The potential of fluorescence resonance energy transfer (FRET) in a photonic crystal (PC) nanostructured array to enhance the speed and sensitivity of a protein-based immunoassay was tested. Forty-nanometer carboxylated particles conjugated with donor-labeled capture antibodies were trapped by electrophoresis and used as a FRET energy donor. The PC array was able to enhance fluorescent excitation and emission by phase matching. To provide a proof of concept for this FRET-based homogeneous assay on a PC chip, an immunoassay was tested with a simple immunoglobulin G (IgG)-based reaction. A standard curve was generated by testing two different antibody reaction times: 20 min. and 1 min. The results were compared directly to those obtained from a FRET assay that used a modern, high-sensitivity plate reader with a 96-well plate and a reaction time of 1 h. The rabbit-IgG detection limits of the FRET-based homogeneous assay on the PC were 0.001 and 0.1 μg/mL for incubation times of 20 and 1 min, respectively; the sensitivities were 10(3) and 10 times better than the 96-well plate reader, respectively. Thus, FRET on a PC immunoplatform was shown to be a facile, effective, rapid, and sensitive detection technology.

A highly ordered array of T7 bacteriophages was created by the electrophoretic capture of phages onto a nanostructured array with wells that accommodated the phages. Electrophoresis of bacteriophages was achieved by applying a positive potential on an indium tin oxide electrode at the bottom of the nanowells. Nanoscale arrays of phages with different surface densities were obtained by changing the electric field applied to the bottom of the nanowells. The applied voltage was shown to be the critical factor in generating a well-ordered phage array. The number of wells occupied by a phage, and hence the concentration of phages in a sample solution, could be quantified by using a DNA intercalating dye that rapidly stains the T7 phage. The fluorescence signal was enhanced by the intrinsic photonic effect made available by the geometry of the platform. It was shown that the quantification of phages on the array was 6 orders of magnitude better than could be obtained with a fluorescent plate reader. The device opens up the possibility that phages can be detected directly without enrichment or culturing, and by detecting phages that specifically infect bacteria of interest, rapid pathogen detection becomes possible.