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22.63University of Barcelona37.41University of Surrey45.36University of Barcelona37.24University of BarcelonaAbstractWe report on the fabrication and characterization of a low-cost micro-Coulter counter fabricated from biocompatible materials (poly-dimethylsiloxane, glass and gold) and incorporating hydrodynamic focusing. The developed micro-Coulter counter offers a low-cost alternative to equivalent existing devices and, thanks to the hydrodynamic focusing, provides high versatility, being able to probe particles with a wide range of sizes within a single device. The device has been successfully tested for counting 20 latex micro beads in suspension.Discover the world's research13+ million members100+ million publications700k+ research projects
Abstract We report on the fabrication and character-ization of a low-cost micro-Coulter counter fabricatedfrom biocompatible materials (poly-dimethylsiloxane,glass and gold) and incorporating hydrodynamicfocusing. The developed micro-Coulter counter offers alow-cost alternative to equivalent existing devices and,thanks to the hydrodynamic focusing, provides highversatility, being able to probe particles with a widerange of sizes within a single device. The device hasbeen successfully tested for counting 20 latex microbeads in suspension.Keywords Micro-Coulter counter AEHydrodynamicfocusing AERapid prototyping AEPoly-dimethylsiloxane1 IntroductionThe design and fabrication of microchips for cell andmolecule handling has recently experienced a period ofrapid development (Huh et al. 2005; Erickson and Li2004; Chova?n and Guttman 2002; Medoro et al. 2003;Vilkner et al. 2004). The aim of these developments isto develop particle counting, analysis and sorting sys-tems to perform a variety of biotechnological applica-tions on a chip. One particularly important applicationis the development of cell counters, which can be usedas a stand alone device for counting, and sizing, or inmore complex devices incorporating flow cytometryanalysis for the discrimination and sorting of differentcell populations (see Huh et al. 2005 for a recent re-view on the subject).Particle counting can be based on two detectionmethods. Optical methods extract information fromlight dispersed by particles and from specific fluores-cent excitation (Schrum et al. 1999; McClain et al.2001; Fu et al. 2004), whereas electrical methods(referred to as Coulter counters) extract informationfrom the modulation of the electrical resistance in anorifice due to the passage of the particle (Larsen et al.1997; Koch et al. 1999; Ayliffe et al. 1999; Saleh andSohn 2001,2003a,b). Optical methods have theadvantage of being able to incorporate fluorescentmarkers that are widely used in biology, but at theprice of increased integration complexity. Electricalmethods, on the other hand, present advantages fromthe point of view of integration, particularly after thedemonstration of entirely electrical-based micro-flowcytometers and sorters utilizing electrical impedancemethods (Cheung et al. 2005; Holmes et al. 2005;Morgan et al. 2005).Micro-Coulter counters, i.e., micro-dimensionedparticle counters based on electrical detection meth-ods, have been fabricated using a variety of materials:e.g., silicon (Schrum et al. 1999; McClain et al. 2001;Fuet al. 2004; Larsen et al. 1997; Koch et al. 1999), glass(Ayliffe et al. 1999), glass–polyimide (Cheung et al.2005; Holmes et al. 2005; Morgan et al. 2005; Gawadet al. 2001), polymer (Saleh and Sohn 2003a,b), andquartz (Saleh and Sohn 2001) and with different par-ticle alignment methods: geometric (Saleh and SohnR. Rodriguez-Trujillo (&)AEC. A. Mills AEJ. Samitier AEG. GomilaLaboratory of Nanobioengineering-CREBEC,Parc Cientific de Barcelona and Department of Electronics,University of Barcelona, C/ Marti i Franques, 1,08028 Barcelona, Spaine-mail: romen@el.ub.esURL: http://www.nanobiolab.pcb.ub.esMicrofluid NanofluidDOI 10.-006-0113-8123RESEARCH PAPERLow cost micro-Coulter counter with hydrodynamic focusingR. Rodriguez-Trujillo AEC. A. Mills AEJ. Samitier AEG. GomilaReceived: 4 July 2006 / Accepted: 4 August 2006?Springer-Verlag 2006
