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Neutron reflectivity was used to obtain spatial distributions within [Os(bipy)2(PVP)3.3(PS)6.7Cl]+ modified Au electrodes (where PVP represents poly(4-vinylpyridine) and PS represents polystyrene) in contact with increasing concentrations of two types of electrolyte, perchlorate and p-toluenesulfonate. Film swelling and corresponding solvent ingress were observed to be more pronounced in p-toluenesulfonate media than in perchlorate media, yet the effects were found to be of lesser magnitude than for the corresponding homopolymer system, [Os(bipy)2(PVP)10Cl]+. Film structural changes upon immersion in solvent and redox cycling in electrolyte were determined. A comparison with the film maintained in OsII and OsIII oxidation states revealed further film swelling in the oxidized state.

Structure−property correlations of two electroactive polymer bilayers fabricated by different methods are investigated using neutron reflectivity to probe the buried polymer/polymer interfaces. Both bilayers utilize electropolymerized poly(2,2‘-bithiophene) as an inner, mediating layer, while the outer layer consists of either electropolymerized polypyrrole or electroprecipitated polyxylylviologen, respectively. These devices have very different current−potential behaviors, which neutron reflectivity shows is a consequence of the fabrication method and the resulting polymer/polymer interfacial structure. The polybithiophene/polypyrrole film is found to be of composite structure while polybithiophene/polyxylylviologen forms a film comprised of segregated polymer layers.

The control of molecular recognition at interfaces is of importance in many areas of bioelectronics and biocatalysis, particularly in the design of biosensors, where it may be desirable to be able to manipulate the degree of interaction between a protein and a metal surface. To develop appropriate models to study such phenomena, we have produced mixed monolayers on gold by the displacement of molecules from a previously formed, homogeneous self-assembled monolayer (SAM) of an alkanethiol (mercaptoethylamine) using a solution containing a thiol with a different functional headgroup (mercaptopropanol). The dynamics of the formation of the resultant surfaces were investigated using high-resolution X-ray photoelectron spectroscopy (XPS) to probe both the C(1s) and N(1s) environments, corresponding to the different species in the SAMs. To illustrate the application of such interfacial arrangements and to further understand their role in controlling protein-surface interactions, two systems were investigated: ...

Neutron reflectivity measurements were made on electroactive films of [Os(bipy) 2 (PVP) 10 Cl] + spin coated onto Au electrodes. Solvent content and film swelling were monitored as functions of the solution pH and counterion (perchlorate vs. p-toluenesulfonate). Film swelling was much greater near the polymer/solution interface than within the interior of the film. Furthermore, this spatial variation in film swelling was more pronounced in p-toluenesulfonate media than in perchlorate media. Structural information is presented here in the form of spatial distribution of polymer and solvent within the film; these profiles could not have been obtained directly from purely electrochemical measurements.

Previously there has been considerable research in producing biosensors by the entrapment of proteins in electrochemically formed conducting polymer films. In this paper we describe a method enabling the amount of the enzyme glucose oxidase, entrapped at the surface of a poly(pyrrole) film to be quantified using X-ray photoelectron spectroscopy (XPS). Components of the biosensor XPS spectrum were deconvoluted as a linear combination of characteristic polymer and enzyme spectra, using primarily the high-energy C(1s) signals (288.2 and 286.4 eV) due to functional groups in the enzyme and the N(1s) signal present in both enzyme and polymer samples at 400.2 eV, together with the lesser shoulder at 398.0 eV, related to iminic nitrogen species in the polymer alone. The O(1s) peak at 531.7 eV, associated with the immobilized enzyme, provided additional compositional information, although here the effects of surface contamination were more pronounced. Further, and in parallel with this XPS study, corroborative re...

