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.

Enhancing the Sensitivity of Lateral Flow Immunoassay by Magnetic Enrichment Using Multifunctional Nanocomposite Probes

“…The number fraction (%) of CRPAb that captured CRP (η) at equilibrium can then be calculated by: where K D = k d / k a (M) is the dissociation constant. K D for the CRP–CRPAb binding interactions has been reported to be 10 –13 mol/mL ( k a = 10 5 M –1 ·s –1 and k d = 10 –5 s –1 ) …”

“…The ratios of η t = 600 to η ∞ were calculated to be 0.3 and 0.1 for V s = 10 and 40, respectively, which also agreed with the experimental observations. Although both k a and k d were 2.5 times higher than those in ref , the values seem to be quite reasonable. In addition, K D remained 10 –13 mol/mL, and thus, the fitting results shown in Figure a,b were not significantly affected by changes of k a and k d .…”

Advanced ELISA-like Biosensing Based on Ultralarge-Pore Silica Microbeads

“…4 On the contrary, the employment of threedimensional (3D) substrates, such as porous materials, would offer the opportunity to overcome or mitigate these limitations. 5 Indeed, the larger exposed surface area would allow increasing the number of available immobilization sites and consequently the loading efficiency. 6 Furthermore, by using a porous particle as a capturing 3D substrate, the kinetics involved in the substrate−analyte interaction is more similar to the binding of two free molecules in the solution, 7 thus reducing the drawbacks connected to the diffusion-limited binding kinetics.…”

“…Unfortunately, two relevant constraints characterize this technique: the small surface area and the diffusion-limited binding kinetics. , In most cases, these issues and the need for time-consuming amplification strategies to reach a low limit of detection (LOD) are linked . On the contrary, the employment of three-dimensional (3D) substrates, such as porous materials, would offer the opportunity to overcome or mitigate these limitations . Indeed, the larger exposed surface area would allow increasing the number of available immobilization sites and consequently the loading efficiency .…”

Transport of biomolecules to binding partners displayed on the surface of microbeads arrayed in traps in a microfluidic cell

“…As a result, diffusive transport is hindered, and one solution which is proposed is to create drains in the wells to enhance convection around the microbead. [25][26][27] The trapping geometry studied here uses an aperture at the back end to accomplish the same goal (as well as providing a gap between the microbead and the top surface of the channel), and is much easier to implement. Another method for constructing a microbead array/probe library in a microfluidic cell is to place the functionalized microbeads in shallow wells arrayed at the bottom of the channel, and then place the channel top on the microbead array.…”