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Microcapsules as assay compartments formed through layer-by-layer deposition

Alorabi, Ali Q.; Tarn, Mark D.; Thomas, Martina; Paunov, Vesselin N.; Pamme, Nicole


Ali Q. Alorabi

Mark D. Tarn

Martina Thomas

Vesselin N. Paunov

Nicole Pamme


We investigate the potential of using microcapsules, generated through layer-by-layer assembly, as reaction compartments for bioassays. A streptavidin-biotin and an esterase-fluorescein diacetate (FDA) assay were employed for proof-of-concept. Streptavidin was incorporated into the microcapsules via two methods: (i) physical adsorption onto MnCO3 microcrystal templates or (ii) co-precipitation with CaCO3 to form mixed microcrystals. The streptavidin-loaded template microparticles were then coated with five bi-layers of polyelectrolytes (polystyrene sulfonate/polyalylamine hydrochloride) (PAH/PSS)5 and the templated cores were dissolved using EDTA to form polyelectrolyte microcapsules loaded with streptavidin. Streptavidin loading of around 77 mg streptavidin per mol of CaCO3 was achieved using the co-precipitation method, compared to 5.1 mg streptavidin per mol of MnCO3 using physical adsorption onto the manganese carbonate crystal surface. The microencapsulated streptavidin was allowed to bind to an analyte which was able to freely diffuse through the polyelectrolyte shell from the aqueous media. Biotin-4-fluorescein was added to the streptavidin-loaded microcapsules, with streptavidin-free capsules serving as the control sample. It was found that both types of microcapsules exhibited a similar fluorescence signal intensity, likely due to non-specific binding of biotin-4-fluorescein to charged groups on the polyelectrolyte shell. Therefore, an alternative esterase-FDA assay was investigated as fluorescence is only produced when FDA penetrates the capsule shell and reacts with the esterase enzyme inside which leads to its hydrolysis. Esterase was loaded into the LbL capsules templated on CaCO3 via co-precipitation. FDA was added to both the esterase-loaded capsules and esterase-free capsules. It was found that the capsules containing esterase fluoresced, while the esterase-free capsules did not. This indicates that the hydrolysis reaction of FDA with esterase occurred inside the LbL microcapsules. These experiments demonstrate the potential of compartmentalised assays to be carried out inside microcapsules which could be applied in complex matrices or in multiplexing experiments, wherein different barcoded microcapsules contain different reagents to provide independent readouts without interference from larger biomolecules present in the surrounding media.


Alorabi, A. Q., Tarn, M. D., Thomas, M., Paunov, V. N., & Pamme, N. (2018). Microcapsules as assay compartments formed through layer-by-layer deposition. Analytical Methods, 10(44), 5335-5340.

Journal Article Type Article
Acceptance Date Oct 25, 2018
Online Publication Date Oct 26, 2018
Publication Date Nov 28, 2018
Deposit Date Jan 11, 2019
Publicly Available Date Oct 27, 2022
Journal Analytical Methods
Print ISSN 1759-9660
Electronic ISSN 1759-9679
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 10
Issue 44
Pages 5335-5340
Keywords General Engineering; Analytical Chemistry; General Chemical Engineering
Public URL
Publisher URL!divAbstract
Additional Information : This document is Similarity Check deposited; : Supplementary Information; : Mark D. Tarn (ORCID); : Mark D. Tarn (ResearcherID); : Vesselin N. Paunov (ORCID); : Vesselin N. Paunov (ResearcherID); : Nicole Pamme (ORCID); : Nicole Pamme (ResearcherID); : Single-blind; : Received 13 September 2018; Accepted 25 October 2018; Accepted Manuscript published 26 October 2018; Advance Article published 6 November 2018


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