyltriethoxysilane (APTES). The LoB concept is centered on low-density microspheres that utilize buoyant force to drive assay separation, while the metallic NPs on the buoyant particles act as SERS nanosensors19. LoBs@APTES@Ag substrates are indifferent of Brownian movement, and serve as a convenient platform to directly detect the target molecules in solution, without draining water.…”

Dynamic Surface Enhanced Raman Spectroscopy (SERS): Extracting SERS from Normal Raman Scattering

“…10,12 Direct SERS assays are commonly reported for chemical analysis and are also affected by the degree of aggregation in the sample. Knowledge of the site of adsorption and the signal from strongly enhancing sites is valuable for assay development.…”

Review of SERS Substrates for Chemical Sensing

“…Two approaches have been taken to make single-use, diposable substrates that can be dispersed through a sample. One approach is to immobilize Ag or Au nanpoparticles on either solid [66] or hollow [158,159,160] aminated silica beads, the latter referred to as ‘lab-on-a-bubble’. The other approach immobilizes Ag or Au nanoparticles on the surface of aminated magnetic beads to create capture matrices [9,23,24,161].…”