The specific and multiplexed detection of DNA underpins many analytical methods, including the de... more The specific and multiplexed detection of DNA underpins many analytical methods, including the detection of microorganisms that are important in the medical, veterinary, and environmental sciences. To achieve such measurements generally requires enzyme-mediated amplification of the low concentrations of the target nucleic acid sequences present, together with the precise control of temperature, as well as the use of enzyme-compatible reagents. This inevitably leads to compromises between analytical performance and the complexity of the assay. The hybridization chain reaction (HCR) provides an attractive alternative, as a route to enzyme-free DNA amplification. To date, the linear nucleic acid products, produced during amplification, have not enabled the development of efficient multiplexing strategies, nor the use of label-free analysis. Here, we show that by designing new DNA nanoconstructs, we are able, for the first time, to increase the molecular dimensionality of HCR products, creating highly branched amplification products, which can be readily detected on label-free sensors. To show that this new, branching HCR system offers a route for enzyme-free, label-free DNA detection, we demonstrate the multiplexed detection of a target sequence (as the initiator) in whole blood. In the future, this technology will enable rapid point-of-care multiplexed clinical analysis or in-the-field environmental monitoring.
Leaky Rayleigh surface acoustic waves (SAWs), generated on piezoelectric substrates, can interact... more Leaky Rayleigh surface acoustic waves (SAWs), generated on piezoelectric substrates, can interact with liquids to generate streaming and fast flows. Although studied extensively, mainly phenomenologically, the limited understanding of the effect of the SAW frequency on streaming in fluids in constrained volumes has resulted in less than good correlations between models and experimental observations. Using microfluidic structures to reproducibly define the fluid volume, we build upon recent advances modeling the body force generated by SAWs to develop a deeper understanding of the effect of acoustic frequency on the magnitude of streaming flows. We implement this as a new predictive tool using a finite element model of fluid motion to establish optimized conditions for streaming. The model is corroborated experimentally over a range of different excitation frequencies and enables us to create a design tool, linking microfluidic channel dimensions with frequencies and streaming efficiencies. We show that in typical microfluidic micro-chambers, the length and height of the chamber are critical in determining the optimum frequency, with smaller geometries requiring higher frequencies.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2018
In this paper, we show that acoustoelasticity in hyperelastic materials can be understood using t... more In this paper, we show that acoustoelasticity in hyperelastic materials can be understood using the framework of nonlinear wave mixing, which, when coupled with an induced static stress, leads to a change in the phase velocity of the propagating wave with no change in frequency. By performing Floquet wave eigenvalue analysis, we also show that band gaps for periodic composites, acting as 1-D phononic crystals, can be tuned using this static stress. In the presence of second-order elastic nonlinearities, the phase velocity of propagating waves in the phononic structure changes, leading to observable shifts in the band gaps. Finally, we present numerical examples as evidence that the band gaps are tuned by both the direction of the stress and its magnitude.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
... Thus, the selectivity of chemically overetched features lies above the balanced line and that... more ... Thus, the selectivity of chemically overetched features lies above the balanced line and that of chemically underetched (physically overetched) features lies below (Fig. ... We have also observed that the remaining silica mask after a CAIBE etch is more resis-tant to RIE than before ...
Linear cationic antimicrobial peptides are a diverse class of molecules that interact with a wide... more Linear cationic antimicrobial peptides are a diverse class of molecules that interact with a wide range of cell membranes. Many of these peptides disrupt cell integrity by forming membrane-spanning pores that ultimately lead to their death. Despite these peptides high potency and ability to evade acquired bacterial drug resistance, there is a lack of knowledge on their selectivity and activity mechanisms. Such an understanding would provide an informative framework for rational design and could lead to potential antimicrobial therapeutic targets. In this paper, we use a high-throughput microfluidic platform as a quantitative screen to assess peptide activity and selectivity by precisely controlling exposure to vesicles with lipid compositions that mimic both bacterial and mammalian cell membranes. We explore the complexity of the lipid–peptide interactions governing membrane-disruptive behaviors and establish a link between peptide pore formation and both lipid–peptide charge and to...
