During decades of nuclear industry activity, tons of radioactive uranium waste have accumulated, contaminating the atmosphere, surrounding regions and groundwater with the potential to cause oncological diseases in humans. Traditional analytical techniques are difficult to apply to real-time uranium analysis due to their expensive instrumentation and time-consuming on-site preparation procedures. As a result, numerous researchers began to look into the topic of uranium sensors.
Credit: Dotted Yeti/Shutterstock.com
Why is uranium monitoring important?
Uranium has been released into the environment due to the growth of the nuclear industry and causes health hazards due to its radioactive and chemical toxicity. All countries increased safety inspection of nuclear power plants after the 2011 Fukushima disaster. Therefore, the development of a highly effective and easy-to-use uranium detection technology is of crucial importance.
Uranium concentrations in uncontaminated waters range from 1-3 ppb, which poses no health or environmental risk, but this number can be far higher in contaminated areas.
Due to its hardness, high density and pyrophoric properties, depleted uranium has been used as armor-piercing ammunition in several international military conflicts. As these munitions are developed and tested, depleted uranium is then released into the environment.
How can sensors help detect uranium?
Numerous analytical techniques have been developed to detect uranium, including X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, mass spectrometry, laser-induced fluorescence spectroscopy, and atomic absorption spectrometry.
Unfortunately, on-site uranium analysis is difficult to perform due to equipment costs and labor-intensive pretreatment methods. Therefore, numerous researchers began to focus on uranium sensors.
Types of uranium sensors
Sensors based on optical detection
Trace amounts of uranium are typically detected using optical sensors based on phosphorescence, colorimetry, UV-Vis absorption and surface plasmon resonance transduction techniques.
Due to the interaction of the sensor with the uranium ions, the solution would change color when the uranium ions were injected. The color of the solution would deepen as the uranium ion concentration is increased.
Sensors based on Ultraviolet-Visible spectrophotometry (UV-Vis).
Significant progress has been made in the last few decades in the development of sensors for the detection of uranium ions using UV-Vis spectrophotometry. UV-Vis spectrophotometry is easy to use and allows for quick analysis.
The key process is to change the UV absorption peak before and after the coupling of the ligand with uranium ions to achieve quantitative and qualitative detection.
Sensors based on electrochemical detection
Electrochemical approaches to detecting uranium ions have also proven useful in the development of uranium sensors. These sensors are classified as impedance measurement, voltammetry and potentiometric approach based on the difference in electrochemical impedance, voltage and current.
Voltammetry is a commonly used technique in uranium sensors. The basic procedure is that a uranium-sensitive substance is doped onto an electrode. Then uranium ions are detected qualitatively or quantitatively by detecting the electrochemical signal change of the electrode in the absence and presence of uranium ions.
Sensors based on impedance measurement technology
Electrochemical impedance spectroscopy (EIS) is non-destructive in the steady state and does not require sample destruction. It measures the AC electrical impedance of the electrode-electrolyte interface at equilibrium.
Small sinusoidal stimulus voltages of different frequencies are used to construct the EIS sensor, which is then used to measure the current (or voltage) resulting from the ligand recognition events. The main advantage for EIS sensors, the sinusoidal excitation voltage is minimal and does not damage or affect the ligand layers.
The potentiometric approach uses an ion selective electrode (ISE) to perform quantitative measurements of metal ions in solution. Sensors based on ion-selective electrodes have been widely used to detect uranium ions in complex mixtures because of their fast response time, low cost, and high selectivity.
Whole cell uranium sensor
Scientists at Lawrence Livermore National Laboratory created a whole-cell uranium sensor by merging two functionally independent signaling systems, UzcRS and UrpRS, within the bacterium Caulobacter Crescentus.
Researchers discovered that their combinatorial strategy to build whole-cell sensors showed higher selectivity in analyte detection than a previous biosensor developed using only UzcRS. They validated the sensor’s operation in an environmental context by identifying uranium in groundwater samples with extremely low uranium concentrations.
Uranium is used extensively in nuclear power plants and its use as a key energy source is expected to increase.
It can be released into the environment during its lifetime. A quick and easy method to detect and quantify uranium will be valuable in environmental remediation and reduction of uranium exposure to the environment and human population.
Although the technology for detecting uranium in the environment exists, it is still a challenge to sample vast areas that are not yet known to be contaminated with uranium. Therefore, new detection methods must be developed to overcome this obstacle.
A mobile sensor system with high spatial resolution is required to assess uranium contamination issues and monitor uranium remediation efficiency.
Read more: CO2 sensors support nuclear power plant safety.
References and further reading
Cennamo N, Pesavento M, Merli D, Profumo A, Zeni L, & Alberti G (2022). A fiber optic sensor system for detecting uranium in water. Engineering Procedures, 16(1), 10. https://doi.org/10.3390/IECB2022-12296
Park, DM, & Taffet, MJ (2019). Combinatorial sensor design in Caulobacter crescentus for the selective detection of uranium in the environment. ACS Synthetic Biology, 8(4), 807-817. https://doi.org/10.1021/acssynbio.8b00484
Wu X, Huang Q, Mao Y, Wang X, Wang Y, Hu Q, … & Wang X (2019). Sensors for determining uranium: an overview. TrAC Trends in Analytical Chemistry, 118, 89-111. https://doi.org/10.1016/j.trac.2019.04.026