With non-invasive properties and high sensitivities, portable optical biosensors are extremely desirable for point-of-care (POC) applications. Lab-on-a-chip technology such as microfluidics has been treated as an ideal approach to integrate complex sample processing and analysis units with optical detection elements. The work in this paper has developed an integrated dispersive component in combination with a microfluidic chip, providing a portable and inexpensive platform for on-chip spectroscopic sensing. We demonstrate an integrated microfluidic spectroscopic sensor by using an arrayed waveguide grating (AWG) device. In particular, a visible AWG device (λc=680nm) with chip size of 12.1mm by 1.5mm was designed and fabricated by employing flamed hydrolysis deposited (FHD) silica as the waveguide material. A straight input waveguide is used to perform device characterization while a perpendicular curved waveguide is employed to introduce laser excitation light. A polymer microfluidic chip is integrated with the AWG device by oxygen plasma bonding. To prove effectiveness of the integrated spectroscopic sensor, fluorescence spectrum of an organic fluorophore (Cy5) was tested. Reconstructed spectrum by using the AWG device is compared with the outcome from a conventional spectrometer and a good consistency is presented.

We present a simple and non-invasive experimental procedure to measure the linear viscoelastic properties of cells by passive particle tracking microrheology. In order to do this, a generalised Langevin equation is adopted to relate the timedependent thermal fluctuations of a probe sensor, immobilised to the cell’s membrane, to the frequency-dependent viscoelastic moduli of the cell. The method has been validated by measuring the linear viscoelastic response of a soft solid and then applied to cell physiology studies. It is shown that the viscoelastic moduli are related to the cell’s cytoskeletal structure, which in this work is modulated either by inhibiting the actin/myosin-II interactions by means of blebbistatin or by varying the solution osmolarity from iso- to hypo-osmotic conditions. The insights gained from this form of rheological analysis promises to be a valuable addition to physiological studies; e.g. cell physiology during pathology and pharmacological response.

We report on a novel experimental study of a pH-responsive polyelectrolyte brush at the silicon/D2O interface. A poly[2-(diethylamino)ethyl methacrylate] brush was grown on a large silicon crystal which acted as both a substrate for a neutron reflectivity solid/liquid experiment but also as an FTIR-ATR spectroscopy crystal. This arrangement has allowed for both neutron reflectivities and FTIR spectroscopic information to be measured in parallel. The chosen polybase brush shows strong IR bands which can be assigned to the N-D(+) stretch, D2O, and a carbonyl group. From such FTIR data, we are able to closely monitor the degree of protonation along the polymer chain as well as revealing information concerning the D2O concentration at the interface. The neutron reflectivity data allows us to determine the physical brush profile normal to the solid/liquid interface along with the corresponding degree of hydration. This combined approach makes it possible to quantify the charge on a polymer brush alongside the morphology adopted by the polymer chains.

Creating patterns of biomolecules and cells has been applied widely in many fields associated with the life sciences, including diagnostics. In these applications it has become increasingly apparent that the spatiotemporal arrangement of biological molecules in vitro is important for the investigation of the cellular functions found in vivo. However, the cell patterning techniques often used are limited to creating 2D functional surfaces on glass and silicon. In addition, in general, these procedures are not easy to implement in conventional biological laboratories. Here, we show the formation of a living poly(ethylene glycol) (PEG) layer that can be patterned with visible light on plastic surfaces. This new and simple method can be expanded to pattern multiple types of biomolecule on either a previously formed PEG layer or a plastic substrate. Using common plastic wares (i.e., polyethylene films and polystyrene cell culture Petri-dishes), we demonstrate that these PEG-modified surfaces have a high resistance to protein adsorption and cell adhesion, while at the same time, being capable of undergoing further molecular grafting with bioactive motifs. With a photomask and a fluid delivery system, we illustrate a flexible way to immobilize biological functions with a high degree of 2D and 3D spatial control. We anticipate that our method can be easily implemented in a typical life science laboratory (without the need for specialized lithography equipment) offering the prospect of imparting desirable properties to plastic products, for example, the creation of functional microenvironments in biological studies or reducing biological adhesion to surfaces.

We demonstrate a polymer resonator microfluidic biosensor that overcomes the complex manufacturing procedures required to fabricate traditional devices. In this new format, we show that a gapless light coupling photonic configuration, fabricated in SU8 polymer, can achieve high sensitivity, label-free chemical sensing in solution and high sensitivity biological sensing, at visible wavelengths.