We study the influence of acoustic fields on the evaporative self-assembly of solute particles su... more We study the influence of acoustic fields on the evaporative self-assembly of solute particles suspended inside sessile droplets of complex fluids. The self-assembly process often results in an undesirable ring-like heterogeneous residue, a phenomenon known as the coffee-ring effect. Here we show that this ring-like self-assembly can be controlled acoustically to form homogeneous disc-like or concentrated spot-like residues. The principle of our method lies in the formation of dynamic patterns of particles in acoustically excited droplets, which inhibits the evaporation-driven convective transport of particles towards the contact line. We elucidate the mechanisms of this pattern formation and also obtain conditions for the suppression of the coffee-ring effect. Our results provide a more general solution to suppress the coffee-ring effect without any physiochemical modification of the fluids, the particles or the surface, thus potentially useful in a broad range of industrial and an...
Soft ionization methods for the introduction of labile biomolecules into a mass spectrometer are ... more Soft ionization methods for the introduction of labile biomolecules into a mass spectrometer are of fundamental importance to biomolecular analysis. Previously, electrospray ionization (ESI) and matrix assisted laser desorption-ionization (MALDI) have been the main ionization methods used. Surface acoustic wave nebulization (SAWN) is a new technique that has been demonstrated to deposit less energy into ions upon ion formation and transfer for detection than other methods for sample introduction into a mass spectrometer (MS). Here we report the optimization and use of SAWN as a nebulization technique for the introduction of samples from a low flow of liquid, and the interfacing of SAWN with liquid chromatographic separation (LC) for the analysis of a protein digest. This demonstrates that SAWN can be a viable, low-energy alternative to ESI for the LC-MS analysis of proteomic samples.
We demonstrate controllable poration within ≈1 µm regions of individual cells, mediated by a near... more We demonstrate controllable poration within ≈1 µm regions of individual cells, mediated by a near-IR laser interacting with thin-layer amorphous silicon substrates. This technique will allow new experiments in single-cell biology, particularly in neuroscience.
We demonstrate surface acoustic wave (SAW) induced microparticle manipulation in a microstructure... more We demonstrate surface acoustic wave (SAW) induced microparticle manipulation in a microstructured disposable glass-polymer composite superstrate, positioned on a piezoelectric substrate with a single, slanted SAW transducer. An excited SAW was coupled from the piezoelectric substrate into the superstrate, which acted as a transversal resonator structure. We show that the energy transmitted into the superstrate allowed acoustophoretic particle manipulation, while the wide frequency response of the SAW transducer enabled tuneable pressure distributions confined by the microchannel layout. The configuration provides a significant tolerance in positioning - making assembly easy.
We present a straightforward method for measuring the relative viscosity of fluids via a simple g... more We present a straightforward method for measuring the relative viscosity of fluids via a simple graphical analysis of the normalised position autocorrelation function of an optically trapped bead, without the need of embarking on laborious calculations. The advantages of the proposed microrheology method are evident when it is adopted for measurements of materials whose availability is limited, such as those involved in biological studies. The method has been validated by direct comparison with conventional bulk rheology methods, and has been applied both to characterise synthetic linear polyelectrolytes solutions and to study biomedical samples.
Proceedings of SPIE - The International Society for Optical Engineering, 2011
Microfluidic systems have faced challenges in handling real samples and the chip interconnection ... more Microfluidic systems have faced challenges in handling real samples and the chip interconnection to other instruments. Here we present a simple interface, where surface acoustic waves (SAWs) from a piezoelectric device are coupled into a disposable ...
Proceedings of SPIE - The International Society for Optical Engineering, 2012
Infectious diseases cause 10 million deaths each year worldwide, accounting for ~60% of all death... more Infectious diseases cause 10 million deaths each year worldwide, accounting for ~60% of all deaths of children aged 5-14. Although these deaths arise primarily through pneumonia, TB, malaria and HIV, there are also the so called "neglected diseases" such as sleeping sickness and bilharzia, which have a devastating impact on rural communities, in sub-Sahara Africa. There, the demands for a successful Developing World diagnostic are particularly rigorous, requiring low cost instrumentation with low power consumption (there is often no fixed power infrastructure). In many cases, the levels of infection within individuals are also sufficiently low that instruments must show extraordinary sensitivity, with measurements being made in blood or saliva. In this talk, a description of these demands will be given, together with a review of some of the solutions that have been developed, which include using acoustics, optics and electrotechnologies, and their combinations to manipulate the fluid samples. In one example, we show how to find a single trypanosome, as the causative agent of sleeping sickness.
