Controlled transport of droplets using conducting polymers

The controlled transport and delivery of dichloromethane through platinum mesh coated with dodecylbenzenesulfonate-doped polypyrrole is demonstrated upon in situ electrochemical redox switching. Droplets of dichloromethane were observed to pass freely through the mesh upon reduction of the polymer as a result of the release of the surfactant dopant into the dichloromethane and the change in the surface energy of the polymer. Planar and liquid-filled tube configurations are investigated. These concepts are envisaged to prove useful for fluid control in microfluidic devices, in the preparation of microparticles for drug delivery, and in the development of organic microreactors.

Photochromism of nitrobenzospiropyran in phosphonium based ionic liquids

The photo-, thermo- and solvatochromic properties of 2,3-dihydro-1',3',3'-trimethyl-6-nitrospiro[1-benzopyran-2,2'-1H-indole] (BSP) and its photo-induced merocyanine isomer (MC) were investigated in phosphonium based ILs by UV-vis absorption spectroscopy. It was found that the kinetics and thermodynamics of the BSP <--> MC equilibrium were sensitive to the nature of the anion. The MC lambda(max) shifted from 560 nm to 578 nm when in solutions of [P(1,4,4,4)][tos] and [P(6,6,6,14)][dca], respectively. The BSP isomer was highly favoured at equilibrium in the ILs studied; K(e) values observed were similar to non-polar solvents such as dichloromethane. The thermal relaxation of MC in all ILs is first order, and in comparison with aprotic polar solvents possessing comparable polarity (such as acetonitrile). Thermal relaxation rates of MC were monitored over a range of temperatures; at 293 K rates varied from 5.19 to 25.03 x 10(-4) s(-1). A non-linear relationship between K(e) and k was observed; this contradicts what is expected for BSP in molecular solvents and suggests the isomers exhibit different molecular/solvation environments. The energetics of the thermal relaxation of MC in ILs were observed; activation energies ranged from 71 to 90 kJ mol(-1) and all ILs exhibit negative activation entropies ranging between -72 and -8.2 J K(-1) mol(-1). A linear relationship between activation energy and entropy was observed.

Wearable technology for bio-chemical analysis of body fluids during exercise

This paper details the development of a textile based fluid handling system with integrated wireless biochemical sensors. Such research represents a new advancement in the area of wearable technologies. The system contains pH, sodium and conductivity sensors. It has been demonstrated during on-body trials that the pH sensor has close agreement with measurements obtained using a reference pH probe. Initial investigations into the sodium and conductivity sensors have shown their suitability for integration into the wearable system. It is thought that applications exist in personal health and sports performance and training.

Chloride selective calix[4]arene optical sensor combining urea functionality with pyrene excimer transduction

A neutral 2-site chloride selective compound has been developed (3), based on a 1,3-alternate tetrasubstituted calix[4]arene providing a preorganized supramolecular scaffold. The resultant supramolecular cavity is among the first to combine urea functional groups bridged with single methylene spacers to pyrene moieties. It combines a naturally and synthetically proven H-bonding system with the elegant ratiometric fluorescent signaling properties of an intramolecular pyrene excimer system, triggered by conformational changes upon anion coordination. The excimer emission of 3 is quenched, with a simultaneous rise in the monomer emission solely by the chloride anion among a wide variety of anions tested. 3 has an association constant of 2.4 x 10(4) M(-1) with chloride. The suitability and advantages of ratiometric optical sensor compounds like 3 for use in practical sensor devices is discussed. 3 has an LOD of 8 x 10(-6) M with chloride in acetonitrile-chloroform (95:5 v/v). A dynamic fluorescence study revealed a response time of < 3 s. A recently developed and simple HPLC-based purification method complimented conventional organic work up methods to yield pure product.

