Micro-cantilever based micro weighing balance was studied using polydimethylsiloxane micro-cantilever beam and water droplet. In this system, micro-cantilever beam acts as spring balance while the droplet acts as weight. Initially, tip defection of cantilever beam under the body load provided by water droplets of sizes 4, 5, 6 and 7 μl were found experimentally. For this study, droplets were placed at dimensionless length ξ = 0.8 from the clamped end. Fluid load augmentation was studied by studying the tip deflection of the beam with droplet under flow velocities between 0.75 and 1.5 m/s. A mini wind tunnel is used to provide fluid load with wind flow occurring along the length of the beam. Experimental results show an increase in tip deflection with flow velocity, suggesting the phenomena of fluid load augmentation. In addition to experimental results, this paper presents details on modelling of natural frequency of the micro-cantilever beam with added mass using Rayleigh’s energy method.
Micro-photosynthetic power cell (μPSC) is one of the emerging energy harvesting technologies which harvests energy using light (photosynthesis) and carbohydrate metabolism in dark (respiration) for low-power (mW range) applications. μPSC is a green technology that not only uses solar power and algae, but also provides power in both dark and light conditions. This perspective article provides state of the art of μPSC technology in terms of fabrication, mathematical modeling and energy harvesting circuit design. Currently, low power densities and high cost are the factors limiting μPSCs commercialization. Key aspects and methods to enhance the performance and decrease the cost are proposed in this paper.
Due to the excellent biocompatibility of gold nanoparticles with human organism, they have great potentials for controlled drug delivery, cancer detection, cancer therapy, cancer management, and biomedical imaging. The unique optical and physiochemical properties of gold nanoparticles have made them a great candidate for intracellular diagnosis using surface-enhanced Raman microscopy and hyperspectral microscopy. These two techniques offer sensitive and non-invasive measurements. Gold nanoparticles also can be utilized to modulate the mechanobiological properties of cells, providing a platform to suppress the metastatic level of cells.
Study of Detection and Capture of Exosomes by Using the Morphologies of Ex Situ and In Situ NanostructuresPublished: 14 December 2018 by The Electrochemical Society in Journal of The Electrochemical Society
Over the past few decades, fabrication of optimal nanostructures for detecting specific bio-entities remained an active area of research. It is well-known that the structure and the plasmonic properties of noble metal nanoparticles can be customized for specific applications such as biosensing, diagnosis, imaging, etc. by tuning the size and shape of the nanoparticles. Thus, by using the plasmonic property of noble metals, the detection at the nano-scale is possible by monitoring the shift of Localized Surface Plasmon Resonance (LSPR) band with respect to the changes in the dielectric constant of the surrounding medium. The present study is aimed to the evaluation of the quality and performance of two nano plasmonic platforms for detection and capture of exosomes.
This paper presents the study of the performance of a novel SU-8 waveguide on a quartz substrate for evanescent fluorescence spectroscopy. The sensitivity of the sensing platform (SU-8/quartz) was compared to a SU-8 waveguide on silica fabricated with the standard protocol. The physical properties of the SU-8/quartz waveguide resulting from a novel fabrication process allowed for a higher fluorescence coupling and lower optical losses than the SU-8/silica waveguide. The impact of the different indices of refraction of both waveguides on the fluorescence collection efficiency was calculated with 3D FDTD simulations by simulating randomly oriented and phased dimensionless current dipoles in the vicinity of their sensing layers. An evanescent fluorescence spectroscopy experiment was performed with different concentrations of Alexa-647 labeled-BSA proteins immobilized on the two polymer waveguides to compare the sensitivity of both sensing platforms. The SU-8/quartz waveguide revealed to have a higher calculated fluorescence collection efficiency and also a greater measured fluorescence light output compared to the SU-8/silica waveguide.
Enhanced Internalization of Indian Ayurvedic Swarna Bhasma (Gold Nanopowder) for Effective Interaction with Human CellsPublished: 01 October 2018 by American Scientific Publishers in Journal of Nanoscience and Nanotechnology
In the ancient traditional Indian Ayurvedic system of natural healing, gold nanoparticles (Swarna Bhasma, gold ash) have been used for its therapeutic benefits as far back as 2500 B.C. Ayurvedic medicinal preparations are complex mixtures that include many plant-derived products and metals. Bhasmas date as far back as the 8th century and are made by samskaras (processings), such as shodhana (purification and potentiation), jarana (roasting), and marana (incineration, trituration) in the presence of plant products, including juices and concoctions. Previous studies characterized the physical properties of gold ash, and the mechanisms of its entry into human cells, but only preliminary data exist on its toxicity. Before using nanoparticles for therapeutic application, it is extremely important to study their toxicity and cellular internalization. In the present study, various imaging techniques were used to investigate Swarna Bhasma's (gold nanopowder) toxicity in both cancerous and noncancerous cells (HeLa and HFF-1) and to characterize its spectral properties. The results showed that gold ash particles had no impact on the cellular viability of both HeLa and HFF-1 cells, even at high concentrations or long incubation times. Moreover, it was found that the internalization level of Swarna Bhasma to cells may be improved by mechanical breaking of the large aggregates into smaller agglomerates. Hyperspectral images revealed that after breaking, the small agglomerates have different spectral properties in cells, compared to the original aggregates, suggesting that size of particles is instrumental for the subcellular interaction with human cells.
