Instruments and Sensors
Oceanography is a science that is highly dependent on observations and measurements. Developing new instruments and sensors is important part of work undertaken at the NOC. We cannot yet buy instruments that will measure everything that interests scientists, so we aim to work with them to develop new technologies.
By bringing together many new technologies and working in collaboration with others, the NOC is at the forefront of innovation in designing, creating and using novel sensors and instruments. Current technology developments being undertaken by the NOC include the following.
The NOC is developing the first of a new generation of miniaturised alkalinity sensor using microfluidic lab-on-chip (LOC) technology. These sensors will allow the collection of in situ data with high spatial-temporal resolution throughout the water column. The technology uses an open cell approach with spectrophotometric pH determination, offering high accuracy and precision. Previously NOC has developed an automated, microfluidic prototype instrument based on the tracer monitored titration (TMT) method. It achieved precision in the region 1–3% but required a ~4-hour sampling time. The new generation of sensors will reduce sample times and power consumption allowing for longer field deployments.
At certain times of year, naturally occurring marine algae can proliferate and pose a threat to human health from the production of potent bio-toxins. These “Harmful Algal Blooms” (HABs) are particularly damaging when algal bio-toxins become concentrated in the bodies of filter feeding bi-valve shellfish, posing a risk to human health when consumed. The current, statutory method for the monitoring of HABs involves the delivery of water samples to a centralised lab and analysis for certain algal species by microscopy. Despite being expensive, this incurs a severe time delay between the detection of a HAB event and the enation of the necessary intervention such as a delay or acceleration in shellfish harvest.
The aim of this project is to improve early warning and event forecasting of harmful algal blooms within and around shellfisheries by developing existing, state of the art, lab-on-chip technology into a new, portable tool that will enable end-users (i.e., shellfish producers, and statutory monitoring authorities) to undertake HAB surveillance in the field. This technology takes the form of a micro-cytometer, a device that measures the properties of cells as they pass through a narrow channel. While conventional cytometers only measure the optical properties of cells, our system (CYTOCHIP) measures multiple optical and electrical properties simultaneously, providing excellent discrimination of cell types and differentiation of toxin-producing and non-toxic species. These capabilities are being exploited to help shellfish producers and authorities to protect consumers and public health, and reduce the costs associated with the existing, delayed analysis methods.
Three-axis acoustic Doppler velocity profiler
The three-axis acoustic Doppler velocity profiler (ADVP) is an autonomous instrument, intended to assist in the study of sediment transport and turbulence processes in the marine bottom boundary layer. NOC has designed and developed this instrument to use three acoustic beams to take co-located Doppler velocity measurements of suspended sediments along a profile potentially up to two metres in length – something no commercial instrument currently available permits. The transducers can be arranged orthogonally or opposing to provide three-dimensional or two-dimensional velocity measurements, respectively.
The instrument uses coherent 1MHz acoustic transmissions plus a dual-PRF technique and post-processing to resolve the recorded Doppler shifts into actual velocities. All data is recorded to an on-board data logger. Operating off battery power with careful selection of recording parameters, the instrument could potentially be deployed for periods of up to one month. A typical deployment is with the instrument configured for 60-cm profile range, recording profiles at ~8Hz with 1-cm range bin resolution.
Chemical dissolved organic nitrogen sensor
The NOC is developing an ultraviolet (UV) photooxidation module for the existing nitrate lab-on-chip sensor that will allow the measurement of the dissolved organic nitrogen (DON) fraction in water samples. DON is a bioavailable nitrogen (N) source for primary production in the ocean and can form the largest dissolved N-fraction in in some oceanic regions. This technology will allow collection of in situ data with high spatio-temporal resolution.
Chemical dissolved organic phosphorus sensor
The NOC is developing an ultraviolet (UV) photo-oxidation module for the existing phosphate lab-on-chip sensor that will allow the measurement of the dissolved organic phosphorus (DOP) fraction in water samples. DOP is a bioavailable phosphorous (P) source for primary production in the ocean and can form the largest dissolved P fraction in in some oceanic regions. This technology will allow collection of in situ data with high spatio-temporal resolution.
Dissolved inorganic carbon sensor
Since the Industrial Revolution, atmospheric levels of carbon dioxide (CO2) have increased by ~40%. It has been estimated that the Ocean has taken up ~30% of the carbon released into the atmosphere over this time. Dissolved Inorganic Carbon (DIC) is the sum of all the dissolved carbonic acid species in seawater. The increase in DIC has resulted in a sustained drop in the Ocean pH known as Ocean Acidification. Increasing DIC reduces the Oceans ability to absorb CO2 in the future and impacts on ecosystem functions.
Quantifying the carbonate system requires measuring at least two of the following parameters: Total Alkalinity (TA), pH, DIC and fugacity. Historically the preferred pair was DIC and TA, however DIC and pH are now the preferred pair as they give lower predicted errors for the remaining derived variables. The NOC are developing a DIC sensor to work alongside a pH sensor in order to quantify carbonate systems.
Dissolved oxygen sensor
Alongside temperature, conductivity and pressure, dissolved oxygen is a critical measurement in understanding the health of the world oceans and can enable us to learn more about the environment in which life exists and thrives.
The NOC is working on a project in partnership with the University of Southampton aiming to provide a small and low-powered sensor that is integrated into and alongside a micro-fabricated chip. This sensor chip has been integrated into a package for evaluation that includes the electronics required to operate the sensor, power, pressure housing and a commercially sourced pressure sensor. Thus far the dissolved oxygen sensor has been deployed at sea on multiple CTD casts to a maximum depth of 4.8km.
