Protein nanoarray made by size-dependent self-assembly for detection of mouse immunoglobulin G and octamer-4

An alternative approach for fabricating a protein array at nanoscale (<100 nm) is suggested with a capability of characterization and/or localization of multiple components on a nanoarray. Basically, fluorescent micro- and nanospheres each conjugated with different proteins are size-dependently self-assembled (SDSA) onto these nanometer wells that were created on the polymethyl methacrylate (PMMA) substrate by electron beam lithography (EBL). Particles of different diameters are added serially, and electrostatically attached to the corresponding wells through electrostatic attraction between the carboxylic groups of the spheres and p-doped silicon substrate underneath the PMMA layer. This SDSA was enhanced by wire-guide manipulation of droplets on the surface containing nanometer wells. Target detection utilizes fluorescence resonance energy transfer (FRET) from fluorescent beads to target (mouse immunoglobulin G = mIgG or Octamer-4 = Oct4) and its antibody bound on the beads. The 180 nm blue beads are conjugated with mIgG to capture anti-mIgG-FITC. The 50 nm green and 100 nm yellow-green beads are conjugated with anti-Oct4 to capture Oct4 peptides; where the secondary anti-Oct4 tagged with phycoerythrin via F(ab)2 fragment is then added to function as an indicator of Oct4 detection. These protein-conjugated particles are added serially from the largest to the smallest and the particles are successfully self-assembled to the respective nanometer wells to achieve sizedependent self-assembly. FRET signals are detected through fluorescence and confocal microscopes, and further confirmed by Fluorolog3 spectrofluorometer. Therefore, SDSA is a valuable approach for the fabrication of multiple components array; and FRET is a useful biorecognition technique for the detection of mIgG, Oct4 or other targets of interest.