Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis

In developing countries, the most common diagnostic method for tuberculosis (TB) is microscopic examination sputum smears. Current assessment requires time-intensive inspection across the microscope slide area, and this contributes to its poor diagnostic sensitivity of ≈50%. Spatially concentrating...

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Autores principales:	Stephanie I. Pearlman, Eric M. Tang, Yuankai K. Tao, Frederick R. Haselton
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	tuberculosis sputum smear microscopy point-of-care diagnosis low-resource Marangoni flow Medicine (General) R5-920
Acceso en línea:	https://doaj.org/article/d7a60ff1d9b74e4588ae2c1896b01425
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spelling	oai:doaj.org-article:d7a60ff1d9b74e4588ae2c1896b014252021-11-25T17:22:07ZControlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis10.3390/diagnostics111121552075-4418https://doaj.org/article/d7a60ff1d9b74e4588ae2c1896b014252021-11-01T00:00:00Zhttps://www.mdpi.com/2075-4418/11/11/2155https://doaj.org/toc/2075-4418In developing countries, the most common diagnostic method for tuberculosis (TB) is microscopic examination sputum smears. Current assessment requires time-intensive inspection across the microscope slide area, and this contributes to its poor diagnostic sensitivity of ≈50%. Spatially concentrating TB bacteria in a smaller area is one potential approach to improve visual detection and potentially increase sensitivity. We hypothesized that a combination of magnetic concentration and induced droplet Marangoni flow would spatially concentrate <i>Mycobacterium tuberculosis</i> on the slide surface by preferential deposition of beads and TB–bead complexes in the center of an evaporating droplet. To this end, slide substrate and droplet solvent thermal conductivities and solvent surface tension, variables known to impact microfluidic flow patterns in evaporating droplets, were varied to select the most appropriate slide surface coating. Optimization in a model system used goniometry, optical coherence tomography, and microscope images of the final deposition pattern to observe the droplet flows and maximize central deposition of 1 μm fluorescent polystyrene particles and 200 nm nanoparticles (NPs) in 2 μL droplets. Rain-X<sup>®</sup> polysiloxane glass coating was identified as the best substrate material, with a PBS-Tween droplet solvent. The use of smaller, 200 nm magnetic NPs instead of larger 1 μm beads allowed for bright field imaging of bacteria. Using these optimized components, we compared standard smear methods to the Marangoni-based spatial concentration system, which was paired with magnetic enrichment using iron oxide NPs, isolating <i>M. bovis</i> BCG (BCG) from samples containing 0 and 10<sup>3</sup> to 10<sup>6</sup> bacilli/mL. Compared to standard smear preparation, paired analysis demonstrated a combined volumetric and spatial sample enrichment of 100-fold. With further refinement, this magnetic/Marangoni flow concentration approach is expected to improve whole-pathogen microscopy-based diagnosis of TB and other infectious diseases.Stephanie I. PearlmanEric M. TangYuankai K. TaoFrederick R. HaseltonMDPI AGarticletuberculosissputum smearmicroscopypoint-of-care diagnosislow-resourceMarangoni flowMedicine (General)R5-920ENDiagnostics, Vol 11, Iss 2155, p 2155 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	tuberculosis sputum smear microscopy point-of-care diagnosis low-resource Marangoni flow Medicine (General) R5-920
spellingShingle	tuberculosis sputum smear microscopy point-of-care diagnosis low-resource Marangoni flow Medicine (General) R5-920 Stephanie I. Pearlman Eric M. Tang Yuankai K. Tao Frederick R. Haselton Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis
description	In developing countries, the most common diagnostic method for tuberculosis (TB) is microscopic examination sputum smears. Current assessment requires time-intensive inspection across the microscope slide area, and this contributes to its poor diagnostic sensitivity of ≈50%. Spatially concentrating TB bacteria in a smaller area is one potential approach to improve visual detection and potentially increase sensitivity. We hypothesized that a combination of magnetic concentration and induced droplet Marangoni flow would spatially concentrate <i>Mycobacterium tuberculosis</i> on the slide surface by preferential deposition of beads and TB–bead complexes in the center of an evaporating droplet. To this end, slide substrate and droplet solvent thermal conductivities and solvent surface tension, variables known to impact microfluidic flow patterns in evaporating droplets, were varied to select the most appropriate slide surface coating. Optimization in a model system used goniometry, optical coherence tomography, and microscope images of the final deposition pattern to observe the droplet flows and maximize central deposition of 1 μm fluorescent polystyrene particles and 200 nm nanoparticles (NPs) in 2 μL droplets. Rain-X<sup>®</sup> polysiloxane glass coating was identified as the best substrate material, with a PBS-Tween droplet solvent. The use of smaller, 200 nm magnetic NPs instead of larger 1 μm beads allowed for bright field imaging of bacteria. Using these optimized components, we compared standard smear methods to the Marangoni-based spatial concentration system, which was paired with magnetic enrichment using iron oxide NPs, isolating <i>M. bovis</i> BCG (BCG) from samples containing 0 and 10<sup>3</sup> to 10<sup>6</sup> bacilli/mL. Compared to standard smear preparation, paired analysis demonstrated a combined volumetric and spatial sample enrichment of 100-fold. With further refinement, this magnetic/Marangoni flow concentration approach is expected to improve whole-pathogen microscopy-based diagnosis of TB and other infectious diseases.
format	article
author	Stephanie I. Pearlman Eric M. Tang Yuankai K. Tao Frederick R. Haselton
author_facet	Stephanie I. Pearlman Eric M. Tang Yuankai K. Tao Frederick R. Haselton
author_sort	Stephanie I. Pearlman
title	Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis
title_short	Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis
title_full	Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis
title_fullStr	Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis
title_full_unstemmed	Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis
title_sort	controlling droplet marangoni flows to improve microscopy-based tb diagnosis
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/d7a60ff1d9b74e4588ae2c1896b01425
work_keys_str_mv	AT stephanieipearlman controllingdropletmarangoniflowstoimprovemicroscopybasedtbdiagnosis AT ericmtang controllingdropletmarangoniflowstoimprovemicroscopybasedtbdiagnosis AT yuankaiktao controllingdropletmarangoniflowstoimprovemicroscopybasedtbdiagnosis AT frederickrhaselton controllingdropletmarangoniflowstoimprovemicroscopybasedtbdiagnosis
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Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis

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