2001,2003a,b), hydrodynamic (Larsen et al. 1997) andelectrokinetic (Schrum et al. 1999; McClain et al. 2001;Fu et al. 2004; Holmes et al. 2005; Morgan et al. 2005;Cheung et al. 2005). Particles with diameters fromseveral micrometers down to tens of nanometers(Saleh and Sohn 2001,2003a,b) have been examinedwith detection ratios varying from a few counts persecond, if electrophoretic forces are utilized for parti-cle manipulation (Saleh and Sohn 2001), to hundredsof counts per second, if pressure forces are utilized(Morgan et al. 2005; Gawad et al. 2001). Recent ad-vances (Holmes et al. 2005; Morgan et al. 2005) suggestthat pressure driven particles combined with dielec-trophoretic alignment and impedance detection meth-ods could provide the appropriate technology for highperformance micro-flow cytometry. However, for var-ious other applications and testing purposes a versatilelow-cost alternative to these micro-Coulter countersmight be desirable. Here we describe the developmentof one such alternative.The micro-Coulter counter presented here consistsof a pressure driven particle counter, with hydrody-namic focusing for particle alignment, and impedancedetection for particle counting. The use of hydrody-namic focusing together with electrical detection [toour knowledge only previously reported in Larsenet al. (1997)] makes the device highly versatile,allowing the possibility of examining particles with abroad range of sizes in a single device. Fabrication ofthe channel structure of the device in a polymer[poly-dimethylsiloxane (PDMS)] using a rapid proto-typing technology (Qin et al. 1996; McDonald et al.2000) offers low fabrication costs compared toequivalent devices based on micromachined silicon(Schrum et al. 1999; McClain et al. 2001; Fu et al.2004; Larsen et al. 1997; Koch et al. 1999) or micro-fabricated glass/pyrex (Cheung et al. 2005; Holmeset al. 2005).2 Device descriptionA diagram of the layout of the micro-Coulter counteris shown in Fig. 1. It has three inlet reservoirs con-nected to their corresponding channels and converginginto a single outlet channel leading to the outlet res-ervoir. All the channels are ~190 lm wide and all thereservoirs are 3 mm in diameter. The channels are all~50 lm deep. Channel structures are fabricated inPDMS and sealed onto a glass substrate containing themicrofabricated Ti–Au electrodes. The microelec-trodes are coplanar and transversal to the direction ofthe flux. They are 40 lm wide, 70 nm tall and have a40 lm separation. The detection zone is the volumelocated between the electrodes.3 Device fabricationFabrication of the PDMS micro-channels has beenperformed by means of rapid prototyping (McDonaldet al. 2000). First, negative masks of the design pre-sented in Fig. 1a are printed on transparent acetatesheets using an Agfa Selectset Avantra 44E printerwith a resolution of 3,600 dpi. Then, this mask is usedto expose a 50 lm thin film of a negative photoresist(SU-8 50, MicroChem Corp., USA) previously spunand cured on a glass substrate. The resin is thendeveloped (SU8 developer, MicroChem Corp., USA)to obtain a negative mould of our required structure.Replication of the mould was achieved using a silicon-based elastomeric polymer, PDMS (Slygard 184,MicroChem Corp., USA), by means of standard softlithography techniques (Qin et al. 1996). To preventadhesion to the polymer in the replication process, afluorosilane monolayer is added to the SU-8 masterfrom the vapour phase, which acts as anti-stickinglayer.Fig. 1 Design of the micro-Coulter counter structure. aPlan view and blongitudinalsection of the central channel(dotted line a). The diagramsare not to scaleMicrofluid Nanofluid123
An array of eight-interdigited Ti–Au electrodes40 lm wide, 70 nm tall and with a 40 lm separationhas been microfabricated on a glass substrate(50 ·70 mm) by means of standard photolithographytechniques.The polymeric microchannels are sealed to the glasssubstrate containing the microelectrodes by exposureto oxygen plasma. This process is irreversible and, dueto the ability of the PDMS to form conformal contactwith a surface, the electrodes are incorporated betweenthe PDMS and the glass. Figure 2presents an opticalimage of the electrode region in the sealed structure.Finally, external fluidic connections (Upchurch Sci-entific) are sealed on the glass surface over holes thatwere previously drilled to be coincident with the inletsand outlet of the PDMS channels. Copper wires arefixed to the external electrodes pads with a silverconductive paint (RS Amidata). For the experimentspresented here only two of the