The pollen tube is a tip growing cell that is able to invade plant tissues in order to accomplish its function — the delivery of sperm cells to the ovule. The pistillar tissues through which the tube has to elongate represent a formidable mechanical obstacle, but it is unknown how much force the growing tube is able to exert, or how mechanical impedance affects its growth behavior. We quantified the invasive force of individual pollen tubes using a microfluidic lab-on-a-chip device featuring a microscopic cantilever. Using finite element method the maximum invasive growth force of the growing pollen tube was determined to be in the microNewton range. Real time monitoring revealed that contact with the mechanical obstacle caused a shift in the peak frequency characterizing the oscillatory behavior of the pollen tube growth rate. This suggests the presence of a feedback-based control mechanism with a mechanical regulatory component.
Detection and study of bioelements using microfluidic systems has been of great interest in the biodiagnostics field. Microcantilevers are the most used systems in biodetection due to their implementation simplicity which have been used for a wide variety of applications ranging from cellular to molecular diagnosis. However, increasing further the sensitivity of the microcantilever systems have a great effect on the cantilever based sensing for chemical and bio applications. In order to improve further the performance of microcantilevers, a flow force augmented 3D suspended microchannel is proposed using which microparticles can be conveyed through a microchannel inside the microcantilever to the detection area. This innovative microchannel design addresses the low sensitivity issue by increasing its sensitivity up to 5 times than the earlier reported similar microsystems. Moreover, fabricating this microsystem out of Polydimethylsiloxane (PDMS) would eliminate external exciter dependency in many detection applications such as biodiagnostics. In this study, the designed microsystem has been analyzed theoretically, simulated and tested. Moreover, the microsystem has been fabricated and tested under different conditions, the results of which have been compared with simulation results. Finally, its innovative fabrication process and issues are reported and discussed. This article is protected by copyright. All rights reserved
The bovine growth hormone is a common growth promoter used in dairy farming to enhance the milk production. Its use is forbidden in Canada, the European Union and many other countries because the hormone could be harmful to the health of animals and humans. For this reason, it is important to develop fast and low-cost methods of detection of the bovine growth hormone at very low concentrations. Conventional methods as well as the recent developments of lab-on-a-chip technologies are reviewed with an emphasis of the work in our laboratory.
This paper presents a current sensing circuit specifically designed and prototyped for power studies of microlevel energy sources such as micro-photosynthetic cells (μ-PSCs). The proposed current sensing circuit takes into consideration recently proposed current sensing topologies. It provides an accurate and dynamic current reading from nA up to few mA range. The dynamic and wide range measurement features aimed to help researchers visualize the effect of each element (temperature, micro-organism, membrane ...) involved in the generation of energy from a μ-FSC. The practical results obtained show an acceptable accuracy up to second digit (in %) for the whole operation range (nA up to mA).
This paper reports a novel method to detect ammonia by using the ninhydrin – PDMS composite. The polymer composite film is prepared by integrating ninhydrin into the PDMS polymer matrix. Further, an optical lab-on-a-chip device is developed by integrating the ninhydrin-polymer composite into a microfluidic device for the detection of ammonia. The chemisorption of ammonia onto the composite resulted in the change in its optical absorption property. The proposed device has an integrated light emitting diode and photoresistor in order to measure the change in absorption and hence the detection and quantification of ammonia are performed. The response time of the sensor was found to be linear for a wide range of ammonia concentrations and it is shortest for the thin (100 μm) composite film. The limit of detection of the proposed device is found to be as low as 2ppm. The proposed sensor platform is also demonstrated for the detection of amino acids.
