Jijo Lukose, Mithun N.a, Priyanka M.a, Ganesh Mohan, Shamee Shastry and Santhosh Chidangil
The dermal penetration of bisphenol-A (BPA) from thermal papers into the human skin is a matter of major health concern due to its extensive use in developing countries like India, one of its largest users in the world. Bisphenol A is widely used in the manufacture of many consumer goods like polycarbonate water bottles, baby bottles, food containers, home appliances, thermal papers used in billing and tickets, the inner lining of food cans, etc. BPA can be easily adsorbed into the blood rapidly. The integration of optical tweezers with Raman spectroscopic techniques has realized avenues for interpreting single cell investigations. In the present work, the impact of BPA from thermal papers on individual human erythrocytes (red blood cells) has been investigated using micro-Raman spectroscopy. Significant intensity variations were noticed for hemoglobin oxygenation markers in the Raman spectra of red blood cells (RBCs). Raman spectral variations supporting RBC hemoglobin depletion were also found in the presence of BPA. Evident morphological changes are also observed in RBCs due to BPA in vitro exposures, which ultimately lead to cell bursting at higher concentrations.
DOI
Showing posts with label RSC Advances. Show all posts
Showing posts with label RSC Advances. Show all posts
Monday, July 15, 2019
Tuesday, April 2, 2019
Normal saline-induced deoxygenation of red blood cells probed by optical tweezers combined with the micro-Raman technique
Jijo Lukose, Mithun N, Ganesh Mohan, Shamee Shastry and Santhosh Chidangil
The use of normal saline for washing red blood cells and treating critically ill patients is a regular medical practice in hospital settings. An optical tweezer in combination with Raman spectroscopy is an analytical tool employed for the investigation of single cell dynamics, thus providing molecular fingerprint of the cell by optically trapping the cell at a laser focus. In this study, the impact of normal saline on individual human red blood cell was compared with that of blood plasma using Raman tweezers spectroscopy. Major spectral variations in the marker frequencies at 1209 cm−1, 1222 cm−1, 1544 cm−1, and 1561 cm−1 of the Raman spectrum of the treated cells imply that the transition of hemoglobin to the deoxygenated state occurs when 0.9% normal saline is used. This may result in serious implications in blood transfusion. The results obtained from the principal component analysis also displayed clear differentiation among the red blood cells diluted in normal saline and those diluted in plasma. In future studies, efforts will be made to correlate the deoxygenation status of red blood cells with various human disorders.
DOI
The use of normal saline for washing red blood cells and treating critically ill patients is a regular medical practice in hospital settings. An optical tweezer in combination with Raman spectroscopy is an analytical tool employed for the investigation of single cell dynamics, thus providing molecular fingerprint of the cell by optically trapping the cell at a laser focus. In this study, the impact of normal saline on individual human red blood cell was compared with that of blood plasma using Raman tweezers spectroscopy. Major spectral variations in the marker frequencies at 1209 cm−1, 1222 cm−1, 1544 cm−1, and 1561 cm−1 of the Raman spectrum of the treated cells imply that the transition of hemoglobin to the deoxygenated state occurs when 0.9% normal saline is used. This may result in serious implications in blood transfusion. The results obtained from the principal component analysis also displayed clear differentiation among the red blood cells diluted in normal saline and those diluted in plasma. In future studies, efforts will be made to correlate the deoxygenation status of red blood cells with various human disorders.
DOI
Thursday, December 6, 2018
Laser-driven structural transformations in dextran-graft-PNIPAM copolymer/Au nanoparticles hybrid nanosystem: the role of plasmon heating and attractive optical forces
Oleg A. Yeshchenko, Antonina P. Naumenko, Nataliya V. Kutsevol and Iulia I. Harahuts
Laser induced structural transformations in a dextran grafted-poly(N-isopropylacrylamide) copolymer/Au nanoparticles (D-g-PNIPAM/AuNPs) hybrid nanosystem in water have been observed. The laser induced local plasmonic heating of Au NPs leads to Lower Critical Solution Temperature (LCST) phase transition in D-g-PNIPAM/AuNPs macromolecules accompanied by their shrinking and aggregation. The hysteresis non-reversible character of the structural transformation in D-g-PNIPAM/AuNPs system has been observed at the decrease of laser intensity, i.e. the aggregates remains in solution after the turn-off the laser illumination. This is an essential difference comparing to the case of usual heating–cooling cycles when there is no formation of aggregates and structural transformations are reversible. Such a fundamental difference has been rationalized as the result of action of attractive optical forces arising due to the excitation of surface plasmons in Au NPs. The attractive plasmonic forces facilitate the formation of the aggregates and counteract their destruction. The laser induced structural transformations have been found to be very sensitive to matching conditions of the resonance of the laser light with surface plasmon resonance proving the plasmonic nature of observed phenomena.