eight electrodes areprobed.The completed device with both electrical and flu-idic connexions present is shown in Fig. 3.4 Device characterization4.1 Fluidic characterizationA Harvard Apparatus PHD2000 syringe pump wasutilised to inject a constant fluid flux during theexperiment. Optical characterisation was made bymeans of a Photonfocus MV-D640C-33 colour cameraconnected to a Zeiss Axio Imager.A1m opticalmicroscope.Nine different fluid focalisation conditions were setby fixing the flux rate in the lateral inlet channels(Qf1=Qf2=10ll/min) and varying the flux rate in thecentral inlet channel (Qi) between 0.1 and 20 ll/min.All channels were filled with deionised water (miliQwater by Millipore) and, in order to distinguish thelimits between the three fluxes, a water-based ink wasutilised to dye the fluid inserted into the centralchannel. For every flux the width of the central flux(w0) was measured. Figure 4shows optical microscopeimages of the focalization region for four different fo-calisation conditions. The results for the width w0ofthe central channel versus the flux rate Qiof the lateralchannels are presented in Fig. 5.The experimental results are in complete agreementwith the expected theoretical relation for this structure(the dashed line in Fig. 5) as (Stiles et al. 2005):w0 1/4 wQiQi?QF?1?where wis the width of the PDMS channel (189.78 lmdirectly measured from an optical image) and QFis thetotal lateral flux (QF=Qf1+Qf2).The maximum fluid focalisation achieved with thepresent experimental set up corresponds to a centralfluid width of about 2 lm. Given the height of thePDMS channel, 50 lm, the present device is expectedto be useful for particles with diameters between ~2and ~50 lm.4.2 Particle focalizationThe effect of hydrodynamic focusing was utilised toprove the correct alignment of particles in our device.The particles 20 lm in diameter (polystyrenes particlesfrom Polysciences) were suspended on water and madepass through the central channel of the micro-Coultercounter. The lateral channels were filled with D.I.Fig. 2 Optical microscope image of the detection zone. The goldelectrodes can be distinguished running perpendicular to thechannel. In the experiments only two consecutive electrodeswere polarizedFig. 3 Optical image of the final device structure incorporatingexternal fluidic and electrical connectionsMicrofluid Nanofluid123
water. Fluxes were adjusted using Eq. 1 in order tohave a central channel width of 20 lm, making parti-cles pass one by one. This process was verified with thehelp of the microscope and the camera. Figure 6showsa single particle passing through the central channel inthe focalised region of the device.4.3 Electrical characterizationA Corning conductivity meter 441 was utilised tomeasure the conductivities of the two solutions giving4.42 lS/cm for the deionised water and 4,200 lS/cm forthe dyed, deionised water. Two neighbouring micro-electrodes were excited with a 1 V AC signal of 1 MHzfrequency and real time measurements of the imped-ance between the electrodes were made by means of anAgilent 4294A impedance analyser controlled withLabView 6.1.Figure 7presents the experimental results for theinterelectrode resistance as a function of the width ofthe central flux when different focalisation conditionswere set.From the expression of the electrical resistance for aparalelepiped of a conductive material (R = L/(rhw);with Lbeing the length in the electrical currentdirection, rthe conductivity of the medium and hw thecross-sectional area of the parallelepiped) and consid-ering the current flux to be homogeneous in theFig. 4 Optical microscopeimages showing the effect ofthe hydrodynamicfocalization. The width of thechannel w is 189.78 lm. Qf1and Qf2are always taken tobe 10 ll/min and Qiisdecreased causing w0to bereduced: (a)Qi=20ll/min,w0= 90.4 lm(b)Qi=5ll/min, w0= 37.52 lm(c)Qi=1ll/min, w0= 11.94 lm(d)Qi= 0.1 ll/min,w0= 2.32 lmFig. 5 Reduction of the central flux width as a consequence ofdecreasing the flux rate in the central fluid flow (hydrodynamicfocalization). The experimental results (dots) are compared to atheoretical curve (dashed line), as described in the text (Eq. 1)Fig. 6 Optical microscope image showing a focalized particlepassing through the central fluxMicrofluid Nanofluid123
