title: Flow-through vs flow-over: analysis of transport and binding in nanohole array plasmonic biosensors.
abstract: We quantify the efficacy of flow-through nanohole sensing, as compared to the established flow-over format, through scaling analysis and numerical simulation. Nanohole arrays represent a growing niche within surface plasmon resonance-based sensing methods, and employing the nanoholes as nanochannels can enhance transport and analytical response. The additional benefit offered by flow-through operation is, however, a complex function of operating parameters and application-specific binding chemistry. Compared here are flow-over sensors and flow-through nanohole array sensors with equivalent sensing area, where the nanohole array sensing area is taken as the inner-walls of the nanoholes. The footprints of the sensors are similar (e.g., a square 20 μm wide flow-over sensor has an equivalent sensing area as a square 30 μm wide array of 300 nm diameter nanoholes with 450 nm periodicity in a 100 nm thick gold film). Considering transport alone, an analysis here shows that given equivalent sensing area and flow rate the flow-through nanohole format enables greatly increased flux of analytes to the sensing surface (e.g., 40-fold for the case of Q = 10 nL/min). Including both transport and binding kinetics, a computational model, validated by experimental data, provides guidelines for performance as a function of binding time constant, analyte diffusivity, and running parameters. For common binding kinetics and analytes, flow-through nanohole arrays offer ∼10-fold improvement in response time, with a maximum of 20-fold improvement for small biomolecules with rapid kinetics.
authors.affiliation: Mechanical Engineering, University of Victoria, Victoria, BC, Canada.
authors.forename: Carlos
authors.initials: C
authors.lastname: Escobedo
authors.forename: Alexandre G
authors.initials: AG
authors.lastname: Brolo
authors.forename: Reuven
authors.initials: R
authors.lastname: Gordon
authors.forename: David
authors.initials: D
authors.lastname: Sinton
mesh_terms: D001692:Biological Transport; D015374:Biosensing Techniques / Q000295:instrumentation*; D004867:Equipment Design; D007700:Kinetics; D046228:Microarray Analysis / Q000295:instrumentation*; D058608:Nanopores; D011485:Protein Binding; D012212:Rheology; D020349:Surface Plasmon Resonance