We have fabricated high-quality planar photonic crystal defect waveguides in InP/InGaAsP material... more We have fabricated high-quality planar photonic crystal defect waveguides in InP/InGaAsP material. Using Fourier analysis of the Fabry-Perot fringes obtained in transmission, we derive the propagation losses. Values as small as 1.8 dB/mm for waveguides consisting of 3 rows of missing holes ("W3") were measured. To the best of our knowledge, this is the smallest loss in III-V semiconductor photonic
Optical Trapping and Optical Micromanipulation IX, 2012
ABSTRACT We present a micromanipulation system based on dielectrophoretic and acoustophoretic par... more ABSTRACT We present a micromanipulation system based on dielectrophoretic and acoustophoretic particle tweezing. The combination of non-uniform electrical fields and standing pressure waves is applied to a microfluidic chip and provides essential functions including concentration, focussing, guiding, trapping and sorting of microparticles. Dielectrophoresis is achieved using a photoconductor integrated into a microchannel chip which generates electric fields upon illumination. Acoustophoresis is achieved utilizing a surface acoustic wave device which transmits ultrasound into the chip and forms a pressure standing wave under resonance conditions. The system is characterized in terms of coupling of acoustic energy into the chip as well as dielectrophoretic trapping and guiding efficiency. The individual control of each techniques is demonstrated and applied for sorting of polystyrene beads by dielectrophoretic and acoustophoretic forces.
We exploit the mechanical action of surface acoustic waves (SAW) to differentially lyse human can... more We exploit the mechanical action of surface acoustic waves (SAW) to differentially lyse human cancer cells in a chemical-free manner. The extent to which cells were disrupted is reported for a range of SAW parameters, and we show that the presence of 10 μm polystyrene beads is required to fully rupture cells and their nuclei. We show that SAW is capable of subcellular fractionation through the chemical-free isolation of nuclei from whole cells. The concentration of protein was assessed in lysates with a sensitive microfluidic antibody capture (MAC) chip. An antibody-based sandwich assay in a microfluidic microarray format was used to detect unlabeled human tumor suppressor protein p53 in crude lysates, without any purification step, with single-molecule resolution. The results are digital, enabling sensitive quantification of proteins with a dynamic range >4 orders of magnitude. For the conditions used, the efficiency of SAW-induced mechanical lysis was determined to be 12.9% ± 0...
The specific and multiplexed detection of DNA underpins many analytical methods, including the de... more The specific and multiplexed detection of DNA underpins many analytical methods, including the detection of microorganisms that are important in the medical, veterinary, and environmental sciences. To achieve such measurements generally requires enzyme-mediated amplification of the low concentrations of the target nucleic acid sequences present, together with the precise control of temperature, as well as the use of enzyme-compatible reagents. This inevitably leads to compromises between analytical performance and the complexity of the assay. The hybridization chain reaction (HCR) provides an attractive alternative, as a route to enzyme-free DNA amplification. To date, the linear nucleic acid products, produced during amplification, have not enabled the development of efficient multiplexing strategies, nor the use of label-free analysis. Here, we show that by designing new DNA nanoconstructs, we are able, for the first time, to increase the molecular dimensionality of HCR products, creating highly branched amplification products, which can be readily detected on label-free sensors. To show that this new, branching HCR system offers a route for enzyme-free, label-free DNA detection, we demonstrate the multiplexed detection of a target sequence (as the initiator) in whole blood. In the future, this technology will enable rapid point-of-care multiplexed clinical analysis or in-the-field environmental monitoring.
Leaky Rayleigh surface acoustic waves (SAWs), generated on piezoelectric substrates, can interact... more Leaky Rayleigh surface acoustic waves (SAWs), generated on piezoelectric substrates, can interact with liquids to generate streaming and fast flows. Although studied extensively, mainly phenomenologically, the limited understanding of the effect of the SAW frequency on streaming in fluids in constrained volumes has resulted in less than good correlations between models and experimental observations. Using microfluidic structures to reproducibly define the fluid volume, we build upon recent advances modeling the body force generated by SAWs to develop a deeper understanding of the effect of acoustic frequency on the magnitude of streaming flows. We implement this as a new predictive tool using a finite element model of fluid motion to establish optimized conditions for streaming. The model is corroborated experimentally over a range of different excitation frequencies and enables us to create a design tool, linking microfluidic channel dimensions with frequencies and streaming efficiencies. We show that in typical microfluidic micro-chambers, the length and height of the chamber are critical in determining the optimum frequency, with smaller geometries requiring higher frequencies.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2018
In this paper, we show that acoustoelasticity in hyperelastic materials can be understood using t... more In this paper, we show that acoustoelasticity in hyperelastic materials can be understood using the framework of nonlinear wave mixing, which, when coupled with an induced static stress, leads to a change in the phase velocity of the propagating wave with no change in frequency. By performing Floquet wave eigenvalue analysis, we also show that band gaps for periodic composites, acting as 1-D phononic crystals, can be tuned using this static stress. In the presence of second-order elastic nonlinearities, the phase velocity of propagating waves in the phononic structure changes, leading to observable shifts in the band gaps. Finally, we present numerical examples as evidence that the band gaps are tuned by both the direction of the stress and its magnitude.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
... Thus, the selectivity of chemically overetched features lies above the balanced line and that... more ... Thus, the selectivity of chemically overetched features lies above the balanced line and that of chemically underetched (physically overetched) features lies below (Fig. ... We have also observed that the remaining silica mask after a CAIBE etch is more resis-tant to RIE than before ...
