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We report an easily assembled, high performance liquid/liquid separator constructed from a drilled-out block of aluminium, a short length of porous polytetrafluoroethylene tubing, and a small number of off-the-shelf components and 3D-printed parts. The separator relies on the two incoming liquids having different wettabilities to the wall of the porous capillary, with the more strongly wetting liquid leeching through the porous wall while the other liquid passes unhindered through the interior channel. To achieve complete separation of the two phases, the fluid streams at the separator outlets are monitored optically, and the back-pressure at one outlet is iteratively adjusted using a motorised needle valve until smooth time-invariant signals are recorded at both outlets. The separator may be applied to many pairings of immiscible liquids over a broad range of flow rates, automatically establishing complete separation within minutes of activation and adjusting dynamically to subsequent changes in the flow conditions. The separator – whose performance is competitive with far costlier commercial systems – is released here as open hardware, with technical diagrams, a full parts list, assembly instructions, and source code for its firmware.

We report an automated procedure for the inline separation of two immiscible liquids based on a porous polytetrafluoroethylene (PTFE) capillary and a small number of inexpensive electronic components. By monitoring the light transmitted through fluid streams at the two outlets of the separator and iteratively adjusting a needle-valve located at one outlet until smooth time-invariant signals are observed at both outlets, the separator is capable of establishing complete liquid/liquid separation within minutes. Using mixtures of water and toluene as a test system, near quantitative recovery of the two liquids was achieved over a wide range of flow conditions without detectable cross contamination at either outlet. In a twenty-four hour test run, departures from complete separation occurred just three times, and on each occasion complete separation was automatically restored within ninety seconds. Further tests on other liquid/liquid mixtures showed that the automated separator is capable of rapidly and reliably inducing the separation of aqueous–organic, aqueous–fluorous and organic–fluorous mixtures, making it a versatile tool for numerous applications in fluidic analysis, synthesis and purification.

We describe a high resolution laser polarimeter built from commodity optical components. The optical rotation angle is determined by measuring the phase difference between two harmonically modulated polarised laser beams – an ‘object beam’ that passes through the sample under test and a ‘reference beam’ that bypasses the sample. The complete polarimeter may be assembled from low cost off-the-shelf parts for less than £300 (UK Sterling). Data acquisition and analysis are carried out on a microcontroller running an efficient algorithm based on the sliding Discrete Fourier Transform. Despite its low cost, the polarimeter is a fully automatic, research-grade instrument with an accuracy of ±0.0013° and a precision of ±0.0028° – comparable to far costlier commercial instruments. The polarimeter’s ease of use, compact size, fast measurement times and high angular resolution make it a capable and versatile tool for analytical science, while its low cost means it is ideally suited for use in resource-constrained environments and process monitoring. The polarimeter is released here as open hardware, with technical diagrams, a full parts list, and source code for its firmware included as Supplementary Information.

Adhesion lithography (“a‐lith”) is a simple method for forming nanoscale gaps between dissimilar metals. In its usual form, a metal is patterned on a substrate, and conformally coated with an alkyl‐functionalized self‐assembled monolayer, rendering it nonadhesive to other metals; a second metal is then deposited uniformly over the full area of the substrate; finally, the parts of the second metal that are in contact with the self‐assembled monolayer are stripped away using an adhesive tape or film, leaving the first and second metals side‐by‐side on the substrate, with a nanoscale spacing between them. It is shown here that, by depositing onto the second metal an adhesive film with high internal strain, it is possible to induce spontaneous delamination of the peeling layer without the need for any applied force. The modified procedure simplifies implementation and eliminates external stresses that can cause unwanted widening of the gap. The resultant electrode separations of ≈10 nm are amongst the smallest values achieved to date using adhesion lithography. © 2019 The Authors. Published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Indium phosphide quantum dots typically exhibit broad and poorly defined ensemble optical properties due to a highly pronounced nucleation period that consumes virtually all phosphorus precursors, leading to subsequent growth by Ostwald ripening and poor final size distributions. Previous attempts to reduce the reactivity of the phosphorus precursor, and thereby limit its consumption during the nucleation phase, have not led to appreciably better optical properties due to an unwanted increase in the duration of nucleation. Here we present an alternative approach to reducing initial precursor consumption using a simple modification of the indium precursor, in which the widely used carboxylate ligand is replaced by a phosphine. The change of ligand leaves residual precursor available for size-focusing growth after nucleation, leading to significantly improved spectral features. Band-edge emission peaks are typically 30% narrower than for the standard method.

We report a simple, non-invasive sensor for monitoring flow-rate and flow-uniformity in absorbing and non-absorbing (colourless) segmented flows, using time-resolved measurements of optical transmission. The self-contained sensor is simple in design, inexpensive, and easy to assemble, comprising just two light-emitting diodes, two photodiodes, a 3D-printed housing and a low-cost microcontroller development board. All calculations are carried out directly on the microcontroller, using a computationally efficient algorithm based on the sliding discrete Fourier transform. The sensor is released as open hardware, with design files, source code and assembly instructions included in the Supporting Information .