The electrochemical quartz crystal microbalance (EQCM) has been used to study overall ion and solvent transfers in surface-immobilized [Os(bipy)2(PVP)10Cl]+ films exposed to aqueous p-toluenesulphonic acid solutions. Crystal impedance measurements were used to identify situations where the observed frequency response was dominated by changes in the viscoelastic characteristics of the films. Unfunctionalized pyridine moieties can be protonated (pKaapp = 2.9 ± 0.1), leading to pH-dependent film properties. The characteristics of films at open circuit and accompanying Os(II)/Os(III) redox switching were studied. In both cases, viscoelastic effects are observed at low and high electrolyte concentrations; at very low and intermediate concentrations the Sauerbrey equation can be used to interpret the frequency response. Even when the layer is non-rigid, isotopic substitution experiments show that solvent transfer accompanies redox switching. The film thickness dependence of the frequency response to redox switching is greater when the films are exposed to aqueous p-toluenesulphonic acid than to perchloric acid.

We have demonstrated a monolithic integrated arrayed waveguide grating (AWG) microspectrometer microfluidic platform capable of fluorescence spectroscopic analysis. The microspectrometer in this proof of concept study has a small (1 cm × 1 cm) footprint and 8 output channels centred on different wavelengths. We show that the signals from the output channels detected on a camera chip can be used to recreate the complete fluorescence spectrum of an analyte. By making fluorescence measurements of (i) mixed quantum dot solutions, (ii) an organic fluorophore (Cy5) and (iii) the propidium iodide (PI)-DNA assay, we illustrate the unique advantages of the AWG platform for simultaneous, quantitative multiplex detection and its capability to detect small spectroscopic shifts. Although the current system is designed for fluorescence spectroscopic analysis, in principle, it can be implemented for other types of analysis, such as Raman spectroscopy. Fabricated using established semiconductor industry methods, this miniaturised platform holds great potential to create a handheld, low cost biosensor with versatile detection capability.

Electrochemical quartz crystal microbalance (EQCM) measurements were used to study redox-induced changes in the ion and solvent content of polybithiophene/polyxylylviologen (PBT/PXV) bilayers. Experimental measurements were taken under slow scan voltammetric conditions in 1 mol dm −3 tetraethylammonium perchlorate + CH 3 CN. Outer (PXV) layer redox conversion occurs only at potentials where the inner (PBT) layer becomes conducting. On the relatively long time-scales employed, bilayer mass changes are dominated by perchlorate anion transfer (ejection on PXV 2+ reduction and entry on PXV 0 oxidation), with relatively little solvent transfer. The mass-charge characteristics of PBT/PXV bilayer and PXV single-layer films are relatively similar, despite their very different mass-potential characteristics.

Electrochemical quartz crystal microbalance measurements are reported for redox switching of thin films of three macromolecule-metal complexes: poly(vinylferrocene) (PVF), 10% osmium-functionalized poly(vinylpyridine) (Os-PVP), and 10% osmium functionalized poly(vinylpyridine-co-styrene) (Os-PVP-co-PS). The data provide insight into the ion and solvent transfer processes associated with electron transfer between the electrode and the electroactive film. Four important parameters are identified: electrolyte composition, (co)polymer composition, prior film history and experimental time scale.

We demonstrate a single-step method for the generation of collagen and poly-l-Lysine (PLL) micropatterns on a poly(ethylene glycol) (PEG) functionalized glass surface for cell based assays. The method involves establishing a reliable silanization method to create an effective non-adhesive PEG layer on glass that inhibits cell attachment, followed by the spotting of collagen or PLL solutions using non-contact piezoelectric printing. We show for the first time that the spotted protein micropatterns remain stable on the PEG surface even after extensive washing, thus significantly simplifying protein pattern formation. We found that adherence and spreading of NIH-3T3 fibroblasts was confined to PLL and collagen areas of the micropatterns. In contrast, primary rat hepatocytes adhered and spread only on collagen micropatterns, where they formed uniform, well defined functionally active cell arrays. The differing affinity of hepatocytes and NIH-3T3 fibroblasts for collagen and PLL patterns was used to develop a simple technique for creating a co-culture of the two cell types. This has the potential to form structured arrays that mimic the in vivo hepatic environment and is easily integrated within a miniaturized analytical platform for developing high throughput toxicity analysis in vitro.

