title: Enhancement of performance in porous bead-based microchip sensors: Effects of chip geometry on bio-agent capture.
abstract: Measuring low concentrations of clinically-important biomarkers using porous bead-based lab-on-a-chip (LOC) platforms is critical for the successful implementation of point-of-care (POC) devices. One way to meet this objective is to optimize the geometry of the bead holder, referred to here as a micro-container. In this work, two geometric micro-containers were explored, the inverted pyramid frustum (PF) and the inverted clipped pyramid frustum (CPF). Finite element models of this bead array assay system were developed to optimize the micro-container and bead geometries for increased pressure, to increase analyte capture in porous bead-based fluorescence immunoassays. Custom micro-milled micro-container structures containing an inverted CPF geometry resulted in a 28% reduction in flow-through regions from traditional anisotropically-etched pyramidal geometry derived from Si-111 termination layers. This novel "reduced flow-through" design resulted in a 33% increase in analyte penetration into the bead and twofold increase in fluorescence signal intensity as demonstrated with C-Reactive Protein (CRP) antigen, an important biomarker of inflammation. A consequent twofold decrease in the limit of detection (LOD) and the limit of quantification (LOQ) of a proof-of-concept assay for the free isoform of Prostate-Specific Antigen (free PSA), an important biomarker for prostate cancer detection, is also presented. Furthermore, a 53% decrease in the bead diameter is shown to result in a 160% increase in pressure and 2.5-fold increase in signal, as estimated by COMSOL models and confirmed experimentally by epi-fluorescence microscopy. Such optimizations of the bead micro-container and bead geometries have the potential to significantly reduce the LODs and reagent costs for spatially programmed bead-based assay systems of this type.
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77005.
authors.forename: Eliona
authors.initials: E
authors.lastname: Kulla
authors.affiliation: Department of Bioengineering, Rice University, Houston, Texas 77005.
authors.forename: Jie
authors.initials: J
authors.lastname: Chou
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77005 ; Department of Bioengineering, Rice University, Houston, Texas 77005.
authors.forename: Glennon
authors.initials: G
authors.lastname: Simmons
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77005 ; Department of Bioengineering, Rice University, Houston, Texas 77005.
authors.forename: Jorge
authors.initials: J
authors.lastname: Wong
authors.affiliation: Department of Bioengineering, Rice University, Houston, Texas 77005.
authors.forename: Michael P
authors.initials: MP
authors.lastname: McRae
authors.affiliation: Department of Bioengineering, Rice University, Houston, Texas 77005.
authors.forename: Rushi
authors.initials: R
authors.lastname: Patel
authors.affiliation: The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Pierre N
authors.initials: PN
authors.lastname: Floriano
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77005 ; Department of Bioengineering, Rice University, Houston, Texas 77005.
authors.forename: Nicolaos
authors.initials: N
authors.lastname: Christodoulides
authors.affiliation: Urology, University of Texas Health Science Center at San Antonio, Texas 78229.
authors.forename: Robin J
authors.initials: RJ
authors.lastname: Leach
authors.affiliation: Urology, University of Texas Health Science Center at San Antonio, Texas 78229.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Thompson
authors.affiliation: Department of Chemistry, Rice University, Houston, Texas 77005 ; Department of Bioengineering, Rice University, Houston, Texas 77005.
authors.forename: John T
authors.initials: JT
authors.lastname: McDevitt
keywords: Lab-on-a-chip; beads; biochips; geometry; hot embossing; immunoassays; microfluidics; optimization; point-of-care; prostate specific antigen; thermoplastics