DOI
Laser induced structural transformations in a dextran grafted-poly(N-isopropylacrylamide) copolymer/Au nanoparticles (D-g-PNIPAM/AuNPs) hybrid nanosystem in water have been observed. The laser induced local plasmonic heating of Au NPs leads to Lower Critical Solution Temperature (LCST) phase transition in D-g-PNIPAM/AuNPs macromolecules accompanied by their shrinking and aggregation. The hysteresis non-reversible character of the structural transformation in D-g-PNIPAM/AuNPs system has been observed at the decrease of laser intensity, i.e. the aggregates remains in solution after the turn-off the laser illumination. This is an essential difference comparing to the case of usual heating–cooling cycles when there is no formation of aggregates and structural transformations are reversible. Such a fundamental difference has been rationalized as the result of action of attractive optical forces arising due to the excitation of surface plasmons in Au NPs. The attractive plasmonic forces facilitate the formation of the aggregates and counteract their destruction. The laser induced structural transformations have been found to be very sensitive to matching conditions of the resonance of the laser light with surface plasmon resonance proving the plasmonic nature of observed phenomena.
DOI
Thursday, October 18, 2018
Sizing and identification of nanoparticles by a tapered fiber
Huiling Pan, Weina Zhang and Hongxiang Lei
There is a strong desire for sizing and identification of nanoparticles in fields of advanced nanotechnology and environmental protection. Although existing approaches can size the nanoparticles, or identify nanoparticles with different refractive indexes, a fast and simple method that combines the two functions still remains challenges. Here, we propose a versatile optical method to size and identify nanoparticles using an optical tapered fiber. By detecting reflection signals in real time, 400–600 nm SiO2 nanoparticles can be sized and 500 nm SiO2, PMMA, PS nanoparticles can be identified. This method requires only an optical tapered fiber, avoiding the use of elaborate nanostructures and making the device highly autonomous, flexible and compact. The demonstrated method provides a potentially powerful tool for biosensing, such as identification of nano-contaminant particles and biological pathogens.
DOI
There is a strong desire for sizing and identification of nanoparticles in fields of advanced nanotechnology and environmental protection. Although existing approaches can size the nanoparticles, or identify nanoparticles with different refractive indexes, a fast and simple method that combines the two functions still remains challenges. Here, we propose a versatile optical method to size and identify nanoparticles using an optical tapered fiber. By detecting reflection signals in real time, 400–600 nm SiO2 nanoparticles can be sized and 500 nm SiO2, PMMA, PS nanoparticles can be identified. This method requires only an optical tapered fiber, avoiding the use of elaborate nanostructures and making the device highly autonomous, flexible and compact. The demonstrated method provides a potentially powerful tool for biosensing, such as identification of nano-contaminant particles and biological pathogens.
DOI
Monday, August 6, 2018
Electrical and thermal properties of silver nanowire fabricated on a flexible substrate by two-beam laser direct writing for designing a thermometer
Gui-Cang He, Heng Lu, Xian-Zi Dong, Yong-Liang Zhang, Jie Liu, Chang-Qing Xie and Zhen-Sheng Zhao
Accurate knowledge of electrical conductivity and thermal conductivity temperature dependence plays a crucial role in the design of a thermometer. Here, by using a two-beam laser direct writing system, an individual silver nanowire (AgNW) with well-defined dimensions is fabricated on a polyethylene terephthalate (PET) substrate. The temperature dependence of the resistivity of the fabricated AgNW is measured ranging from 10 to 300 K, and fitted with the Bloch–Grüneisen formula. The residual resistivity ((1.62 ± 0.20) × 10−7 Ω m) of the AgNW is larger than that of the bulk material (1 × 10−11 Ω m). The electron–phonon coupling constant of the AgNW is (1.08 ± 0.13) × 10−7 Ω m, which is larger than that of the bulk silver (5.24 × 10−8 Ω m). Moreover, the Debye temperature of the AgNW is 199.30 K and is lower than that of the bulk silver (235 K). The Lorenz number of the fabricated AgNW is found to decrease as the temperature increases. Besides, the Lorenz number (2.66 × 10−7 W Ω K−2) is larger than the Sommerfeld value (2.44 × 10−8 W Ω K−2) at room temperature. The measurement results allow one to design a thermometer in the temperature range 40–300 K. The flexibility of the AgNW is also excellent, and the resistance increase of the AgNW is only 2.58% when the AgNW bending about 1000 times with a bending radius of 1 mm.