Gold is the most widely used electrode material for bioelectronic applications due to its high electrical conductivity, good chemical stability and proven biocompatibility. However, it adheres only weakly to widely used substrate materials such as glass and silicon oxide, typically requiring the use of a thin layer of chromium between the substrate and the metal to achieve adequate adhesion. Unfortunately, this approach can reduce biocompatibility relative to pure gold films due to the risk of the underlying layer of chromium becoming exposed. Here we report on an alternative adhesion layer for gold and other metals formed from a thin layer of the negative-tone photoresist SU-8, which we find to be significantly less cytotoxic than chromium, being broadly comparable to bare glass in terms of its biocompatibility. Various treatment protocols for SU-8 were investigated, with a view to attaining high transparency and good mechanical and biochemical stability. Thermal annealing to induce partial cross-linking of the SU-8 film prior to gold deposition, with further annealing after deposition to complete cross-linking, was found to yield the best electrode properties. The optimized glass/SU8-Au electrodes were highly transparent, resilient to delamination, stable in biological culture medium, and exhibited similar biocompatibility to glass.

We describe an effective means of defining optimisation criteria for self-optimising reactors, applicable to situations where a compromise is sought between several competing objectives. The problem is framed as a constrained optimisation, in which a lead property is optimised subject to constraints on the values that other properties may assume. Compared to conventional methods (using weighted-sum- and weighted-product-based merit functions), the approach described here is more intuitive, easier to implement, and yields an optimised solution that more faithfully reflects user preferences. The method is applied here to the synthesis of o-xylenyl adducts of Buckminsterfullerene, using a cascadic reaction of the form X0 → X1 → X2 → … XN. Specifically, we selectively target the formation of the (technologically useful) first- and second-order adducts X1 and X2, while at the same time suppressing the formation of unwanted higher-order products. More generally, the approach is applicable to any chemical optimisation involving a trade-off between competing criteria. To assist with implementation we provide a self-contained software package for carrying out constrained optimisation, together with detailed tutorial-style instructions.

This study compares the performance of a microfluidic technique and a conventional bulk method to manufacture conjugated polymer nanoparticles (CPNs) embedded within a biodegradable poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG5K-PLGA55K) matrix. The influence of PEG5K-PLGA55K and conjugated polymers cyano-substituted poly(p-phenylene vinylene) (CN-PPV) and poly(9,9-dioctylfluorene-2,1,3-benzothiadiazole) (F8BT) on the physicochemical properties of the CPNs was also evaluated. Both techniques enabled CPN production with high end product yields (∼70-95%). However, while the bulk technique (solvent displacement) under optimal conditions generated small nanoparticles (∼70-100 nm) with similar optical properties (quantum yields ∼35%), the microfluidic approach produced larger CPNs (140-260 nm) with significantly superior quantum yields (49-55%) and tailored emission spectra. CPNs containing CN-PPV showed smaller size distributions and tuneable emission spectra compared to F8BT systems prepared under the same conditions. The presence of PEG5K-PLGA55K did not affect the size or optical properties of the CPNs and provided a neutral net electric charge as is often required for biomedical applications. The microfluidics flow-based device was successfully used for the continuous preparation of CPNs over a 24 hour period. On the basis of the results presented here, it can be concluded that the microfluidic device used in this study can be used to optimize the production of bright CPNs with tailored properties with good reproducibility.

In the past decade microreactors have emerged as a compelling technology for the highly controlled synthesis of colloidal nanocrystals, offering multiple advantages over conventional batch synthesis methods (including improved levels of control, reproducibility, and automation). Initial work in the field employed simple continuous phase reactors that manipulate miscible streams of a single reagent phase. Recently, however, there has been increasing interest in segmented flow reactors that use an immiscible fluid to divide the reagent phase into discrete slugs or droplets. Key advantages of segmented flow include the elimination of velocity dispersion (a significant cause of polydispersity) and greatly reduced susceptibility to reactor fouling. In this progress report we review the operation of segmented flow microreactors, their application to the controlled synthesis of nanocrystals, and some of the principal challenges that must be addressed before they can become a mainstream technology for the controlled production of nanomaterials.

We report a versatile capillary-based droplet reactor for the controlled synthesis of nanoparticles over a wide range of flow conditions and temperatures. The reactor tolerates large flow-rate differentials between individual reagent streams, and allows droplet composition to be varied independently of residence time and volume. The reactor was successfully applied to the synthesis of metal (Ag), metal-oxide (TiO(2)) and compound semiconductor (CdSe) nanoparticles, and in each case exhibited stable droplet flow over many hours of operation without fouling, even for reactions involving solid intermediates. For CdSe formed by the reaction of Cd oleate and Se, highly controlled growth could be achieved at temperatures of up to 250 °C, with emission spectra varying smoothly and reproducibly with temperature and flow-rate. The droplet reactor showed exceptional stability when operated under constant flow-rate and temperature conditions, yielding particles with well-defined band-edge emission spectra that did not vary over the course of a full day's continuous operation.

