Date of Award

May 2018

Degree Type


Degree Name

Master of Science



First Advisor

Junhong Chen


Excessive phosphates in water can lead to eutrophication and algae growth. Management of phosphorus in water requires accurate and accessible detection technologies to ensure real-time monitoring of phosphorus. Current sensing technologies for phosphorus have limitations and disadvantages. This thesis study will explore a low-cost, ultrasensitive, and real-time water sensor for monitoring phosphates in agriculture runoff, wastewater, and surface water by collaborating with MWRD (Metropolitan Water Reclamation District of Greater Chicago), Grande Cheese Company and Wisconsin DNR (Department of Natural Resources). The innovative sensing technology takes advantage of nanomaterial advancements to realize real-time phosphorus detection.

Specifically, we report an ultrasensitive phosphate ion sensor based on field-effect transistor with reduced graphene oxide (rGO) as the channel material (GOFET). To avoid interference response, a thin aluminum oxide layer (Al2O3, ~4 nm thickness) was applied in our work to isolate graphene oxide sheet (GO) from detection solution samples, and gold nanoparticles (AuNP ~2 nm diameter) were deposited on the Al2O3 film surface for ferritin probe modification. After annealing under argon environment, rGO demonstrated a good current on/off ratio and p-type semiconductor FET performance. The sensing test results showed that the sensor responded to phosphate ions instantaneously and ferritin probes had good affinity to phosphate ions in water solutions. The lower limit of detection for the sensor can reach down to 0.025 mg/L in real water samples.

The low-cost microsensor can provide a new opportunity for real-time monitoring of phosphates. The project results will benefit water industry, agriculture, and environmental regulators by providing real-time sensing capabilities for phosphorus aiming for better evaluation and control of water quality or improving the operation efficiency of phosphate removal in wastewater treatment.