Sivashankar Krishnamoorthy | Luxembourg Institute of Science and Technology (original) (raw)
Papers by Sivashankar Krishnamoorthy
Proceedings of SPIE, Feb 7, 2008
We present a novel concept for an optical biosensor based on Whispering Gallery Mode (WGM) excita... more We present a novel concept for an optical biosensor based on Whispering Gallery Mode (WGM) excitations in clusters of spherical microresonators. WGM are specific optical modes that arise when light is trapped by Total Internal Reflection (TIR) inside of a sphere and circulates close to its circumference. These modes are sensitive to the adsorption of (bio-) molecules onto the resonator surface upon which the WGM spectrum is shifted towards higher wavelengths. Compared to single particles, clusters of microresonators offer the advantage of being more easily detected due to their higher radiative emission power. Further, the lineshape of the spectra obtained from clusters depends crucially on their composition and therefore may be used as a fingerprint for their identification, e.g., for sensing applications in array formats. Our results demonstrate that clusters of microresonators show the same sensitivity and performance as single spheres. The adsorption of layers of polyelectrolytes and bovine serum albumin (BSA) onto clusters of spheres with 10 μm diameter has been monitored in situ. Depending on the choice of materials, we achieved a mass sensitivity limit of 50 fg, which is about 100 times more sensitive than that of state-of-the-art WGM biosensors.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2018
International audienc
HAL (Le Centre pour la Communication Scientifique Directe), Jun 17, 2019
International audienc
Sensors, Jun 22, 2010
Whispering gallery modes (WGMs) in surface-fixated fluorescent polystyrene microbeads are studied... more Whispering gallery modes (WGMs) in surface-fixated fluorescent polystyrene microbeads are studied in view of their capability of sensing the formation of biochemical adsorption layers on their outer surface with the well-established biotin-streptavidin specific binding as the model system. Three different methods for analysis of the observed shifts in the WGM wavelength positions are applied and used to quantify the adsorbed mass densities, which are then compared with the results of a comparative surface plasmon resonance (SPR) study.
Sensitive transduction of bio-molecular binding events on chip carries profound implications to t... more Sensitive transduction of bio-molecular binding events on chip carries profound implications to the outcome of a range of in vitro sensors. This includes biosensors that address research as well as diagnostic questions of clinical relevance, e.g., profiling of biomarkers, protein expression, drug and toxicity screening, drug-efficacy monitoring, among others. Nanostructured biosensors in general, and plasmonic biosensors in specific constitute a promising advance in this direction owing to their ability to cater to better sensitivity, response times, and miniaturization, in addition to imparting smart, intelligent capabilities to interfaces. Plasmonic biosensors take advantage of electromagnetic (EM) near-field enhancements at nanoscale geometries such as curvatures or gaps of the order of only a few nanometers, in order to transduce molecular binding events with high sensitivity. The geometric length scales involved, typically overlap with the size of small proteins. For a successful outcome and rational design of plasmonic sensors, it is crucial to attain a control over fabrication down to molecular resolutions. Such control should enable an orthogonal access to the different geometric attributes (e.g., size, separation, curvatures, topography) and uniformly so, across macroscopic areas (of at least a few square millimeters). This is necessary to ensure that the influence of the geometric variables on the optical or biomolecular response is adequately mapped. The uniformity across macroscopic lengthscales will enable correlating the macroscopic response with what happens at the nanoscale, and further enabling the use of analytical tools with macroscopic foot prints (e.g., XPS, IR, SPR). In this direction, the talk would present approaches to fabrication of gold nanoarrays of different types, their optical and spectroscopic investigations correlated with their geometries in application to surface-enhanced Raman spectroscopy based molecular sensing. The fabrication schemes exploit combination of molecular and colloidal self-assembly, delivering nanoarrays with feature separations down to sub-10nm regime, systematic and orthogonal control over different geometric variables, exhibiting low standard deviations (<; 10%) across full-wafer level. These approaches enable a promising nanoscale platform to efficient investigations and rational optimization of plasmonic biointerfaces.