We describe the creation of CdSe/ZnS quantum dot assemblies using layer-by-layer construction strategies, using self-assembly. In the first approach, a dithiol linker was used to make multilayers of CdSe/ZnS quantum dots, while in the second biotin- and streptavidin-conjugated CdSe/ZnS quantum dots were used to make multilayer constructs. Both the chemical bonding nature and fluorescence spectroscopic properties of quantum dot films were characterized using X-ray photoelectron spectroscopy (XPS) and fluorescence spectroscopy.

Biosensing now spans a range of medical, environmental and industrial applications. New optical techniques based on scattering, absorbance, transmission and photonic crystal technology will allow for compact, low-cost and reliable automatic analysis that can be easily produced on a mass scale.

Prussian blue (PB, iron(III)hexacyanoferrate(II) films that exhibit redox state dependent polyelectrochromicity have been the subject of intensive recent study. Chronoamperometric results over a scale of several seconds supported by scanning electron microscopy (SEM), are now presented for the electrodeposition of PB onto indium-tin oxide (ITO) and platinum by electroreduction from iron(III)hexacyanoferrate(III)-containing solutions. Variation of electrode potential, supporting electrolyte and electroactive species concentration have established a three-stage electrodeposition mechanism. The main features of the mechanism which are inferred largely from the chronoamperometry are as follows. In the first growth phase the surface becomes uniformly covered as small PB nuclei form and grow on platinum sites. This results in a decrease in the number of sites at which direct electroreduction can occur and a decrease in the film formation rate. In the second growth phase there is an increase in rate towards maximal roughness as the electroactive area increases by formation and three-dimensional growth of PB nuclei attached to the PB interface formed in the initial stage. These processes are evident in the SEM. In the final growth phase, diffusion of locally depleted electroactive species to the now three-dimensional PB interface plays an increasingly dominant role and limits electron transfer resulting in a fall in rate.

We describe the fabrication of a controllable microfluidic valve coupled with an electrochemical pump, which has been designed to deliver reagents to an integrated microfluidic biosensing system. Fluid, retained within an insertion reservoir using a stop valve, was pumped using electrochemical actuation, providing a low power, low voltage integrated Laboratory-on-a-Chip for reproducible, small volume fluidic manipulation. The properties of the valve were characterized using both X-ray photoelectron spectroscopy and contact angle measurements, enabling the calculation of the magnitude of the forces involved (which were subsequently verified through experimental measurement). Electrochemical generation of oxygen and hydrogen acted as an on-demand pressure system to force fluid over the stop valve barrier. The process of filling-up the biosensing chamber was characterized in terms of the time to fill, the energy used, and the peak power consumed. The potential of the device was illustrated using a glucose biosensor.

Biomineralization is the process where biological systems produce well-defined composite structures such as shell, teeth, and bones. Currently, there is substantial momentum to investigate the processes implicated in biomineralization and to unravel the complex roles of proteins in the control of polymorph switching. An understanding of these processes may have wide-ranging significance in health care applications and in the development of advanced materials. We have demonstrated a microfluidic approach toward these challenges. A reversibly sealed T-junction microfluidic device was fabricated to investigate the influence of extrapallial (EP) fluid proteins in polymorph control of crystal formation in mollusk shells. A range of conditions were investigated on chip, allowing fast screening of various combinations of ion, pH, and protein concentrations. The dynamic formation of crystals was monitored on chip and combined with in situ Raman to reveal the polymorph in real time. To this end, we have demonstrated the unique advantages of this integrated approach in understanding the processes involved in biomineralization and revealing information that is impossible to obtain using traditional methods.

We use quartz crystal oscillator impedance measurements in the vicinity of resonance to probe the viscoelastic characteristics of a conducting polymer film during its electrochemical deposition and subsequent undoping

In this paper we demonstrate the fabrication of arrays of gold rings and split-rings on glass slides. Nano-scale ring arrays are promising structures for sensing applications as they act as optical antennae, producing high localised electric fields. However, in order to fully exploit the properties of these structures, an in-depth understanding of the optical properties coupled with a highly reproducible and flexible fabrication technique is needed. In this work we use electron-beam lithography as it allows not only precise control of the size, shape and spacing of the arrays, but also the scope to design novel shapes at will.

