Optically driven pumps and flow sensors for microfluidic systems

This paper describes techniques for generating and measuring fluid flow in microfluidic devices. The first technique is for the multi-point measurement of fluid flow in microscopic geometries. The flow sensing method uses an array of optically trapped microprobe sensors to map out the fluid flow. The optical traps are alternately turned on and off such that the probe particles are displaced by the flow of the surrounding fluid and then retrapped. The particles' displacements are monitored by digital video microscopy and directly converted into velocity field values. The second is a method for generating flow within a microfluidic channel using an optically driven pump. The optically driven pump consists of two counter-rotating birefringent vaterite particles trapped within a microfluidic channel and driven using optical tweezers. The transfer of spin angular momentum from a circularly polarized laser beam causes the particles to rotate at up to 10 Hz. The pump is shown to be able to displace fluid in microchannels, with flow rates of up to 200 m−3 s−1 (200 fL s−1). In addition a flow sensing method, based upon the technique mentioned above, is incorporated into the system in order to map the magnitude and direction of fluid flow within the channel.

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Photokinetic analysis of the forces and torques exerted by optical tweezers carrying angular momentum

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2015.0432 ◽

2017 ◽

Vol 375 (2087) ◽

pp. 20150432 ◽

Cited By ~ 9

Author(s):

Aaron Yevick ◽

Daniel J. Evans ◽

David G. Grier

Keyword(s):

Angular Momentum ◽

Optical Tweezers ◽

Optical Traps ◽

Gradient Term ◽

Strength Anisotropy ◽

Spin Angular Momentum ◽

Intensity Gradient ◽

First Order ◽

Interference Contribution ◽

Focused Beam

The theory of photokinetic effects expresses the forces and torques exerted by a beam of light in terms of experimentally accessible amplitude and phase profiles. We use this formalism to develop an intuitive explanation for the performance of optical tweezers operating in the Rayleigh regime, including effects arising from the influence of light’s angular momentum. First-order dipole contributions reveal how a focused beam can trap small objects, and what features limit the trap’s stability. The first-order force separates naturally into a conservative intensity-gradient term that forms a trap and a non-conservative solenoidal term that drives the system out of thermodynamic equilibrium. Neither term depends on the light’s polarization; light’s spin angular momentum plays no role at dipole order. Polarization-dependent effects, such as trap-strength anisotropy and spin-curl forces, are captured by the second-order dipole-interference contribution to the photokinetic force. The photokinetic expansion thus illuminates how light’s angular momentum can be harnessed for optical micromanipulation, even in the most basic optical traps. This article is part of the themed issue ‘Optical orbital angular momentum’.

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Positioning Accuracy in Holographic Optical Traps

Micromachines ◽

10.3390/mi12050559 ◽

2021 ◽

Vol 12 (5) ◽

pp. 559

Author(s):

Frederic Català-Castro ◽

Estela Martín-Badosa

Keyword(s):

Optical Tweezers ◽

Dynamic Control ◽

Optical Trap ◽

Optical Traps ◽

Spatial Light Modulators ◽

Positioning Accuracy ◽

Light Modulators ◽

Holographic Optical Tweezers ◽

The One ◽

Optically Trapped

Spatial light modulators (SLMs) have been widely used to achieve dynamic control of optical traps. Often, holographic optical tweezers have been presumed to provide nanometer or sub-nanometer positioning accuracy. It is known that some features concerning the digitalized structure of SLMs cause a loss in steering efficiency of the optical trap, but their effect on trap positioning accuracy has been scarcely analyzed. On the one hand, the SLM look-up-table, which we found to depend on laser power, produces positioning deviations when the trap is moved at the micron scale. On the other hand, phase quantization, which makes linear phase gratings become phase staircase profiles, leads to unexpected local errors in the steering angle. We have tracked optically trapped microspheres with sub-nanometer accuracy to study the effects on trap positioning, which can be as high as 2 nm in certain cases. We have also implemented a correction strategy that enabled the reduction of errors down to 0.3 nm.

