Robert Stewart

Three-dimensional tracking of sensor capsules mobilised by fluid flow

A new technique for simultaneously measuring particle trajectories and temperature in fluids using specially designed light-emitting sensor capsules/particles is reported. The sensor capsules each contain a microcontroller (with integrated temperature sensor), uniquely coloured light emitting diodes (LEDs), a battery, and other components. When inserted into a fluid, the sensor capsules are mobilised by fluid flow. As they emit light they can be readily tracked and their 3D position over time measured, using an externally positioned camera along with a planar mirror in a calibrated set-up. The capsules can also take intra-fluid temperature measurements and transmit encoded data by modulating their LEDs whilst moving. Controlled experiments with a sensor capsule placed on a rotating turntable and unconstrained fluid-driven motion of multiple sensor capsules placed in a mixing tank are reported. The results demonstrate how the pathlines of capsules (and instantaneous velocities) and temperature can be simultaneously measured.

Capillary electrophoresis (CE) peak detection using a wavelet transform technique

Capillary Electrophoresis (CE) is a separation technique that can be used as a sample pre-treatment step in chemical analysis. When coupled with a detection technique, identification of chemical species can be performed on the basis of the elution signals. However, the sensor signals are often complicated by high signal noise, varying baseline and overlapping peaks. There is thus a need for a signal processing technique capable of robustly detecting peaks in acquired sensor data. Here, we report on an algorithm that utilises the Continuous Wavelet Transform (CWT) for the detection of analyte peaks. The algorithm that has been developed makes use of a wavelet equal to the first derivative of a Gaussian function and has been successfully applied to data obtained from a CCD sensor fabricated on a polymer microfluidic separation chip. The algorithm operates by taking the CWT of the sensor response. It then analyses patterns in the local maximum and minimum points evident across scales in the CWT coefficients to find the peaks in the time series data. The performance of two versions of the algorithm have been compared for synthetic data sets each with known baseline, peaks and noise. The improved algorithm has been shown to successfully find peaks with a high sensitivity and low False Discovery Rate within a range of sensitivities.

Perceptive communicating capsules for fluid flow measurement and visualisation

A new approach to flow measurement and visualisation in fluid dynamics based on a group of perceptive communicating capsules has been developed. Experiments were carried out with fluid-mobilised and stationary capsules deployed in a fluid flow test rig (raceway pond). Each capsule contains a microcontroller, battery, infra-red and visible LEDs and other electronics. Using optical communications, capsules can record encounters with one another. From the resulting interaction patterns, fluid flow speed and path-frequency measurements were obtained. Additionally, the capsules have shown the capacity for distributed sensing, and their streaklines provide a valuable means of external visualisation.

Identifying ovine transcranial acoustic windows

Transcranial Doppler ultrasound (TCD) is used to measure cerebral blood flow velocity in patients with cerebrovascular pathology. The task of locating an adequate acoustic window, through which TCD may be performed, is frequently time consuming or impossible for patients with thick or dense temporal bones. We examined the possibility of utilising B-Mode ultrasound images to guide detection of acoustic windows prior to TCD. B-Mode images of the temporal bone were acquired on deceased sheep shortly after death. We found that on selected sheep, the inner table of the temporal bone was visible on B-Mode imaging. We suggest that visibility of the inner table of the temporal bone on B-Mode imaging is associated with a high probability of successful TCD at that location.

Integrated microdroplet-based system for enzyme synthesis and sampling

Microdroplet-based microfluidic devices are emerging as powerful tools for a wide range of biochemical screenings and analyses. Monodispersed aqueous microdroplets from picoliters to nanoliters in volume are generated inside microfluidic channels within an immiscible oil phase. This results in the formation of emulsions which can contain various reagents for chemical reactions and can be considered as discrete bioreactors. In this paper an integrated microfluidic platform for the synthesis, screening and sorting of libraries of an organophosphate degrading enzyme is presented. The variants of the selected enzyme are synthesized from a DNA source using in-vitro transcription and translation method. The synthesis occurs inside water-in-oil emulsion droplets, acting as bioreactors. Through a fluorescence based detection system, only the most efficient enzymes are selected. All the necessary steps from the enzyme synthesis to selection of the best genes (producing the highest enzyme activity) are thus integrated inside a single and unique device. In the second part of the paper, an innovative design of the microfluidic platform is presented, integrating an electronic prototyping board for ensuring the communication between the various components of the platform (camera, syringe pumps and high voltage power supply), resulting in a future handheld, user-friendly, fully automated device for enzyme synthesis, screening and selection. An overview on the capabilities as well as future perspectives of this new microfluidic platform is provided.

Ultrasound detection of the skull-brain interface: A phantom study

Transcranial Sonography is a clinical procedure for monitoring cerebral blood flow in patients suspected of suffering from severe blood flow disruption in the brain. The Transcranial Doppler (TCD) clinicians are currently only guided by their experience and the temporal bone surface to position the Doppler probe on a suitable site for TCD. This site is known as an acoustic window. Neither experience nor the bone surface can sufficiently improve TCD procedure time for new patients. A suitable acoustic window for transcranial Doppler ultrasound can be difficult to find, and in some patients, no such acoustic window is possible. It is hypothesized that the visibility of the temporal bone in an acousto-spectroscopic image suggests an appropriate transcranial Doppler ultrasound acoustic window. The aim of this research is to investigate the ultrasonic detection of such a pathological acoustic window. It was anticipated that an acoustic window would best be detected by its Acousto-spectroscopic properties in an attenuation-velocity image. These images contrast hard tissue from soft tissue based on their acousto-spectroscopic properties. Identifying where the temporal bone is the thinnest could potentially indicate the best location for performing a Transcranial Doppler procedure. Experimental investigations on a specially designed layered transcranial phantom were carried out to detect the region where the temporal bone is the thinnest and hence suggest an adequate acoustic window. It was shown that a plausible transcranial acoustic window is visible in an ultrasound image, a previously unreported and very promising result. Attenuation-velocity images showed greater boundary contrast between hard and soft tissue. However, hard and soft tissue regions appear similar in comparison to B-Mode images. It was determined that nonuniform scattering from inhomogeneous life-like tissues causes attenuation-velocity images to display less media contrast such as bone versus soft tissue contrast. This research is the first to report that B-Mode images are currently the best method for visually detecting a plausible potential acoustic window for Transcranial Doppler.

Hand-held analyser based on microchip electrophoresis with contactless conductivity detection for measurement of chemical warfare agent degradation products

This paper reports on the development of a hand-held device for on-site detection of organophosphonate nerve agent degradation products. This field-deployable analyzer relies on efficient microchip electrophoresis separation of alkyl methylphosphonic acids and their sensitive contactless conductivity detection. Miniaturized, low-powered design is coupled with promising analytical performance for separating the breakdown products of chemical warfare agents such as Soman, Sarin and VX . The detector has a detection limit of about 10 μg/mL and has a good linear response in the range 10-300 μg/mL concentration range. Applicability to environmental samples is demonstrated .The new hand-held analyzer offers great promise for converting conventional ion chromatography or capillary electrophoresis sophisticated systems into a portable forensic laboratory for faster, simpler and more reliable on-site screening.