A combination of XPS, reflectance infrared spectroscopy, and neutron reflectivity measurements has been used to probe the spatial and global extents to which carboxylic acid motifs in electrodeposited conducting polymer films can be functionalized by reaction with vapor phase reagents (a carbodiimide together with trifluoroethanol) with the goal of controlling hydrophobicity. Across a range of polymer deposition and reaction temperatures, neutron reflectivity showed that, surprisingly, functionalization of the polymer matrix at depths >5-10 nm into the polymer film was always significantly lower than at the exposed surface. The most efficient functionalization was found to occur when a low-density polymer matrix was prepared by elution of motifs cleaved from the polymer by base hydrolysis. Finally, when trifluoroethanol functionalization was performed, the macroscopic property of hydrophobicity was related to the surface, internal microstructure, and composition of the reacted films as elucidated by the above combination of probes.

The electropolymerization of trans-[RuCl2(vpy)4] (vpy = 4-vinylpyridine) on Au or Pt electrodes was studied by cyclic voltammetry and the electrochemical quartz crystal microbalance (EQCM) technique. Cyclic voltammetry of the monomer in DMSO on Au shows reductions at −2.0 and −2.2 V. Potential cycling over the first wave leads to polymer formation; however, scanning over the second wave leads to desorption of the polymer. These observations were confirmed by EQCM measurements which also revealed a high polymerization efficiency. Electrolysis, EQCM and XPS measurements showed that desorption was associated with substitution of chloride ligands by DMSO when the polymer was in a highly reduced state. The film also showed reversible mass changes due to the oxidation and accompanying ingress of charge-balancing anions and solvent into the film. Measurements on the dried films revealed that large quantities of solvent are trapped in the film during the electropolymerization process.

We describe in situ neutron reflectivity (NR) and RAIRS studies of the chemical modification of films of a polypyrrole-based conducting polymer derived from the pentafluorophenyl ester of poly(pyrrole-N-propanoic acid) (PFP) electrodeposited on electrode surfaces. We explore the role of the solvent in controlling the rate of reaction with solution-based nucleophiles (amines, which react with the ester to form amides). By varying the identity of the solvent (water vs acetonitrile) and the neutron contrast (deuteration), we find that both the identity of the solvent and its population within the film are paramount in determining chemical reactivity and electroactivity. IR signatures allow monitoring of the reaction of solution-based amine-tagged species such as amino-terminated poly(propylene glycol), ferrocene ethylamine, and lysine with film-based ester functionalities: the carbonyl bands show ester/amide interconversion and some hydrolysis to acid. Time-dependent spectral analysis shows marked variations in reaction rate with (i) (co-)polymer composition (replacement of some fluorinated ester-functionalized pyrrole with unfunctionalized pyrrole), (ii) the solvent to which the polymer film is exposed, and (iii) the rate of polymer deposition. NR data provide solvent profiles as a function of distance perpendicular to the interface, the variations of which provide an explanation for film reactivity patterns. Homopolymer films are relatively hydrophobic, thus hindering reaction with species present in water solutions. Incorporating pyrrole groups raises the solvent population-dramatically for water-thereby facilitating entry and reaction of aqueous-based lysine. Changing film deposition rate yields films with different absolute levels of solvent and reactivity patterns that are dependent on the size of the reactant molecules: more rapid deposition of polymer gives films with a more open structure leading to a higher solvent content and thence increased reactivity. These results, supported by XPS and AFM data, allow assembly of composition-structure-reactivity correlations, in which the controlling feature is film solvation.

Magnesium-ion-mediated RNA-RNA loop-receptor interactions, in conjunction with gold nanoparticles derivatized with DNA, have been used to make self-assembled nanowires. A wire located between lithographically fabricated nanoelectrodes is demonstrated that exhibits activated conduction by electron hopping at temperatures in the 150-300 K range. These techniques have the ability to link particles between devices and in the future may be used to assemble practical circuits.

