December 7, 2012
DR MARK WELLS
Dr Mark Wells Solid partnerships form the foundations for success as lays testament to efforts to bridge the gap between nanotechnologies and research on marine environmental systems
To begin, could you offer a brief explanation of nanostructure sensors and their functions?
Environmental sensors, by definition, interact with their surroundings either chemically, optically or acoustically to obtain information about the conditions nearby. The fields of nanoscience and nanotechnology are opening up brand new ways to facilitate these interactions. This is happening in two ways. First, nanotechnology allows us to take current sensor systems and miniaturise them to unbelievably small size scales, allowing the possibility of deploying not one but hundreds of sensors in a given system to better characterise the processes being measured. Second, chemistry itself changes at the nanoscale, where single or multiple chemical bonds control signal strength. As a consequence, new and novel sensor strategies become feasible that cannot be accomplished at the macro scale.
Are advances in nanotechnology contributing significantly to developments of new sensors and technologies in marine monitoring?
While the fields of nanoscience and engineering have flourished over the past two decades, there has been very little, if any, cross-transfer of these innovations to study marine environmental systems. There remain ripe opportunities for merging these disciplines that are yet to be realised. We are on the cusp of uniting these fields, and advances in marine monitoring capabilities will change rapidly over the next 20 years.
In what ways do you expect these technologies to impact on ocean monitoring as a whole?
We have developed tremendous platforms (moored, floating and moving), that provide the potential for vastly improving our understanding of the ocean system, how it interacts with our atmosphere and how we can develop a sustainable relationship with this resource. But we only have a few tools – as sensors can be considered – to put on these networks and, while scientists have made an excellent start, there continues to be a lack of techniques with which to assess the primary driving factors of marine ecosystems. The development of new sensor technologies is a vital step forward but one that lies along the ‘bleeding-edge’ of science, where many research paths lead into blind corners and only a few discover a path forward. We are very fortunate to have stumbled upon one such path, which makes it so very exciting for our research groups.
What have been the major challenges in developing this nanostructure technology?
The most vexing problem for someone like myself – an oceanographer with a desire to find easier ways to measure parameters required by my research – is how to find partners with both the expertise and interest in working on the question. A large chasm lies between those of us working in marine sciences and those with expertise in the chemistry and engineering foundations essential for sensor development. Finding that link, that synergy, is perhaps the largest roadblock to sensor development.
How are you collaborating with other academic institutions?
The work in my laboratory would not be possible without strong collaboration with Dr Carl Tripp based in the Laboratory for Surface Science and Technology, University of Maine and Dr Whitney King at the Department of Chemistry, Colby College. The synergy of this association is the sole reason for any of the accomplishments we have achieved so far. The partnership involves frequent joint laboratory meetings, exchanges of students as well as joint memberships on thesis committees. Advances in one laboratory are passed to another for testing and improvements, and to a third for field testing, the results of each being shared to move the sensor interface design forward.
What do you think is the secret to your research progressing to its current stage?
The project would be impossible without such a solid team approach. This is most definitely a collaborative effort, resulting from both my work and that of my co-principal investigators. Much of the fundamental testing is being conducted by undergraduate students, who are learning hands-on about science, its pitfalls and euphoria, and who enables this experience to be put into practice. Two of the undergraduates at Colby College have joined my laboratory for graduate studies and they also have been key to our successes to date. That synergy among departments and institutions, the lead faculty, graduate students and undergraduate students is relatively unique in my experience, and is part of what has made this project so rewarding.
DR MARK WELLS
Pioneering marine nanostructure sensors
University of Maine’s School of Marine Sciences Driven by frustrations over technological limitations, researchers at have developed an innovative biologically-inspired membrane sensor interface, which they hope will help to address challenges faced by ocean-observing systems
AS SCIENTISTS, GOVERNMENTS and communities grow increasingly concerned about the impacts of climate change on ocean environments, the ability to precisely measure marine systems is becoming ever more critical. Supported by funding from the US National Science Foundation Ocean Sciences progamme, researchers at the University of Maine’s School of Marine Sciences have been developing novel nanostructure sensors which can be used for measuring concentrations of dissolved iron and copper in seawater. Dr Mark Wells, the project’s Principal Investigator, oversees the group’s efforts to advance the use of a reactive biomimetic film designed to trace these metals. This will help improve knowledge on numerous oceanographic processes, in particular those which are poorly understood due to difficulties in gathering adequate temporal and spatial data. The work is strongly collaborative, with substantial participation from co-Principal Investigators Dr Carl Tripp based at the Laboratory for Surface Science and Technology, University of Maine; Dr Whitney King at the Department of Chemistry, Colby College; and their joint graduate student, Zachary Helm.
One of the main drivers behind this project is the knowledge that marine phytoplankton production in much of the world’s oceans is regulated by the presence of micronutrient iron. Little is understood about this type of iron and what processes are impacting its availability to phytoplankton. In addition, it is believed that copper availability can influence the ability of phytoplankton to sequester iron, but even less is understood about this process at present. Current technology limits the ability of researchers to quantify the abundance of these and other micronutrients that drive the global oceanic food web, which ultimately impacts all marine biogeochemical cycling processes. New technology would open opportunities to improve our knowledge on dissolved iron and copper, and the ways in which these metals impact phytoplankton production. “Developing solid phase sensors capable of simultaneously capturing and measuring these elements would transform our ability to characterise the chemistry and distribution of these elements, how they are involved and regulate the marine biogeochemical cycle of carbon and what influence these micronutrients have on climate change,” explains Wells.
