protocol-for-biofilm-streamer-formation-microfluidic-device-with

Protocol for Biofilm Streamer Formation in a Microfluidic Device with Micro-pillars

Several bacterial species possess the ability to attach to surfaces and colonize them in the form of thin films called biofilms. Biofilms that grow in ...

microbiologically-induced-calcite-precipitation-mediated-sporosarcina

Microbiologically Induced Calcite Precipitation Mediated by <em>Sporosarcina pasteurii</em>

The particular bacterium under investigation here (S. pasteurii) is unique in its ability, under the right conditions, to induce the hydrolysis of urea ...

University of Alberta

One of the central puzzles concerning the interaction of low Reynolds number fluid transport with bacterial biomass is the formation of filamentous structures called streamers. In this manuscript, we report our discovery of a new kind of low Re bacterial streamers, which appear from pre-formed bacterial flocs. In sharp contrast to the biofilm-mediated streamers, these streamers form over extremely small timescales (less than a second). Our experiments, carried out in a microchannel with micropillars rely on fluorescence microscopy techniques to illustrate that floc-mediated streamers form when a freely-moving floc adheres to the micropillar wall and gets rapidly sheared by the background flow. We also show that at their inception the deformation of the flocs is dominated by recoverable large strains indicating significant elasticity. These strains subsequently increase tremendously to produce filamentous streamers. Interestingly, we find that these fully formed streamers are not static structures and show viscous response at time scales larger than their formation time scales. Finally, we show that such novel streamer formation can lead to rapid clogging of microfluidic devices.

Bacterial floc mediated rapid streamer formation in creeping flows.

Experiments studying transport phenomena during directional solidification of a hypereutectic binary solution in a top-cooled rectangular cavity are often characterized by the descendence of fragmented solid crystals through the unfrozen fluid. This observation, however, is yet to be fundamentally explained from a theoretical perspective. In this Letter, we propose a new model to describe stochastic dynamics of the falling crystals, which is not only applicable to this specific situation, but also appropriate for a generalized mathematical description of evolution of solid particles in the presence of stochastic fluctuations from the ambience accompanied by the growth or dissolution of crystals. Simulations of the proposed model also show an extremely good agreement between the theoretical predictions and earlier experimental findings.

Transport mechanisms of falling crystals detached from the freezing front during solidification of a hypereutectic binary mixture.

A total of 860 tribal tea garden women in the Jalpaiguri district were surveyed by means of detailed questionnaires to obtain information of their contraceptive knowledge and practices and also to see the literacy rate among themselves. Analysis was done of their literacy level, family planning awareness, access to information and communication, methods of contraception adopted and utilisation of healthcare facilities. Majority (85%) of the tea garden women including all the age groups were illiterate. The overall contraceptive prevalence was 40.2% but most of the current users (22.6%) subjected to tubal sterilisation for family planning, couples were not enthusiastic about using the reversible methods; 59.7% women had lack of adequate information regarding various contraceptives. Contraceptive practice, as birth spacing method, needs to be given tremendous emphasis in order to improve the reproductive health of the tribal women. Education, information, choices and rights for decision-making only can achieve this.

Contraceptive practice of the tribal women in tea garden area of North Bengal.

We demonstrate an opto-electrokinetic technique for non-invasive particle manipulation on the surface of a parallel-plate indium tin oxide (ITO) electrode that is biased with an alternating current (AC) signal and illuminated with near-infrared (1064 nm) optical landscapes. This technique can generate strong microfluidic vortices at higher AC frequencies (>100 kHz) and dynamically and rapidly aggregate and pattern particle groups at low frequencies (<100 kHz).

Electrokinetic patterning of colloidal particles with optical landscapes.

We study a recently demonstrated AC electrokinetic technique for manipulation and concentration of colloidal particles on an electrode surface. The technique uses indium tin oxide (ITO)-based parallel-plate electrodes on which highly localized infrared (1064 nm) laser illumination is shone. We show that the highly localized laser illumination leads to a highly nonuniform heating of the electrode substrate, which in turn drives an electrothermal microvortex resulting in a rapid transport of particles toward the illuminated site. Hundreds of polystyrene particles, with diameters ranging from 2.0 to 0.1 microm, suspended in a low conductivity solution (2.0 mS/m) could be aggregated at selected locations on the electrode by activating the laser illumination at suitable AC frequencies. Subsequent deactivation of the laser illumination causes the particles to scatter, and we explore this dynamical behavior for 1.0 microm particles using Delaunay tessellations and high-speed videography. We establish that drag from the electrothermal microvortex acts against a repulsive force, which decreases with increasing AC frequency, to create stable particle clusters. Moreover, experimentally we show that this particle capturing technique can be characterized by a critical frequency: a frequency at which the captured colloidal particle cluster becomes unstable and particles are carried away into the bulk by the electrothermal microvortex. This critical frequency increases with decreasing particle diameter for similar particles. For 0.1 microm particles, comparison of aggregation at different AC frequencies is achieved by the comparison of fluorescent intensity profiles of the aggregations.

