SBIR-STTR Award

The world's oceans may absorb a large part of the C02 emissions generated by burning fossil fuels, thereby lessening the greenhouse effect. However, measuring this global process will require highly accurate, precise new chemical sensors that can operate unattended for long periods on buoys deployed at sea. This project will develop a fiber optical pH sensor and instrument package that does not require calibration with external standards and therefore can operate unattended. The inherently calibrated sensor is made possible by a proprietary process that produces thin, physically resilient transparent films of pH indicator dyes. Optical absorbance measurements made at multiple wavelengths will provide accurate (0.001 pH units) and precise pH measurements free from the drift displayed by conventional pH electrodes. Phase I will demonstrate that the immobilized dyes, because they have optical properties and acid/base chemistries that are similar to dyes in solution, are therefore capable of inherent calibration. Phase 11 will develop an instrument that can exploit the benefits of inherent calibration. The self-calibrating instrument will be constructed using low-power Composite Metal-Oxide Semiconductor technology on a circuit board that can be plugged into a personal computer (PC). Multiplexing will allow several pH sensors to use a single linear diode array detector. Internal shutdown software will schedule measurements around low current idle periods so that long-term, unattended operation on buoys at sea will be possible using solar trickle recharging of the power supply. The sensors and instrument package will allow oceanographers to deploy large numbers of sensors for extended periods and will provide the data necessary to measure oceans' response to anthropogenic inputs of C02.Anticipated Results/Potential Commercial Applications as described by the awardee:The inherently calibrated pH sensors and PC board-mounted optical instrument will give the highly accurate and precise data necessary for evaluating C02 flux into the oceans. More importantly, the technology will find direct and immediate application in the $100 million process control instrumentation industry. The pH sensors and PC plug-in instrument are ideally suited for control of bioreactors and fermentors. Unlike existing electrodes, inherently calibrated sensors can be sterilized without changing their calibration and can be left for long periods without drifting. The improved yields from better pH control of fermentations can be measured in the millions of dollars. The principle of inherent calibration can be applied to a wide array of chemical sensors.

Oceanic uptake of CO2 reduces the atmospheric burden of this greenhouse gas. Quantification of this process will require highly accurate and precise sensors capable of unattended operation at sea. Phase I demonstrated the feasibility of an optical pH sensor that is inherently calibrated and therefore capable of unattended operation. Immobilized dyes in transparent films are interrogated by a fiber optic spectrometer. Absorbance spectra of the dye can be related to the pH of surrounding media with chemical and optical constants alone. These constants can be independently determined to high levels of precision and can be used to calculate the pH of the film to 0.001 pH units. Because of inherent calibration, deployment for long time periods in seawater and fouling of the film were found not to affect the accuracy of pH measurements. A proof-of-principle diode array spectrometer was able to couple to the sensor with optical fibers and collect data for in situ pH measurements. The Phase II program will include the design, building, deployment, and testing of a sensor and spectrometer system that will collect pH data from several depths in a continuous and unattended mode. The spectrometer will use hybrid dual beam optics and software strategies to correct for source and detector sensitivity and shifts in background absorbance of the sensor. The array will be tested at sea with sensors reaching 1000 m water depth.Anticipated Results/Potential CommerciAI Applications as described by the awardee:The inherently calibrated pH sensor and fiber optic spectrometer will allow researchers to collect the highly precise data necessary for characterizing the ocean'sresponse to anthropogenic CO2 inputs. Additional applications include monitoring of acidic precipitation with instruments deployed on land. Phase III activities will lead to commercialproduction of an inherently calibrated pH monitor for wastewater streams. Because the sensor can be autoclaved, bioprocess control uses are expected.