Linear cationic antimicrobial peptides are a diverse class of molecules that interact with a wide... more Linear cationic antimicrobial peptides are a diverse class of molecules that interact with a wide range of cell membranes. Many of these peptides disrupt cell integrity by forming membrane-spanning pores that ultimately lead to their death. Despite these peptides high potency and ability to evade acquired bacterial drug resistance, there is a lack of knowledge on their selectivity and activity mechanisms. Such an understanding would provide an informative framework for rational design and could lead to potential antimicrobial therapeutic targets. In this paper, we use a high-throughput microfluidic platform as a quantitative screen to assess peptide activity and selectivity by precisely controlling exposure to vesicles with lipid compositions that mimic both bacterial and mammalian cell membranes. We explore the complexity of the lipid–peptide interactions governing membrane-disruptive behaviors and establish a link between peptide pore formation and both lipid–peptide charge and to...
We study the influence of acoustic fields on the evaporative self-assembly of solute particles su... more We study the influence of acoustic fields on the evaporative self-assembly of solute particles suspended inside sessile droplets of complex fluids. The self-assembly process often results in an undesirable ring-like heterogeneous residue, a phenomenon known as the coffee-ring effect. Here we show that this ring-like self-assembly can be controlled acoustically to form homogeneous disc-like or concentrated spot-like residues. The principle of our method lies in the formation of dynamic patterns of particles in acoustically excited droplets, which inhibits the evaporation-driven convective transport of particles towards the contact line. We elucidate the mechanisms of this pattern formation and also obtain conditions for the suppression of the coffee-ring effect. Our results provide a more general solution to suppress the coffee-ring effect without any physiochemical modification of the fluids, the particles or the surface, thus potentially useful in a broad range of industrial and an...
Soft ionization methods for the introduction of labile biomolecules into a mass spectrometer are ... more Soft ionization methods for the introduction of labile biomolecules into a mass spectrometer are of fundamental importance to biomolecular analysis. Previously, electrospray ionization (ESI) and matrix assisted laser desorption-ionization (MALDI) have been the main ionization methods used. Surface acoustic wave nebulization (SAWN) is a new technique that has been demonstrated to deposit less energy into ions upon ion formation and transfer for detection than other methods for sample introduction into a mass spectrometer (MS). Here we report the optimization and use of SAWN as a nebulization technique for the introduction of samples from a low flow of liquid, and the interfacing of SAWN with liquid chromatographic separation (LC) for the analysis of a protein digest. This demonstrates that SAWN can be a viable, low-energy alternative to ESI for the LC-MS analysis of proteomic samples.
We demonstrate controllable poration within ≈1 µm regions of individual cells, mediated by a near... more We demonstrate controllable poration within ≈1 µm regions of individual cells, mediated by a near-IR laser interacting with thin-layer amorphous silicon substrates. This technique will allow new experiments in single-cell biology, particularly in neuroscience.
We demonstrate surface acoustic wave (SAW) induced microparticle manipulation in a microstructure... more We demonstrate surface acoustic wave (SAW) induced microparticle manipulation in a microstructured disposable glass-polymer composite superstrate, positioned on a piezoelectric substrate with a single, slanted SAW transducer. An excited SAW was coupled from the piezoelectric substrate into the superstrate, which acted as a transversal resonator structure. We show that the energy transmitted into the superstrate allowed acoustophoretic particle manipulation, while the wide frequency response of the SAW transducer enabled tuneable pressure distributions confined by the microchannel layout. The configuration provides a significant tolerance in positioning - making assembly easy.
