Immunological diagnostics were the first to be adopted in a disposable point-of-care format and are still the leading type of microfluidic diagnostic today.

Microfluidic immunological diagnostics can often reduce the assay to just a few process steps allowing rapid results with little user interaction. This can result in very low cost, simple to use devices. That being said, achieving these elegant solutions still requires significant expertise.

One excellent illustration of this is the lateral flow assay format that has been well adopted. Despite the potential simplicity of this type of assay, tight controls are still required to ensure that the antibodies used are preserved in a stable condition and that reagents are introduced in a repeatable, controlled fashion.

Where quantitative results or multiple targets are required, multiple reaction sites and controls must be used which calls for greater complexity in implementation. Microfluidics enables this increased complexity and extends this simple approach to a powerful and flexible suite of diagnostic tools.

In the classic sandwich immunoassay, a capture antibody is used to immobilise the target analyte in the specimen. The specimen must be prepared on a cartridge and the target introduced over the capture surface at a flow rate appropriate to the protein binding kinetics. A detection antibody is then introduced which is typically labelled to allow detection by optical, magnetic, electrochemical or mass sensing methods.

Whilst microfluidic immunological diagnostics can produce simple, elegant end products it is important to note that achieving this simplicity takes significant skill, knowledge and experience.