The fabrication and characterization of SU-8 multimode optical waveguides on fused quartz and silicon oxide substrates were successfully realized and analyzed. Optical losses for the transverse electric (TE) mode polarization of 0.58 dB cm−1 and 1.44 dB cm−1 and transverse magnetic (TM) mode polarization of 0.73 dB cm−1 and 1.16 dB cm−1 were measured for SU-8 waveguides on fused quartz and silicon oxide substrates, respectively. The fabrication process for SU-8 waveguides on quartz developed herein could be applied for SU-8 optical integrated devices on other substrate materials.
Nano-Integrated Suspended Polymeric Microfluidics (SPMF) Platform for Ultra-Sensitive Bio-Molecular Recognition of Bovin...Published: 08 September 2017 by Springer Nature in Scientific Reports
The development of sensitive platforms for the detection of biomolecules recognition is an extremely important problem in clinical diagnostics. In microcantilever (MC) transducers, surface-stress is induced upon bimolecular interaction which is translated into MC deflection. This paper presents a cost-effective and ultra-sensitive MC-based biosensing platform. To address these goals, the need for costly high-resolution read-out system has been eliminated by reducing the cantilever compliance through developing a polymer-based cantilever. Furthermore a microfluidic system has been integrated with the MC in order to enhance sensitivity and response time and to reduce analytes consumption. Gold nanoparticles (AuNPs) are synthesized on the surface of suspended microfluidics as the selective layer for biomolecule immobilization. The biosensing results show significant improvement in the sensitivity of the proposed platform compared with available silicon MC biosensor. A detection limit of 2 ng/ml (100pM) is obtained for the detection of bovine growth hormones. The results validated successful application of suspended polymeric microfluidics (SPMF) as the next generation of biosensing platforms which could enable femtomolar (fM) biomolecular recognition detection.
Comparative study on cellular entry of incinerated ancient gold particles (Swarna Bhasma) and chemically synthesized gol...Published: 06 September 2017 by Springer Nature in Scientific Reports
Gold nanoparticles (AuNPs) are used for a number of imaging and therapeutic applications in east and western part of the world. For thousands of years, the traditional Indian Ayurvedic approach to healing involves the use of incinerated gold ash, prepared with a variety of plant extracts and minerals depending on the region. Here, we describe the characterization of incinerated gold particles (IAuPs) in HeLa (human cells derived from cervical cancer) and HFF-1 (human foreskin fibroblast cells) in comparison to synthesized citrate-capped gold nanoparticles (AuNPs). We found that while individual IAuP crystallites are around 60 nm in size, they form large aggregates with a mean diameter of 4711.7 nm, some of which can enter cells. Fewer cells appeared to have IAuPs compared to AuNPs, although neither type of particle was toxic to cells. Imaging studies revealed that IAuPs were in vesicles, cytosol, or in the nucleus. We found that their nuclear accumulation likely occurred after nuclear envelope breakdown during cell division. We also found that larger IAuPs entered cells via macropinocytosis, while smaller particles entered via clathrin-dependent receptor-mediated endocytosis.
This paper discusses the electrochemical modeling of a microphotosynthetic power cell (μ-PSC) in a similar way as the conventional fuel cell model while taking into consideration the electrochemical dynamics of the chemical contents of the cell. It also presents the development of an electrical equivalent circuit that represents the operation of the fabricated cell. The developed equivalent circuit is different from previous works in which they used the equivalent circuit of an ordinary solar cell. The proposed model predicts the performance of this type of power harvesting cell. The study includes the steady-state and transient responses when the cell is connected to an external load. In particular, the focus of this paper is related to the development of an electrical representation with a computationally efficient parameter model for real-time simulation and control. The performance of this model is simulated and results are evaluated and compared with experimental data.
Micro photosynthetic cell for power generation from algae: Bio-electrochemical modeling and verificationPublished: 01 December 2016 by World Scientific Pub Co Pte Lt in TECHNOLOGY
A simple first-principles mathematical model is developed to predict the performance of a micro photosynthetic power cell (μPSC), an electrochemical device which generates electricity by harnessing electrons from photosynthesis in the presence of light. A lumped parameter approach is used to develop a model in which the electrochemical kinetic rate constants and diffusion effects are lumped into a single characteristic rate constant K. A non-parametric estimation of K for the μPSC is performed by minimizing the sum square errors (SSE) between the experimental and model predicted current and voltages. The developed model is validated by comparing the model predicted v−i characteristics with experimental data not used in the parameter estimation. Sensitivity analysis of the design parameters and the operational parameters reveal interesting insights for performance enhancement. Analysis of the model also suggests that there are two different operating regimes that are observed in this μPSC. This modeling approach can be used in other designs of μPSCs for performance enhancement studies.