Determination of phosphate using a highly sensitive paired emitter–detector diode photometric flow detector

The use of a novel inexpensive photometric device, a paired emitter-detector diode (PEDD) has been applied to the colorimetric determination of phosphate using the malachite green spectrophotometric method. The novel miniaturized flow detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based detector. The optical flow cell was constructed from two LEDs, whereby one is the light source and the second is the light detector, with the LED light source forward biased and the LED detector reversed biased. The photocurrent generated by the LED light source discharges the junction capacitance of the detector diode from 5 V (logic 1) to 1.7 V (logic 0) and the time taken for this process to occur is measured using a simple timer circuit. The malachite green (MG) method employed for phosphate determination is based on the formation of a green molybdophosphoric acid complex, the intensity of which is directly related to phosphate concentration. Optimum analytical parameters such as reaction kinetics, reagent to sample concentration ratio and emitter wavelength intensity were investigated for the spectrophotometric method. Linear calibration plots that obeyed the Beer-Lambert law were obtained for phosphate in the range of 0.02-2 microM. The dynamic range, sensitivity and limits of detection are reported.

Low pressure ion chromatography with a low cost paired emitter–detector diode based detector for the determination of alkaline earth metals in water samples

The use of a low pressure ion chromatograph based upon short (25 mm x 4.6 mm) surfactant coated monolithic columns and a low cost paired emitter-detector diode (PEDD) based detector, for the determination of alkaline earth metals in aqueous matrices is presented. The system was applied to the separation of magnesium, calcium, strontium and barium in less than 7min using a 0.15M KCl mobile phase at pH 3, with post-column reaction detection at 570 nm using o-cresolphthalein complexone. A comparison of the performance of the PEDD detector with a standard laboratory absorbance detector is shown, with limits of detection for magnesium and calcium using the low cost PEDD detector equal to 0.16 and 0.23 mg L(-1), respectively. Finally, the developed system was used for the determination of calcium and magnesium in a commercial spring water sample.

Fast electrophoretic analysis of individual mitochondria using microchip capillary electrophoresis with laser induced fluorescence detection

The analysis of mitochondria by capillary electrophoresis usually takes longer than 20 min per replicate which may compromise the quality of the mitochondria due to degradation. In addition, low sample consumption may be beneficial in the analysis of rare or difficult samples. In this report, we demonstrate the ability to analyze individual mitochondrial events in picoliter-volume samples (approximately 80 pL) taken from a bovine liver preparation using microchip capillary electrophoresis with laser-induced fluorescence detection (micro-chip CE-LIF). Using a commercial "double-T" glass microchip, the sample was electrokinetically loaded in the "double-T" intersection and then subjected to electrophoretic separation along the main separation channel. In order to decrease interactions of mitochondria with channel walls during the analysis, poly(vinyl alcohol) was used as a dynamic coating. This procedure eliminates the need for complicated covalent surface modifications within the channels that were previously used in capillary electrophoresis methods. For analysis, mitochondria, isolated from bovine liver tissue, were selectively labelled using 10-nonyl acridine orange (NAO). The results consist of electropherograms where each mitochondrial event is a narrow spike (240 +/- 44 ms). While the spike intensity is representative of its NAO content, its migration time is used to calculate and describe its electrophoretic mobility, which is a property still largely unexplored for intracellular organelles. The five-fold decrease in separation time (4 min for microchip versus 20 min for capillary electrophoresis) makes microchip electrophoretic separations of organelles a faster, sensitive, low-sample volume alternative for the characterization of individual organelle properties and for investigations of subcellular heterogeneity.

Chemo/bio-sensor networks

The concept of wireless sensor networks conjures up images of a world of ubiquitous sensing, but it requires a massive increase in the number of sensors available. Although there has been considerable activity in transducer-based 'sensor nets', there have been virtually no corresponding deployments of chemical- or biological-sensing networks - considerable advances in materials science are needed before these can be used on a large scale.

