title: Properties of coatings on RFID p-Chips that support plasmonic fluorescence enhancement in bioassays.
abstract: Microtransponders (RFID p-Chips) derivatized with silver island film (SIF) have previously seen success as a platform for the quantification of low-abundance biomolecules in nucleic acid based assays and immunoassays. In this study, we further characterized the morphology of the SIF as well as the polymer matrix enveloping it by scanning electron microscopy (SEM). The polymer was a two-layer silane-based matrix engulfing the p-Chip and SIF. Through a series of SEM and confocal fluorescence microscopy experiments, we found the depth of the polymer matrix to be 1-2 μm. The radiative effects of the SIF/polymer layer were assessed by fluorescence lifetime imaging (FLIM) of p-Chips coated with the polymer to which a fluorophore (Alexa Fluor 555) was conjugated. FLIM images showed an 8.7-fold increase in fluorescence intensity and an increased rate of radiative decay, the latter of which is associated with improved photostability and both of which are linked to plasmonic enhancement by the SIF. Plasmonic enhancement was found to extend uniformly across the p-Chip and, interestingly, to a depth of about 1.2 μm. The substantial depth of enhancement suggests that the SIF/polymer layer constitutes a three-dimensional matrix that is accessible to solvent and small molecules such as fluorescent dyes. Finally, we confirmed that no surface-enhanced Raman scattering is seen from the SIF/polymer combination. The analysis provides a possible mechanism by which the SIF/polymer-coated p-Chips allow a highly sensitive immunoassay and, as a result, leads to an improved bioassay platform.
authors.affiliation: Center for Commercialization of Fluorescence Technologies, Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, TX 76107, USA. ryan.rich@unthsc.edu
authors.forename: Ryan
authors.initials: R
authors.lastname: Rich
authors.forename: Ji
authors.initials: J
authors.lastname: Li
authors.forename: Rafal
authors.initials: R
authors.lastname: Fudala
authors.forename: Zygmunt
authors.initials: Z
authors.lastname: Gryczynski
authors.forename: Ignacy
authors.initials: I
authors.lastname: Gryczynski
authors.forename: Wlodek
authors.initials: W
authors.lastname: Mandecki
mesh_terms: D001681:Biological Assay / Q000295:instrumentation*; D005453:Fluorescence; D007118:Immunoassay; D008855:Microscopy, Electron, Scanning; D011108:Polymers / Q000737:chemistry; D057233:Radio Frequency Identification Device; D012834:Silver / Q000737:chemistry*; D020349:Surface Plasmon Resonance; D013499:Surface Properties
chemical_list: D011108:Polymers; D012834:Silver