A simple first-principles mathematical model is developed to predict the performance of a micro photosynthetic power cell ($\mu$PSC), an electrochemical device which generates electricity by harnessing electrons from photosynthesis in the presence of light. A lumped parameter approach is used to develop a model in which the electrochemical kinetic rate constants and diffusion effects are lumped into a single characteristic rate constant $K$. A non-parametric estimation of $K$ for the $\mu$PSC is performed by minimizing the sum square errors (SSE) between the experimental and model predicted current and voltages. The developed model is validated by comparing the model predicted $v-i$ characteristics with experimental data not used in the parameter estimation. Sensitivity analysis of the design parameters and the operational parameters reveal interesting insights for performance enhancement. Analysis of the model also suggests that there are two different operating regimes that are observed in this $\mu$PSC. This modeling approach can be used in other designs of $\mu$PSCs for performance enhancement studies.
Lab-on-chip technology is attracting great interest due to its potential as miniaturized devices that can automate and integrate many sample-handling steps, minimize consumption of reagent and samples, have short processing time and enable multiplexed analysis. Microfluidic devices have demonstrated their potential for a broad range of applications in life sciences, including point-of-care diagnostics and personalized medicine, based on the routine diagnosis of levels of hormones, cancer markers, and various metabolic products in blood, serum, etc. Microfluidics offers an adaptable platform that can facilitate cell culture as well as monitor their activity and control the cellular environment. Signaling molecules released from cells such as neurotransmitters and hormones are important in assessing the health of cells and the effect of drugs on their functions. In this review, we provide an insight into the state-of-art applications of microfluidics for monitoring of hormones released by cells. In our works, we have demonstrated efficient detection methods for bovine growth hormones using nano and microphotonics integrated microfluidics devices. The bovine growth hormone can be used as a growth promoter in dairy farming to enhance the milk and meat production. In the recent years, a few attempts have been reported on developing very sensitive, fast and low-cost methods of detection of bovine growth hormone using micro devices. This paper reviews the current state-of-art of detection and analysis of hormone using integrated optical micro and nanofluidics systems. In addition, the paper also focuses on various lab-on-a-chip technologies reported recently, and their benefits for screening growth hormones in milk.
Effect of Gradual Heating of Gold Nanoparticle Multilayers on Polymer Substrates on the Characteristics of their LSPR Ba...Published: 01 July 2016 by Avestia Publishing in The 2nd World Congress on New Technologies
Influence of Electric Fields and Conductivity on Pollen Tube Growth assessed via Electrical Lab-on-ChipPublished: 25 January 2016 by Springer Nature in Scientific Reports
Pollen tubes are polarly growing plant cells that are able to rapidly respond to a combination of chemical, mechanical, and electrical cues. This behavioural feature allows them to invade the flower pistil and deliver the sperm cells in highly targeted manner to receptive ovules in order to accomplish fertilization. How signals are perceived and processed in the pollen tube is still poorly understood. Evidence for electrical guidance in particular is vague and highly contradictory. To generate reproducible experimental conditions for the investigation of the effect of electric fields on pollen tube growth we developed an Electrical Lab-on-Chip (ELoC). Pollen from the species Camellia displayed differential sensitivity to electric fields depending on whether the entire cell or only its growing tip was exposed. The response to DC fields was dramatically higher than that to AC fields of the same strength. However, AC fields were found to restore and even promote pollen growth. Surprisingly, the pollen tube response correlated with the conductivity of the growth medium under different AC frequencies—consistent with the notion that the effect of the field on pollen tube growth may be mediated via its effect on the motion of ions.
Highlights•We propose a MEMS based optical tactile sensor.•The paper describes the opto-mechanical modelling, FEM simulation, fabrication and characterization of the tactile sensor.•The proposed sensor can measure the local force distribution, relative hardness and local discontinuities in the softness of soft objects, under static and dynamic loading conditions.•The sensor is magnetic resonance compatible, electrically passive, and compatible with the minimally invasive surgical tasks. AbstractThe demand for miniaturized tactile sensing devices have greatly increased ever since the introduction of minimally invasive surgical (MIS) procedures. In this work, a tactile sensor is presented that provides essential artificial fingertip perception during such procedures. The proposed sensor can measure tactile information under various static/dynamic loading conditions by precisely measuring the quantity and position of a concentrated force, the local variation in force distribution, relative hardness and local discontinuities in the hardness of soft objects. The sensor, which is fabricated using fiber-optics and microsystems technology, can be used for most MIS tasks since it meets the necessary requirements of being electrically passive and magnetic resonance compatible.