DOI
Accurate knowledge of electrical conductivity and thermal conductivity temperature dependence plays a crucial role in the design of a thermometer. Here, by using a two-beam laser direct writing system, an individual silver nanowire (AgNW) with well-defined dimensions is fabricated on a polyethylene terephthalate (PET) substrate. The temperature dependence of the resistivity of the fabricated AgNW is measured ranging from 10 to 300 K, and fitted with the Bloch–Grüneisen formula. The residual resistivity ((1.62 ± 0.20) × 10−7 Ω m) of the AgNW is larger than that of the bulk material (1 × 10−11 Ω m). The electron–phonon coupling constant of the AgNW is (1.08 ± 0.13) × 10−7 Ω m, which is larger than that of the bulk silver (5.24 × 10−8 Ω m). Moreover, the Debye temperature of the AgNW is 199.30 K and is lower than that of the bulk silver (235 K). The Lorenz number of the fabricated AgNW is found to decrease as the temperature increases. Besides, the Lorenz number (2.66 × 10−7 W Ω K−2) is larger than the Sommerfeld value (2.44 × 10−8 W Ω K−2) at room temperature. The measurement results allow one to design a thermometer in the temperature range 40–300 K. The flexibility of the AgNW is also excellent, and the resistance increase of the AgNW is only 2.58% when the AgNW bending about 1000 times with a bending radius of 1 mm.
DOI
Friday, September 29, 2017
Enhanced optical confinement of dielectric nanoparticles by two-photon resonance transition
Aungtinee Kittiravechote, Anwar Usman, Hiroshi Masuhara and Ian Liau
Despite a tremendous success in the optical manipulation of microscopic particles, it remains a challenge to manipulate nanoparticles especially as the polarizability of the particles is small. With a picosecond-pulsed near-infrared laser, we demonstrated recently that the confinement of dye-doped polystyrene nanobeads is significantly enhanced relative to bare nanobeads of the same dimension. We attributed the enhancement to an additional term of the refractive index, which results from two-photon resonance between the dopant and the optical field. The optical confinement is profoundly enhanced as the half-wavelength of the laser falls either on the red side, or slightly away from the blue side, of the absorption band of the dopant. In contrast, the ability to confine the nanobeads is significantly diminished as the half-wavelength of the laser locates either at the peak, or on the blue side, of the absorption band. We suggest that the dispersively shaped polarizability of the dopant near the resonance is responsible to the distinctive spectral dependence of the optical confinement of nanobeads. This work advances our understanding of the underlying mechanism of the enhanced optical confinement of doped nanoparticles with a near-infrared pulsed laser, and might facilitate future research that benefits from effective sorting of selected nanoparticles beyond the limitations of previous approaches.
DOI
Despite a tremendous success in the optical manipulation of microscopic particles, it remains a challenge to manipulate nanoparticles especially as the polarizability of the particles is small. With a picosecond-pulsed near-infrared laser, we demonstrated recently that the confinement of dye-doped polystyrene nanobeads is significantly enhanced relative to bare nanobeads of the same dimension. We attributed the enhancement to an additional term of the refractive index, which results from two-photon resonance between the dopant and the optical field. The optical confinement is profoundly enhanced as the half-wavelength of the laser falls either on the red side, or slightly away from the blue side, of the absorption band of the dopant. In contrast, the ability to confine the nanobeads is significantly diminished as the half-wavelength of the laser locates either at the peak, or on the blue side, of the absorption band. We suggest that the dispersively shaped polarizability of the dopant near the resonance is responsible to the distinctive spectral dependence of the optical confinement of nanobeads. This work advances our understanding of the underlying mechanism of the enhanced optical confinement of doped nanoparticles with a near-infrared pulsed laser, and might facilitate future research that benefits from effective sorting of selected nanoparticles beyond the limitations of previous approaches.
DOI
Friday, August 25, 2017
Controlled shaping of lipid vesicles in a microfluidic diffusion chamber
M. Mally, B. Božič, S. Vrhovec Hartman, U. Klančnik, M. Mur, S. Svetina and J. Derganc
Synthetic lipid vesicles represent an important model system for studying membrane processes, which often depend on membrane shape, but controlled shaping of vesicles remains a challenging experimental task. Here, we present a novel method for shaping giant lipid vesicles by independently regulating osmotic conditions and the concentration of membrane-shaping molecules, which intercalate into the membrane and drive membrane bending. The method is based on the microfluidic diffusion chamber, where the solution around the vesicles can be repeatedly exchanged solely by diffusion, without any hydrodynamic flow that could deform the membrane. By using lipopolysaccharide (LPS) as a vesicle shape-modifying molecule, we demonstrate controlled and reversible transformations across three shape classes, from invaginated to evaginated vesicles. We show that extensive shape transformations can lead to shapes that are assumed to comprise narrow membrane necks that hinder equilibration of the membrane and the vesicle interior. All the observed shapes are in good agreement with the predictions of the area-difference-elasticity model applied to the vesicles that were denser than their surrounding solution. Our results validate the microfluidic diffusion chamber as a universal framework for membrane shaping that could also pave the way towards controlled fabrication of synthetic membranes resembling cell-compartments with large surface-to-volume ratios.