Zenodo (CERN European Organization for Nuclear Research), Dec 7, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
arXiv (Cornell University), Nov 27, 2020
Electromagnetic hot-spots at ultra-narrow plasmonic nanogaps carry immense potential to drive det... more Electromagnetic hot-spots at ultra-narrow plasmonic nanogaps carry immense potential to drive detection limits down to few molecules in sensors based on surface enhanced Raman or Fluorescence spectroscopies. However, leveraging the EM hot-spots requires access to the gaps, which in turn depends on the size of the analyte in relation to gap distances. Herein we leverage a well-calibrated process based on self-assembly of block copolymer colloids on fullwafer level to produce high density plasmonic nanopillar arrays exhibiting large number (> 10 10 cm-2) of uniform inter-pillar EM hot-spots. The approach allows convenient handles to systematically vary the inter-pillar gap distances down to sub-10 nm regime. The results show 2 compelling trends of the impact of analyte dimensions in relation to the gap distances towards their leverage over inter-pillar hot-spots, and the resulting sensitivity in SERS based molecular assays. Comparing the detection of labelled proteins in surface-enhanced Raman and metalenhanced Fluorescence configurations further reveal the relative advantage of Fluorescence over Raman detection while encountering the spatial limitations imposed by the gaps. Quantitative assays with limits of detection down to picomolar concentrations is realized for both the small organic molecules and the proteins. The well-defined geometries delivered by nanofabrication approach is critical to arriving at realistic geometric models to establish meaningful correlation between structure, optical properties and sensitivity of nanopillar arrays in plasmonic assays. The findings emphasize the need for the rational design of EM hot-spots that take into account the analyte dimensions to drive ultra-high sensitivity in plasmonenhanced spectroscopies.
Several clinical studies have reported the benefit of the administration of Mesenchymal stromal c... more Several clinical studies have reported the benefit of the administration of Mesenchymal stromal cells (MSC) in various cell therapies. However, these studies have also highlighted that their routine application need urgently new cell substrates to multiply MSC in vitro in GMP conditions. Indeed, MSC are scarce in the human body. It is therefore necessary to amplify MSC in vitro to achieve clinically relevant cell doses. Microcarriers are attractive substrate. However, in practice, MSC cultivation on the microcarriers currently available on the market has been demonstrated unsuccessful. The main aim of our research relies upon the optimization of the surface properties of microcarriers promoting MSC culture in vitro. To achieve this purpose, the outer surface of microcarriers is functionalized by grafting a thin layer composed of a “smart polymer”, mostly poly N-isopropylacrylamide (pNIPAM), whose composition has been tailored to promote the adhesion and spreading of MSC with the ability to control their fast and efficient detachment following a small change in temperature. Due to particular shape of microcarriers, specific microscopy technique must be adapted to analyse the efficiency of grafting reaction. At this stage, we have demonstrated some reliable characterization methods based on Time-of-Flight and Nanoscale Secondary Ion Mass Spectrometry (ToF and NanoSIMS), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Fluorescent Microscopy for two type of microcarriers: Dextran and Polystyrene based carriersPeer reviewe
HAL (Le Centre pour la Communication Scientifique Directe), Jul 7, 2020
International audienc
Sensors and Actuators B-chemical, Sep 1, 2022
Journal of Physical Chemistry C, Mar 23, 2016
Sequential vapor infiltration synthesis (SVIS) within block-copolymer templates has emerged as an... more Sequential vapor infiltration synthesis (SVIS) within block-copolymer templates has emerged as an attractive means for the controlled formation of metal oxide nanoarrays on arbitrary substrates. This approach takes advantage of the molecular-level controls that are inherent in the production of the template and the exposure tools that are available for the vapor-phase growth of materials. To take adequate advantage of these controls and their dependencies on any environmental factors, it is essential to understand the mechanisms that govern nanostructure morphology at different stages of the growth process. To this end, this work correlates the evolution of the internal structure with the chemical functionality of block-copolymer templates in response to different conditions of exposure to volatile titania precursors. The evolution is followed by mapping structural and functional information at lateral and vertical resolutions down to a few nanometers through a combination of electron microscopies [scanni...
Sensors
Label-free field-effect transistor-based immunosensors are promising candidates for proteomics an... more Label-free field-effect transistor-based immunosensors are promising candidates for proteomics and peptidomics-based diagnostics and therapeutics due to their high multiplexing capability, fast response time, and ability to increase the sensor sensitivity due to the short length of peptides. In this work, planar junctionless field-effect transistor sensors (FETs) were fabricated and characterized for pH sensing. The device with SiO2 gate oxide has shown voltage sensitivity of 41.8 ± 1.4, 39.9 ± 1.4, 39.0 ± 1.1, and 37.6 ± 1.0 mV/pH for constant drain currents of 5, 10, 20, and 50 nA, respectively, with a drain to source voltage of 0.05 V. The drift analysis shows a stability over time of −18 nA/h (pH 7.75), −3.5 nA/h (pH 6.84), −0.5 nA/h (pH 4.91), 0.5 nA/h (pH 3.43), corresponding to a pH drift of −0.45, −0.09, −0.01, and 0.01 per h. Theoretical modeling and simulation resulted in a mean value of the surface states of 3.8 × 1015/cm2 with a standard deviation of 3.6 × 1015/cm2. We h...
