4.7.4. Microfluidics and nanobarcodes

With the aim of developing assays that are highly amenable for automation and point-of-care usage with the ability to concomitantly detect many analytes that are prepared in minute volumes with very high sensitivity, technologies such as microfluidics and nanobarcodes are implemented as bioassays for many molecules including the detection of autoantibodies in autoimmune diseases [112, 114, 115]. These assays are not yet implemented in clinical use, but they are highly promising as near-future diagnostics.

Microfluidics (also known as lab-on-a-chip microtechnologies) from its name is a technology that involves the analysis of ultra-low amounts of sample that are applied into specific devices that are fabricated to be in tens to hundreds of micrometers in dimensions [112]. These devices can be made in different configurations such as channels, pumps, pipes, or valves. The technology of microfluidics makes use of the flow characteristics of fluids in such micro-sized channels such as laminar flow and increased surface tension and capillary forces to move the sample through the microdevice [116]. In the detection of autoantibodies, the walls of such microdevices are coated with an array of antigens, and sample containing autoantibodies is applied to flow through the microdevice where immobilized antigens catch their respective antigens. A washing step is then applied to remove unbound antibodies followed by the application of a labeled secondary antibody, and signal can be detected by specific detectors [112, 114].

Nanobarcodes fall under the bigger science of nanotechnology in which systems, devices, or materials are fabricated in the nano-range to render them new and enhanced properties [117]. Unlike microfluidics that are fabricated at the micron scale, nanobarcodes are made even smaller to the nanoscale [117]. In the detection of autoantibodies, nanobarcodes consist of different stripes where each stripe is composed of a different metal such as gold, silver, platinum, or nickel that are electroplated into templates [115]. Different antigens are coupled to each metal stripe which are then incubated with the serum sample allowing the binding of each autoantibody to its respective coupled antigen. Detection of immune complexes is achieved via the addition of secondary antibody that is fluorescently labeled, and different antigens can be identified by fluorescence microscopy through the differential reflectivity of each stripe creating a pattern that resembles that of a barcode [112, 115, 117].

Microfluidics and nanobarcodes offer many advantages including the application of minute amounts of the sample and reagents which reduce costs and minimize chemical waste. Moreover, these devices are amenable to complete automation and maybe well applied as point-ofcare diagnostics without the need of specialized labs and technical skills. In addition, they produce data that allow simultaneous comparison of the different analytes and at the same time reliable due to the inclusion of multiple internal controls [112, 115, 116].