Electrically Conducting PDMS Nanocomposite Using In Situ Reduction of Gold Nanostructures and Mechanical Stimulation of ...Published: 26 August 2015 by The Electrochemical Society in ECS Journal of Solid State Science and Technology
Electrically conducting nanocomposite has numerous application potential in flexible MEMS and wearable electronics. Polydimethylsiloxane (PDMS) has been identified as an attractive candidate for the fabrication of Bio-MEMS devices due to several benefits such as biocompatibility, good optical properties, easy and low-cost fabrication using soft-lithography, etc. Until now, the synthesis of electrically conducting nanocomposite is proposed only by mechanical stimulation of electrically conducting nano materials such as carbon nanotubes, gold or silver nanoparticles in polymer matrix. In this work, an electrically conducting PDMS nanocomposite is synthesized using a novel combined process of in situ reduction by curing agent of PDMS from aqueous gold chloride solution, and mechanical stimulation of multi-wall carbon nanotubes and silver nanoparticles. The optical, electrical and thermal properties of the PDMS- nanocomposite are characterized. Further, the nanocomposite is micro patterned to fabricate heating elements and electrical signal routing lines in flexible PDMS sheets. The resistivity of the nanocomposite is measured as 3.5 × 10−3 Ω.m, which is much lower than the previously reported value of 1 Ω.m.
Technical note: A portable on-chip assay system for absorbance and plasmonic detection of protein hormone in milkPublished: 01 July 2015 by American Dairy Science Association in Journal of Dairy Science
This paper reports a portable device and method to extract and detect protein hormone in milk samples. Recombinant protein hormone spiked into milk samples was extracted by solid-phase extraction, and detection was carried out using the plasmonic property of gold nanoislands deposited on a glass substrate. Trace levels of hormone spiked in milk were analyzed by their optical absorbance property using a microfluidic chip. We built a portable assay system using disposable lab-on-chip devices. The proposed method is able to detect spiked recombinant protein hormone in milk at concentrations as low as 5ng/mL.
Evaluation of optical properties and biocompatibility of polymer materials for microfluidic applicationsPublished: 01 June 2015 by Institute of Electrical and Electronics Engineers (IEEE) in 2015 Photonics North
Microfluidic technologies have become increasingly effective for diagnostic, physiological, and biochemical applications. The biocompatibility of MEMS devices, which are evolving rapidly in their practicality, has become the paramount property to investigate and optimize through biological and optical testing. Potential applications comprise cell culture, biosensing, immunoisolation, bioparticle sorting, and biomaterial synthesis. In this work we undertake the study of various polymer and nanocomposite materials, such as cyclic olefin copolymer (COC), polymethylmethacrylate (PMMA), polydimethylsiloxane (PDMS), SU-8, polycarbonate (PC) and polystyrene (PS). After the polymer is adequately functionalized, tagged antibodies are attached to the polymer films and, then, the corresponding antigens are brought in contact with the antibodies. The work is novel and complements the contemporary research involving other methods to evaluate the biocompatibility, such as for example, cell culture. The affinity of antibodies toward the polymer is evaluated by the amount of attached antibodies measured by fluorescence spectroscopy.
Dynamic, high precision targeting of growth modulating agents is able to trigger pollen tube growth reorientationPublished: 13 August 2014 by Wiley in The Plant Journal
The pollen tube is the most rapidly growing cell in the plant kingdom and has the function to deliver the sperm cells for fertilization. The growing tip region of the cell behaves in a chemotropic manner to respond to the guidance cues emitted by the pistil and the female gametophyte, but how it perceives and responds to these directional triggers is virtually unknown. Quantitative assessment of chemotropic behavior can greatly be enhanced by the administration of pharmacological or other biologically active agents at subcellular precision, which is a technical challenge when the target area moves as it grows. We developed a laminar flow based microfluidic device that allows for continuous administration of two different solutions with a movable interface that permits the dynamic targeting of the growing pollen tube apex over prolonged periods of time. Asymmetric administration of calcium revealed that rather than following the highest calcium concentration as would be expected with simple chemotropic behavior, the pollen tube of Camellia targets an optimal concentration suggesting the presence of two superimposed mechanisms. Subcellular application of pectin methyl esterase (PME), an enzyme that modifies the growth behavior by rigidifying the pollen tube cell wall, caused the tube to turn away from the agent – providing important evidence for a previously proposed conceptual model of the growth mechanism.