Structure and functionality of molecular layers play a crucial role in determining the outcome of... more Structure and functionality of molecular layers play a crucial role in determining the outcome of analyte-receptor interactions on affinity biosensors. The control over the structure of these molecular layers gives an independent means to enhance the sensor performance. Here we study the impact of the length and flexibility of molecular tethers on analyte capture by tethered receptors on quartz crystal microbalance and surface plasmon resonance sensors. Our results show clear enhancement of analyte-receptor interactions when receptors are bound to the sensor via flexible, and longer tethers. The findings further reveal a qualitative similarity of the impact of tether length on widely different type of binding interactions, viz. gold nanoparticle binding to tethered amine layers, and neutravidin binding to tethered biotin layers. By independent determination of tether densities, our investigations decouple the impact of receptor densities, and the tether conformations, and confirm th...
SSRN Electronic Journal, 2022
Applied Sciences, 2021
Human mesenchymal stem cells (hMSCs) respond to the characteristics of their surrounding microenv... more Human mesenchymal stem cells (hMSCs) respond to the characteristics of their surrounding microenvironment, i.e., their extracellular matrix (ECM). The possibility of mimicking the ECM offers the opportunity to elicit specific cell behaviors. The control of surface properties of a biomaterial at the scale level of the components of the ECM has the potential to effectively modulate cell response. Ordered nanoscale silicon pillar arrays were fabricated using reverse micelles of block copolymers on full wafers, with standard deviations lower than 15%. Bioactive synthetic peptides were covalently grafted on nanoarrays to evaluate possible synergies between chemistry and topography on osteogenic differentiation of hMSCs. Functionalization with RGD (Arg-Gly-Asp) and BMP-2 (bone morphogenetic protein-2) mimetic peptides lead to an enhancement of osteogenic differentiation. Bare nanopillar arrays of reduced pitch were found to promote faster hMSC differentiation. These findings highlight the...
Proceedings of SPIE, Feb 7, 2008
We present a novel concept for an optical biosensor based on Whispering Gallery Mode (WGM) excita... more We present a novel concept for an optical biosensor based on Whispering Gallery Mode (WGM) excitations in clusters of spherical microresonators. WGM are specific optical modes that arise when light is trapped by Total Internal Reflection (TIR) inside of a sphere and circulates close to its circumference. These modes are sensitive to the adsorption of (bio-) molecules onto the resonator surface upon which the WGM spectrum is shifted towards higher wavelengths. Compared to single particles, clusters of microresonators offer the advantage of being more easily detected due to their higher radiative emission power. Further, the lineshape of the spectra obtained from clusters depends crucially on their composition and therefore may be used as a fingerprint for their identification, e.g., for sensing applications in array formats. Our results demonstrate that clusters of microresonators show the same sensitivity and performance as single spheres. The adsorption of layers of polyelectrolytes and bovine serum albumin (BSA) onto clusters of spheres with 10 μm diameter has been monitored in situ. Depending on the choice of materials, we achieved a mass sensitivity limit of 50 fg, which is about 100 times more sensitive than that of state-of-the-art WGM biosensors.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2018
International audienc
HAL (Le Centre pour la Communication Scientifique Directe), Jun 17, 2019
International audienc
Sensors, Jun 22, 2010
Whispering gallery modes (WGMs) in surface-fixated fluorescent polystyrene microbeads are studied... more Whispering gallery modes (WGMs) in surface-fixated fluorescent polystyrene microbeads are studied in view of their capability of sensing the formation of biochemical adsorption layers on their outer surface with the well-established biotin-streptavidin specific binding as the model system. Three different methods for analysis of the observed shifts in the WGM wavelength positions are applied and used to quantify the adsorbed mass densities, which are then compared with the results of a comparative surface plasmon resonance (SPR) study.