volume between the electrodes (the equivalent ofconsidering the electrodes to be facing each other,perpendicular to the flux, instead of being coplanar) wecan obtain the theoretical dependence of the resistanceRmeasured between two consecutive electrodes withthe width of the central flux w0. To this end one has toconsider that the measured resistance is the parallelcombination of two resistances: one corresponding tothe central flow and another corresponding to theoutside flows (which are assumed to have the sameconductivity). One then has:R 1/4 1R?1lateral ?R?1central
1/4 ahw?w0??rL?hLr0w0?2?where rand r?are the conductivities of the deionisedwater and the dyed, deionised water, respectively, Listhe distance between electrodes and his the height ofthe channel. In Eq. 2 ais a geometrical factor takinginto account the effect of having coplanar electrodesinstead of facing electrodes. This relation is presentedin Fig. 7(dashed line) and is in excellent agreementwith the experimental data, when taking a= 11.3. Thedistance L=113 lm has been taken as the distancefrom the beginning of the first polarised electrode tothe end of the second polarised electrode, directlymeasured from an optical microscope image (thiswould correspond to the inter-electrode distance in theapproximation of electrodes facing one another).Equations 1 and 2 prove that hydrodynamic focal-ization plays a double role in the present device: on theone hand it allows the particles to be aligned singlywhen passing over the measuring electrodes (Eq. 1), onthe other hand, it allows the active area of the device tobe effectively confined to the size of the focalizedstream, thus enhancing the device sensitivity (Eq. 2)(Spielman and Goren 1968; Merkus et al. 1990). Thislast property is simply achieved by using fluids withmuch higher conductivity in the central flow than in thelateral flows. Under such conditions the measuredresistance is practically solely due to the central flux,whose width is comparable to the particle diameter, asdictated by the requirement for particle alignment.This property is what gives great versatility to thedeveloped device and allows it to be used for thecounting of particles with a broad range of sizes withina single channel.5 Particle countingIn order to provide a test of the capabilities of thedeveloped device, counting of latex micro beads insuspension has been performed. A suspension of latexmicro beads in an aqueous solution of NaCl ions wasprepared and introduced into the central channel ofour device. The outside channels were filled withdeionised water in order to confine the electrical cur-rent to the volume filled by the central channel. Theconductivities of liquids were 10,670 lS/cm for thecentral channel solution and 4.42 lS/cm for the lateraldeionised water. The diameter of the particles was20 lm. We have set the conductivity at 10,670 lS/cmafter optimization experiments to produce the bestsignal to noise ratio, while remaining inside the limitsof a characteristic PBS solution.Two neighbouring microelectrodes were excitedwith a 1 V AC signal of 1 MHz frequency and realtime measures of the impedance between the elec-trodes were made. Focalization conditions where ar-ranged so as to have a central channel width of 20 lm,Fig. 7 Resistance measured between two neighbouring elec-trodes as a function of the width of the central (dyed) flux (w0).The experimental measurements (circles) can be compared tothe expected behaviour derived from theory [Eq. 2] (dashedline). The cases where w0= 0 and w0= 189.78 lm correspond tofilling the entire channel with deionised water and with dyedwater, respectivelyFig. 8 Time evolution of the resistance signal showing eight20 lm particle transitionsMicrofluid Nanofluid123
thus guaranteeing the correct alignment of the latexmicro beads and at the same time confining the activedetection width to the width of the latex micro-beads.The particles were monitored with the aid of anoptical microscope in order to correlate particle pas-sage and particle detection. To achieve this, low flowvelocities where used. Each time a single particle pas-sed the electrodes, a peak in the measured resistancewas observed. Some characteristic peaks correspondingto the passage of 20 lm diameter latex micro-beads areshown in Fig. 8. A resistance variation of approxi-mately 6% has been obtained with respect to thebaseline. A relative noise ratio of 2% enables us toeasily distinguish the transitions. Characteristic