An all-digital interface, application specific integrated circuit (ASIC) has been developed for the control and data sampling of a quartz crystal microbalance (QCM)-based electronic nose. The ASIC is capable of measuring QCM resonant frequency between 0 and 11 MHz with a resolution of 1 Hz and ±1 Hz precision. The ASIC has been used to obtain measurements from polymer coated QCM sensors, in conjunction with polymer/carbon-black coated micro-resistance (μR) sensors, in the detection of primary alcohols. A full system-on-a-chip (SoC) electronic nose, currently under test, which supports arrays of eight QCM and eight μR sensors along with on-chip processing capability, is also described. © 2004 Elsevier B.V. All rights reserved.

Electron-beam irradiation of germanium-doped silica allows the fabrication of integrated optical circuits and offers several advantages over traditional fabrication methods based on photolithography and reactive ion etching. The increment of refractive index after electron-beam irradiation is mainly due to compaction of the irradiated material. In this paper, we present results on the densification behaviour as a function of different parameters such as size of patterns written, Ge-concentration and dose, the understanding of which is needed for the design of integrated optical circuits with the required properties.

The effect in depth of electron-beam irradiation has been characterized for Ge-doped planar-FHD and tube-deposited MCVD silica. Step height measurements followed by elastic calculations allowed the study of the densification depth profile. Confocal Raman spectroscopy showed the structural rearrangements in depth.

This paper describes the systematic investigation of a range of microelectrode arrays with varying dimensions fabricated by standard photolithographic and reactive-ion etching techniques. As expected from theory, the electrochemical behavior of microelectrode arrays with a constant individual diameter varied strongly with center-to-center spacing, the larger the spacing the more sigmoidal the recorded voltammogram. Furthermore, the behavior of arrays with a constant relative center-to-center spacing is shown to vary with individual electrode diameter, the arrays with the smallest electrodes producing strongly peaked voltammograms. Peak current densities and signal-to-noise ratios were also obtained for a variety of array geometries, and the use of electrodeposited platinum black electrodes was investigated. To demonstrate one advantage of using a loosely packed microelectrode array in electroanalysis, a ferrocene-mediated enzyme-linked assay involving the biocatalytic reduction of H2O2 was investigated. Results showed an improved temporal response, with current-time transients reaching a steady-state response more quickly using arrays with increased center-center spacings.

A picoliter-volume electrochemical analytical chamber has been developed for detecting the metabolic flux resulting from the stress responses of a single plant cell. Electrochemical cells, with volumes as small as 100 pL, were fabricated by controlled electrochemical dissolution of a gold wire sealed in glass (the back-etching of the metal realizing an ultralow-volume titer chamber). In the first instance, the electrode contained within the chamber was characterized by the microinjection of standard aliquots of either ascorbic acid or hydrogen peroxide. In all cases, experimental currents obtained correlated well with theoretical calculations. Subsequently, single plant cells were micromanipulated into the chambers and were exposed to amounts of the detergent SDS (which permeabilized the cell membrane and released the intracellular contents). The flux of metabolite released from a single cell was estimated by using electrochemical-linked assays based upon the enzymes catalase, ascorbate oxidase, and horseradish peroxidase (in each case), in the presence of a mediator. In so doing, we investigated the activity of the cellular protection mechanisms through the determination of peroxides, while the individual cell was "stressed". The technique was found to provide a reliable and reproducible method for making single-cell measurements, using fabrication procedures that are both simple and do not require photolithographic methods.

The fabrication of microelectrodes integrated within ultra-low-volume microtiter chambers for the amperometric determination of metabolites continues to be of interest in the subject of single-cell and high-throughput screening. The microsystem described in this paper consists of a two-microelectrode sensor with a microfluidic dispensation technology, which is able to deliver both very low titers (6.5 pL) and single heart cells into a low-volume microphotoelectrochemical cell. Devices were fabricated using photolithography and liftoff giving reproducible sensors integrated within high aspect ratio titer chambers (with a volume of 360 pL), made of the photoepoxy SU8. In this paper, the determination of lactate was optimized using an enzyme-linked assay based upon lactate oxidase, involving the amperometric determination of hydrogen peroxide at +640 mV versus an internal Ag/AgCl pseudoreference. The microsystem (including the microfluidic dispensers and structures as well as the microsensor) was subsequently used to measure the lactate content of single heart cells. Dynamic electrochemical measurements of lactate during cell permeabilization are presented. We also show the use of respiratory uncouplers to simulate ischemia in the single myocyte and show that, as expected, the rate of lactate production from the hypoxic heart cell is greater than that within the normoxic healthy myocyte.

