A Chinese research team has developed a portable field technology that uses a smartphone camera to detect water contamination by uranyl ions, analysing changes between green and red light signals and converting them within moments into a measurement of uranium concentration.
System sensitivity exceeds drinking-water requirements
A recent study published in Sustainable Carbon Materials showed that the system’s sensitivity reaches a level below half the maximum permitted worldwide in drinking water, allowing it to be used as an early-warning tool. The technology is intended to facilitate environmental monitoring of activities linked to the nuclear fuel cycle, including mining, the transport of radioactive materials and waste treatment at plants.
Accidents or unforeseen environmental factors could carry accidental leaks into freshwater sources or coastal waters, increasing the need for rapid tests that can be carried out on site as nuclear power expands globally to generate electricity and reduce carbon emissions.
Monitoring this type of contamination usually relies on advanced laboratory equipment, including inductively coupled plasma mass spectrometry. Such equipment provides high accuracy, but is large and expensive and requires complex, advance sample preparation. This makes immediate field testing difficult and confines much of the analysis to equipped central laboratories.
Ahmad Qasim, a researcher in the chemistry department at the US-based Virginia Commonwealth University who was not involved in the study, said uranium is usually found in water in the form of the uranyl ion, which is highly soluble and easily transported.
A small kit measures uranyl with a phone camera
According to the study’s results, the new system can detect uranyl ions at a level below half that limit, providing a margin that allows contamination to be detected before it reaches the specified threshold. The testing tool consists of equipment that can be carried in a small bag.
The technician adds drops of the suspected water sample to a test tube containing a liquid suspension of the sensing material, then exposes the tube to light from a portable ultraviolet torch. The phone camera then photographs the tube under the specified illumination. A digital application analyses the image’s primary colour system, focusing on the mathematical ratio between green and red.
The application converts the change in this ratio into a specific value for uranium concentration, which appears on the phone screen within a short time. The measurement therefore does not rely on the intensity of a single colour, but on the relationship between the decline in red light and the increase in green light when uranyl is present.
Sensing material converts reaction into two light signals
Qasim explained that the organic molecule used in the material, pyromellitic acid, acts as a sensor that absorbs ultraviolet radiation and transfers its energy to europium ions, producing red light at a wavelength of 616 nanometres. When uranyl binds to the carboxyl groups in the molecule, the energy-transfer pathway is disrupted and the red signal fades.
At the same time, green light appears at a wavelength of 513 nanometres, which the researchers attribute to charge transfer from the organic molecule to uranium. The emergence of the two signals in opposite directions allows a relative measurement to be established: as the uranyl concentration rises, the red intensity falls and the green intensity increases, after which the application calculates the green-to-red signal ratio.
The sensing material is based on a hybrid framework containing zinc and europium, one of the rare-earth elements known for its light emission, together with bonded organic molecules. Qasim said zinc does not glow or bind directly to uranium, but plays a structural role in forming and organising the material, while europium provides the light signal needed for the measurement.
He explained that zinc alone forms stacked sheets, while europium alone forms irregular masses. Mixing the two elements produces uniform spheres about 0.5 micrometres in diameter, with regular pores and a surface area of 69 square metres per gram.
This organisation helps the material disperse in water in a repeatable and reliable way, a requirement for quantitative measurements. The two-element material also showed noticeably stronger red luminescence, with a luminescence lifetime of 278 microseconds, longer than that recorded for europium alone, indicating lower energy loss.
This mechanism differs from conventional sensors that measure the intensity of a single colour, as that intensity can be affected by the quantity of material added, water turbidity and fluctuations in the lamp, even without a change in uranium concentration. In the new system, both signals are measured from the same particle. If the lamp’s illumination weakens, for example, the intensity of both colours falls while the ratio between them remains approximately stable.
Relative comparison also reduces the effect of differences in camera angle or ambient light, providing a form of self-calibration and improving the consistency of results compared with measuring a single colour flash. The researchers tested the sensor’s ability to operate in the presence of ions commonly found in natural and industrial waters.
Salts and carbonates reveal the limits of field measurement
Qasim said the signal was not significantly affected by sodium, calcium or magnesium, or even thorium. However, the results revealed important interference when uranyl was mixed with other ions at a concentration three times higher than its own. Carbonates, bicarbonates, sulphide and iodide reduced the signal by between 30 and 50%.
Qasim considered this effect significant because carbonates are abundant in natural water and seawater and bind strongly to the uranyl ion, which could affect the sensor’s response and requires the sample’s composition to be considered when interpreting field measurements. The experiments included real samples collected from natural lakes and seawater, which were then supplemented with measured concentrations of uranium.
The system identified the quantities of the contaminant with accuracy exceeding 95%, with statistical margins of error described as extremely small. This indicates that the principle could be used beyond simplified laboratory solutions once further development and validation are complete. However, the technology remains a prototype requiring more development before commercial release or widespread field deployment.
The system achieves its best accuracy in a neutral medium with a pH of about seven. Testing highly acidic or alkaline wastewater may therefore require rapid preliminary adjustment of the sample’s pH before it is mixed with the sensing material. The use of europium presents another challenge because of manufacturing costs, prompting a search for more economical alternatives.
The system also requires additional testing to assess measurement stability under direct sunlight and in environments containing complex mixtures of chemical contaminants.
If these limitations are addressed, the technology could provide environmental safety teams and communities near industrial facilities with a portable means of monitoring water quality in real time.