transi-tion times are approximately 50 ms, potentially allow-ing us to measure up to 20 particles per second.However, this was at a low flow velocity so that thepassage of the beads could be optically monitored,higher flow velocities are expected to reduce thetransition time and hence increase the counting rate.Finally, it is worth emphasising that the hydrody-namic focalization allows the detection of particles assmall as 20 lm in diameter in a device with a physicalcross-section as large as 190 ·50 lm2.6 ConclusionsIn the present work we have reported on the design,fabrication and characterization of a low cost micro-Coulter counter made using biocompatible materials.The device incorporates hydrodynamic focalizationdesigned to both increase device sensitivity and toanalyze particles of different diameter in a single de-vice. The present device could offer a valid low costalternative to equivalent devices based on microma-chined silicon or microfabricated glass/pyrex.Acknowledgments We kindly acknowledge support from B.Sanahuja for the development of the Labview software and fromM. Castellarnau for assistance in the impedance measurements.The device was fully fabricated within the NanotechnologyPlatform facility of the Barcelona Science Park. We gratefullyacknowledge the work performed by E. Mart??nez and M. J.Lo?pez. This research was supported by the Spanish Ministry ofEducation and Science under project TEC-C03-02.ReferencesAyliffe HE et al (1999) Electric impedance spectroscopy usingmicrochannels with integrated metal electrodes. IEEE JMicroelectromech S 8:50-57. DOI: 10.402Cheung K et al (2005) Impedance spectroscopy flow cytometry:on-chip label-free cell differentiation. Cytom Part A65A:124–132. 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CitationsCitations59ReferencesReferences29Such polarization effects can be avoided by using an AC electric field which can decrease the polarization resistance by increasing the excitation frequency[33]. In order to minimize the stray capacitance effects[34], however, appropriate frequency must be carefully determined depending on the specific chip design[31,32,[35][36][37]. For particle sizing with the RPS method, the most important question is how to evaluate particle's size based on the detected signal. ABSTRACT: The resistive pulse sensing (RPS) method based on the Coulter principle is a powerful method for particle counting and sizing in electrolyte solutions. With the advancement of micro- and nano-fabrication technologies, microfluidic and nanofluidic resistive pulse sensing technologies and devices have been developed. Due to the unique advantages of microfluidics and nanofluidics, RPS sensors are enabled with more functions with greatly improved sensitivity and throughput and thus have wide applications in fields of biomedical research, clinical diagnosis, and so on. Firstly, this paper reviews some basic theories of particle sizing and counting. Emphasis is then given to the latest development of microfuidic and nanofluidic RPS technologies within the last 6 years, ranging from some new phenomena, methods of improving the sensitivity and throughput, and their applications, to some popular nanopore or nanochannel fabrication techniques. The future research directions and challenges on microfluidic and nanofluidic RPS are also outlined. Full-text · Article · Jun 2017 For hydrodynamic focusing, there are two approaches: 1D hydrodynamic focusing [41][42][43]and 2D hydrodynamic focusing [44][45][46]. For these devices, the channels are typically larger and low conductivity sheath fluids such as deionized water [40,41,45] or oil [40,42] are used to achieve particle focusing. A three-inlet device was designed, in which two additional focalisation lateral inlets were used to provide focusing stream for pinching sample stream. ABSTRACT: Microfluidics impedance cytometry is an emerging research tool for high throughput analysis of dielectric properties of cells and internal cellular components. This label-free method can be used in different biological assays including particle sizing and enumeration, cell phenotyping and disease diagnostics. Herein, we review recent developments in single cell impedance cytometer platforms, their biomedical and clinical applications, and discuss the future directions and challenges in this field. Full-text · Article · Mar 2017 However, the interplay of focusing and sensitivity is only cursorily discussed in theory or experiments, respectively. Rodri- Trujillo et al. (2007) implemented deionized (DI)