DOI
Synthetic lipid vesicles represent an important model system for studying membrane processes, which often depend on membrane shape, but controlled shaping of vesicles remains a challenging experimental task. Here, we present a novel method for shaping giant lipid vesicles by independently regulating osmotic conditions and the concentration of membrane-shaping molecules, which intercalate into the membrane and drive membrane bending. The method is based on the microfluidic diffusion chamber, where the solution around the vesicles can be repeatedly exchanged solely by diffusion, without any hydrodynamic flow that could deform the membrane. By using lipopolysaccharide (LPS) as a vesicle shape-modifying molecule, we demonstrate controlled and reversible transformations across three shape classes, from invaginated to evaginated vesicles. We show that extensive shape transformations can lead to shapes that are assumed to comprise narrow membrane necks that hinder equilibration of the membrane and the vesicle interior. All the observed shapes are in good agreement with the predictions of the area-difference-elasticity model applied to the vesicles that were denser than their surrounding solution. Our results validate the microfluidic diffusion chamber as a universal framework for membrane shaping that could also pave the way towards controlled fabrication of synthetic membranes resembling cell-compartments with large surface-to-volume ratios.
DOI
Tuesday, January 10, 2017
Active bioparticle manipulation in microfluidic systems
Mohd Anuar Md Ali, Kostya (Ken) Ostrikov, Fararishah Abdul Khalid, Burhanuddin Y. Majlis and Aminuddin A. Kayani
The motion of bioparticles in a microfluidic environment can be actively controlled using several tuneable mechanisms, including hydrodynamic, electrophoresis, dielectrophoresis, magnetophoresis, acoustophoresis, thermophoresis and optical forces. These mechanisms are applied to obtain desired bioparticle motions which are important in facilitating different biological processes. In this work, we review the fundamentals, features and applications of these tuneable mechanisms for the manipulation of bioparticles such as proteins, nucleic acids, viruses, bacteria, stem cells, cancer and tumor cells, blood cells and multicellular organisms in microfluidic systems. We focus on applications that can realize biomedical devices potentially suitable in diagnostic, therapeutic or analytical applications. Future perspectives of microfluidic systems incorporating active bioparticle manipulation mechanisms are included.
DOI
The motion of bioparticles in a microfluidic environment can be actively controlled using several tuneable mechanisms, including hydrodynamic, electrophoresis, dielectrophoresis, magnetophoresis, acoustophoresis, thermophoresis and optical forces. These mechanisms are applied to obtain desired bioparticle motions which are important in facilitating different biological processes. In this work, we review the fundamentals, features and applications of these tuneable mechanisms for the manipulation of bioparticles such as proteins, nucleic acids, viruses, bacteria, stem cells, cancer and tumor cells, blood cells and multicellular organisms in microfluidic systems. We focus on applications that can realize biomedical devices potentially suitable in diagnostic, therapeutic or analytical applications. Future perspectives of microfluidic systems incorporating active bioparticle manipulation mechanisms are included.
DOI
Thursday, November 17, 2016
Unraveling the physical chemistry and the mixed binding modes of complex DNA ligands by single molecule stretching experiments
W. F. P. Bernal, E. F. Silva and M. S. Rocha
In this work we present a complete methodology to unravel the physical chemistry and the mixed binding modes of complex DNA ligands. Single molecule stretching experiments were performed with complexes formed between a DNA binding drug that exhibits multiple mixed binding modes (Berenil) and the biopolymer. From these experiments we determine the changes of the two basic mechanical properties, the contour and persistence lengths, as a function of the drug concentration in the sample. Combining a modeling analysis for the two mechanical properties, we were able to extract the physicochemical parameters of the interaction and to determine the effective binding mechanisms. In particular, we have shown that in this case the binding modes can be modulated by changing the ionic strength of the surrounding buffer: for high ionic strengths (150 mM), Berenil behaves as a typical minor groove ligand in its interaction with λ-DNA; while, for low ionic strengths (10 mM), the drug also partially intercalates into the double-helix. The methodology developed in the present analysis can be promptly applied to other complex DNA ligands, therefore allowing one to investigate and decouple different binding mechanisms.