Sensitive transduction of bio-molecular binding events on chip carries profound implications to t... more Sensitive transduction of bio-molecular binding events on chip carries profound implications to the outcome of a range of in vitro sensors. This includes biosensors that address research as well as diagnostic questions of clinical relevance, e.g., profiling of biomarkers, protein expression, drug and toxicity screening, drug-efficacy monitoring, among others. Nanostructured biosensors in general, and plasmonic biosensors in specific constitute a promising advance in this direction owing to their ability to cater to better sensitivity, response times, and miniaturization, in addition to imparting smart, intelligent capabilities to interfaces. Plasmonic biosensors take advantage of electromagnetic (EM) near-field enhancements at nanoscale geometries such as curvatures or gaps of the order of only a few nanometers, in order to transduce molecular binding events with high sensitivity. The geometric length scales involved, typically overlap with the size of small proteins. For a successful outcome and rational design of plasmonic sensors, it is crucial to attain a control over fabrication down to molecular resolutions. Such control should enable an orthogonal access to the different geometric attributes (e.g., size, separation, curvatures, topography) and uniformly so, across macroscopic areas (of at least a few square millimeters). This is necessary to ensure that the influence of the geometric variables on the optical or biomolecular response is adequately mapped. The uniformity across macroscopic lengthscales will enable correlating the macroscopic response with what happens at the nanoscale, and further enabling the use of analytical tools with macroscopic foot prints (e.g., XPS, IR, SPR). In this direction, the talk would present approaches to fabrication of gold nanoarrays of different types, their optical and spectroscopic investigations correlated with their geometries in application to surface-enhanced Raman spectroscopy based molecular sensing. The fabrication schemes exploit combination of molecular and colloidal self-assembly, delivering nanoarrays with feature separations down to sub-10nm regime, systematic and orthogonal control over different geometric variables, exhibiting low standard deviations (<; 10%) across full-wafer level. These approaches enable a promising nanoscale platform to efficient investigations and rational optimization of plasmonic biointerfaces.
Zenodo (CERN European Organization for Nuclear Research), Dec 7, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
arXiv (Cornell University), Nov 27, 2020
Electromagnetic hot-spots at ultra-narrow plasmonic nanogaps carry immense potential to drive det... more Electromagnetic hot-spots at ultra-narrow plasmonic nanogaps carry immense potential to drive detection limits down to few molecules in sensors based on surface enhanced Raman or Fluorescence spectroscopies. However, leveraging the EM hot-spots requires access to the gaps, which in turn depends on the size of the analyte in relation to gap distances. Herein we leverage a well-calibrated process based on self-assembly of block copolymer colloids on fullwafer level to produce high density plasmonic nanopillar arrays exhibiting large number (> 10 10 cm-2) of uniform inter-pillar EM hot-spots. The approach allows convenient handles to systematically vary the inter-pillar gap distances down to sub-10 nm regime. The results show 2 compelling trends of the impact of analyte dimensions in relation to the gap distances towards their leverage over inter-pillar hot-spots, and the resulting sensitivity in SERS based molecular assays. Comparing the detection of labelled proteins in surface-enhanced Raman and metalenhanced Fluorescence configurations further reveal the relative advantage of Fluorescence over Raman detection while encountering the spatial limitations imposed by the gaps. Quantitative assays with limits of detection down to picomolar concentrations is realized for both the small organic molecules and the proteins. The well-defined geometries delivered by nanofabrication approach is critical to arriving at realistic geometric models to establish meaningful correlation between structure, optical properties and sensitivity of nanopillar arrays in plasmonic assays. The findings emphasize the need for the rational design of EM hot-spots that take into account the analyte dimensions to drive ultra-high sensitivity in plasmonenhanced spectroscopies.