Pollen tube, the fastest tip growing plant cell, plays essential role in life cycle of flowering plants. It is extremely sensitive to external cues and this makes it as a suitable cellular model for characterizing the cell response to the influence of various signals involved in cellular growth metabolism. For in-vitro study of pollen tube growth, it is essential to provide an environment the mimics the internal microenvironment of pollen tube in flower. In this context, microfluidic platforms take advantage of miniaturization for handling small volume of liquids, providing a closed environment for in-vitro single cell analysis, and characterization of cell response to external cues. These platforms have shown their ability for high-throughput cellular analysis with increased accuracy of experiments, and reduced cost and experimental times. Here, we review the recent applications of microfluidic devices for investigating several aspects of biology of pollen tube elongation.
This work presents simulation, analysis and implementation of morphology tuning of gold nano-island structures deposited by a novel convective assembly technique. The gold nano-islands were simulated using 3D Finite-Difference Time-Domain (FDTD) techniques to investigate the effect of morphological changes and adsorption of protein layers on the localized surface plasmon resonance (LSPR) properties. Gold nano-island structures were deposited on glass substrates by a novel and low-cost convective assembly process. The structure formed by an uncontrolled deposition method resulted in a nano-cluster morphology, which was annealed at various temperatures to tune the optical absorbance properties by transforming the nano-clusters to a nano-island morphology by modifying the structural shape and interparticle separation distances. The dependence of the size and the interparticle separation distance of the nano-islands on the LSPR properties were analyzed in the simulation. The effect of adsorption of protein layer on the nano-island structures was simulated and a relation between the thickness and the refractive index of the protein layer on the LSPR peak was presented. Further, the sensitivity of the gold nano-island integrated sensor against refractive index was computed and compared with the experimental results.
A lab-on-a-chip device with a knot shaped microfluidic network is presented to enable trapping of single pollen grains at the entrances of a series of microchannels. This set-up serves to create identical growth conditions for serially arranged tip growing plant cells such as pollen tubes. The design consists of an inlet to introduce the pollen suspension into the chip, three outlets to evacuate excess medium or cells, a distribution chamber to guide the pollen grains toward the growth microchannels and a serial arrangement of microchannels with different geometries connected to the distribution chamber. These microchannels are to harbor the individual pollen tubes. Two different criteria were established to assess the efficiency and optimize the device: trapping probability and uniformity of fluid flow conditions within the microchannels. The performance of different geometries of the microfluidic network was numerically analyzed and experimentally tested.
Monolithically Integrated Optical Microfluidic Chip by Single Step Lithography and Etching for Detection of Fluorophore ...Published: 09 January 2014 by The Electrochemical Society in Journal of The Electrochemical Society
An optical microfluidic sensor is developed on silica-on-silicon planar waveguide by using a novel single step lithography and etching of silicon dioxide layers deposited on silicon wafer. The proposed sensor consists of a multiple waveguide system designed with optical couplers of S-bends integrated with microfluidic channel on silicon-on-silicon. The microfluidics channel is bonded with PDMS having the refractive index lower than the core of the waveguide, hence the PDMS layer acts both as the sealing layer and top cladding of the silica-on-silicon waveguide. The fluorescence detection efficiency of the device is demonstrated with laser induced fluorescence detection of Alexa-647 tagged recombinant bovine somatotropin (rbST). The lowest concentration of rbST that could be detected by the proposed lab-on-a-chip is as low as 120 ng/ml. Further, the sensitivity of the monolithically integrated single waveguide and multiple waveguides are compared for the fluorescence detection of the rbST.
Assessing the Influence of Electric Cues and Conductivity on Pollen Tube Growth via Lab-On-A-Chip TechnologyPublished: 01 January 2014 by Elsevier BV in Biophysical Journal
A hallmark of tip-growing cells such as pollen tubes and fungal hyphae is their oscillatory growth dynamics. The multiple aspects of this behavior have been studied to identify the regulatory mechanisms that drive the growth in walled cells. However, the limited temporal and spatial resolution of data acquisition has hitherto prevented more detailed analysis of this growth behavior. To meet this challenge, we employed a microfluidic device that is able to trap pollen grains and to direct the growth of pollen tubes along microchannels filled with liquid growth medium. This enabled us to observe the growth behavior of Camellia pollen tubes without the use of the stabilizer agarose and without risking displacement of the cell during time lapse imaging. Using an acquisition interval of 0.5 s, we demonstrate the existence of primary and secondary peak frequencies in the growth dynamics. The effect of sucrose concentration on the growth dynamics was studied through the shift in these peak frequencies indicating the pollen tube's ability to modulate its growth activity.