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Bio-Molecular Applications of Recent Developments in Optical Tweezers

Biomolecules ◽

10.3390/biom9010023 ◽

2019 ◽

Vol 9 (1) ◽

pp. 23 ◽

Cited By ~ 17

Author(s):

Dhawal Choudhary ◽

Alessandro Mossa ◽

Milind Jadhav ◽

Ciro Cecconi

Keyword(s):

Photonic Crystal ◽

Optical Tweezers ◽

Single Molecule ◽

Continuous Wave ◽

Imaging Techniques ◽

Resolving Power ◽

Optical Traps ◽

Laser Source ◽

One Dimensional

In the past three decades, the ability to optically manipulate biomolecules has spurred a new era of medical and biophysical research. Optical tweezers (OT) have enabled experimenters to trap, sort, and probe cells, as well as discern the structural dynamics of proteins and nucleic acids at single molecule level. The steady improvement in OT’s resolving power has progressively pushed the envelope of their applications; there are, however, some inherent limitations that are prompting researchers to look for alternatives to the conventional techniques. To begin with, OT are restricted by their one-dimensional approach, which makes it difficult to conjure an exhaustive three-dimensional picture of biological systems. The high-intensity trapping laser can damage biological samples, a fact that restricts the feasibility of in vivo applications. Finally, direct manipulation of biological matter at nanometer scale remains a significant challenge for conventional OT. A significant amount of literature has been dedicated in the last 10 years to address the aforementioned shortcomings. Innovations in laser technology and advances in various other spheres of applied physics have been capitalized upon to evolve the next generation OT systems. In this review, we elucidate a few of these developments, with particular focus on their biological applications. The manipulation of nanoscopic objects has been achieved by means of plasmonic optical tweezers (POT), which utilize localized surface plasmons to generate optical traps with enhanced trapping potential, and photonic crystal optical tweezers (PhC OT), which attain the same goal by employing different photonic crystal geometries. Femtosecond optical tweezers (fs OT), constructed by replacing the continuous wave (cw) laser source with a femtosecond laser, promise to greatly reduce the damage to living samples. Finally, one way to transcend the one-dimensional nature of the data gained by OT is to couple them to the other large family of single molecule tools, i.e., fluorescence-based imaging techniques. We discuss the distinct advantages of the aforementioned techniques as well as the alternative experimental perspective they provide in comparison to conventional OT.

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Piezoresistive Carbon Nanofiber-Based Cilia-Inspired Flow Sensor

Nanomaterials ◽

10.3390/nano10020211 ◽

2020 ◽

Vol 10 (2) ◽

pp. 211 ◽

Cited By ~ 1

Author(s):

Debarun Sengupta ◽

Duco Trap ◽

Ajay Giri Prakash Kottapalli

Keyword(s):

Carbon Nanofiber ◽

Detection Threshold ◽

Flow Sensor ◽

Oxygen Intake ◽

Mems Devices ◽

Flow Sensors ◽

Flow Monitoring ◽

Flow Sensing ◽

Artificial Cilia ◽

Lower Detection

Evolving over millions of years, hair-like natural flow sensors called cilia, which are found in fish, crickets, spiders, and inner ear cochlea, have achieved high resolution and sensitivity in flow sensing. In the pursuit of achieving such exceptional flow sensing performance in artificial sensors, researchers in the past have attempted to mimic the material, morphological, and functional properties of biological cilia sensors, to develop MEMS-based artificial cilia flow sensors. However, the fabrication of bio-inspired artificial cilia sensors involves complex and cumbersome micromachining techniques that lay constraints on the choice of materials, and prolongs the time taken to research, design, and fabricate new and novel designs, subsequently increasing the time-to-market. In this work, we establish a novel process flow for fabricating inexpensive, yet highly sensitive, cilia-inspired flow sensors. The artificial cilia flow sensor presented here, features a cilia-inspired high-aspect-ratio titanium pillar on an electrospun carbon nanofiber (CNF) sensing membrane. Tip displacement response calibration experiments conducted on the artificial cilia flow sensor demonstrated a lower detection threshold of 50 µm. Furthermore, flow calibration experiments conducted on the sensor revealed a steady-state airflow sensitivity of 6.16 mV/(m s−1) and an oscillatory flow sensitivity of 26 mV/(m s−1), with a lower detection threshold limit of 12.1 mm/s in the case of oscillatory flows. The flow sensing calibration experiments establish the feasibility of the proposed method for developing inexpensive, yet sensitive, flow sensors; which will be useful for applications involving precise flow monitoring in microfluidic devices, precise air/oxygen intake monitoring for hypoxic patients, and other biomedical devices tailored for intravenous drip/urine flow monitoring. In addition, this work also establishes the applicability of CNFs as novel sensing elements in MEMS devices and flexible sensors.