Novel integrated paired emitter-detector diode (PEDD) as a miniaturized photometric detector in HPLC

A novel low power, low cost, highly sensitive, miniaturized light emitting diode (LED) based flow detector has been used as optical detector for the detection of sample components in high performance liquid chromatography (HPLC). This colorimetric detector employs two LEDs, one operating in normal mode as a light source and the other is reverse biased to work as a light detector. Instead of measuring the photocurrent directly, a simple timer circuit is used to measure the time taken for the photocurrent generated by the emitter LED (lambda(max) 500 nm) to discharge the detector LED (lambda(max) 621 nm) from 5 V (logic 1) to 1.7 V (logic 0) to give digital output directly without using an A/D converter. Employing a post-column reagent method, a Nucleosil 100-7 column (functionalized with iminodiacetic acid (IDA) groups) was used to separate a mixture of transition metal complexes, manganese(II) and cobalt(II) in 4-(2-pyridylazo)-resorcinol (PAR). All optical measurements were taken by using both the in-built HPLC variable wavelength detector and the proposed paired-emitter-detector-diode (PEDD) optical detector configured in-line for data comparison. The concentration range investigated using the PEDD was found to give a linear response to the Mn(II) and Co(II) PAR complexes. The effects of flow rate and emitter LED light source intensity were investigated. Under optimised conditions the PEDD detector offered a linear range of 0.9-100 microM and LOD of 0.09 microM for Mn-PAR complex. A linear range of 0.2-100 microM and LOD of 0.09 microM for Co-PAR complex was achieved.

Initial development and testing of a novel foam-based pressure sensor for wearable sensing

Background

This paper provides an overview of initial research conducted in the development of pressure-sensitive foam and its application in wearable sensing. The foam sensor is composed of polypyrrole-coated polyurethane foam, which exhibits a piezo-resistive reaction when exposed to electrical current. The use of this polymer-coated foam is attractive for wearable sensing due to the sensor's retention of desirable mechanical properties similar to those exhibited by textile structures.

Methods

The development of the foam sensor is described, as well as the development of a prototype sensing garment with sensors in several areas on the torso to measure breathing, shoulder movement, neck movement, and scapula pressure. Sensor properties were characterized, and data from pilot tests was examined visually.

Results

The foam exhibits a positive linear conductance response to increased pressure. Torso tests show that it responds in a predictable and measurable manner to breathing, shoulder movement, neck movement, and scapula pressure.

Conclusion

The polypyrrole foam shows considerable promise as a sensor for medical, wearable, and ubiquitous computing applications. Further investigation of the foam's consistency of response, durability over time, and specificity of response is necessary.

Photometric detection in flow analysis systems using integrated PEDDs

A novel inexpensive optical-sensing technique has been developed for colorimetric flow analysis. This sensing system employs two LEDs whereby one is used as the light source and the other as a light detector. The LED used as light detector is reverse biased with a 5-V supply so that the photocurrent generated by the incident light discharges the capacitance. Direct digital output is provided by a simple timer circuit that measures the time taken for this discharge process from 5V (logic 1) to 1.7V (logic 0). This sensing concept has been applied in flow analysis by constructing an optical flow cell with a pair of LEDs. Calibration of the integrated optical flow cell using a dye resulted in a linear response that obeys the Beer-Lambert law. The flow rate, dynamic range, sensitivity and limits of detection were investigated. The system was also used for pH determination in the range of pH 2.5-6.8 using bromocresol green (BCG). The pK(a) of BCG was successfully determined by this technique.

Wearable Sensors? What is there to sense?

This paper provides an overview of research conducted in the development of ambulatory devices for wearable sensing applications. Two configurations of wearable sensing are shown, the first a wearable chemosensor in a wrist-watch configuration, and the second a textile with an integrated foam sensor. The foam sensor is composed of polypyrrole-coated polyurethane foam, which exhibits a piezo-resistive response when exposed to electrical current. The potential of wearable sensing is discussed using these examples to illustrate the relevant concerns.

