A Novel Lab-on-Chip Spectrophotometric pH Sensor for Autonomous In Situ Seawater Measurements to 6000 m Depth on Stationary and Moving Observing Platforms.

We report a new, autonomous Lab-on-Chip (LOC) microfluidic pH sensor with a 6000 m depth capability, ten times the depth capability of the state of the art autonomous spectrophotometric sensor. The pH is determined spectrophotometrically using purified meta-Cresol Purple indicator dye offering high precision (<0.001 pH unit measurement reproducibility), high frequency (every 8 min) measurements on the total proton scale from the surface to the deep ocean (to 600 bar). The sensor requires low power (3 W during continuous operation or ∼1300 J per measurement) and low reagent volume (∼3 µL per measurement) and generates small waste volume (∼2 mL per measurement) which can be retained during deployments. The performance of the LOC pH sensor was demonstrated on fixed and moving platforms over varying environmental salinity, temperature, and pressure conditions. Measurement accuracy was +0.003 ± 0.022 pH units (n = 47) by comparison with validation seawater sample measurements in coastal waters. The combined standard uncertainty of the sensor in situ pHT measurements was estimated to be ≤0.009 pH units at pH 8.5, ≤ 0.010 pH units at pH 8.0, and ≤0.014 pH units at pH 7.5. Integrated on autonomous platforms, this novel sensor opens new frontiers for pH observations, especially within the largest and most understudied ecosystem on the planet, the deep ocean.

Decreased 14-3-3 expression correlates with age-related regional reductions in CNS dopamine and motor function in the pond snail, Lymnaea.

Ageing is associated in many organisms with a reduction in motor movements. We have previously shown that the rate of feeding movements of the pond snail, Lymnaea, decreased with age but the underlying cause is not fully understood. Here, we show that dopamine in the cerebro-buccal complex is an important signalling molecule regulating feeding frequency in Lymnaea and that ageing is associated with a decrease in CNS dopamine. A proteomic screen of young and old CNSs highlighted a group of proteins that regulate stress responses. One of the proteins identified was 14-3-3, which can enhance the synthesis of dopamine. We show that the Lymnaea 14-3-3 family exists as three distinct isoforms. The expression of the 29 kDa isoform (14-3-3Lym3) in the cerebro-buccal complex decreased with age and correlated with feeding rate. Using a 14-3-3 antagonist (R18) we were able to reduce the synthesis of L-DOPA and dopamine in ex vivo cerebro-buccal complexes. Together these data suggest that an age-related reduction in 14-3-3 can decrease CNS dopamine leading to a consequential reduction in feeding rate.

The anti-bacterial effect of an electrochemical anti-fouling method intended for the protection of miniaturised oceanographic sensors.

An electrochemical anti-fouling method, based upon the generation of chlorine from seawater, was applied to a proprietary design of Lab on a Chip conductivity, temperature and dissolved oxygen sensor. The method was evaluated using PCR after a six-week field trial in which it significantly reduced the burden of bacterial biofouling.

Electrokinetic DNA transport in 20 nm-high nanoslits: evidence for movement through a wall-adsorbed.

The electrokinetic transport behavior of λ-DNA (48 kbp) in 20 nm-high fused-silica nanoslits in the presence of short-chain PVP is investigated. Mobility and video data show a number of phenomena that are typical of DNA transport through gels or polymer solutions, thus indicative of rigid migration obstacles in the DNA pathway. Calculations show that a several nanometer thin layer of wall-adsorbed PVP ('nano-gel') can provide such a rigid obstacle matrix to the DNA. Such ultrathin wall-adsorbed polymer layers represent a new type of matrix for electrokinetic DNA separation.

Integration of a macro/micro architectured compartmentalised neuronal culture device using a rapid prototyping moulding process.

The rapid prototyping of a reversible and one step moulded compartmentalised neuron glass/PDMS device with a thin wall barrier directly adjacent to the reservoirs is presented. A simple moulding technique to produce these devices results in a barrier of 560 µm where the 3 µm deep by 8 µm wide channels can be reversibly fabricated in either the glass base or PDMS compartmentalised mould depending on the type of application required. Using glass substrates with commercially laser engraved microchannels, both the PDMS planar and PDMS channelled device can be easily fabricated in a standard laboratory. The compartmentalised device has several advantages including good experimental accessibility and versatility with a variety of end user applications.

Microelectrode investigation of neuroneal ageing from a single identified neurone.

Microelectrode amperometry is uniquely suited for characterising the dynamics of neurotransmitter release, as it offers unparalleled spatial and temporal resolution. We have used carbon fibre microelectrodes to study release of the monoamine neurotransmitter serotonin (5-HT) and the gaseous transmitter nitric oxide (NO) in intact central nervous system of the water snail, Lymnaea stagnalis. Analysis of spontaneous vesicular release of 5-HT and depolarisation-induced release of NO reveals significant differences with ageing that may be associated with changes in protein structure and function.

High flow rate microfluidic device for blood plasma separation using a range of temperatures.

