Shake It or Shrink It: Mass Transport and Kinetics in Surface Bioassays Using Agitation and Microfluidics

TL;DR

This paper explores how transport mechanisms like agitation and microfluidics influence surface bioassays, providing practical guidelines and fundamental insights to optimize assay performance and consistency.

Contribution

It offers an intuitive framework and rules of thumb for understanding and controlling transport effects in surface bioassays, especially in microfluidic systems.

Findings

Transport plays a critical role in assay kinetics.

Microfluidics can improve reagent delivery and reaction uniformity.

Guidelines help optimize assay conditions for better reproducibility.

Abstract

Surface assays, such as ELISA and immunofluorescence, are nothing short of ubiquitous in biotechnology and medical diagnostics today. The development and optimization of these assays generally focuses on three aspects: immobilization chemistry, ligand-receptor interaction and concentrations of ligands, buffers and sample. A fourth aspect, the transport of the analyte to the surface, is more rarely delved into during assay design and analysis. Improving transport is generally limited to the agitation of reagents, a mode of flow generation inherently difficult to control, often resulting in inconsistent reaction kinetics. However, with assay optimization reaching theoretical limits, the role of transport becomes decisive. This perspective develops an intuitive and practical understanding of transport in conventional agitation systems and in microfluidics, the latter underpinning many new life science technologies. We give rules of thumb to guide the user on system behavior, such as advection regimes and shear stress, and derive estimates for relevant quantities that delimit assay parameters. Illustrative cases with examples of experimental results are used to clarify the role of fundamental concepts such as boundary and depletion layers, mass diffusivity or surface tension.