ACHIEVING REQUIRED SENSITIVITY
Crucial progress has been made in recent years in this field; for example, the deployment of sensor arrays on autonomous platforms which deliver high resolution time series data. However, there is still a significant gap in the capabilities of technology to sense trace metals, specifically iron. This is a result of the very low detection limits being a major challenge for currently available tools and that the traditional methods do not work well autonomously.
The biomimetic reactive film used in this latest research relies on a biomolecule that has been covalently attached to a porous and optically transparent membrane. When complexed with iron this molecule alters its optical signature, and the magnitude of the altered signal is proportional to the concentrations of dissolved iron. The optical response of the most recent sensor design yields a preliminary detection limit of 0.24 nM for a 1 litre sample, although this limit should be improved tenfold by optimising the sensor interface and optical detectors. This
FIGURE 1. The flow cell housing design allows continuous optical measurement of the membrane sensor during seawater processing.
94 INTERNATIONAL INNOVATION
represents a significant step forwards in being able to analyse trace metals in distant oceans. “Iron profiles measured by this method in the subarctic Pacific were consistent in both the distributions and concentrations measured in parallel by chemiluminescent analysis,” observes Wells. “These promising results are a first step towards applying active nanostructures to sensing iron and other trace metals of interest using autonomous platforms.”
Such encouraging preliminary findings mean that the group has built a solid foundation for developing practical sensor systems which can quantify dissolved iron and utilise many of the current ocean-observing platforms.
The team is exploring the development of a number of different sensor technologies capable of this work. They have been looking at several options to quantifying iron and copper in aqueous systems, including both freshwater and marine environments. Freshwater systems have significantly higher concentrations of metals, so the required sensitivity of the sensors is easier to attain, but this does not apply to oceanic systems. One of the biggest hurdles when developing this type of analytical technology is being able to achieve the necessary selectivity, sensitivity and precision to achieve a robust quantification. “The challenge is to create sensor platforms capable of quantifying oceanic trace element concentrations which can fall 100 to 1,000 times lower than levels of the major nutrients nitrate and phosphate,” Wells points out. The group is now investigating a range of sensory interfaces that better mimic the biological systems already operating in the natural environment.
FROM LABORATORY TO OCEAN
Testing of the sensors is an important part of readying the technology for the next phase – being a practical field application. This is managed in two steps. The sensitivity and precision of the sensor interface is improved as much as practicable and the interface is then applied to various substrates. These processes allow the researchers to test the sensor’s performance by analysing how it reacts to different aqueous samples. According to Wells, the greatest obstacle that they have come across during the testing stage is being able to appreciate how the molecules configure at the substrate-water interface and the ways in which they can improve the control of the configurations: “We are attempting to maximise the surface coverage of this molecule on the sensor substrate and, at the same time, to optimise the orientation of these molecules to facilitate faster metal complexation”. Achieving this will mean that smaller samples can be analysed much faster, thus decreasing the sensor power demands and allowing it to be deployed remote battery-operated observing platforms.
One of the most exciting findings to date has been the discovery that biological molecules can be used to optically sense dissolved iron in the ocean where concentrations are so low that it is actually curbing ecosystem productivity. From Wells’ perspective this realisation has provided the research team with the impetus necessary to take the next step and progress their sensor technology from research into practical application: “The outcomes of this preliminary work have inspired a move towards using optical approaches that are more amenable for deployment on moorings and autonomous vehicles, finally taking it from the laboratory to where this technology can make a real difference”. The field deployment phase of this project has been eagerly awaiting and is now close. “We are now rapidly approaching the stage where we can launch the newest sensor technology into the field in both coastal and offshore seawaters to compare our measurements of dissolved iron with other accepted, chemically-based methods,” enthuses Wells. It would appear that this kind of cutting-edge technology is not short of willing end-users, and with the National Science Foundation (NSF) and other agencies already putting considerable funds into establishing mature ocean-observing networks, it looks like the efforts put into this project in developing new oceanic sensor capabilities has so far certainly been well worth it.
A NANOSTRUCTURE SENSOR FOR MEASURING DISSOLVED IRON AND COPPER CONCENTRATIONS IN COASTAL AND OFFSHORE SEAWATER
• To optimise the sensor by tuning the active nanostructures to measure dissolved Fe and Cu
• To develop a detection device that migrates the current ship-board method to operate on rosette profiling platforms as well as on moorings and autonomous vehicles
Dr Carl Tripp, Laboratory for Surface Science and Technology, University of Maine, USA
Dr D Whitney King, Department of Chemistry, Colby College, Waterville, Maine, USA
US National Science Foundation (NSF) – award no. 0826098
Professor Mark WellsPrincipal Investigator School of Marine Sciences Room 201 Libby Hall University of MaineOrono, ME 04469 US
T +1 207 581 4322E firstname.lastname@example.org
MARK WELLS is a field-going oceanographer studying marine biogeochemistry, with particular emphasis on how trace metal nutrients affect the structure and composition of marine plankton communities. He has held positions at the Scripps Institution of Oceanography, University of California Santa Cruz, and now at the University of Maine School of Marine Sciences, and has participated in over 30 coastal and deep ocean research cruises spanning the Pacific and Atlantic oceans. His current research interests focus on the marine chemistry of trace metals, their bioavailability to marine phytoplankton, the ecophysiology of harmful algal blooms and the development of aquatic sensors.
Current technology limits the ability of researchers to quantify the abundance of micronutrients that drives the global oceanic food web
WWW.RESEARCHMEDIA.EU 95 UMaine SMS Webb Slocum glider, ‘NEMO’, deployed on a survey of the Maine Coastal Current, offshore of Penobscot Bay, summer 2006.