DOI
In this work we present a complete methodology to unravel the physical chemistry and the mixed binding modes of complex DNA ligands. Single molecule stretching experiments were performed with complexes formed between a DNA binding drug that exhibits multiple mixed binding modes (Berenil) and the biopolymer. From these experiments we determine the changes of the two basic mechanical properties, the contour and persistence lengths, as a function of the drug concentration in the sample. Combining a modeling analysis for the two mechanical properties, we were able to extract the physicochemical parameters of the interaction and to determine the effective binding mechanisms. In particular, we have shown that in this case the binding modes can be modulated by changing the ionic strength of the surrounding buffer: for high ionic strengths (150 mM), Berenil behaves as a typical minor groove ligand in its interaction with λ-DNA; while, for low ionic strengths (10 mM), the drug also partially intercalates into the double-helix. The methodology developed in the present analysis can be promptly applied to other complex DNA ligands, therefore allowing one to investigate and decouple different binding mechanisms.
DOI
Monday, September 19, 2016
Trapping analyte molecules in hotspots with modified free-standing silver bowtie nanostructures for SERS detection
Daren Xu, Lingxiao Liu, Fei Teng, Feifei Wu and Nan Lu
In this paper, we present a method to trap analyte molecules in hotspots by fabricating free-standing silver bowtie nanostructures with supporting bridges. The existence of supporting bridges makes more analyte molecules in hotspots, which efficiently enhance the Raman intensity. An enhancement factor of 2.4 × 108 is obtained for the structures, and a low concentration of analyte (10−10 M) can be detected. Furthermore, the relative standard deviation for Raman measurement is down to 5.91% for the structures. This method may be applied for SERS measurements.
DOI
In this paper, we present a method to trap analyte molecules in hotspots by fabricating free-standing silver bowtie nanostructures with supporting bridges. The existence of supporting bridges makes more analyte molecules in hotspots, which efficiently enhance the Raman intensity. An enhancement factor of 2.4 × 108 is obtained for the structures, and a low concentration of analyte (10−10 M) can be detected. Furthermore, the relative standard deviation for Raman measurement is down to 5.91% for the structures. This method may be applied for SERS measurements.
DOI
Friday, August 5, 2016
Dynamic motions of DNA molecules in an array of plasmonic traps
Jun-Hee Choi, Jung-Dae Kim and Yong-Gu Lee
DNA molecules can undergo dynamic motion by fluidic and plasmonic forces. The latter, very weak compared to the former, can alter the trajectory of DNA molecules from their original fluid direction. For analyzing the trajectory of DNA molecules, it is easier to view the force exerting plasmonic trap as a potential well. The potential well can be placed periodically forming a kinetically biased landscape. The motion of DNA molecules in this is the main subject of this study. In this paper, a scaled-up mock-up of DNA molecules and the unit-cell of the periodic potential landscape is fabricated by 3D printing and they are used to experimentally obtain the trajectory data. The data is then inputted into a computer simulation to check the trajectory of DNA molecules along the entire array of plasmonic traps. The novel analysis method provided in this paper can be used in the design of an array of plasmonic traps.
DOI
DNA molecules can undergo dynamic motion by fluidic and plasmonic forces. The latter, very weak compared to the former, can alter the trajectory of DNA molecules from their original fluid direction. For analyzing the trajectory of DNA molecules, it is easier to view the force exerting plasmonic trap as a potential well. The potential well can be placed periodically forming a kinetically biased landscape. The motion of DNA molecules in this is the main subject of this study. In this paper, a scaled-up mock-up of DNA molecules and the unit-cell of the periodic potential landscape is fabricated by 3D printing and they are used to experimentally obtain the trajectory data. The data is then inputted into a computer simulation to check the trajectory of DNA molecules along the entire array of plasmonic traps. The novel analysis method provided in this paper can be used in the design of an array of plasmonic traps.
DOI
Monday, April 18, 2016
Nanomechanics of a fibroblast suspended using point-like anchors reveal cytoskeleton formation
Sabato Fusco, Pasquale Memmolo, Lisa Miccio, Francesco Merola, Martina Mugnano, Antonio Paciello, Pietro Ferraro and Paolo A. Netti
In an attempt to better elucidate the material–cytoskeleton crosstalk during the initial stage of cell adhesion, here we report how suspended cells anchored to point-like bonds are able to assemble their cytoskeleton when subjected to mechanical stress. The combination of holographic optical tweezers and digital holography gives the cell footholds for adhesion and mechanical stimulation, and at the same time, acts as a label-free, force-revealing system over time, detecting the cell nanomechanical response in the pN range. To confirm the formation of the cytoskeleton structures after the stimulation, a fluorescence imaging system was added as a control. The strategy here proposed portends broad applicability to investigate the correlation between the forces applied to cells and their cytoskeleton assembly process in this or other complex configurations with multiple anchor points.