Development of a biosensor for endocrine disrupting compounds based on tyrosinase entrapped within a poly(thionine) film

Preparation of semiconducting films by electropolymerisation of a monomer which is itself a redox mediator is an attractive and simple method for biosensor fabrication. A polymeric film of the redox dye thionine (phenothiazine) enables the stable immobilisation of polyphenol oxidase (tyrosinase) while acting as mediator for the enzymatic process. The immobilisation method is based on an inner crosslinked tyrosinase layer which contains thionine with an electropolymerised film of poly(thionine) on top. This method gave the most stable redox couple for poly(thionine) and exhibited the greatest response stability. The sensor was tested using a range of synthetic oestrogens and phenolic compounds, which are suspected endocrine disruptors/oestrogen mimics. The device responded well to all compounds tested with limits of detection ranging from 1 to 23 microM (based on three times S/N ratio). The tyrosinase/poly(thionine) electrode response to phenol was 3 orders of magnitude greater than the unmediated response in the absence of poly(thionine).

CO2 laser microfabrication of an integrated polymer microfluidic manifold for the determination of phosphorus

A simple colorimetric technique is implemented in a polymer microfluidic manifold. The simple chemistry aids an uncomplicated microchannel design, which is fabricated by CO(2) laser ablation. Issues such as bonding of multiple layers, alignment of micro-fabricated structures and integration of optical components are addressed. A demonstration of a stopped flow regime in the microfluidic manifold is also presented.

Blueberry supplementation enhances signaling and prevents behavioral deficits in an Alzheimer disease model

Previously, we showed that blueberry (BB) supplementation reversed the deleterious effects of aging on motor behavior and neuronal signaling in senescent rodents. We now report that BB-fed (from 4 months of age) APP + PS1 transgenic mice showed no deficits in Y-maze performance (at 12 months of age) with no alterations in amyloid beta burden. It appeared that the protective mechanisms are derived from BB-induced enhancement of memory-associated neuronal signaling (e.g. extracellular signal-regulated kinase) and alterations in neutral sphingomyelin-specific phospholipase C activity. Thus, our data indicate for the first time that it may be possible to overcome genetic predispositions to Alzheimer disease through diet.

Monitoring of headspace total volatile basic nitrogen from selected fish species using reflectance spectroscopic measurements of pH sensitive films

The release of amines from decomposing fish such as trimethylamine (TMA), dimethylamine (DMA) and ammonia, collectively known as total volatile basic nitrogen (TVB-N), are in high enough concentrations in headspace to be monitored by a colour change in a pH-sensitive sensor. A method developed here uses a pH indicator dye physically trapped in a cellulose polymer film to respond to the headspace TVB-N released from selected fish species during spoilage. Two species were selected for analysis on the basis of economic importance and the levels of volatile amines released were followed with time using uv/vis reflectance spectroscopic measurements. The results show that there is a significant increase in the TVB-N content in the headspace of fish samples after an incubation period of 8-12 h for cod and 12-15 h for orange roughy.

Analysis of river water samples utilising a prototype industrial sensing system for phosphorus based on micro-system technology

The application of a phosphorus monitoring device based on microsystems technology (MST) to the analysis of river water is presented. An alternative to the standard molybdenum blue method known as the yellow vanadomolybdophosphoric acid method has been very effectively implemented. The method is simple, a reagent and sample are mixed in a 1:1 ratio forming a yellow complex that absorbs strongly below 400 nm in the UV spectrum. The kinetics of the reaction are rapid and sample turnaround is typically 3 min at room temperature. Therefore a very uncomplicated microfluidic design can be adopted. The working wavelength was chosen as 380 nm to coincide with the peak output of a UV-LED narrow bandwidth light source recently developed by Nichia. The limit of detection for the yellow method in the microfluidic system is 0.2 ppm with a dynamic linear range from 0-50 ppm. The method was applied to a measurement of phosphorus in a local river at specific sampling points along its course.