Brendan Heery

A low-cost autonomous optical sensor for water quality monitoring.

A low-cost optical sensor for monitoring the aquatic environment is presented, with the construction and design described in detail. The autonomous optical sensor is devised to be environmentally robust, easily deployable and simple to operate. It consists of a multi-wavelength light source with two photodiode detectors capable of measuring the transmission and side-scattering of the light in the detector head. This enables the sensor to give qualitative data on the changes in the optical opacity of the water. Laboratory tests to confirm colour and turbidity-related responses are described and the results given. The autonomous sensor underwent field deployments in an estuarine environment, and the results presented here show the sensors capacity to detect changes in opacity and colour relating to potential pollution events. The application of this low-cost optical sensor is in the area of environmental pollution alerts to support a water monitoring programme, where multiple such sensors could be deployed as part of a network.

ColiSense, today's sample today: A rapid on-site detection of β-D-Glucuronidase activity in surface water as a surrogate for E. coli.

A sensitive field-portable fluorimeter with incubating capability and triplicate sample chambers was designed and built. The system was optimised for the on-site analysis of E. coli in recreational waters using fluorescent based enzyme assays. The target analyte was β-D-Glucuronidase (GUS) which hydrolyses a synthetic substrate 6-Chloro-4-Methyl-Umbelliferyl-β-D-Glucuronide (6-CMUG) to release the fluorescent molecule 6-Chloro-4-Methyl-Umbelliferyl (6-CMU). The system was calibrated with 6-CMU standards. A LOD of 5 nM and a resolution of less than 1 nM was determined while enzyme kinetic tests showed detection of activities below 1 pmol min(-1) mL(-1) of sample. A field portable sample preparation, enzyme extraction protocol and continuous assay were applied with the system to analyse freshwater and marine samples. Results from a one day field trial are shown which demonstrated the ability of the system to deliver results on-site within a 75 min period.

ChromiSense: A colourimetric lab-on-a-disc sensor for chromium speciation in water

The development of a centrifugal device for quantitative analysis of both chromium (III) and (VI) species in water is reported. ChromiSense is a colourimetric sensor system that has been applied to the measurement of chromium in spiked river water samples. For analysis, the sample is loaded into a reservoir on the disposable microfluidic disc, along with reagents. A centrifugal force is created by spinning the disc to pump liquids through microchannels, causing them to mix and react to form a coloured product. The coloured product is then presented to a low-cost optical detection system, where absorbance measurements can be recorded. The optical detection system consists of a light emitting diode (LED) and photodiode (PD) couple. Chromium (III) was measured using 2,6-pyridine dicarboxylic acid as a ligand, forming a complex that was measured at 535nm and at 335nm. While measuring at 535nm allowed for the use of a low cost LED, the sensitivity was improved 2.5 times by measuring at 335nm. However, 335nm also yielded a diminished linear range with little improvement in limit of deteciton (LOD), and required a lengthier manufacturing process due to the need for a UV-transparent material. Chromium (VI) was detected using 1,5-diphenyl carbazide (DPC). This standard analysis method was simplified for automation on-disc, and optimised to achieve a low LOD. The LOD for trivalent and hexavalent chromium using this device were 21mgL-1 and 4μgL-1, respectively. The linear range for quantitative analysis was found to be 69-1000mgL-1 for Cr(III) and 14-1000μgL-1 for Cr (VI). While this range is high for Cr(III), incorporation of an off-disc pre-concentration method would make this technology suitable for environmental sample analysis. The device is simple to use, low in cost, and could provide rapid on-site measurements, with results comparable to those obtained using a benchtop spectrophotometer.

Novel Microfluidic Analytical Sensing Platform for the Simultaneous Detection of Three Algal Toxins in Water

Globally, the need for “on-site” algal-toxin monitoring has become increasingly urgent due to the amplified demand for fresh-water and for safe, “toxin-free” shellfish and fish stocks. Herein, we describe the first reported, Lab-On-A-Disc (LOAD) based-platform developed to detect microcystin levels in situ, with initial detectability of saxitoxin and domoic acid also reported. Using recombinant antibody technology, the LOAD platform combines immunofluorescence with centrifugally driven microfluidic liquid handling to achieve a next-generation disposable device capable of multianalyte sampling. A low-complexity “LED-photodiode” based optical sensing system was tailor-made for the platform, which allows the fluorescence signal of the toxin-specific reaction to be quantified. This system can rapidly and accurately detect the presence of microcystin-LR, domoic acid, and saxitoxin in 30 min, with a minimum of less than 5 min end-user interaction for maximum reproducibility. This method provides a robust “point of need” diagnostic alternative to the current laborious and costly methods used for qualitative toxin monitoring.

A centrifugal microfluidic-based approach for multi-toxin detection for real-time marine water-quality monitoring

Globally, fresh and brackish water sources are constantly under treat of exposure to toxins. Two of the most prevalent toxins from fresh and brackish water blooms are the cyclic peptide toxins of the microcystin family, formed from cyanobacterial, and the kainic acid analog neurotoxin known as domoic acid. There is therefore a significant need for constant and cost-effective ‘on-site’ algal-toxin monitoring to respond to constantly increasing demand for safe and ‘toxin-free’ freshwater, shellfish and fish stocks. Herein, we describe a Lab-On-A-Disc (LOAD) platform which was developed to assess microcystin and domoic acid concentration levels in-situ. Using recombinant antibody technology, the LOAD platform combines immunofluorescence with centrifugally driven microfluidic liquid handling to achieve a next-generation disposable device for high throughput sampling.