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Comparison of blocking reagents for antibody microarray-based immunoassays on glass and paper membrane substrates. Anal Bioanal Chem 2023; 415:1967-1977. [PMID: 36829042 DOI: 10.1007/s00216-023-04614-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 02/14/2023] [Accepted: 02/17/2023] [Indexed: 02/26/2023]
Abstract
Background noise due to nonspecific binding of biomolecules on the assay substrates is one of the most common challenges that limits the sensitivity of microarray-based immunoassays. Background signal intensity usually increases when complex biological fluids are used because they have a combination of molecules and vesicles that can adsorb onto substrate surfaces. Blocking strategies coupled with surface chemistries can reduce such nonspecific binding and improve assay sensitivity. In this paper, we conducted a systematic optimization of blocking strategies on a variety of commonly used substrates for protein measurement in complex biofluids. Four blocking strategies (BSA, non-fat milk, PEG, and a protein-free solution) coupled with four surface chemistries (3-glycidoxypropyltrimethoxysilane (GPS), poly-L-lysine (PLL), aminoalkylsilane (AAS), and nitrocellulose (NC)) were studied for their effect on background, microspot, and net signal intensities. We have also explored the effect that these blocking strategies have when proteins in complex samples (plasma, serum, cell culture media, and EV lysate) are measured. Irregular spot morphology could affect signal extraction using automated software. We found that the microspots with the best morphology were the ones printed on GPS glass surfaces for all immunoassays. On NC membrane, the protein-based blocking strategies yielded the highest net fluorescent intensity with the antigen contained in PBS, plasma, serum, and serum-free cell culture media. Differently, with EV lysate samples, Pierce™ protein-free blocker yielded the best net signal intensity on both GPS and NC surfaces. The choice of blocking strategies highly depends on the substrate. Moreover, the findings discovered in this study are not limited to microarray-based immunoassays but can provide insights for other assay formats.
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Bueno-Alejo C, Santana Vega M, Chaplin AK, Farrow C, Axer A, Burley GA, Dominguez C, Kara H, Paschalis V, Tubasum S, Eperon IC, Clark AW, Hudson AJ. Surface Passivation with a Perfluoroalkane Brush Improves the Precision of Single-Molecule Measurements. ACS APPLIED MATERIALS & INTERFACES 2022; 14:49604-49616. [PMID: 36306432 PMCID: PMC9650645 DOI: 10.1021/acsami.2c16647] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 10/17/2022] [Indexed: 06/16/2023]
Abstract
Single-molecule imaging is invaluable for investigating the heterogeneous behavior and interactions of biological molecules. However, an impediment to precise sampling of single molecules is the irreversible adsorption of components onto the surfaces of cover glasses. This causes continuous changes in the concentrations of different molecules dissolved or suspended in the aqueous phase from the moment a sample is dispensed, which will shift, over time, the position of chemical equilibria between monomeric and multimeric components. Interferometric scattering microscopy (iSCAT) is a technique in the single-molecule toolkit that has the capability to detect unlabeled proteins and protein complexes both as they adsorb onto and desorb from a glass surface. Here, we examine the reversible and irreversible interactions between a number of different proteins and glass via analysis of the adsorption and desorption of protein at the single-molecule level. Furthermore, we present a method for surface passivation that virtually eliminates irreversible adsorption while still ensuring the residence time of molecules on surfaces is sufficient for detection of adsorption by iSCAT. By grafting high-density perfluoroalkane brushes on cover-glass surfaces, we observe approximately equal numbers of adsorption and desorption events for proteins at the measurement surface (±1%). The fluorous-aqueous interface also prevents the kinetic trapping of protein complexes and assists in establishing a thermodynamic equilibrium between monomeric and multimeric components. This surface passivation approach is valuable for in vitro single-molecule experiments using iSCAT microscopy because it allows for continuous monitoring of adsorption and desorption of protein without either a decline in detection events or a change in sample composition due to the irreversible binding of protein to surfaces.
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Affiliation(s)
- Carlos
J. Bueno-Alejo
- School
of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Marina Santana Vega
- School
of Engineering, Advanced Research Centre, University of Glasgow, 11 Chapel Lane, Glasgow G11 6EW, United Kingdom
| | - Amanda K. Chaplin
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
- Department
of Molecular and Cellular Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Chloe Farrow
- School
of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Alexander Axer
- Strathclyde
Centre for Molecular Bioscience & Department of Pure & Applied
Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, United Kingdom
| | - Glenn A. Burley
- Strathclyde
Centre for Molecular Bioscience & Department of Pure & Applied
Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, United Kingdom
| | - Cyril Dominguez
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
- Department
of Molecular and Cellular Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Hesna Kara
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
- Department
of Molecular and Cellular Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Vasileios Paschalis
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
- Department
of Molecular and Cellular Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Sumera Tubasum
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
- Department
of Molecular and Cellular Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Ian C. Eperon
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
- Department
of Molecular and Cellular Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
| | - Alasdair W. Clark
- School
of Engineering, Advanced Research Centre, University of Glasgow, 11 Chapel Lane, Glasgow G11 6EW, United Kingdom
| | - Andrew J. Hudson
- School
of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom
- Leicester
Institute of Structural & Chemical Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 7HB, United Kingdom
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