The long-established ferric ferrocyanide chromophore Prussian Blue (PB) has often been studied for electrochromic use. New observations and conclusions are now presented. Detailed analyses, chemical and by means of EDX, of films deposited on Pt in a variety of conditions and solution compositions, are presented, and a remarkably efficient uptake of Cs+ noted. In particular, the pH for stablest film from KCl- containing solution should be high, ca 4-5. Details of the electrodeposition on ITO glass were examined, where earlier suppositions regarding the nature of the foundation layers are confirmed by direct observation. Unexpectedly, this is substantially of ferric-ferricyanide composition. The spectroscopic shifts of the intervalence charge-transfer absorption on incorporation of different univalent cations into PB are reported and analysed. The preparative precautions needed for deposition on larger (10 x 10 cm2) ITO glass electrodes are thoroughly examined. The electrochromic response of a dual-PB electrode setup in which one electrode can be switched to clear Prussian White and the other to the deep yellow of Prussian Yellow, presents an unlikely prospect for windows or other intensity-attenuation applications, but may serve e.g. in displays. In an alternative dual-PB array a metallic silver electrode is peripherally interposed, to act as a silver/silver- chloride counter electrode. The response time in the 10 x 10 cm2 system is approximately 90 s and is accompanied by a pronounced iris (racoon) effect. The assembly provides an interesting example of two-electrode operation of a larger (cf lab-scale) device. Two-electrode operation is discussed and clarified.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Latent fingerprints on metal surfaces may be visualized by exploiting the insulating characteristics of the fingerprint deposit as a “mask” to direct electrodeposition of an electroactive polymer to the bare metal between the fingerprint ridges. This approach is complementary to most latent fingerprint enhancement methods, which involve physical or chemical interaction with the fingerprint residue. It has the advantages of sensitivity (a nanoscale residue can block electron transfer) and, using a suitable polymer, optimization of visual contrast. This study extends the concept in two significant respects. First, it explores the feasibility of combining observation based on optical absorption with observation based on fluorescence. Second, it extends the methodology to materials (here, polypyrrole) that may undergo post-deposition substitution chemistry, here binding of a fluorophore whose size and geometry preclude direct polymerization of the functionalised monomer. The scenario involves a lateral spatial image (the whole fingerprint, first level detail) at the centimetre scale, with identification features (minutiae, second level detail) at the 100–200 μm scale and finer features (third level detail) at the 10–50 μm scale. However, the strategy used requires vertical spatial control of the (electro)chemistry at the 10–100 nm scale. We show that this can be accomplished by polymerization of pyrrole functionalised with a good leaving group, ester-bound FMOC, which can be hydrolysed and eluted from the deposited polymer to generate solvent “voids”. Overall the “void” volume and the resulting effect on polymer dynamics facilitate entry and amide bonding of Dylight 649 NHS ester, a large fluorophore. FTIR spectra demonstrate the spatially integrated compositional changes. Both the hydrolysis and fluorophore functionalization were followed using neutron reflectivity to determine vertical spatial composition variations, which control image development in the lateral direction.

We report upon the application of quantum dot barcodes prepared by layer-by-layer biological self-assembly of quantum dot-biotin and quantum dot-streptavidin conjugates on magnetic beads for qualitative multiplexed immunoassay.

Specular neutron reflectivity measurements were performed on electropolymerised films of poly(pyrrole-N-propionic acid) to determine the degree to which the solvents are capable of supporting biological macromolecules can penetrate the polymer film. The permeation profile of Ni2+ ions which chelate to the polymer's carboxylic acid moieties for subsequent modified protein binding was also determined.