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Fluid Flow Sensors Design Based on Electromagnetic Drag Effect

2019 International Conference on Control, Artificial Intelligence, Robotics & Optimization (ICCAIRO) ◽

10.1109/iccairo47923.2019.00017 ◽

2019 ◽

Author(s):

Kirill Zeyde ◽

Vadim Sharov

Keyword(s):

Fluid Flow ◽

Drag Effect ◽

Flow Sensors

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COUNTING UNFOLDING EVENTS IN STRETCHED HELICES WITH INDUCED OSCILLATION BY OPTICAL TWEEZERS

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512007921 ◽

2012 ◽

Vol 17 ◽

pp. 44-53

Author(s):

ROMMEL GAUD BACABAC ◽

ROLAND OTADOY

Keyword(s):

Optical Tweezers ◽

Viscoelastic Properties ◽

Globular Proteins ◽

Optical Traps ◽

Living Matter ◽

Damped Harmonic Oscillator ◽

Catch Up ◽

Correlation Measures ◽

Complex Phenomena ◽

First Time

Correlation measures based on embedded probe fluctuations, single or paired, are now widely used for characterizing the viscoelastic properties of biological samples. However, more robust applications using this technique are still lacking. Considering that the study of living matter routinely demonstrates new and complex phenomena, mathematical and experimental tools for analysis have to catch up in order to arrive at newer insights. Therefore, we derive ways of probing non-equilibrium events in helical biopolymers provided by stretching beyond thermal forces. We generalize, for the first time, calculations for winding turn probabilities to account for unfolding events in single fibrous biopolymers and globular proteins under tensile stretching using twin optical traps. The approach is based on approximating the ensuing probe fluctuations as originating from a damped harmonic oscillator under oscillatory forcing.

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Biomimetic flow sensors for biomedical flow sensing in intravenous tubes

2016 IEEE SENSORS ◽

10.1109/icsens.2016.7808905 ◽

2016 ◽

Author(s):

Zhiyuan Shen ◽

Ajay Giri Prakash Kottapalli ◽

Vignesh Subramaniam ◽

Mohsen Asadnia ◽

Jianmin Miao ◽

...

Keyword(s):

Flow Sensors ◽

Flow Sensing

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Direct demonstration of tubular fluid flow sensing by macula densa cells

AJP Renal Physiology ◽

10.1152/ajprenal.00469.2009 ◽

2010 ◽

Vol 299 (5) ◽

pp. F1087-F1093 ◽

Cited By ~ 22

Author(s):

Arnold Sipos ◽

Sarah Vargas ◽

János Peti-Peterdi

Keyword(s):

Smooth Muscle ◽

Fluid Flow ◽

Smooth Muscle Cells ◽

Flow Rate ◽

Muscle Cells ◽

Macula Densa ◽

Fluid Composition ◽

Apical Surface ◽

Fluid Flow Rate ◽

Flow Sensing

Macula densa (MD) cells in the cortical thick ascending limb (cTAL) detect variations in tubular fluid composition and transmit signals to the afferent arteriole (AA) that control glomerular filtration rate [tubuloglomerular feedback (TGF)]. Increases in tubular salt at the MD that normally parallel elevations in tubular fluid flow rate are well accepted as the trigger of TGF. The present study aimed to test whether MD cells can detect variations in tubular fluid flow rate per se. Calcium imaging of the in vitro microperfused isolated JGA-glomerulus complex dissected from mice was performed using fluo-4 and fluorescence microscopy. Increasing cTAL flow from 2 to 20 nl/min (80 mM [NaCl]) rapidly produced significant elevations in cytosolic Ca2+ concentration ([Ca2+]i) in AA smooth muscle cells [evidenced by changes in fluo-4 intensity (F); F/F0 = 1.45 ± 0.11] and AA vasoconstriction. Complete removal of the cTAL around the MD plaque and application of laminar flow through a perfusion pipette directly to the MD apical surface essentially produced the same results even when low (10 mM) or zero NaCl solutions were used. Acetylated α-tubulin immunohistochemistry identified the presence of primary cilia in mouse MD cells. Under no flow conditions, bending MD cilia directly with a micropipette rapidly caused significant [Ca2+]i elevations in AA smooth muscle cells (fluo-4 F/F0: 1.60 ± 0.12) and vasoconstriction. P2 receptor blockade with suramin significantly reduced the flow-induced TGF, whereas scavenging superoxide with tempol did not. In conclusion, MD cells are equipped with a tubular flow-sensing mechanism that may contribute to MD cell function and TGF.

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