We report the use of interlayer lithography for the micron-scale patterning of high conductivity poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The interlayer method was used to fabricate PEDOT:PSS source and drain electrodes with conductivities >360 S/cm and pattern gaps ⩾4 μm for top - gate / bottom - contact organic field-effect transistors (OFETs). p-Type OFETs based on 2,8-difluoro-5,11-bis(triethylsilylethynyl)-anthradithiophene (diF-TESADT) and blends of diF-TESADT with poly(tri-arylamine) (PTAA) exhibited high hole mobilities of up to 1 and 0.25 cm 2 /V s, respectively, while ambipolar OFETs based on methanofullerene [6,6]-phenyl-C 61 -butyric acid methyl-ester (PCBM) exhibited respective electron and hole mobilities of 0.05 and 0.005 cm 2 /V s. Complementary voltage inverters based on the diF-TESADT/PTAA and PCBM OFETs exhibited excellent operating characteristics with wide noise margin and high signal gain, indicating that the interlayer method offers a viable route to cost efficient, solution-processed, and flexible organic electronics.

Organic bulk-heterojunction solar cells using thin-film single-walled carbon-nanotube (SWCNT) anodes deposited on glass are reported. Two types of SWCNT films are investigated: spin-coated films from dichloroethane (DCE), and spray-coated films from deionized water using sodium dodecyl sulphate (SDS) or sodium dodecyl benzene sulphonate (SDBS) as the surfactant. All of the films are found to be mechanically robust, with no tendency to delaminate from the underlying substrate during handling. Acid treatment with HNO 3 yields high conductivities >1000 S cm ―1 for all of the films, with values of up to 7694 ± 800 S cm ―1 being obtained when using SDS as the surfactant. Sheet resistances of around 100 Ω sq ―1 are obtained at reasonable transmission, for example, 128 ± 2 Ω sq ―1 at 90% for DCE, 57 ± 3 Ω sq ―1 at 65% for H 2 O:SDS, and 68 ± 5 Ω sq ―1 at 70% for H 2 O:SDBS. Solar cells are fabricated by successively coating the SWCNT films with poly(3,4-ethylenedioxythiophene) : p o l y(st y rene sulphonate) (PEDOT:PSS), a blend of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxy-carbonyl)-propyl-1-phenyl-(6,6)C 61 (PCBM), and LiF/Al. The resultant devices have respective power conversions of 2.3, 2.2 and 1.2% for DCE, H 2 O:SDS and H 2 O:SDBS, with the first two being at a virtual parity with reference devices using ITO-coated glass as the anode (2.3%).

We present electroabsorption spectroscopy to measure the internal electric field in green phosphorescent polymer light-emitting-diodes with crosslinked interlayer between PEDOT:PSS and emissive layer. The phenomenon of trapped electrons screening the bulk semiconductor from the external field can explain the efficiency improvement by adding a 5–30 nm MUPD film near the anode.

We report the use of a porous polytetrafluoroethylene capillary for the inline separation of liquid–liquid segmented flows, based on the selective wetting and permeation of the porous capillary walls by one of the liquids. Insertion of a narrow flow restriction at the capillary outlet allows the back pressure to be tuned for multiple liquid–liquid combinations and flow conditions. In this way, efficient separation of aqueous–organic, aqueous–fluorous and organic–fluorous segmented flows can be readily achieved over a wide range of flow rates. The porous-capillary-separator enables the straightforward regeneration of a continuous flow from a segmented flow, and may be applied to various applications, including inline analysis, biphasic reactions, and purification. As a demonstration of the latter, we performed a simple inline aqueous–organic extraction of the pH indicator 2,6-dichloroindophenol. An aqueous solution of the conjugate base was mixed with hydrochloric acid in continuous flow to protonate the indicator and render it organic-soluble. The indicator was then extracted from the aqueous feed into chloroform using a segmented flow. The two liquids were finally separated inline using a porous PTFE capillary, with the aqueous phase emerging as a continuous stream from the separator outlet. UV-visible absorption spectroscopy showed the concentration of indicator in the outflowing aqueous phase to be less than one percent of its original value, confirming the efficacy of the extraction and separation process.

We report the use of thin-film organic photodiodes as integrated optical detectors for microscale chemiluminescence. The copper phthalocyanine–fullerene (CuPc–C 60 ) small molecule photodiodes have an external quantum efficiency of ∼30% at 600–700 nm, an active area of 2 mm × 8 mm and a total thickness of ∼2 mm. Simple detector fabrication, based on layer-by-layer vacuum deposition, allows facile integration with planar chip-based systems. To demonstrate the efficacy of the approach, CuPc–C 60 photodiodes were used to monitor a peroxyoxalate based chemiluminescence reaction (PO-CL) within a poly(dimethylsiloxane) (PDMS) microfluidic device. Optimum results were obtained for applied reagent flow rates of 25 μL/min, yielding a CL signal of 8.8 nA within 11 min. Reproducibility was excellent with typical relative standard deviations (R.S.D.) below 1.5%. Preliminary quantitation of hydrogen peroxide yielded a detection limit of ∼1 mM and linearity over at least three decades. With improved sensitivity and when combined with enzymatic assays the described integrated devices could find many applications in point-of-care diagnostics.

