Broadband absorption spectroscopy for rapid pH measurement in small volumes using an integrated porous waveguide.

Broadband absorption spectroscopy integrated with microfluidics is widely used to measure the pH of samples available in small volumes. Single pass absorption spectroscopy, however, suffers from poor minimum detectable absorption coefficient because the optical path length is determined by the physical dimensions of microchannels. As a result, either large amounts of indicator dyes are added or instrumentally complex techniques are used to determine sample pH.

Enhanced photoacoustic gas analyser response time and impact on accuracy at fast ventilation rates during multiple breath washout.

Background: The Innocor device contains a highly sensitive photoacoustic gas analyser that has been used to perform multiple breath washout (MBW) measurements using very low concentrations of the tracer gas SF6. Use in smaller subjects has been restricted by the requirement for a gas analyser response time of <100 ms, in order to ensure accurate estimation of lung volumes at rapid ventilation rates.

Methods: A series of previously reported and novel enhancements were made to the gas analyser to produce a clinically practical system with a reduced response time.

A polymeric waveguide resonant mirror (RM) device for detection in microfluidic flow cells.

A novel resonant mirror (RM) device, which consisted of silica sol-gel spacer and polystyrene waveguide layers on a standard microscope slide glass substrate, was developed in this work. The device was successfully used to measure the absorption spectrum of methylene blue with a limit of detection (LOD) of at most 20.8 μM at 635 nm and a minimum detectable absorption coefficient of 0.

A novel leaky waveguide grating (LWG) device for evanescent wave broadband absorption spectroscopy in microfluidic flow cells.

Evanescent wave (EW) broadband absorption spectroscopy is commonly interfaced with a range of analytical systems, including microfluidic flow cells, for identification and quantitation of species. A miniaturised spectrometer integrated with a microfluidic flow cell is useful to permit on-site analysis of samples. This work reports a novel leaky waveguide grating (LWG) device, which is able to obtain an absorption spectrum of an analyte of interest (in this case, methylene blue) without an external spectrometer.

Using droplet-based microfluidic technology to study the precipitation of a poorly water-soluble weakly basic drug upon a pH-shift.

The purpose of this study is to develop a droplet-based microfluidic device capable of monitoring drug precipitation upon a shift from gastric pH (pH 1.5) to intestinal pH (pH 6.5-7.

Chemiluminescence detection flow cells for flow injection analysis and high-performance liquid chromatography.

We have examined a range of new and previously described flow cells for chemiluminescence detection. The reactions of acidic potassium permanganate with morphine and amoxicillin were used as model systems representing the many fast chemiluminescence reactions between oxidising agents and organic analytes, and the preliminary partial reduction of the reagent was exploited to further increase the rates of reaction. The comparison was then extended to high-performance liquid chromatography separations of α- and β-adrenergic agonists, with permanganate chemiluminescence detection.

A microfluidic device for self-synchronised production of droplets.

The primary requirement for a mixing operation in droplet-based microfluidic devices is an accurate pairing of droplets of reaction fluids over an extended period of time. In this paper, a novel device for self-synchronous production of droplets has been demonstrated. The device uses a change in impedance across a pair of electrodes introduced due to the passage of a pre-formed droplet to generate a second droplet at a second pair of electrodes.

Assessment of the feasibility of the use of conductive polymers in the fabrication of ion mobility spectrometers.

The development of an ion mobility spectrometer with an injection molded plastic drift tube made from carbon-loaded nylon and the cyclo-olefinpolymer Zeonex is described. Thermogravimetric assessment combined with headspace analysis by ion mobility spectrometry and gas chromatography-mass spectrometry indicated that Zeonex encapsulated carbon-loaded nylon could be used to fabricate a snap-together injection molded stacked ring drift tube, 4.25 cm long that could be substituted for a conventional wire-wound heated ceramic drift tube of the same length into a high temperature ion mobility spectrometer.

Continuous two-phase flow miniaturised bioreactor for monitoring anaerobic biocatalysis by pentaerythritol tetranitrate reductase.

A novel continuous recirculating two-phase flow miniaturised bioreactor was developed for biocatalytic transformations with the enzyme pentaerythritol tetranitrate reductase using on-chip spectroscopic detection of the organic and aqueous phases. A phase separation technique is described that uses electrostatic attraction to force charged droplets to merge back into the aqueous phase and thus allow the monitoring of both reaction phases during enzymatic turnover. We report an increased rate of enzyme catalysed reduction of trans-2-(2-nitrovinyl)thiophene, which was used as a model system to demonstrate the principles of the bioreactor design, compared to conventional macroscale experiments.

Christiansen filters realized with spherical lenses.

We propose the use of a smooth spherical lens in the Christiansen filter cell. The realization of common filtering functions with such a filter configuration is discussed. A systematic design technique based on inverse Fourier cosine transform or inverse Laplace transform is established, with which a desired, prescribed response can be tailored by properly configuring the lens of the filter.

Precision milled flow-cells for chemiluminescence detection.

Novel flow-cells with integrated confluence points and reaction channels designed for efficient mixing of fast chemiluminescence systems were constructed by machining opposing sides of a polymer chip and sealing the channels with transparent epoxy-acetate films. A hole drilled through the chip provided the conduit from the confluence point on one side to the centre of the reaction zone on the other side, allowing rapid presentation of the reacting mixture to the photodetector. The effectiveness of each flow-cell was evaluated by comparing the chemiluminescence intensity using flow injection analysis methodology, and examining the distribution of light emanating from the reaction zone (captured by photography in a dark room) when the reactants were continuously merged.

Optimisation and analysis of microreactor designs for microfluidic gradient generation using a purpose built optical detection system for entire chip imaging.

This paper presents and fully characterises a novel simplification approach for the development of microsystem based concentration gradient generators with significantly reduced microfluidic networks. Three microreactors are presented; a pair of two-inlet six-outlet (2-6) networks and a two-inlet eleven-outlet (2-11) network design. The mathematical approach has been validated experimentally using a purpose built optical detection system.

Young people at risk of offending: their views on a specialist mental health service in south east London.

This article explores the views of young people regarding their involvement with a specialist mental health service for adolescents who offend or are at risk of offending. The main aims are to shed light on means of engaging this group in therapeutic work, and to illustrate the use of qualitative techniques in the evaluation of health services. Twenty clients and ex-clients were interviewed using a semistructured schedule.

Free flow isotachophoresis in an injection moulded miniaturised separation chamber with integrated electrodes.

An injection moulded free flow isotachophoresis (FFITP) microdevice with integrated carbon fibre loaded electrodes with a separation chamber of 36.4mm wide, 28.7 mm long and 100 microm deep is presented.

The psychosocial needs of young offenders and adolescents from an inner city area.

To date, assessments of the prevalence of mental health problems in young offenders have largely focused on incarcerated samples. This paper describes a quantitative study of a sample of 47 male young offenders under the supervision of an inner city Youth Offending Team. A semi-structured interview, modified from previous studies, was used to investigate the type and frequency of psychosocial and health problems they experienced.