We present a straightforward method for measuring the relative viscosity of fluids via a simple g... more We present a straightforward method for measuring the relative viscosity of fluids via a simple graphical analysis of the normalised position autocorrelation function of an optically trapped bead, without the need of embarking on laborious calculations. The advantages of the proposed microrheology method are evident when it is adopted for measurements of materials whose availability is limited, such as those involved in biological studies. The method has been validated by direct comparison with conventional bulk rheology methods, and has been applied both to characterise synthetic linear polyelectrolytes solutions and to study biomedical samples.
Proceedings of SPIE - The International Society for Optical Engineering, 2011
Microfluidic systems have faced challenges in handling real samples and the chip interconnection ... more Microfluidic systems have faced challenges in handling real samples and the chip interconnection to other instruments. Here we present a simple interface, where surface acoustic waves (SAWs) from a piezoelectric device are coupled into a disposable ...
Proceedings of SPIE - The International Society for Optical Engineering, 2012
Infectious diseases cause 10 million deaths each year worldwide, accounting for ~60% of all death... more Infectious diseases cause 10 million deaths each year worldwide, accounting for ~60% of all deaths of children aged 5-14. Although these deaths arise primarily through pneumonia, TB, malaria and HIV, there are also the so called "neglected diseases" such as sleeping sickness and bilharzia, which have a devastating impact on rural communities, in sub-Sahara Africa. There, the demands for a successful Developing World diagnostic are particularly rigorous, requiring low cost instrumentation with low power consumption (there is often no fixed power infrastructure). In many cases, the levels of infection within individuals are also sufficiently low that instruments must show extraordinary sensitivity, with measurements being made in blood or saliva. In this talk, a description of these demands will be given, together with a review of some of the solutions that have been developed, which include using acoustics, optics and electrotechnologies, and their combinations to manipulate the fluid samples. In one example, we show how to find a single trypanosome, as the causative agent of sleeping sickness.
We have fabricated high-quality planar photonic crystal defect waveguides in InP/InGaAsP material... more We have fabricated high-quality planar photonic crystal defect waveguides in InP/InGaAsP material. Using Fourier analysis of the Fabry-Perot fringes obtained in transmission, we derive the propagation losses. Values as small as 1.8 dB/mm for waveguides consisting of 3 rows of missing holes ("W3") were measured. To the best of our knowledge, this is the smallest loss in III-V semiconductor photonic
Optical Trapping and Optical Micromanipulation IX, 2012
ABSTRACT We present a micromanipulation system based on dielectrophoretic and acoustophoretic par... more ABSTRACT We present a micromanipulation system based on dielectrophoretic and acoustophoretic particle tweezing. The combination of non-uniform electrical fields and standing pressure waves is applied to a microfluidic chip and provides essential functions including concentration, focussing, guiding, trapping and sorting of microparticles. Dielectrophoresis is achieved using a photoconductor integrated into a microchannel chip which generates electric fields upon illumination. Acoustophoresis is achieved utilizing a surface acoustic wave device which transmits ultrasound into the chip and forms a pressure standing wave under resonance conditions. The system is characterized in terms of coupling of acoustic energy into the chip as well as dielectrophoretic trapping and guiding efficiency. The individual control of each techniques is demonstrated and applied for sorting of polystyrene beads by dielectrophoretic and acoustophoretic forces.
We exploit the mechanical action of surface acoustic waves (SAW) to differentially lyse human can... more We exploit the mechanical action of surface acoustic waves (SAW) to differentially lyse human cancer cells in a chemical-free manner. The extent to which cells were disrupted is reported for a range of SAW parameters, and we show that the presence of 10 μm polystyrene beads is required to fully rupture cells and their nuclei. We show that SAW is capable of subcellular fractionation through the chemical-free isolation of nuclei from whole cells. The concentration of protein was assessed in lysates with a sensitive microfluidic antibody capture (MAC) chip. An antibody-based sandwich assay in a microfluidic microarray format was used to detect unlabeled human tumor suppressor protein p53 in crude lysates, without any purification step, with single-molecule resolution. The results are digital, enabling sensitive quantification of proteins with a dynamic range >4 orders of magnitude. For the conditions used, the efficiency of SAW-induced mechanical lysis was determined to be 12.9% ± 0...
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Papers by Rab Wilson