We use electromodulation spectroscopy and modeling studies to probe the electric-field distribution in polyfluorene-based polymer light-emitting diodes containing poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate). The bulk internal field is shown to be zero under ordinary operating conditions, with trapped electrons close to the anode fully screening the bulk semiconductor from the external field. The effect has far-reaching implications for the understanding and optimization of organic devices.

The past decade has seen a steady rise in the use of microfluidic reactors for nanocrystal synthesis, with numerous studies reporting improved reaction control relative to conventional batch chemistry. However, flow synthesis procedures continue to lag behind batch methods in terms of chemical sophistication and the range of accessible materials, with most reports having involved simple one- or two-step chemical procedures directly adapted from proven batch protocols. Here we examine the current status of microscale methods for nanocrystal synthesis, and consider what role microreactors might ultimately play in laboratory-scale research and industrial production., Lab on a Chip, 14 (17), ISSN:1473-0197, ISSN:1473-0189

Top-down fabrication of sub-50nm silicon nanowire sensors with various geometries.Excellent performance as backgated junctionless nanowire transistors (JNTs).Very good sensing capabilities.Among the smallest top-down fabricated nanowire sensing devices reported to date. This article reports the fabrication of sub-50nm field effect transistor (FET)-type silicon (Si) nanowire (Si NW) chemical and biological sensing devices with a junctionless architecture, as well as on the initial characterisation of their electrical and sensing performance.The devices were fabricated using a fully complementary metal-oxide-semiconductor (CMOS)-compatible top-down process on silicon-on-insulator (SOI) wafers. The fabrication process was mainly based on high-resolution electron beam lithography (EBL) and reactive ion etching (RIE) but also included photolithography (mix-and-match lithography), thin film deposition by electron beam evaporation, lift-off, thermal annealing and wet etching.The sensing performance of a matrix of nanowire devices, i.e. containing 1, 3 and 20 NWs with lengths of 0.5, 1 and 10µm was examined. Each element of the matrix also contained five devices with different NW widths: 10, 20, 30, and 50nm and 5µm (a Si belt reference device). Electrical characterisation of the devices showed excellent performance as backgated junctionless nanowire transistors (JNTs): high on-currents in the range of 1-10µA and high ratios between the on-state and off-state currents (Ion/Ioff) of 6-7 orders of magnitude. In addition, the results of ionic strength sensing experiments demonstrate the very good sensing capabilities of these devices. To the best of our knowledge, these nanowire sensors are among the smallest top-down fabricated Si NW devices reported to date.

In this chapter, we introduce two specific types of junctionless nanowire transistors (JNTs): (i) silicon-on-insulator (SOI) back-gated JNTs for sensing applications and (ii) germanium-on-insulator (GeOI) top-gated JNTs for digital logic applications. We discuss in detail the suitability of junctionless architecture for these particular applications and present results on device fabrication and characterisation. Back-gated JNTs of 45 different channel geometries (different numbers, lengths, and widths of channel nanowires) have been designed and fabricated with very high precision (down to 10 nm widths of the nanowires) on SOI wafers using a fully CMOS-compatible fabrication process. Electrical characterisation of the fabricated devices has demonstrated their excellent performance as back-gated JNTs. Furthermore, data from pH and streptavidin sensing experiments have proven their good sensing properties. These JNTs are among the smallest top-down fabricated nanowire sensing devices reported to date. Top-gated JNTs with Ge nanowire channels of widths down to 20 nm have been fabricated by a simple CMOS-compatible process on GeOI wafers with a highly p-doped (~1×1019 cm−3) top germanium layer. The fabricated devices have demonstrated decent output and transfer characteristics with relatively high I on /I off current ratios of up to 2.0 × 105 and steep subthreshold slopes of 189 mV/dec. To the best of our knowledge, these are the first reported Ge JNTs.

Recently, an intermixed phase has been identified within organic photovoltaic (OPV) bulk heterojunction (BHJ) systems that can exist in addition to relatively phase-pure regions, highlighting the need for a refined picture of the solid-state microstructure of donor–acceptor blends and for gaining further understanding of the exact nature and role such intermixed phases play in such devices. Here we manipulate the microstructure of polymer–fullerene systems via processing means and the selection of the molecular weight of the donor polymer. This manipulation is used as a tool to vary the fraction of intermixed phase present and its effects on the structure and subsequently the opto-electronic processes. We find clear relationships between the state of mixing and amount of exciton quenching and number of polarons generated per absorbed photon. Furthermore, we observe that blend systems incorporating higher molecular weight polymer result in a greater yield of dissociated polarons, likely due to the increase of the intermixed fraction.