Rapid Microwave-Induced Synthesis of Gold-Polydimethylsiloxane Nanocomposites for Biosensing of ProteinsPublished: 01 October 2013 by American Scientific Publishers in Journal of Nanoscience and Nanotechnology
Rapid microwave-induced synthesis of gold-polydimethylsiloxane nanocomposites for biosensing of proteins.Published: 01 October 2013
In this paper a novel in-situ microwave-induced synthesis of the gold-polydimethylsiloxane nanocomposite is presented. Microwave-induced synthesis has the advantages of a very short reaction time, small particle size and narrow size distribution of the particles. The ethanol solution of gold chloroauric acid is used as the precursor solution. The mechanism of formation and growth of nanoparticles are discussed in detail. UV/Vis spectroscopy and SEM imaging were used to characterize the optical properties and the size distribution of the particles. To improve the sensing properties of the nanocomposite, an annealing process were used. The results show that the annealed samples have the high sensitivity of 102 nm/RIU toward the surrounding medium which makes the nanocomposite suitable for biosensing applications. In addition, the elasticity of the platform in the presence of gold nanoparticles was found to be enhanced up to 20%. Finally, the immunosensing of the bovine growth hormone was performed by using the localized surface plasmon resonance (LSPR) band of gold nanoparticles. The results demonstrate suitability of the nanocomposite platform for biosensing applications. The results are highly relevant for microfluidic-based biosensors.
Optimization of flow assisted entrapment of pollen grains in a microfluidic platform for tip growth analysisPublished: 07 September 2013 by Springer Nature in Biomedical Microdevices
A biocompatible polydimethylsiloxane (PDMS) biomicrofluidic platform is designed, fabricated and tested to study protuberance growth of single plant cells in a micro-vitro environment. The design consists of an inlet to introduce the cell suspension into the chip, three outlets to conduct the medium or cells out of the chip, a main distribution chamber and eight microchannels connected to the main chamber to guide the growth of tip growing plant cells. The test cells used here were pollen grains which produce cylindrical protrusions called pollen tubes. The goal was to adjust the design of the microfluidic network with the aim to enhance the uniformly distributed positioning of pollen grains at the entrances of the microchannels and to provide identical fluid flow conditions for growing pollen tubes along each microchannel. Computational fluid analysis and experimental testing were carried out to estimate the trapping efficiencies of the different designs.
A major limitation in the study of pollen tube growth has been the difficulty in providing an in vitro testing microenvironment that physically resembles the in vivo conditions. Here we describe the development of a lab-on-a-chip (LOC) for the manipulation and experimental testing of individual pollen tubes. The design was specifically tailored to pollen tubes from Camellia japonica, but it can be easily adapted for any other species. The platform is fabricated from polydimethylsiloxane (PDMS) using a silicon/SU-8 mold and makes use of microfluidics to distribute pollen grains to serially arranged microchannels. The tubes are guided into these channels where they can be tested individually. The microfluidic platform allows for specific testing of a variety of growth behavioral features as demonstrated with a simple mechanical obstacle test, and it permits the straightforward integration of further single-cell test assays.
Integration of gold nanoparticles in PDMS microfluidics for lab-on-a-chip plasmonic biosensing of growth hormonesPublished: 01 June 2013 by Elsevier BV in Biosensors and Bioelectronics
Gold nanoparticles were synthesized in a poly(dimethylsiloxane) (PDMS) microfluidic chip by using an in-situ method, on the basis of reductive properties of the cross-linking agent of PDMS. The proposed integrated device was further used as a sensitive and low-cost LSPR-based biosensor for the detection of polypeptides. Synthesis of nanoparticles in the microfluidic environment resulted in improvement of size distribution with only 8% variation, compared with the macro-environment that yields about 67% variation in size. The chemical kinetics of the in-situ reaction in the microfluidic environment was studied in detail and compared with the reaction carried out at the macro-scale. The effect of temperature and gold precursor concentration on the kinetics of the reaction was investigated and the apparent activation energy was estimated to be Ea*=30 kJ/mol. The sensitivity test revealed that the proposed sensor has a high sensitivity of 74 nm/RIU to the surrounding medium. The sensing of bovine growth hormone also known as bovine somatotropin (bST) shows that the proposed biosensor can reach a detection limit of as low as 3.7 ng/ml (185 pM). The results demonstrate the successful integration of microfluidics and nanoparticles which provides a potential alternative for protein detection in clinical diagnostics.
