Protein microarrays are widely used tools for diagnostic biomarker analysis, with proven utility in such varied fields of human medicine as for instance autoimmunity, allergy, infection and cancer [1
]. In particular, the ability of protein microarrays to simultaneously determine presence or levels of a large number of biomolecules is useful as a means to screen a clinical sample for a variety of different conditions such as cancers or autoimmune diseases that have not yet started to manifest as symptoms or other detectable signs of disease [2
], or it can serve to refine the resolution in the differentiation between for instance infections from closely related bacterial hosts [3
]. Further, protein microarrays may improve the diagnostic accuracy in cancer diagnosis [4
]. As all the individual microspot assays simultaneously taking place on a microarray are directed to the exact same sample, the potential variability arising from aliquot preparations for the same number of simplex-assays is also conveniently avoided.
The assay procedures for protein microarrays are low- to moderately labor-intensive, and may due to the ambient-analyte conditions governing the microspot assay dynamics offer excellent sensitivity on par with ELISAs [1
]. However, due to the many assay steps involved and the required convective mixing in the sample incubation step, microarray assays are typically carried out manually, requiring skilled personnel and well-equipped laboratories. Further, as fluorescent probes remain the preferred choice for detection due to excellent sensitivity and high dynamic range, expensive and bulky laser-equipped high-end scanners are usually needed.
Manual handling and advanced detection strategies result in assay times normally spanning several hours and consequently current microarray technologies are not well suited for mobile, on-site or point of care applications. While it is likely that a large proportion of microarray analyses could preferentially continue to be performed within advanced health care sites such as hospitals or centralized laboratories, portable microarray solutions may support more rapid clinical decision making in emergency situations in the field or in such areas where little healthcare infrastructure exists. Further, point of care microarray tests might serve to relieve health care resources when patients or care-givers are able to conduct regular testing themselves. Finally, such portable tests could facilitate those unable to go to a hospital or health care point for testing [5
While there is a wide variety of simple portable tests commercially available, including for instance rapid tests for sexually transmitted diseases, cardiovascular disease and allergies, such tests are typically simplex or low-plex, with limited quantitative ability and sensitivity, and may further suffer in diagnostic accuracy [6
]. Thus, considering the great advances made in diagnostic protein microarrays, we believe that there exists a major potential health care benefit if microarray technologies could be made amenable for portable, rapid point-of-care use.
A considerable hurdle for creating portable, easy to use planar microarray solutions appears to be the accommodation of many sequential assay steps on-chip, as well as the need for comprehensive sample mixing in order to avoid long assay times due to large diffusion coefficients of protein biomarkers. These challenges are largely avoided in immunochromatographic/lateral flow-based tests, and to this end we previously demonstrated the feasibility of combining a lateral flow/dipstick assay framework commonly used in simplex/low-plex rapid tests with protein microarray patterning for rapid and accurate determination of levels of bovine IgG raised towards mycoplasma infection [7
] using a cell phone digital camera or consumer table top scanner for array imaging.
In this paper, we expand the concept into a general high-plexed lateral flow protein microarray (LFM) strategy, with 384 protein fragments (approximately 80–100 aa) [8
] immobilized in a 24 × 16 microarray pattern on nitrocellulose. The protein fragments are a subset of antigens used for the large-scale generation of monospecific antibodies within the Human Protein Atlas (HPA) [9
] where the aim is to by 2015 generate a set of highly specific antibody binders for the complete human proteome. In the HPA, bioinformatically designed protein fragments are employed as immunogens, as well as ligands in the subsequent affinity purification and quality control/validation of the generated antibody reagents. Together with the obvious benefit of providing reagents for determining presence or levels of virtually any expressed human protein in tissues or body fluids, there is ongoing work exploring the potential of using the protein immunogens as affinity binders for detection of disease-specific antibody populations [10
]. Thus, investigating alternative microarray assay formats employing protein immunogens as affinity binders could result in improved strategies for quality control of raised antibodies as well as in novel methods for diagnostic antigen microarray tests.
In this work, by employing a prototype lateral flow protein microarray device, we were able to accurately determine levels of 26 individual HPA antibodies, as well as up to 8 concurrent specific IgG analytes in approximately 10 min total assay time. We argue that: (a) the demonstrated concordance with an established glass/fluorescence microarray assay; (b) the simplicity of the assay procedure drawing from the benefits of common lateral flow/dipstick tests; (c) the highly multiplexed capacity of the assay; (d) the short assay time; and (e) the convenient read-out options, make the presented assay framework an interesting tool for rapid quality control of raised antibody reagents, and may further find use in translating the capabilities of protein microarrays to point of care/low resource settings.