For quantum dots (QDs) synthesized in solvents that are immiscible in water, dietary, rather than aqueous, exposure is expected to be the primary route of uptake. The estuarine snail Peringia ulvae was presented with mats of simulated detritus spiked with oleic acid capped cadmium sulfide (CdS; 3.1 ± 0.4 nm) or cadmium selenide (CdSe; 4.2 ± 0.8 nm) nanoparticles, synthesized using a microfluidics method, or Cd2+ (added as Cd[NO3]2) as a control. A biodynamic modeling approach was used to quantify parameters that describe the dietary accumulation of the Cd forms. Ingestion rates decreased across treatments at higher exposure concentrations, indicating a metal-induced stress response related to Cd dose rather than form. Although Cd was bioavailable from both CdS and CdSe QDs, uptake rate constants from diet were significantly lower than that of Cd2+ (p

A micro-power energy harvesting system based on core(crystalline Si)-shell(amorphous Si) nanowire solar cells together with a nanowire-modified CMOS sensing platform have been developed to be used in a dust-sized autonomous chemical sensor node. The mote (SiNAPS) is augmented by low-power electronics for power management and sensor interfacing, on a chip area of 0.25mm(2). Direct charging of the target battery (e. g., NiMH microbattery) is achieved with end-to-end efficiencies up to 90% at AM1.5 illumination and 80% under 100 times reduced intensity. This requires matching the voltages of the photovoltaic module and the battery circumventing maximum power point tracking. Single solar cells show efficiencies up to 10% under AM1.5 illumination and open circuit voltages, Voc, of 450-500mV. To match the battery's voltage the miniaturised solar cells (similar to 1mm(2) area) are connected in series via wire bonding. The chemical sensor platform (mm 2 area) is set up to detect hydrogen gas concentration in the low ppm range and over a broad temperature range using a low power sensing interface circuit. Using Telran TZ1053 radio to send one sample measurement of both temperature and H-2 concentration every 15 seconds, the average and active power consumption for the SiNAPS mote are less than 350nW and 2.1 mu W respectively. Low-power miniaturised chemical sensors of liquid analytes through microfluidic delivery to silicon nanowires are also presented. These components demonstrate the potential of further miniaturization and application of sensor nodes beyond the typical physical sensors, and are enabled by the nanowire materials platform.

Electromodulation (EM) spectroscopy has been used to probe the electric field distribution in polymer light-emitting diodes. Below the turn-on bias, the EM spectrum is dominated by electroabsorption of the emissive layer. The electroabsorption signal vanishes above the turn-on bias. Under operation, the EM spectrum is composed of bleaching of the emissive layer absorption and excited state absorption from trapped charge with no trace of the electroabsorption signal remaining. We conclude that the internal electric field is effectively screened by accumulation of trapped electrons at the anode.

For quantum dots (QDs) synthesized in solvents that are immiscible in water, dietary, rather than aqueous, exposure is expected to be the primary route of uptake. The estuarine snail Peringia ulvae was presented with mats of simulated detritus spiked with oleic acid capped cadmium sulfide (CdS; 3.1 ± 0.4 nm) or cadmium selenide (CdSe; 4.2 ± 0.8 nm) nanoparticles, synthesized using a microfluidics method, or Cd(2+) (added as Cd[NO3 ]2 ) as a control. A biodynamic modeling approach was used to quantify parameters that describe the dietary accumulation of the Cd forms. Ingestion rates decreased across treatments at higher exposure concentrations, indicating a metal-induced stress response related to Cd dose rather than form. Although Cd was bioavailable from both CdS and CdSe QDs, uptake rate constants from diet were significantly lower than that of Cd(2+) (p 0.05). After 72 h depuration, however, no loss of Cd was observed from snails that had accumulated Cd from either type of QD. In comparison, snails ingesting Cd(2+) -spiked detritus eliminated 39% of their accumulated body burden per day. The almost identical uptake and efflux rates for Cd in both QDs suggest no effect of the chalcogenide conjugates (S or Se). The findings of the present study indicate that the availability of Cd in the form of nanoparticles and its apparent in vivo persistence will lead to bioaccumulation. The implications of this are discussed.

We report the fabrication of non-emissive short- and long-pass filters on plastic for high sensitivity fluorescence detection. The filters were prepared by overnight immersion of titania-coated polyethylene terephthalate (PET) in an appropriate dye solution - xylene cyanol for short-pass filtering and fluorescein disodium salt for long-pass filtering - followed by repeated washing to remove excess dye. The interface between the titania and the dye molecule induces efficient quenching of photo-generated excitons in the dye molecule, reducing auto-fluorescence to negligible values and so overcoming the principal weakness of conventional colour filters. Using the filters in conjunction with a 505 nm cyan light-emitting diode and a Si photodiode, dose-response measurements were made for T8661 Transfluosphere beads in the concentration range 1 × 10(9) to 1 × 10(5) beads μL(-1), yielding a limit of detection of 3 × 10(4) beads μL(-1). The LED/short-pass filter/T8661/long-pass filter/Si-photodiode combination reported here offers an attractive solution for sensitive, low cost fluorescence detection that is readily applicable to a wide range of bead-based immunodiagnostic assays.