ABSTRACT: We present the first in-depth system integration study of in-plane hydrodynamic focusing in a microfluidic impedance cytometry lab-on-a-chip. The method relies on constricting the detection volume with non-conductive sheath flows and characterizing particles or cells based on changes in impedance. This approach represents an avenue of overcoming current limitations in sensitivity with translating cytometers to the point of care for rapid, low-cost blood analysis. While examples of integrated devices are present in the literature, no systematic study of the interplay between hydrodynamics and electrodynamics has been carried out as of yet. We develop analytical and numerical models to describe the impedimetric response of the sensor as a function of cellular characteristics, physical flow properties, and device geometry. We fabricate a working prototype lab-on-a-chip for experimental validation using latex particles. We find that ionic diffusion can be a critical limiting factor even at high Péclet number. Moreover, we explore geometric variations, revealing that the ionic diffusion-related distance between the center of the hydrodynamic focusing junction and the impedance measurement electrodes plays a dominant role. With our device, we demonstrate over fivefold enhancement in impedance signals and population separation with in-plane hydrodynamic focusing. It is only through such in-depth system studies, in both models and experiments, that optimal utilization of microsystem capabilities becomes possible. Full-text · Article · Sep 2016 impedance, when the objects pass through a pair of coplanar electrodes (Trujillo et al. 2007) and (b) optical 24 detection based on the scattering or fluorescence signals, when objects pass through a detection region (Frankowski et 25 al. 2015). The axial interdistance between the objects in a focused sample stream is an important parameter, which 26 could affect the measurements. ABSTRACT: Single-file focusing and minimum interdistance of micron-size objects in a sample is a prerequisite for accurate flow cytometry measurements. Here, we report analytical models for predicting the focused width of a sample stream b as a function of channel aspect ratio α, sheath-to-sample flow rate ratio f and viscosity ratio λ in both 2D and 3D focusing. We present another analytical model to predict spacing between an adjacent pair of objects in a focused sample stream as a function of sample concentration C, mobility ? of the objects in the prefocused and postfocused regions and flow rate ratio f in both 2D and 3D flow focusing. Numerical simulations are performed using Ansys Fluent VOF model to predict the width of sample stream in 2D and 3D hydrodynamic focusing for different sample-to-sheath viscosity ratios, aspect ratios and flow rate ratios. Experiments are performed on both planar and three-dimensional devices fabricated in PDMS to demonstrate focusing of sample stream and spacing of polystyrene beads in the unfocused and focused stream at different sample concentrations C. The predictions of the analytical model and simulations are compared with experimental data, and a good match is found (within 12 %). Further, mobility of objects is experimentally studied in 2D and 3D focusing, and the spread of the mobility data is used as tool for the demonstration of particle focusing in flow cytometer applications.Article · Jun 2016 +1 more author...The microfluidic aggregation analyzer is based on resistive pulse sensing (RPS) (Coulter, 1956; Deblois and Wesley, 1977), which provides a simple electrical detection and size measurement method, where single particles flowing through a narrow constriction change the electrical resistance of the constriction by an amount proportional to the volume of the particle. With advances in microfluidic technology, a number of on-chip RPS architectures have been proposed for the counting and sizing of submicron and micron-sized particles (Carbonaro and Sohn, 2005; Rodriguez-Trujillo et al., 2007; Sridhar et al., 2008; Zhe et al., 2007). Previously, we demonstrated a particle analyzer with high throughput and very accurate nanoscale size characterization (Fraikin et al., 