In this paper, a simple practical method is presented to fabricate a high aspect ratio horizontal polydimethylsiloxane (PDMS) microcantilever-based flow sensor integrated into a microfluidic device. A multilayer soft lithography process is developed to fabricate a thin PDMS layer involving the PDMS microcantilever and the microfluidics network. A three-layer fabrication technique is explored for the integration of the microflow meter. The upper and lower PDMS layers are bonded to the thin layer to release the microcantilever for free deflection. A 3-D finite element analysis is carried out to simulate fluid-structure interaction and estimate cantilever deflection under various flow conditions. The dynamic range of flow rates that is detectable using the flow sensor is assessed by both simulation and experimental methods and compared. Limited by the accuracy of the 1.76- μm resolution of the image acquisition method, the present setup allows for flow rates as low as 35 μL/min to be detected. This is equal to 0.8-μN resolution in equivalent force at the tip. This flow meter can be integrated into any type of microfluidic-based lab-on-a-chip in which flow measurement is crucial, such as flow cytometry and particle separation applications.
Large‐scale phenotyping of tip‐growing cells such as pollen tubes has hitherto been limited to very crude parameters such as germination percentage and velocity of growth. To enable efficient and high‐throughput execution of more sophisticated assays, an experimental platform, the TipChip, was developed based on microfluidic and microelectromechanical systems (MEMS) technology. The device allows positioning of pollen grains or fungal spores at the entrances of serially arranged microchannels equipped with microscopic experimental set‐ups. The tip‐growing cells (pollen tubes, filamentous yeast or fungal hyphae) may be exposed to chemical gradients, microstructural features, integrated biosensors or directional triggers within the modular microchannels. The device is compatible with Nomarski optics and fluorescence microscopy. Using this platform, we were able to answer several outstanding questions on pollen tube growth. We established that, unlike root hairs and fungal hyphae, pollen tubes do not have a directional memory. Furthermore, pollen tubes were found to be able to elongate in air, raising the question of how and where water is taken up by the cell. The platform opens new avenues for more efficient experimentation and large‐scale phenotyping of tip‐growing cells under precisely controlled, reproducible conditions.
Quantification of the Young's modulus of the primary plant cell wall using Bending-Lab-On-Chip (BLOC)Published: 01 January 2013 by Royal Society of Chemistry (RSC) in Lab on a Chip
Biomechanical and mathematical modeling of plant developmental processes requires quantitative information about the structural and mechanical properties of living cells, tissues and cellular components. A crucial mechanical property of plant cells is the mechanical stiffness or Young's modulus of its cell wall. Measuring this property in situ at single cell wall level is technically challenging. Here, a bending test is implemented in a chip, called Bending-Lab-On-a-Chip (BLOC), to quantify this biomechanical property for a widely investigated cellular model system, the pollen tube. Pollen along with culture medium is introduced into a microfluidic chip and the growing pollen tube is exposed to a bending force created through fluid loading. The flexural rigidity of the pollen tube and the Young's modulus of the cell wall are estimated through finite element modeling of the observed fluid-structure interaction. An average value of 350 MPa was experimentally estimated for the Young's modulus in longitudinal direction of the cell wall of Camellia pollen tubes. This value is in agreement with the result of an independent method based on cellular shrinkage after plasmolysis and with the mechanical properties of in vitro reconstituted cellulose-callose material.
Quantification of Force Generation during Invasive Cellular Growth using Microfluidics and Reverse EngineeringPublished: 01 January 2013 by Elsevier BV in Biophysical Journal
High performance cascaded PDMS micromixer based on split-and-recombination flows for lab-on-a-chip applicationsPublished: 01 January 2013 by Royal Society of Chemistry (RSC) in RSC Advances
In this paper a cost-effective and simple 3-layer PDMS passive micromixer has been designed, optimized, simulated, fabricated and successfully characterized. The mixing mechanism is based on splitting and recombining the flow. The designed micromixer was simulated and a method was formulated to assess the mixing performance. The mixer has shown excellent mixing efficiency over a wide range of flow rates specifically at low flow rates. The experimental measurements were performed to qualify the mixing performance of the realized mixer. The results show that predicted mixing efficiency is comparable with experimental results. A high mixing efficiency of 85% was obtained at flow rates below 40 μL min−1 meaning the possibility of obtaining full mixing for Reynolds number Re <5.5. Due to the simple channels' configuration of the device, the simulations show that its pressure drop is less than 1 kPa at flow rate of 50 μL min−1. In cases where very high mixing efficiency is demanded, several micromixers (mixing units) can be easily combined to form a cascaded mixing module. The results show even with a combination of two units, an efficiency as high as 80% can be achieved at a high flow rate of 100 μL min−1, which can be considered as full mixing. One of the main advantages of the device explored in this work is its small dimensions (1.5 × 2.3 mm) which makes it possible to be easily integrated with PDMS based microfluidic devices for different point-of-care applications.
Muthukumaran Packirisamy participated at conference 4th International Symposium on Sensor Science.