We report efficient organic bulk heterojunction solar cells, utilizing spray-patterned films of single-wall carbon nanotubes for the transparent electrode. High power conversion efficiencies of up to 3.6% were obtained using a blend of poly(3-hexylthiophene) and phenyl-C61 butyric acid methyl ester as the active layer, comparable to conventional devices utilizing indium tin oxide as the transparent electrode.

We demonstrate a compact, low cost and practical fluorescence detection system for lab-on-a-chip applications. The system comprises a commercially available InGaN light emitting diode (501 nm) as light source, an organic or silicon photodiode detector, absorptive dye coated colour filters and linear and reflective polarisers. An injection moulded polystyrene microfluidic chip is used as the platform for fluorescence immunoassays for cardiac markers myoglobin and CK-MB. The optical limit of detection (LOD) is measured using a TransFluoSphere® suspension at 5.6 × 10(4) beads µl(-1) which can be equated to ∼3 nM fluorescein equivalent concentration. The LOD for the human plasma immunoassays is measured as 1.5 ng ml(-1) for both myoglobin and CK-MB.

High resolution patterning of single-wall carbon nanotubes is achieved using interlayer lithography. Minimum feature sizes of 6 and 0.7 μm are demonstrated on glass and silicon, using the negative photoresist SU-8 and the positive photoresist AZ7220, respectively. Films patterned using SU-8 have a good balance of transparency and sheet-resistance, and are shown to be effective electrodes for organic solar cells. Copyright © 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

The difficulty of preparing nanomaterials in a controlled, reproducible manner is a key obstacle to the proper exploitation of many nanoscale phenomena. An automated chemical reactor capable of producing (on demand and at the point of need) high-quality nanomaterials, with optimized physicochemical properties, would find numerous applications in nanoscale science and technology, especially in the areas of photonics, optoelectronics, bio-analysis, and targeted drug-delivery. In addition such a device would find immediate and important applications in toxicology, where it is essential to characterize the physiological effects of nanoparticles not only in terms of chemical composition but also in terms of size, shape, and surface functionalization. In this chapter, we describe recent advances in the development of microfluidic reactors for controlled nanoparticle synthesis and, more specifically, work in our group aimed at developing just such an automated reactor.

Herein we discuss two broad approaches for performing high sensitivity optical detection within microfluidic environments. First, we describe recent work in which fluorescence lifetime imaging has been shown to be a sensitive probe of environmental parameters such as pH, viscosity, molecular concentration and temperature. Additionally, we demonstrate how dynamic fluorescence lifetime imaging can be used to probe mixing dynamics in segmented-flow microfluidic systems. Moreover, we describe recent work at Imperial College London in which semiconducting polymer light emitting diodes and polymer photodetectors are integrated with microfluidic systems to define a novel format for point-of-care diagnostics.

We report current-voltage-luminance and electromodulation measurements on a series of polymer light-emitting diodes, using indium tin oxide (ITO) coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the anode, poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)-diphenylamine) (TFB) as an optional anodic interlayer material, poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) as the emissive layer, and either aluminium or (aluminium-capped) calcium as the cathode. Four device structures were investigated: ITO/PEDOT:PSS/F8T2/Al, ITO/PEDOT:PSS/F8T2/Ca, ITO/PEDOT:PSS/TFB/F8T2/Al, and ITO/PEDOT:PSS/TFB/F8T2/Ca. The devices with interlayers had substantially higher luminance and power efficiencies than their interlayer-free counterparts--a fact we attribute to the energy and mobility barriers that exist at the TFB-F8T2 interface. These barriers play two crucial roles in enhancing device efficiency: firstly, they cause the most easily injected charge carrier to accumulate at the TFB-F8T2 interface until efficient injection of the opposite carrier type becomes favourable; and, secondly, they inhibit electron and hole 'seepage' across the interface, thereby reducing leakage currents. The beneficial influence of these two effects is most marked for the interlayer-containing Al device which, in spite of a sizeable 0.9 eV barrier to electron injection at the cathode, exhibited surprisingly high luminous and power efficiencies of 2.4 cd A(-1) and 1.1 lm W(-1) at an arbitrary reference luminance of 2500 cd m(-2). This compares with peak values of just 0.11 cd A(-1) and 0.07 lm W(-1) at 25 cd m(-2) for the equivalent interlayer-free device (falling to 0.058 cd A(-1) and 0.025 lm W(-1) at 100 cd m(-2)). The interlayer-containing Ca device had luminous and power efficiencies of 3.5 cd A(-1) and 2.9 lm W(-1) at 2500 cd m(-2) compared to 1.1 cd A(-1) and 0.7 lm W(-1) for the equivalent interlayer-free device at 2500 cd m(-2).

