Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis

Area of Science:

• Biomedical Engineering
• Microfluidics
• Diagnostic Technologies

Background:

• Microscopic examination of sputum smears is the primary tuberculosis (TB) diagnostic method in developing countries.
• Current methods suffer from low sensitivity (≈50%) due to time-intensive slide inspection and poor bacterial concentration.
• Improving spatial concentration of Mycobacterium tuberculosis is crucial for enhanced visual detection.

Purpose of the Study:

• To develop a novel method combining magnetic concentration and Marangoni flow for spatial concentration of Mycobacterium tuberculosis.
• To optimize slide substrate and droplet solvent properties for efficient bacterial deposition.
• To improve the sensitivity and diagnostic potential of microscopy-based TB detection.

Main Methods:

• Varied slide substrate thermal conductivity and droplet solvent surface tension to influence microfluidic flow.
• Utilized goniometry, optical coherence tomography, and microscopy to optimize particle deposition.
• Employed 200 nm magnetic nanoparticles (NPs) with Rain-X® coated slides and PBS-Tween droplets for optimized concentration.
• Compared the developed system with standard smear preparation using Mycobacterium bovis BCG (BCG).

Main Results:

• Identified Rain-X® polysiloxane glass coating and PBS-Tween as optimal for central deposition.
• Demonstrated that smaller 200 nm magnetic NPs enable bright-field imaging of bacteria.
• Achieved a 100-fold combined volumetric and spatial sample enrichment compared to standard smear preparation.
• Successfully isolated BCG from samples with varying bacilli concentrations.

Conclusions:

• The magnetic concentration and Marangoni flow approach significantly enhances spatial concentration of bacteria.
• This method shows promise for improving the sensitivity of microscopy-based diagnosis for tuberculosis (TB).
• Further refinement is expected to advance whole-pathogen microscopy for TB and other infectious diseases.