A hybrid microfluidic device that uses hydrodynamic forces to separate human plasma from blood cells has been designed and fabricated and the advantageous effects of temperature and flow rates are investigated in this paper. The blood separating device includes an inlet which is reduced by approximately 20 times to a small constrictor channel, which then opens out to a larger output channel with a small lateral channel for the collection of plasma. When tested the device separated plasma from whole blood using a wide range of flow rates, between 50 microl min(-1) and 200 microl min(-1), at the higher flow rates injected by hand and at temperatures ranging from 23 degrees C to 50 degrees C, the latter resulting in an increase in the cell-free layer of up to 250%. It was also tested continuously using between 5% and 40% erythrocytes in plasma and whole blood without blocking the channels or hemolysis of the cells. The mean percentage of plasma collected after separation was 3.47% from a sample of 1 ml. The percentage of cells removed from the plasma varied depending on the flow rate used, but at 37 degrees C ranged between 95.4 +/- 1% and 97.05 +/- 05% at 100 microl min(-1) and 200 microl min(-1), respectively. The change in temperature also had an effect on the number of cells removed from the plasma which was between 93.5 +/- 0.65% and 97.01 +/- 0.3% at 26.9 degrees C and 37 degrees C, respectively, using a flow rate of 100 microl min(-1). Due to its ability to operate in a wide range of conditions, it is envisaged that this device can be used in in vitro 'lab on a chip' applications, as well as a hand-held point of care (POC) device.

Synapse-specific changes in serotonin signalling contribute to age-related changes in the feeding behaviour of the pond snail, Lymnaea.

This study utilised the pond snail, Lymnaea to examine the contribution that alterations in serotonergic signalling make to age-related changes in feeding. Age-related decreases in 5-HIAA levels in feeding ganglia were positively correlated with a decrease in the number of sucrose-evoked bites and negatively correlated with an increase in inter-bite interval, implicating alterations in serotonergic signalling in the aged phenotype. Analysis of the serotonergic cerebral giant cell (CGC) input to the protraction motor neurone (B1) demonstrated that fluoxetine (10-100 nM) increased the amplitude/duration of the evoked EPSP in both young and middle aged but not in old neurones, suggesting an age-related attenuation of the serotonin transporter. 5-HT evoked a concentration-dependent increase in the amplitude/duration of B1 EPSP, which was greater in old neurones compared to both young and middle aged. Conversely, the 5-HT-evoked depolarisation and conditional bursting of the swallow motor neurone (B4) were attenuated in old neurones, functions critical for a full feeding rhythm. The CGCs' ability to excite B1 was blocked by cinanserin but not by methysergide. Conversely, the CGC to B4 connection was completely blocked by methysergide and only partially by cinanserin suggesting that age-related changes may be receptor-specific. In summary, synapse-specific attenuation of the CGC-B4 connection and enhancement of the CGC-B1 connection would slow the swallow phase and maintain protraction, consistent with behavioural observations.

High-speed particle detection in a micro-Coulter counter with two-dimensional adjustable aperture.

This article presents the fabrication and characterisation of a high-speed detection micro-Coulter counter with two-dimensional (2D) adjustable aperture and differential impedance detection. The developed device has been fabricated from biocompatible and transparent materials (polymer and glass) and uses the principle of hydrodynamic focusing in two dimensions. The use of a conductive solution for the sample flux and non-conductive solutions for the focalising fluxes provides an adjustable sample flow where particles are aligned and the resistive response concentrated, consequently enhancing the sensitivity and versatility of the device. High-speed counting of 20 microm polystyrene particles and 5 microm yeast cells with a rate of up to 1,000 particles/s has been demonstrated. Two-dimensional focusing conditions have been used in devices with physical cross-sectional areas of 180 microm x 65 microm and 100 microm x 43 microm, respectively, in which particles resulted undetectable in the absence of focusing. The 2D-focusing conditions have provided, in addition, increased detection sensitivity by a factor of 1.6 as compared to 1D-focusing conditions.

Individually addressable microelectrode array for monitoring oxygen and nitric oxide release.

We have fabricated a six individual addressable gold working electrode microarray. The device is wirebonded to an eight-pin DIL package that can be easily interconnected to an external multi-channel potentiostat. A polyion complex film coating on the electrode surface provides a suitable coating for the growth of cells. The responses of oxygen and nitric oxide were assessed on uncoated and coated devices using electroanalytical methods. The film coating reduced the diffusion current by approximately 20% in both cases. No changes in the electrochemical mechanism were observed. Simultaneous recordings were obtained for 2 h in the presence of the cells, thus the device is stable for the duration of the bioanalytical measurements. Measurements were conducted to study the simultaneous changes in oxygen and nitric oxide levels in cultured fibroblast cells in the presence of growth hormones that cause cell proliferation. Increases in oxygen consumption of the cells were coupled with increases in nitric oxide levels when in the presence of the growth hormones. Use of a biological detergent to cause an oxidative burst resulted in a large increase in the current for potentials set to detect nitric oxide and oxygen.