We describe an adaptive grid method-of-lines (MOL) solution procedure for modelling charge transport and recombination in organic semiconductor devices. The procedure we describe offers an efficient, robust and versatile means of simulating semiconductor devices that allows for much simpler coding of the underlying equations than alternative simulation procedures. The MOL technique is especially well-suited to modelling the extremely stiff (and hence difficult to solve) equations that arise during the simulation of organic-and some inorganic-semiconductor devices. It also has wider applications in other areas, including reaction kinetics, combustion and aero- and fluid dynamics, where its ease of implementation also makes it an attractive choice. The MOL procedure we use converts the underlying semiconductor equations into a series of coupled ordinary differential equations (ODEs) that can be integrated forward in time using an appropriate ODE solver. The time integration is periodically interrupted, the numerical solution is interpolated onto a new grid that is better matched to the solution profile, and the time integration is then resumed on the new grid. The efficacy of the simulation procedure is assessed by considering a single layer device structure, for which exact analytical solutions are available for the electric potential, the charge distributions and the current-voltage characteristics. Two separate state-of-the-art ODE solvers are tested: the single-step Runge-Kutta solver Radau5 and the multi-step solver ODE15s, which is included as part of the Matlab ODE suite. In both cases, the numerical solutions show excellent agreement with the exact analytical solutions, yielding results that are accurate to one part in 1 x 10(4). The single-step Radau5 solver, however, is found to provide faster convergence since its efficiency is not compromised by the periodic interruption of the time integration when the grid is updated.

We describe an autonomous ‘black-box’ system for the controlled synthesis of fluorescent nanoparticles. The system uses a microfluidic reactor to carry out the synthesis and an in-line spectrometer to monitor the emission spectra of the emergent particles. The acquired data is fed into a control algorithm which reduces each spectrum to a scalar ‘dissatisfaction coefficient’ and then intelligently updates the reaction conditions in an effort to minimise this coefficient and so drive the system towards a desired goal. In the tests reported here, CdSe nanoparticles were prepared by separately injecting solutions of CdO and Se into the two inlets of a heated y-shaped microfluidic reactor. A noise-tolerant global search algorithm was then used to efficiently identify—without any human intervention—the injection rates and temperature that yielded the optimum intensity for a chosen emission wavelength.

The synthesis of one-dimensional titanium oxide nanostructures has been accelerated by performing the reaction in a microfluidic environment as opposed to a classical batch process.

We report the use of solution-processed thin-film organic photodiodes for microscale chemiluminescence. The active layer of the photodiodes comprised a 1 : 1 blend by weight of the conjugated polymer poly(3-hexylthiophene) [P3HT] and [6,6]-phenyl-C(61)-butyric acid-methylester [PCBM]--a soluble derivative of C(60). The devices had an active area of 1 mm x 1 mm, and a broad-band response from 350 to 700 nm, with an external quantum efficiency of more than 50% between 450 and 550 nm. The photodiodes have a simple layered structure that permits facile integration with planar chip-based systems. To evaluate the suitability of the organic devices as integrated detectors for microscale chemiluminescence, a peroxyoxalate based chemiluminescence reaction (PO-CL) was monitored within a poly(dimethyl-siloxane) (PDMS) microfluidic device. Quantitation of hydrogen peroxide indicated excellent linearity and yielded a detection limit of 10 microM, comparable with previously reported results using micromachined silicon microfluidic chips with integrated silicon photodiodes. The combination of organic photodiodes with PDMS microfluidic chips offers a means of creating compact, sensitive and potentially low-cost microscale CL devices with wide-ranging applications in chemical and biological analysis and clinical diagnostics.

We have measured the built-in potential of a series of polyfluorene-containing light-emitting diodes (LEDs) by electroabsorption spectroscopy. When the anode incorporates a layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the inferred anode work function is equal to the ionization potential of the emissive polyfluorene. This result requires that the Fermi level of PEDOT:PSS is pinned to the highest occupied molecular orbital of the emissive polymer. Pinning of the anode Fermi level eliminates the injection barrier to holes and explains the low turn-on bias of polymer LEDs that incorporate PEDOT:PSS. We attribute this phenomenon to electron trapping at the interface between PEDOT:PSS and the emissive layer.

We investigate the influence of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) on the optoelectronic properties of polymer light-emitting diodes containing poly(9,9-dioctylfluorene) (PFO). Electromodulation and $IV$ luminance measurements are reported for a series of devices with bare indium tin oxide (ITO) or PEDOT:PSS-coated ITO anodes and Ba or Al cathodes. The ITO/PFO/Al, ITO/PFO/Ba, and ITO/PEDOT:PSS/PFO/Al devices all exhibit conventional field-induced electromodulation behavior, in both forward and reverse bias, consistent with the Stark effect (SE). The ITO/PEDOT:PSS/PFO/Ba devices by contrast exhibit conventional behavior only for applied biases below the flat-band voltage; at higher biases, the field-induced SE features vanish and are replaced by anomalous charge-induced electromodulation features. This anomalous behavior is observed only when PEDOT:PSS is used in conjunction with a strongly electron-injecting cathode such as Ba, and is attributed to the presence of trapped electrons at the PEDOT:PSS-emitter interface, which screen the electric field from the bulk of the device. The enhanced field at the interface increases the rate of field-assisted hole injection into the highest occupied molecular orbital (HOMO) of the PFO, resulting in lower drive voltages and increased electroluminescence efficiencies.