Dissolved silica sensor
Dissolved silica (DSi) is a macronutrient and is required by marine life including diatoms, some sponges, radiolarians, silicoflagellates, some species of choanoflagellates and picocyanobacteria. While DSi occurs at much larger concentrations by comparison with dissolved phosphorus for example, the development of an in situ device to measure it is challenging due to the large range of environmental concentrationsi – rivers: 10– >200µM; euphotic zone in tropics/subtropics: <0.1–0.6µM; deep ocean water: >200µM.
The reduction of molybdosilicic acid by ascorbic acid to a blue colour of intensity proportional to silicate concentration is used as the basis for the silicate sensor design. The oxalic acid is used to suppress the phosphate interference, while the ascorbic acid reduces the molybdosilicic acid.
Microfluidic pH sensor
NOC is developing a semi-integrated microfluidic lab-on-chip system to measure pH, which is one of the first of its kind employing microfluidics for autonomous oceanographic measurements. It utilises the standard spectrophotometric analytical method offering high accuracy (<0.005) and precision (<0.001) pH measurements for ocean acidification research. It can be deployed for periods of longer than a year on autonomous platforms measuring at a maximum frequency of 6hrs-1. It has low power consumption and can be powered by either on-board batteries or an external power source. High performance electronics and communication systems allow on-board data processing and output of temperature and salinity corrected pH measurements. Pressure tolerant components allow deployments at a depth of 6000 metres.
The pH sensor has competed at the Wendy Schmidt Ocean Health XPRIZE competition reaching the semi-final stage. Since then it has been deployed at the Gullmar Fjord capturing the daily variation in pH caused by biological processes including primary production and respiration. The pH sensor has also been deployed in Southampton waters on several occasions mainly for testing and optimisation work. Upcoming deployments will include coral reef monitoring in the Seychelles, CCS storage site monitoring in the North Sea and long term pH monitoring in Germany.
The lab-on-chip (LOC) iron sensor is a miniaturised wet chemical analyser capable of in situ measurements of iron (II) and iron (III). The system uses the ferrozine assay, and is based on the same hardware platform as the LOC nitrate and phosphate sensors. Like all instruments based on this platform, the iron analyser is designed to work at full ocean pressure. The iron analyser can also be adapted to perform manganese II analysis using the PAN method. The range is 0.027 to 500µM; LOD is 0.027µM.
Early prototypes of the LOC Fe sensor were successfully deployed in rivers and on CTD profiles in the Baltic. The platform has recently been re-engineered in line with the nitrate and phosphate sensors to improve robustness and reliability.
The lab-on-chip (LOC) nitrate sensor is a miniaturised wet chemical analyser capable of in situ nitrate plus nitrite measurements in almost any aquatic environment. The system uses the Griess assay with cadmium reduction to perform measurements comparable in quality to standard laboratory analysis methods, and of superior quality to UV absorbance measurements. The system carries an on-board standard to correct against drift, and is capable of performing hourly measurements for three months with a typical reagent payload. Range is 0.025 to 1000µM; LOD is 0.025 µM.
LOC nitrate sensors have been successfully deployed in a range of marine and freshwater aquatic environments. These include rivers (both pristine and polluted), estuaries, glacial meltwater (proglacial streams), shelf seas, the surface ocean (buoys and moorings in the Arctic), the seafloor (on benthic landers) and profiling in the deep ocean (deepest deployment 4800m). We have recently completed a number of deployments on board autonomous vehicles (the sensor and reagents can be deployed inside the payload bay of a Kongsberg Seaglider).
Nucleic acid amplification sensor
Nucleic Acid Amplification is one of the most specific and sensitive techniques used to measure harmful micro-organisms in environmental samples. However, it requires bulky equipment and specialist personnel, and therefore there is a significant delay between the collection of samples in the field and the output of results in a centralised laboratory. Using lab-on-chip technology together with the robust, miniaturised electronics and optics currently used in our range of chemical and nutrient sensors, we are developing a new device capable of carrying out nucleic acid amplification in the field, and which can be operated remotely to provide near real time, in situ data. By reducing the time lag associated with conventional, laboratory analysis we will enable water quality monitoring authorities and stakeholders who rely upon clean water supplies (e.g., for food production, drinking water, leisure, etc.) to improve the management and forecasting of water contamination events, and ultimately reduce the risks to public health and the environment.
Temperature and conductivity sensor
Temperature and conductivity measurements are ubiquitous throughout ocean research. These measurements are fundamental in understanding the physical structure of the ocean but also provide valuable contextual information for other co-located biogeochemical measurements.
A project in partnership between the NOC and the University of Southampton aims to provide a small and low powered sensor that is mounted on a fingernail sized micro-fabricated chip. This sensor chip has been integrated into a package for evaluation that includes the electronics required to operate the sensor, power, pressure housing and a commercially sourced pressure sensor. The system is still undergoing research and development but extensive laboratory testing, along with recent deployments have repeatedly shown promising results.
Successive developments of the temperature and conductivity sensor have been carried out in the Atlantic over the last three years using CTD (conductivity, temperature, depth instrument) casts to a maximum depth of 4.8km. After pressure correction the results for both temperature and conductivity compare well with the industry standard technologies.