Optically modulated electrokinetic manipulation and concentration of colloidal particles near an electrode surface.

We demonstrate a new hybrid optoelectric technique that can manipulate objects across several length scales. The technique leverages a variety of different physical mechanisms to achieve the dynamic manipulation of droplets and also the in situ concentration of colloidal particles suspended in the droplets. Various physical mechanisms such as optoelectrowetting, electrothermal flows, and ac electroosmosis are leveraged through different modes of operation of the device. Each operational mode, which is activated through the proper combination of an applied ac bias and the illumination used, is characterized by the ability to manipulate objects on a certain length scale. We also demonstrate that the device lends itself to the active control of microstructure patterns that emerge from a droplet evaporation process.

Dynamic manipulation by light and electric fields: micrometer particles to microliter droplets.

We demonstrate an optically induced electrokinetic technique that continuously concentrates nanoparticles on the surface of a parallel plate electrode that is biased with an AC signal. A highly focused beam of near-infrared light (1064 nm) was applied, inducing an electrothermal microfluidic vortex that carried nanoparticles to its center where they were accumulated. This technique was demonstrated with 49 nm and 100 nm fluorescent polystyrene particles and characterized as a function of applied AC frequency and voltage. With this technique the location and shape of colloidal concentration was reconfigured by controlling the optical landscape, yielding dynamic control of the aggregation. Colloidal concentration was demonstrated with a plain parallel plate electrode configuration without the need of photoconductive materials or complex microfabrication procedures.

A simple, optically induced electrokinetic method to concentrate and pattern nanoparticles.

Hybrid opto-electric manipulation in microfluidics/nanofluidics refers to a set of methodologies employing optical modulation of electrokinetic schemes to achieve particle or fluid manipulation at the micro- and nano-scale. Over the last decade, a set of methodologies, which differ in their modulation strategy and/or the length scale of operation, have emerged. These techniques offer new opportunities with their dynamic nature, and their ability for parallel operation has created novel applications and devices. Hybrid opto-electric techniques have been utilized to manipulate objects ranging in diversity from millimetre-sized droplets to nano-particles. This review article discusses the underlying principles, applications and future perspectives of various hybrid opto-electric techniques that have emerged over the last decade under a unified umbrella.

Hybrid opto-electric manipulation in microfluidics-opportunities and challenges.

Hybrid optoelectric techniques for molecular diagnostics.

Techniques d&#39;OPTOELECTRONIQUE hybride pour le diagnostic mol&eacute;culaire.

Tecniche ibride optoelettriche per diagnostica molecolare.

This communication first demonstrates bio-compatibility of a recently developed opto-electrokinetic manipulation technique, using microorganisms. Aggregation, patterning, translation, trapping and size-based separation of microorganisms performed with the technique firmly establishes its usefulness for development of a high-performance on-chip bioassay system.

Opto-electrokinetic manipulation for high-performance on-chip bioassays.

Using a microfabricated porous media mimic platform, we investigated how fluid flow influences the formation of filamentous structures, known as streamers, between porous media structures. We demonstrate how hydrodynamics govern the formation, morphology and the distribution of these biofilm streamers in the device. Our work establishes that, under favorable hydrodynamic conditions, streamers can often act as precursors to mature microbial structures found in complex geometries, such as those involved in porous media.

A web of streamers: biofilm formation in a porous microfluidic device.