We characterise the behaviour of bilayer organic light emitting devices using numerical simulations based on the method-of-lines. The algorithm offers rapid convergence and avoids the problem of ill-conditioned systems of differential equations.

We report low threshold blue polyfluorene distributed-feedback (DFB) lasers. Second-order lasers exhibit a laser threshold of 0.28 nJ/pulse while the threshold is reduced to 0.16 nJ/pulse for first-order gratings. Laser diode pumping is demonstrated.

The properties of electrically pumped organic laser devices are investigated by the self consistent numerical solution of the spatially inhomogeneous laser rate equations coupled to a drift-diffusion model for the electrons, holes and singlet excitons. By fully taking into account the effect of stimulated emission on the exciton population, we determine the spatial and temporal evolution of the photon density in organic multilayer structures. We apply the model to calculate laser threshold current densities and investigate transient phenomena like the delay of radiation onset. By performing systematic parameter variations, we derive design rules for potential organic laser diode structures.

As a first step towards a fully disposable stand-alone diagnostic microchip for determination of urinary human serum albumin (HSA), we report the use of a thin-film organic light emitting diode (OLED) as an excitation source for microscale fluorescence detection. The OLED has a peak emission wavelength of 540 nm, is simple to fabricate on flexible or rigid substrates, and operates at drive voltages below 10 V. In a fluorescence assay, HSA is reacted with Albumin Blue 580, generating a strong emission at 620 nm when excited with the OLED. Filter-less discrimination between excitation light and generated fluorescence is achieved through an orthogonal detection geometry. When the assay is performed in 800 microm deep and 800 microm wide microchannels on a poly(dimethylsiloxane)(PDMS) microchip at flow rates of 20 microL min(-1), HSA concentrations down to 10 mg L(-1) can be detected with a linear range from 10 to 100 mg L(-1). This sensitivity is sufficient for the determination of microalbuminuria (MAU), an increased urinary albumin excretion indicative of renal disease (clinical cut-off levels: 15-40 mg L(-1)).

We report electromodulation (EM) studies of polyfluorene-based light-emitting diodes containing poly(3,4-ethylene-dioxythiophene)-poly(styrene-sulfonate) (PEDOT:PSS), in which the barrier to hole injection is large $(\ensuremath{\sim}0.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$. Measurements are reported on devices fabricated with aluminium and barium cathodes to provide respectively poor and efficient electron injection into the active layer. The Al devices exhibit low currents, indicating low rates of electron and hole injection, whereas the Ba devices exhibit high currents and high electroluminescence efficiencies, implying efficient injection of both electrons and holes despite the large hole injection barrier. The Al devices show conventional field-induced EM behavior consistent with the Stark effect (SE). The Ba devices show conventional SE behavior for low applied biases but, above turn-on, the (field-induced) SE features vanish, indicating suppression of the internal field, and are replaced by charge-induced bleaching and absorption features. The behavior of the devices is attributed to the presence of electron traps close to the PEDOT:PSS/organic interface. The experimental findings are consistent with earlier findings by Murata et al., Van Woudenbergh et al., Poplavskyy et al., and Lane et al.

We use electromodulation (EM) spectroscopy to probe the electric field distribution in polymer light-emitting diodes. The EM spectrum below the turn-on bias is dominated by electroabsorption of the emissive layer but vanishes completely above the turn-on bias. The EM spectrum above turn-on is due entirely to absorption and bleaching effects arising from injected charge. The total elimination of the electroabsorption signal indicates that the internal electric field is effectively screened by the injected charge, and this effect is attributed to accumulation of trapped electrons close to the anode.

We describe the use of continuous-flow, microfluidic reactors for the controllable synthesis of compound semiconductor nanoparticles. Specifically, CdS nanoparticles are synthesised by rapid mixing of Na/sub 2/S and Cd(NO/sub 3/)/sub 2/.4H/sub 2/O flow streams within a silicon/glass micromixer based on the principle of flow lamination. Room temperature syntheses at a variety of volumetric flow rates yield CdS nanoparticles of variable polydispersity. Analysis of absorption spectra of the CdS nanoparticles suggests that varying volumetric flow rates of reagent streams provides a simple and direct method of controlling population dispersity. Simple, single layer glass microstructures are also used to synthesis CdSe nanoparticles in continuous flow at temperatures between 180 and 240/spl deg/C.

We report the use of a thin-film polymer light emitting diode as an integrated excitation source for microfabricated capillary electrophoresis. The polyfluorene-based diode has a peak emission wavelength of 488 nm, an active area of 40 microm x 1000 microm and a thickness of similar 2 mm. The simple layer-by-layer deposition procedures used to fabricate the polymer component allow facile integration with planar chip-based systems. To demonstrate the efficacy of the approach, the polyfluorene diode is used as an excitation source for the detection of fluorescent dyes separated on-chip by electrophoresis. Using a conventional confocal detection system the integrated pLED is successfully used to detect fluorescein and 5-carboxyfluorescein at concentrations as low as 10(-6) M with a mass detection limit of 50 femtomoles. The drive voltages required to generate sufficient emission from the polymer diode device are as low as 3.7 V.