2011) and in this work, the same high throughput and sizing accuracy is leveraged for the rapid and precise quantification of LIA utilizing sub-micron particles, such as those commonly used in commercial agglutination kits intended for turbidity measurements (Fujita et al., 1994; Phillip and Andrews, 1987). ABSTRACT: Portable and low-cost platforms for protein biomarker detection are highly sought after for point of care applications. We demonstrate a simple microfluidic device for the rapid, electrically-based detection of proteins in serum. Our aggregation analyzer relies on detecting the protein-induced aggregation of sub-micron particles, using a one-step procedure followed by a fast, particle-by-particle measurement with a very high count rate. This enables the rapid and precise quantification of C-Reactive protein levels, within the clinically relevant range, using unprocessed human serum and a disposable no optics are involved in the implementation. Due to the single particle detection format and the use of microfluidics, only a small volume of serum (~50nL) is needed to complete the analysis. The method can be easily extended to multiplexed biomarker detection by combining an assay using differently sized particles, each targeting a separate protein. We illustrate this by using two sizes of latex beads and demonstrating the simultaneous detection of two different proteins in a serum environment with minimal cross-interference. This confirms that our aggregation analyzer platform provides a simple and straightforward method for multiplexed biomarker detection in a low cost, portable design. Full-text · Article · Nov 2015 +1 more author...The 8-bit greyscale images were used for image processing throughout the experiment. In general, the values of greyscale pixels represent a level of greyness or brightness, and pixels with a value of 0 or 255 are related to the black and white colours, respectively, in an 8-bit greyscale image (Pratt 1978). Although greyscale images with bit depth of 2, 4, 6, 12, 16 and 32 exist, 8-bit greyscale images are the most common.
File · Data · Jan 2013 · Biosensors & BioelectronicsProject[...]Private ProfileThis project which is funded by the Lverhulme Trust aims to develop low cost, flexible direct radiaiotn detectors through the incoporation of radiation sensitive inorganic nanoparticles into organi…& Project[...]Deleted ProfileProject[...]Project[...]ArticleMay 2008 · Biosensors & Bioelectronics · Impact Factor: 6.41This article presents the fabrication and characterisation of a high-speed detection micro-Coulter counter with two-dimensional (2D) adjustable aperture and differential impedance detection. The developed device has been fabricated from biocompatible and transparent materials (polymer and glass) and uses the principle of hydrodynamic focusing in two dimensions. The use of a conductive solution... ArticleJanuary 2013 · Microfluidics and Nanofluidics · Impact Factor: 2.53Here we describe a high-throughput impedance flow cytometer on a chip. This device was built using compact and inexpensive electronic instrumentation. The system was used to count and size a mixed cell sample containing red blood cells and white blood cells. It demonstrated a counting capacity of up to similar to 500 counts/s and was validated through a synchronised high-speed optical... ArticleA novel microfluidic chip able to detect a wide range of different cell sizes at very high rates is reported. The device uses two-dimensional hydrodynamic focus-ing [1] of the sample (conducting) flow by three non-conducting flows and high-speed differential impedance detection electronics. High-speed counting of 15μm polystyrene particles and 5μm yeast cells with a rate of up to 1000... ArticleMay 2006 · Physica Status Solidi (A) Applications and Materials · Impact Factor: 1.62The design and method for the production of an all-polymer microfluidic particle sorter, for use in biomedical applications, is described. The sorter is made from biocompatible materials with properties, such as high optical transparency, that make it useful in a biological laboratory. The method of sorting is designed to be gentle on biological species, using a method of guiding the particles... Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.This publication is from a journal that may support self archiving.Last Updated: 03 May 17