We describe the design and fabrication of nanostructured silver split-ring resonators and demonstrate their application as dichroic sensors for multipurpose visible wavelength molecular spectroscopy. By producing arrays of these identical nanostructures, with critical dimensions of 30–150nm, we demonstrate the controllable generation of plasmonic resonances at two common visible laser wavelengths, produced as a consequence of the polarization of the light with respect to structural geometry. We show the application of these devices in surface enhanced Raman spectroscopy, using their dichroic properties to perform molecular sensing of a self-assembled monolayer of 2-mercaptopyridine at both 532 and 633nm.

The reactivity of an activated ester group in a suitably functionalised electrodesposited conducting polymer can be modulated electrochemically, providing a mechanism for the patterning of immobilised species at discrete electrodes.

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Electron beam lithography was used to fabricate gold crescent shaped split-ring resonators with 30nm minimum feature size. By varying the crescent’s arc length over a range of nanometer-scale dimensions the authors demonstrate the tuneability of visible resonances within such structures. Results, which correlate closely with those predicted using finite-difference time-domain modeling, open the way for these devices to be used in near-field biological sensing.

The authors describe the integration of low-loss optical waveguides with lab-on-a-chip structures to produce an integrated optical-microfluidic platform for time-correlated single-photon counting of fluorescent molecules. Waveguides were fabricated using electron beam densification of planar silica on silicon, eliminating any requirement for depositing upper cladding silica layers. Microfluidic channels were dry etched directly through the waveguides and the device was sealed using a poly(dimethylsiloxane) gasket. Time-resolved fluorescence lifetime measurements of the fluorophore nile blue were used as a model system to demonstrate the operation of the microfluidic device, with dye concentrations as low as 1.5nM (equivalent to

Understanding and controlling plasmon resonances from metallic nanoscale structures have been the focus of much attention recently, with applications including local surface plasmon resonance sensing, surface enhanced Raman spectroscopy, and negative refractive index materials. In this letter the authors demonstrate the fabrication of uniform arrays of split rings from gold and show that such structures are capable of supporting multiple plasmon resonances. The authors show that up to five plasmon resonances can be identified and use finite difference time domain modeling and absorption spectroscopy to fully characterize and identify each resonance. The implications of higher order surface plasmon resonances for sensing are discussed.

Metallic structures with dimensions smaller than the wavelength of light demonstrate optical properties which depend strongly on the nanoparticle size, shape, and interparticle spacing. The optical properties are caused by the excitation of localized surface plasmon resonances that lead to strong enhancement and confinement of the optical field and can be exploited for many applications including surface-enhanced Raman spectroscopy, near-field scanning optical microscopy, and negative refractive index materials. In order to fully exploit the properties of these structures, both a highly reproducible and flexible fabrication technique and an in-depth understanding of the optical properties are needed. In this article, the authors demonstrate the fabrication of arrays of gold rings and split rings on glass using electron beam lithography. Electron beam lithography allows not only precise control of the size, shape, and spacing of the arrays but also the scope to design novel shapes at will. We characterize these arrays using polarization dependent spectroscopy. The structures can support multiple plasmon resonances, demonstrating that excellent uniformity across the array is achieved. These resonances are further characterized using a finite difference time domain method to model the electric field distribution around the ring structures.

Here we have studied the electrocopolymerisation of binary mixtures of functionalised thiophenes in varying compositions and determined independently for each copolymer the spectroelectrochemical responses and the composition of the material using X-ray photoelectron spectroscopy. We have observed strong correlations between the composition of the copolymer material and the composition of the binary solution from which the polymer was grown. In addition, we have shown that the spectroelectrochemical properties of the copolymers indicate the presence of random copolymer material where the lambda(Max) values of the neutral, undoped, polymer scales with composition but also suggest that there may be small amounts of block copolymer or phase-separated mixtures of the homopolymer components.

The simultaneous responses from a conductance sensor and a gravimetric quartz crystal sensor can be combined as a hybrid measurement which yields the analyte vapour’s molecular density.

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Self-assembly or bottom-up techniques based on molecular recognition are attracting a great deal of interest for nanofabrication. One such technology is based on the use of self-assembling tecto-RNA that has been shown to be able to make structures with nanoscale features (