A guide to design, fabricate and apply nanoparticle-based lateral flow immunoassays

by Virginia Greco

A tutorial published in Nature Protocols, authored by researchers of the ICN2 Nanobioelectronics and Biosensors Group led by ICREA Prof. Arben Merkoçi, describes how to design nanoparticle-based lateral flow assays for detecting biomolecules in clinical, biological and environmental samples.

Since their first appearance in the 1970s as fast pregnancy tests, lateral flow assays (LFAs) have found multiple applications in diagnostics, environmental and safety analysis, becoming some of the most used point-of-care sensors for detection of biomolecules and other kinds of particles (such as heavy metals). Their indisputable advantages are their fast response, portability, user-friendly readout, low cost and zero-energy operation.

Thanks to capillary forces, the sample to be analysed flows along a strip, passing through a series of pads with different functionalities. The interaction of the sample with these pads (and, ultimately, of the analyte with specific receptors) leads to the generation of a signal that can be detected either by naked eye or through a smartphone, revealing the presence or absence of a specific biomarker. Despite LFAs’ extreme simplicity of operation for the end-users, though, their design and optimisation is not straightforward, since various interconnected parameters have to be taken into account and tuned for best performance.

Researchers of the ICN2 Nanobioelectronics and Biosensors Group, led by ICREA Prof. Arben Merkoçi, have recently published in Nature Protocols a tutorial to describe how to design nanoparticle-based lateral flow assays for detecting biomolecules in clinical, biological and environmental samples. Dr Claudio Parolo and Dr Amadeo Sena-Torralba are the first authors of this paper, while Prof. Arben Merkoçi is the corresponding one. The tutorial is also signed by Dr Daniel Quesada González, previously a member of Prof. Merkoçi’s group and currently Research and Technological Development Scientist at Paperdrop Diagnostics S.L., a spin-off company founded in 2018 to develop rapid diagnostic tests based on paper microfluidics.

As the design of an efficient LFA strongly depends on the type of sample to be analysed and the molecule to be detected, the tutorial starts off by providing an overview of the different samples that can be used (water, blood, urine, foodstuff, water, soil, and many more) and the specific challenges each of them raises. It continues by explaining how to select and characterise the appropriate bioreceptors for the analyte to detect, which is a crucial step to guarantee the desired sensitivity and specificity of the test. Then, different nanoparticles that can be used for labelling (such as gold nanoparticles and quantum dots) are discussed, relating their characteristics to the available readout techniques.

Following, the tutorial analyses in detail the various physical components of the lateral flow strip — sample pad, conjugate pad, membrane and absorbent pad —, their function in the detection process, and the parameters the developer has to consider when choosing the optimal materials and reagents for the specific target of interest. The assay evaluation and the devices to perform a quantitative analysis are also presented. Further aspects of LFAs developments are covered as well, including costs, patents and regulations. Finally, a detailed step-by-step example procedure for the assembly and operation of an LF strip for detecting Human Immunoglobulin G is provided.

Accompanied by a rich bibliography, many explicative figures and tables, this thorough tutorial aims to guide researchers and developers throughout the entire process of designing, building and operating LFAs for their specific application. Although the target-specific nature of the assay requires fine-tuning of the process to the particular case, this tutorial provides a general roadmap and a useful starting point for developing LFAs. In addition, this Nature protocol may prove very useful nowadays due to the important role that lateral flow immunoassays can play in the COVID-19 related parameters detection, where cheap but efficient devices are particularly needed.

Reference article:

Claudio Parolo, Amadeo Sena-Torralba, José Francisco Bergua, Enric Calucho, Celia Fuentes-Chust, Liming Hu, Lourdes Rivas, Ruslan Álvarez-Diduk, Emily P. Nguyen, Stefano Cinti, Daniel Quesada-González and Arben Merkoçi, Tutorial: design and fabrication of nanoparticle-based lateral-flow immunoassays, Nat Protoc (2020). DOI: 10.1038/s41596-020-0357-x