DOI
In an attempt to better elucidate the material–cytoskeleton crosstalk during the initial stage of cell adhesion, here we report how suspended cells anchored to point-like bonds are able to assemble their cytoskeleton when subjected to mechanical stress. The combination of holographic optical tweezers and digital holography gives the cell footholds for adhesion and mechanical stimulation, and at the same time, acts as a label-free, force-revealing system over time, detecting the cell nanomechanical response in the pN range. To confirm the formation of the cytoskeleton structures after the stimulation, a fluorescence imaging system was added as a control. The strategy here proposed portends broad applicability to investigate the correlation between the forces applied to cells and their cytoskeleton assembly process in this or other complex configurations with multiple anchor points.
DOI
Tuesday, March 1, 2016
Nanomechanics of Suspended Fibroblast by Point-like Anchors Reveals Cytoskeleton Formation
Sabato Fusco, Pasquale Memmolo, Lisa Miccio, Francesco Merola, Martina Mugnano, Antonio Paciello, Pietro Ferraro and Paolo Antonio Netti
In an attempt to better elucidate the material-cytoskeleton crosstalk during the initial stage of cell adhesion, here we report how suspended cells anchored to point-like bonds are able to assemble their cytoskeleton when subjected to mechanical stress. The combination of holographic optical tweezers and digital holography gives cells footholds for the adhesion and mechanical stimulation and, at the same time, acts as a label-free, force-revealing system over time, detecting the cell nanomechanical response in the pN range. To confirm the formation of cytoskeleton structures after the stimulation, a fluorescence image system was added as a control. The strategy here proposed portends broad applicability to investigate the correlation between the forces applied to the cells and their cytoskeleton assembly process in this or other complex configurations with multiple anchor points.
DOI
In an attempt to better elucidate the material-cytoskeleton crosstalk during the initial stage of cell adhesion, here we report how suspended cells anchored to point-like bonds are able to assemble their cytoskeleton when subjected to mechanical stress. The combination of holographic optical tweezers and digital holography gives cells footholds for the adhesion and mechanical stimulation and, at the same time, acts as a label-free, force-revealing system over time, detecting the cell nanomechanical response in the pN range. To confirm the formation of cytoskeleton structures after the stimulation, a fluorescence image system was added as a control. The strategy here proposed portends broad applicability to investigate the correlation between the forces applied to the cells and their cytoskeleton assembly process in this or other complex configurations with multiple anchor points.
DOI
Tuesday, February 2, 2016
Measuring the interaction between a pair of emulsion droplets using dual-trap optical tweezers
Bill Williams, Marjorie Griffiths, Allan Raudsepp and Kate McGrath
Optical tweezers have been used to investigate the dependance of electrostatic inter-particle forces on separation, in systems consisting of pairs of either model silica beads or emulsion droplets. Measurements were carried out as a function of ionic strength and, at salt concentrations where the Debye length was larger than the standard deviation of Brownian fluctuations of the particles in the traps, results were found to agree reasonably well with the predictions of DLVO theory. Experiments were also carried out where the salt concentration of the environment was changed in real-time while interactions were continuously measured. Specifically, single pairs of particles or emulsion droplets were held in a microfluidic channel in close proximity to an interface created between milliQ water and a 5 mM NaCl solution. Changes in the force-separation curves were measured as a function of time and used to monitor changes in the Debye length, and thus the local salt concentration, as ions diffused away from the interface. The results were shown to be consistent with expectations based on a relevant diffusion equation.
DOI
Optical tweezers have been used to investigate the dependance of electrostatic inter-particle forces on separation, in systems consisting of pairs of either model silica beads or emulsion droplets. Measurements were carried out as a function of ionic strength and, at salt concentrations where the Debye length was larger than the standard deviation of Brownian fluctuations of the particles in the traps, results were found to agree reasonably well with the predictions of DLVO theory. Experiments were also carried out where the salt concentration of the environment was changed in real-time while interactions were continuously measured. Specifically, single pairs of particles or emulsion droplets were held in a microfluidic channel in close proximity to an interface created between milliQ water and a 5 mM NaCl solution. Changes in the force-separation curves were measured as a function of time and used to monitor changes in the Debye length, and thus the local salt concentration, as ions diffused away from the interface. The results were shown to be consistent with expectations based on a relevant diffusion equation.
