Project III.1.4: Derivatizing sensors

Project Title: III.1.4 Derivatizing sensors
Project Leads: Paul Tratnyek and Jim Nurmi

Project Description
The need for robust and simple sensors for long-term deployment in coastal waters has been a challenge for many years. Simple sensors, such as the CTD’s that measure conductivity, temperature, and depth are used routinely. However, sensors for other, specific chemical or biological agents are much more challenging, and more research on these is needed on these enabling technologies.

In this part of the CMOP research program, novel sensors are under development for key biogeochemical processes in the Columbia river-ocean ecosystem. We are using relatively simple sensors (Type I and II) for oxygen and redox potential to characterize sediment chemical conditions for correlation with Crenarchaea populations determined by molecular microbial methods (collaboration with Prof. Holly Simon). More novel sensors (Type III) are being made by surface modification of solid-state electrodes. Mercury amalgamated microelectrodes are being used to determine H₂O₂, Fe²⁺, Mn²⁺ in river, and sediment pore water (collaboration with Prof. Brad Tebo).

The approach we have taken to the latter objective involves derivatizing solid state electrodes with two forms of nano manganese dioxide, (i) synthetic MnO₂, and (ii) biogenic MnO₂ produced by the spores of Bacillus species SG-1. We are using these derivatized sensors to measure pH and hydrogen peroxide concentrations in aqueous solutions. Using various electrochemical techniques, we are also able to characterize and compare various nano-sized biogenic manganese dioxides to synthetic manganese dioxides.

Another sensor that we have recently developed is being called a Deployable In-Situ Nitrate Sensor for Real-Time Analysis of Sediments. It couples the use of ion selective membranes, microelectrode size and a computer driven robotic arm to deploy and move the nitrate sensor into sediments. High school intern A. Cramer won Intel's environmental management category with this project at this years Intel International Science and Engineering Fair held in San Jose, California.

Read article about Cramer.

Fit in program
The development initiatives described above were selected to support several CMOP related scientific themes: (i) The geochemical profiles of water and sediment columns that can be used to correlate with microbiological populations and assemblages, which ultimately leads to a better understanding of the processes which drive biogeochemical cycles as a function of time, climate, and human impact. (ii) field application of these electrodes will provide increased spatial resolution of Mn²⁺, Fe²⁺, and several other sulfide species as a function of time. (iii) The biogenic MnO₂ may prove to be a unique material for the production of H₂O₂ sensors due to its unusually high surface area and ability to oxidize H₂O₂ at a lower overpotential. Aggregates of MnO₂particles can be found in the river-ocean system and this work might be the first to indicate that the aggregate particles may have some unique reactivity properties.

Outcomes
Several conference presentations.