Development of In-field Portable Sensor for Detection of Phosphates and Heavy Metals in Everglades Water Systems. Presented by: Shradha Prabhulkar Nanobioengineering/Bioelectronics Lab Biomedical Engineering Department Florida International University Everglades Foundation Fellows - First Symposium January 13 th , 2009
Introduction • The Everglades National Park is the largest remaining subtropical wilderness in the continental United States. • These sub-tropical wetlands support a rich diversity of plants, fish and other animals. The Everglades support eight distinct ecosystems. • However, the Everglades ecosystem is suffering due to human intervention from as early as the late 1800s. • In 1948, a massive project to provide flood protection and water management for the ever growing South Florida human settlements was approved. More than 1,700 miles of canals and levees were built to divert valuable freshwater from the wetlands into the sea. This interrupted the everglades natural sheet flow and caused the destruction of more than half the wetlands. • While this project allowed the rapid growth of the region it worsened the Everglade’s problems. Historical Flow of water in Everglades Present Day Flow of water in Everglades
• In 2000, Congress approved a federal effort to restore the Everglades, named the Comprehensive Everglades Restoration Plan (CERP), with the objectives of restoration, preservation and protection of the South Florida ecosystem while providing for other water related needs of the region". • Besides rerouting water flow, reducing pollution and improving water quality is also a major concern for the CERP. • The southern part of the wetlands has been converted into agriculture land for the growth of sugarcane. Phosphate containing fertilizers used in these fields get washed into the Everglades due to rainfall.
• Heavy metal pollution comes from the dumping of untreated storm water discharge and street water discharge by the South Florida Water Management District into the Everglades. • When it rains urban fertilizers, detergents, household chemicals, gas, oil and other pollutants wash off roads, parking lots and driveways and are carried by storm water into drainage canals. • Most pumping stations which treat the water before letting it flow into the Everglades do not focus on the removal of heavy metals. • Hence heavy metals such as lead, selenium, mercury, cadmium, arsenic etc. are accumulating in the waters of the everglades. • Heavy metal toxicity disrupts natural ecosystems and affects the food chain, leading to health problems in humans and animals. • Heavy metals are hazardous even if they are present in extremely minute quantities. • The US EPA and the World Health Organization (WHO) lists them as a known carcinogen.
• In the case of the Everglades, they lie in the path of trade winds, and the climate is perfect for the type of thunderstorms that pull mercury out of the air. • Gaseous mercury poured into the atmosphere naturally and by human industry gets accumulated into the everglades. • Around 900 pounds of gaseous mercury is dumped into the Everglades each year. • Twice as high Mercury levels found in parts of the Everglades, and in some of its animal population, is seven times higher than federal safety limits. • Hence, the state of Florida warns against eating fish from the Everglades. Regularly eating fish contaminated with mercury can cause brain damage and blindness in humans. • Mercury can also be transferred from a pregnant mother to her child Mercury Cycle in Everglades
Current Methods for Assessing Water Quality • Surface water is monitored in a variety of locations, including canals, pumping stations, agricultural discharges, and many other types of aquatic environments. • Current monitoring methods are accomplished by invasively collecting samples in the field and transporting them to centralized laboratories for analysis. • Unfortunately, since contaminant specification or properties can be changed quickly as a result of chemical, biological and physical reactions, the long time delays associated with this procedure are frequently unacceptable. • Thus, one of the best preventive measures is to rapidly determine the concentration of toxic compounds on-site. • Advanced monitoring techniques such as ion chromatography , UV visible spectrophotometry, X-ray absorption spectroscopy, atomic absorption spectrometry , and inductively coupled plasma-mass spectrometry are currently used for detection. • But these techniques require large, expensive, sophisticated equipment that can not typically be used in the field. • Hence field assays which can provide highly sensitive, portable, easy to use, real time detection of pollutants, at relatively inexpensive cost are needed.
Research Objectives • The objective of my research is to develop a rapid, low cost, easy-to-use, portable, multi-array sensor to measure various pollutants such as phosphates and heavy metals. • The sensor will be based on a chip based platform enabling in-field usage. • These sensors will provide the advantages of real time monitoring without compromising on sensitivity. • The sensors will also be cost effective and reusable. • The use of a chip based platform will allow in-field, one-step, real time detection of multiple pollutants.
Mechanism Of Detection • Electrochemical methods will be used for the detection of phosphates and heavy metals. • The advantages of using Electrochemical detection methods: 1. Cost effective 2. Easy to use 3. Sensors can be miniaturized for in-field detection • Electroactive materials. Oxidation or Reduction. • The flow of electrons will generate a current which is proportional to the concentration of the electroactive substance present in the water sample. • The proposed sensor will be able to measure the current that will be generated as a result of the flow of electrons. Current (A) Concentration of analyte (ppb)
TASK 1: To measure electroactivity of phosphates and heavy metals. • Electrochemical experiments were conducted to test if phosphates and heavy metals such as lead, selenium, mercury, cadmium, arsenic are electroactive. • Commercially available phosphates and heavy metals were obtained and dissolved in water. Gold electrodes were used to conduct voltammetric experiments using these samples. • We observed that all the above mentioned pollutants are electroactive as they undergo either reduction or oxidation at a certain potential. Hence at a certain potential either lose or gain electrons. This flow of electrons causes a current which can be measured by our proposed sensor. C Reference Electrode (Ag/AgCl) Working Electrode (Gold) Counter Electrode (Platinum) e e e e
TASK 2: Design and Fabrication of Sensor Chip
TASK 3: Testing limits of detection for phosphates and heavy metals using fabricated chip • We have tested sample solutions of phosphates and heavy metals using the above mentioned fabricated chip. • The lowest concentrations that we were able to measure were in the range of ppm (parts per million). • However the concentration of pollutants in the Everglades system is in the range of ppb (parts per billion). • Hence we had to modify our procedure to measure lower concentrations. • To enhance the sensitivity of our sensor we decided to use Magnetic Nanoparticles. • Magnetic nanoparticles coated with chemicals which show an affinity for heavy metals will enable their preconcentration and highly sensitive detection using small sample volumes. DMSA Cd Pb Phosphate α -Glucose + H 2 O 2 Cd Hg Pb Se Hg Ar Magnet Ar Se Alkaline Phosphatase
Objectives Achieved • Testing electroactivity of phosphates and heavy metals. • Successful fabrication of sensor chip. • Testing of sensor chip for detection of phosphates and heavy metals. Calculated detection limit of sensor chip. • Fabrication of gold nanoparticles and magnetic gold nanoparticles. • Coating gold nanoparticles with phosphate sensitive enzyme – alkaline phosphatase. • Coating magnetic gold nanoparticles with heavy metal sensitive DMSA.
Work to be Done • Test if using magnetic nanoparticles is helping to reduce the detection limit for phosphates and heavy metals. • Testing fabricated sensor using real water samples from various sites in the Everglades such as Okeechobee lake. • The results obtained using the portable in-field sensors will be compared to the concentration of pollutants obtained using the current gold standard laboratory techniques. • This will enable us to verify the performance of our sensors. • Successful development of this portable multi-analyte chip based sensing system may have broad applications for monitoring surface water, sediments, wastewater treatment, and bioreactors where small size and ability to measure multiple analytes is desired. • The novelty of our research lies in the use of nanoparticles which can be help detection miniscule amounts of pollutants. • The ability to measure multiple analytes using a single sensor chip will unable hassle free, rapid monitoring.
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