DOI
Wednesday, December 16, 2015
Plasmonic absorption activated trapping and assembling of colloidal crystals with non-resonant continuous gold films
Zhiwen Kang, Jiajie Chen, Shu-Yuen Wu and Ho-Pui Ho
Here we report the realization of trapping and assembly of colloidal crystals on continuous gold thin films based on the combined effect of thermophoresis and thermal convection associated with plasmonic optical heating. In the system, the stabilized trapping phenomenon is driven by thermophoretic forces caused by a temperature gradient which pushes the target particles from cold to hot regions and always in an opposite direction to the axial convective drag forces. Furthermore, the lateral convective flow of an aqueous medium accelerates the formation of the trap considerably by dragging target particles into the hot region from a long distance. The influence of salt concentration on the trapping behavior has also been investigated. Typically the threshold optical power density is in the order of microwatts per square micrometer (∼μW μm−2). We anticipate that the reported optical trapping approach may find many potential applications in biophysics, life sciences, and lab-on-a-chip devices.
DOI
Here we report the realization of trapping and assembly of colloidal crystals on continuous gold thin films based on the combined effect of thermophoresis and thermal convection associated with plasmonic optical heating. In the system, the stabilized trapping phenomenon is driven by thermophoretic forces caused by a temperature gradient which pushes the target particles from cold to hot regions and always in an opposite direction to the axial convective drag forces. Furthermore, the lateral convective flow of an aqueous medium accelerates the formation of the trap considerably by dragging target particles into the hot region from a long distance. The influence of salt concentration on the trapping behavior has also been investigated. Typically the threshold optical power density is in the order of microwatts per square micrometer (∼μW μm−2). We anticipate that the reported optical trapping approach may find many potential applications in biophysics, life sciences, and lab-on-a-chip devices.
DOI
Monday, December 7, 2015
FACS-style detection for real-time cell viscoelastic cytometry
Aditya Kasukurti, Charles Eggleton, Sanjay A Desai and David W M Marr
Cell mechanical properties have been established as a label-free biophysical marker of cell viability and health; however, real-time methods with significant throughput for accurately and non-destructively measuring these properties remain widely unavailable. Without appropriate labels for use with fluorescence activated cell sorters (FACS), easily implemented real-time technology for tracking cell-level mechanical properties remains a current need. Employing modulated optical forces and enabled by a low-dimensional FACS-style detection method introduced here, we present a viscoelasticity cytometer (VC) capable of real-time and continuous measure. We demonstrate utility of this approach by tracking the high-frequency cell physical properties of populations of chemically-modified cells at rates of ~ 1 s-1 and explain observations within the context of a simple theoretical model.
DOI
Cell mechanical properties have been established as a label-free biophysical marker of cell viability and health; however, real-time methods with significant throughput for accurately and non-destructively measuring these properties remain widely unavailable. Without appropriate labels for use with fluorescence activated cell sorters (FACS), easily implemented real-time technology for tracking cell-level mechanical properties remains a current need. Employing modulated optical forces and enabled by a low-dimensional FACS-style detection method introduced here, we present a viscoelasticity cytometer (VC) capable of real-time and continuous measure. We demonstrate utility of this approach by tracking the high-frequency cell physical properties of populations of chemically-modified cells at rates of ~ 1 s-1 and explain observations within the context of a simple theoretical model.
DOI
Tuesday, November 3, 2015
Scaling of optical forces on Au–PEG core–shell nanoparticles
Donatella Spadaro, Maria A. Iatì, Maria G. Donato, Pietro G. Gucciardi, Rosalba Saija, Anurag R. Cherlakola, Stefano Scaramuzza, Vincenzo Amendola and Onofrio M. Maragò
Optical trapping of hybrid core–shell gold–polymer particles is studied. Optical forces are measured for different gold core size and polymer shell thickness, revealing how a polymer shell increases the trapping efficiency with respect to the bare gold nanoparticles. Data are in agreement with calculations of optical trapping based on electromagnetic scattering theory in the T-matrix approach. The scaling behaviour of optical forces with respect to the ratio between polymer layer thickness and the whole particle radius is found and discussed.
DOI
Optical trapping of hybrid core–shell gold–polymer particles is studied. Optical forces are measured for different gold core size and polymer shell thickness, revealing how a polymer shell increases the trapping efficiency with respect to the bare gold nanoparticles. Data are in agreement with calculations of optical trapping based on electromagnetic scattering theory in the T-matrix approach. The scaling behaviour of optical forces with respect to the ratio between polymer layer thickness and the whole particle radius is found and discussed.
