Cyclic on-chip bacteria separation and preconcentration – A short review

This short review originates from an article titled “Cyclic on-chip bacteria separation and preconcentration” and written by Vitaly V. Ryzhkov, Alexander V. Zverev, Vladimir V. Echeistov, Mikhail Andronic, Ilya A. Ryzhikov, Igor A. Budashov, Arkadiy V. Eremenko, Ilya N. Kurochkin and Ilya A. Rodionov. It has been published in the journal Scientific Reports, Nature Publishing Group.  

In their work, a team of researchers from the Bauman Moscow State Technical University and the Institute of Biochemical Physics, Russian Academy of Sciences demonstrate on-chip automatic efficient bacteria separation and preconcentration method with the use of pressure-driven flow-controlled microfluidics.

Abstract

The unique advantages of microfluidic analytical systems over traditional laboratory methods are portability, operator-free operation, on-chip microcontrol capabilities, reduction of analysis time and dramatic sample volume shrinking [1]. Microfluidic systems that comprise electrophoresis, immunochromatography, polymerase chain reaction, droplet reactions and a number of other analysis methods, have demonstrated their superior efficiency to standard methods [2]. However, the performance of many microfluidic assay systems can be significantly improved if pathogens present in the sample are preliminary separated, concentrated and purified from substances that interfere with the accurate detection of pathogens and determination of their concentrations.

Introduction

Nanoparticles and biological molecules high throughput robust separation is of significant interest in many healthcare and nanoscience industrial applications. 

Modern microfluidic separation methods include various types of filtration, particles size-dependent techniques based on microstructures capturing, deterministic lateral in-flow displacement using objects with various shapes, methods utilizing biomimetic effects, affinity methods for analyst isolation, inertia- and gravity-based techniques, as well as on-chip magnetophoresis, acoustophoresis, electrophoresis and dielectrophoresis. 

The prior challenge in the development of state-of-the-art on-chip separation technique is to combine the highest separation efficiency with the best throughput [3]. 

The proposed approach implies microfiltration of particles of different sizes on a multilayer microfluidic chip with built-in membrane valves.

The on-chip automatic sorting sequence consisted of four steps: filling chip with buffer, a sample filtration, dead volume washout and retentate backflush in reverse flow. This work has shown that pulse backflush mode and volume control can dramatically increase microparticles sorting and preconcentration efficiency.

Aim & objectives

The primary objective of this work was to create an automatic microfluidic system for bacteria and viruses separation and bacteria preconcentration. To do so, the following targets were achieved:

• Design the topology of a multilayer microfluidic chip.
• Develop a fabrication technology of multilayer microfluidic chip with on-chip valves.
• Evaluate the efficiency of the proposed system in separation and preconcentration of living cells.

Materials & methods

The microfluidic chip had two input inlets for supplying the sample and the buffer, six integrated membrane valves (<100 nL dead volume), hydrophilic PVDF filter with 0.45 μm pore diameter, six pneumatic valve control lines and three outlets for filtrate, retentate and waste. The team used multilayer soft lithography technology to fabricate the chip from fully biocompatible materials. 

The experimental separation setup consisted of a control PC, a microfluidic flow controller OB1 MK3+ pneumatic valves controller (Elveflow, France), an image capture system based on a high-speed Pixelink camera (Navitar, USA), a Nikon SMZ800N microscope, the home-made stage holder and reservoirs for inflow and outflow liquids.

During the experiments, the valves actuation and the supply of liquids to the chip occurred automatically according to a previously created algorithm in the developed homemade software package. The real-time valves control was carried out using the image capture system.

Key findings

A scalable microfluidic solution for batch micro- and nanoparticle separation based on microfiltration principle and robust on-chip valve flow control was introduced. The team demonstrated a novel implementation of batch filtration method for on-chip automated separation and preconcentration of 1 mL colloid solution of E.coli bacteria cells.

The developed method allows micro- and nanoparticles separation from sub-mL liquid samples using automatic on-chip cyclic operations— at the end of each cycle, the microfluidic system gets back to the initial state and ready to separate the next sample portion.

Due to such an approach, both filtrate (nanoparticles) and retentate (bacteria) are available in the system’s output channels for subsequent processing or analysis. The great scaling potential of on-chip platforms allows several microfluidic chips with purposefully chosen filters to be sequentially connected for two or more dissimilar sized particles separation and preconcentration.

The method made it possible to reach the separation efficiency of 81.33% at a throughput of 120.42 μL/min, which is competitive to the best published results.

Furthermore, with the same microfluidic setup and suggested cyclic on-chip separation technique researchers achieved tunable preconcentration of E.coli cells with efficiency up to 536% at a throughput of 1.98 μL/min or 294% at a maximum throughput of 10.9 μL/min for 8·105–5·106 cells/mL concentrations.

Conclusion

With the help of pressure-driven flow controlled microfluidics, the presented platform performs a basic yet essential operation, which makes it highly application-flexible and scalable. For more information about what the authors have achieved, please refer to the original paper published in Scientific Reports, available here. 

Engineered and assembled with different microfluidic modules for sequent steps of sample preparation, chemical reactions and analyte detection, the results of this work will serve as a stepping-stone for the development of future cost-effective fully automated point-of-care devices.

If you’re interested in reproducing what the authors have done, feel free to contact our team of experts for additional information!

References