Semi-Automated Paper-Based Immunoassay System
At A Glance
Researchers at Colorado State University have developed an inexpensive, reusable 3D-printed manifold to hold and control interchangeable, disposable paper-based devices and perform automated immunoassays. The manifold provides manipulation of the paper-based device for sequential reagent delivery to the sample to perform the immunoassay.
Microfluidic paper-based analytical devices (µPADs) have become a common platform for point-of-care and field-based assays. µPADs are small, portable, inexpensive, easy to dispose of, frequently require no external instrumentation, and can effectively store reagents.
Recently, µPADs have been used to detect multiple foodborne pathogens with the goal of creating a simple screening test. In these works, traditional antibody-based immunoassays, enzymatic detection, and electrochemical methods were adapted for use in µPADs. Although they are a promising technology, µPADs frequently suffer from inadequate sensitivity and high detection limits compared to traditional methods like PCR and ELISA. To improve detection limits and sensitivity in traditional immunoassays, washing steps and signal enhancement reagents are used. However, these steps require timed and sequential delivery of reagents and/or washing agents, which µPADs are not typically designed to do without significant manual intervention from the end user.
By combining a 3D-printed manifold with paper layers we have increased the capabilities of a µPAD without sacrificing user-friendliness. We believe that many of the pitfalls of traditional µPADs may be solved by integrating inexpensive plastic platforms or manifolds like the one described here.
The approach for these immunoassays uses two separate paper-based devices, one to contain reagents, the other to house the sample. Both devices are fabricated by securing paper channels with custom geometries into layers of lamination film with predefined channel regions. The reagent layer consists of equally spaced channels arranged in a radial fashion. Each reagent for the individual steps of an immunoassay is deposited into a separate channel for sequential delivery to the sample.
Reagents can be deposited and dried into the channels in advance, decreasing the steps required by the user at the time of sample analysis. The sample layer of the device consists of a single channel onto which the sample is deposited. The sample channel connects the reagent channel to a large waste pad housed in the reagent layer, providing the volume capacity necessary to perform multistep immunoassays.
The 3D-printed manifold consists of three primary parts to house and manipulate the paper-based devices. The bottom part securely holds the sample layer of the device in position and contains a buffer reservoir to hold and supply buffer for the assay. The center part of the manifold holds the reagent layer of the device and is able to rotate relative to the rest of the manifold. The top part of the manifold provides pressure between the paper channels of the device.
Interfacing the paper-based devices with the 3D-printed manifold and components provides a simple, automated format for users to perform immunoassays. The user must simply rotate the center of the manifold to transport pre-deposited reagents to a sample for each step of the immunoassay.
- Eliminates time-consuming and tedious manual steps
- Detect numerous pathogens, proteins, or biomarkers
- Portable, in-field testing
Carrell, Cody S., et al. “Rotary Manifold for Automating a Paper-Based Salmonella Immunoassay.” RSC Advances, The Royal Society of Chemistry, 17 Sept. 2019, pubs.rsc.org/en/content/articlelanding/2019/ra/c9ra07106g#!divAbstract.
Chuck Henry, Chuck S. Henry