DOI
Wednesday, October 28, 2015
Scaling of optical forces on Au-PEG core-shell nanoparticles
Donatella Spadaro, Antonella Iatì, Maria Grazia Donato, Pietro Giuseppe Gucciardi, Rosalba Saija, Anurag Cherlakola, Stefano Scaramuzza, Vincenzo Amendola and Onofrio Marago
Optical trapping of hybrid core-shell gold-polymer particles is studied. Optical forces are measured for different gold core size and polymer shell thickness, revealing how a polymer shell increases the trapping efficiency with respect to the bare gold nanoparticles. Data are in agreement with calculations of optical trapping based on electromagnetic scattering theory in the T-matrix approach. The scaling behaviour of optical forces with respect to the ratio between polymer layer thickness and the whole particle radius is found and discussed.
DOI
Optical trapping of hybrid core-shell gold-polymer particles is studied. Optical forces are measured for different gold core size and polymer shell thickness, revealing how a polymer shell increases the trapping efficiency with respect to the bare gold nanoparticles. Data are in agreement with calculations of optical trapping based on electromagnetic scattering theory in the T-matrix approach. The scaling behaviour of optical forces with respect to the ratio between polymer layer thickness and the whole particle radius is found and discussed.
DOI
Thursday, September 10, 2015
Nanofiber-excited plasmonic manipulation of polystyrene nanospheres
Y. Li, Y. J. Hu and Q. Wu
This paper reports optical nanofiber-excited plasmonic manipulation of polystyrene nanospheres. Gold nanoparticles (200 nm in diameter) are deposited on the surface of a nanofiber, and their local surface plasmon resonance (LSPR) is excited by the evanescent wave around the nanofiber. Theoretical results indicate that, the field enhancement resulting from the LSPR excitation can generate an enhanced gradient and scattering forces acting on the spheres, and an accelerated propulsion occurred. To verify the prediction, experiments were performed to trap and transport polystyrene nanospheres along a 500 nm diameter fiber decorated with gold nanoparticles, the average enhancement factor of the velocity of spheres for the LSPR case is found to be about 5 times with respect to the nanofiber case.
DOI
This paper reports optical nanofiber-excited plasmonic manipulation of polystyrene nanospheres. Gold nanoparticles (200 nm in diameter) are deposited on the surface of a nanofiber, and their local surface plasmon resonance (LSPR) is excited by the evanescent wave around the nanofiber. Theoretical results indicate that, the field enhancement resulting from the LSPR excitation can generate an enhanced gradient and scattering forces acting on the spheres, and an accelerated propulsion occurred. To verify the prediction, experiments were performed to trap and transport polystyrene nanospheres along a 500 nm diameter fiber decorated with gold nanoparticles, the average enhancement factor of the velocity of spheres for the LSPR case is found to be about 5 times with respect to the nanofiber case.
DOI
Tuesday, June 23, 2015
Low-cost optical manipulation using hanging droplets of PDMS
Craig McDonald and David McGloin
We propose and demonstrate a low-cost optical micromanipulation system that makes use of simple microfabricated components coupled to a smartphone camera for imaging. Layering hanging droplets of polydimethylsiloxane (PDMS) on microscope coverslips, and curing with a 100 W bulb, creates lenses capable of optical trapping. Optically trapped 3.93 μm silica beads were imaged with a second hanging droplet lens, doped with 1400 μg mL−1 Sudan II dye. Through doping, a lens with an integrated long-pass filter that effectively blocks the 532 nm trapping light was produced. Illumination was provided by shining a lamp into polystyrene foam packaging, perpendicular to the imaging path, producing a diffuse light source. We observed two dimensional trapping and report a Q value of [similar]8.9 × 10−3. The techniques here are an addition to the growing body of work on low cost and adaptable microfluidics.
DOI
We propose and demonstrate a low-cost optical micromanipulation system that makes use of simple microfabricated components coupled to a smartphone camera for imaging. Layering hanging droplets of polydimethylsiloxane (PDMS) on microscope coverslips, and curing with a 100 W bulb, creates lenses capable of optical trapping. Optically trapped 3.93 μm silica beads were imaged with a second hanging droplet lens, doped with 1400 μg mL−1 Sudan II dye. Through doping, a lens with an integrated long-pass filter that effectively blocks the 532 nm trapping light was produced. Illumination was provided by shining a lamp into polystyrene foam packaging, perpendicular to the imaging path, producing a diffuse light source. We observed two dimensional trapping and report a Q value of [similar]8.9 × 10−3. The techniques here are an addition to the growing body of work on low cost and adaptable microfluidics.
DOI
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