Several clinical studies have reported the benefit of the administration of Mesenchymal stromal c... more Several clinical studies have reported the benefit of the administration of Mesenchymal stromal cells (MSC) in various cell therapies. However, these studies have also highlighted that their routine application need urgently new cell substrates to multiply MSC in vitro in GMP conditions. Indeed, MSC are scarce in the human body. It is therefore necessary to amplify MSC in vitro to achieve clinically relevant cell doses. Microcarriers are attractive substrate. However, in practice, MSC cultivation on the microcarriers currently available on the market has been demonstrated unsuccessful. The main aim of our research relies upon the optimization of the surface properties of microcarriers promoting MSC culture in vitro. To achieve this purpose, the outer surface of microcarriers is functionalized by grafting a thin layer composed of a “smart polymer”, mostly poly N-isopropylacrylamide (pNIPAM), whose composition has been tailored to promote the adhesion and spreading of MSC with the ability to control their fast and efficient detachment following a small change in temperature. Due to particular shape of microcarriers, specific microscopy technique must be adapted to analyse the efficiency of grafting reaction. At this stage, we have demonstrated some reliable characterization methods based on Time-of-Flight and Nanoscale Secondary Ion Mass Spectrometry (ToF and NanoSIMS), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Fluorescent Microscopy for two type of microcarriers: Dextran and Polystyrene based carriersPeer reviewe
HAL (Le Centre pour la Communication Scientifique Directe), Jul 7, 2020
International audienc
Sensors and Actuators B-chemical, Sep 1, 2022
Journal of Physical Chemistry C, Mar 23, 2016
Sequential vapor infiltration synthesis (SVIS) within block-copolymer templates has emerged as an... more Sequential vapor infiltration synthesis (SVIS) within block-copolymer templates has emerged as an attractive means for the controlled formation of metal oxide nanoarrays on arbitrary substrates. This approach takes advantage of the molecular-level controls that are inherent in the production of the template and the exposure tools that are available for the vapor-phase growth of materials. To take adequate advantage of these controls and their dependencies on any environmental factors, it is essential to understand the mechanisms that govern nanostructure morphology at different stages of the growth process. To this end, this work correlates the evolution of the internal structure with the chemical functionality of block-copolymer templates in response to different conditions of exposure to volatile titania precursors. The evolution is followed by mapping structural and functional information at lateral and vertical resolutions down to a few nanometers through a combination of electron microscopies [scanni...
Sensors
Label-free field-effect transistor-based immunosensors are promising candidates for proteomics an... more Label-free field-effect transistor-based immunosensors are promising candidates for proteomics and peptidomics-based diagnostics and therapeutics due to their high multiplexing capability, fast response time, and ability to increase the sensor sensitivity due to the short length of peptides. In this work, planar junctionless field-effect transistor sensors (FETs) were fabricated and characterized for pH sensing. The device with SiO2 gate oxide has shown voltage sensitivity of 41.8 ± 1.4, 39.9 ± 1.4, 39.0 ± 1.1, and 37.6 ± 1.0 mV/pH for constant drain currents of 5, 10, 20, and 50 nA, respectively, with a drain to source voltage of 0.05 V. The drift analysis shows a stability over time of −18 nA/h (pH 7.75), −3.5 nA/h (pH 6.84), −0.5 nA/h (pH 4.91), 0.5 nA/h (pH 3.43), corresponding to a pH drift of −0.45, −0.09, −0.01, and 0.01 per h. Theoretical modeling and simulation resulted in a mean value of the surface states of 3.8 × 1015/cm2 with a standard deviation of 3.6 × 1015/cm2. We h...
Structure and functionality of molecular layers play a crucial role in determining the outcome of... more Structure and functionality of molecular layers play a crucial role in determining the outcome of analyte-receptor interactions on affinity biosensors. The control over the structure of these molecular layers gives an independent means to enhance the sensor performance. Here we study the impact of the length and flexibility of molecular tethers on analyte capture by tethered receptors on quartz crystal microbalance and surface plasmon resonance sensors. Our results show clear enhancement of analyte-receptor interactions when receptors are bound to the sensor via flexible, and longer tethers. The findings further reveal a qualitative similarity of the impact of tether length on widely different type of binding interactions, viz. gold nanoparticle binding to tethered amine layers, and neutravidin binding to tethered biotin layers. By independent determination of tether densities, our investigations decouple the impact of receptor densities, and the tether conformations, and confirm th...
SSRN Electronic Journal, 2022
Applied Sciences, 2021
Human mesenchymal stem cells (hMSCs) respond to the characteristics of their surrounding microenv... more Human mesenchymal stem cells (hMSCs) respond to the characteristics of their surrounding microenvironment, i.e., their extracellular matrix (ECM). The possibility of mimicking the ECM offers the opportunity to elicit specific cell behaviors. The control of surface properties of a biomaterial at the scale level of the components of the ECM has the potential to effectively modulate cell response. Ordered nanoscale silicon pillar arrays were fabricated using reverse micelles of block copolymers on full wafers, with standard deviations lower than 15%. Bioactive synthetic peptides were covalently grafted on nanoarrays to evaluate possible synergies between chemistry and topography on osteogenic differentiation of hMSCs. Functionalization with RGD (Arg-Gly-Asp) and BMP-2 (bone morphogenetic protein-2) mimetic peptides lead to an enhancement of osteogenic differentiation. Bare nanopillar arrays of reduced pitch were found to promote faster hMSC differentiation. These findings highlight the...