Technologies that can enable concentration of low-abundance biomarkers are essential for early diagnosis of diseases. In this study, an optoelectrokinetic technique, termed Rapid Electrokinetic Patterning (REP), was used to enable dynamic particle manipulation in bead-based bioassays. Various manipulation capabilities, such as micro/nanoparticle aggregation, translation, sorting and patterning, were developed. The technique allows for versatile multi-parameter (voltage, light intensity and frequency) based modulation and dynamically addressable manipulation with simple device fabrication. Signal enhancement of a bead-based bioassay was demonstrated using dilute biotin-fluorescein isothiocyanate (FITC) solutions mixed with streptavidin-conjugated particles and rapidly concentrated with the technique. As compared with a conventional ELISA reader, the REP-enabled detection achieved a minimal readout of 3.87 nM, which was a 100-fold improvement in sensitivity. The multi-functional platform provides an effective measure to enhance detection levels in more bead-based bioassays.

An optoelectrokinetic technique for programmable particle manipulation and bead-based biosignal enhancement.

It has been recently reported that in presence of low Reynolds number (Re ≪ 1) transport, preformed bacterial biofilms, several hours after their formation, may degenerate in form of filamentous structures, known as streamers. In this work, we explain that such streamers form as the highly viscous liquid states of the intrinsically viscoelastic biofilms. Such "viscous liquid" state can be hypothesized by noting that the time of appearance of the streamers is substantially larger than the viscoelastic relaxation time scale of the biofilms, and this appearance is explained by the inability of a viscous liquid to withstand external shear. Further, by identifying the post formation dynamics of the streamers as that of a viscous liquid jet in a surrounding flow field, we can interpret several unexplained issues associated with the post-formation dynamics of streamers, such as the clogging of the flow passage or the exponential time growth of streamer dimensions. Overall our manuscript provides a biophysical basis for understanding the evolution of biofilm streamers in creeping flows.

Formation and post-formation dynamics of bacterial biofilm streamers as highly viscous liquid jets.

Polymeric filament like type IV Pilus (TFP) can transfer forces in excess of 100 pN during their retraction before stalling, powering surface translocation(twitching). Single TFP level experiments have shown remarkable nonlinearity in the retraction behavior influenced by the external load as well as levels of PilT molecular motor protein. This includes reversal of motion near stall forces when the concentration of the PilT protein is loweblack significantly. In order to explain this behavior, we analyze the coupling of TFP elasticity and interfacial behavior with PilT kinetics. We model retraction as reaction controlled and elongation as transport controlled process. The reaction rates vary with TFP deformation which is modeled as a compound elastic body consisting of multiple helical strands under axial load. Elongation is controlled by monomer transport which suffer entrapment due to excess PilT in the cell periplasm. Our analysis shows excellent agreement with a host of experimental observations and we present a possible biophysical relevance of model parameters through a mechano-chemical stall force map.

ArticleTotal : 2	Year
Publication title	2014
Publication title	2016

Article	Year
Bacterial floc mediated rapid streamer formation in creeping flows. Scientific reports\| PubMed ID: 26278133	2015
Transport mechanisms of falling crystals detached from the freezing front during solidification of a hypereutectic binary mixture. Physical review letters\| PubMed ID: 16090688	2005
Contraceptive practice of the tribal women in tea garden area of North Bengal. Journal of the Indian Medical Association\| PubMed ID: 18236906	2007
Electrokinetic patterning of colloidal particles with optical landscapes. Lab on a chip\| PubMed ID: 18941688	2008
Optically modulated electrokinetic manipulation and concentration of colloidal particles near an electrode surface. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 20232836	2010
Dynamic manipulation by light and electric fields: micrometer particles to microliter droplets. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 20429538	2010
A simple, optically induced electrokinetic method to concentrate and pattern nanoparticles. Nanoscale\| PubMed ID: 20644872	2009
Hybrid opto-electric manipulation in microfluidics-opportunities and challenges. Lab on a chip\| PubMed ID: 21603691	2011
Hybrid optoelectric techniques for molecular diagnostics. Expert review of molecular diagnostics\| PubMed ID: 22133113	2012
Opto-electrokinetic manipulation for high-performance on-chip bioassays. Lab on a chip\| PubMed ID: 23099738	2012
A web of streamers: biofilm formation in a porous microfluidic device. Lab on a chip\| PubMed ID: 23123600	2012
An optoelectrokinetic technique for programmable particle manipulation and bead-based biosignal enhancement. Lab on a chip\| PubMed ID: 25109364	2014
Formation and post-formation dynamics of bacterial biofilm streamers as highly viscous liquid jets. Scientific reports\| PubMed ID: 25410423	2014
Type-IV Pilus deformation can explain retraction behavior. PloS one\| PubMed ID: 25502696	2014

Aloke Kumar

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