Researchers Turn Waste Wood into Formaldehyde Sensor That Changes Color with Contamination Level

The development of new fluorescent sensors reveals an ongoing trend of developing new technology to combat some of the most pressing environmental problems. One of these use cases include detecting contaminants in drinking water.

In a recent study conducted by scientists at Nanjing Forestry University, a newly developed low-cost fluorescent probe was tested to evaluate its performance in detecting formaldehyde in drinking water at concentrations well below international safety thresholds.¹ This sensor used carbon quantum dots derived from discarded spruce packaging wood.¹

What did the researchers discuss in their study?

In their study, the researchers describe the synthesis of four varieties of carbon quantum dots (CQDs) from spruce waste via a hydrothermal process. The key advance is a dual-nitrogen-doped variant, which is co-doped with urea and o-phenylenediamine, that achieves a detection limit of 0.0016 mM for formaldehyde.¹ That figure sits significantly below the World Health Organization (WHO)'s exposure limit of 0.00333 mM and the upper limits set by two Chinese national standards for drinking water quality.¹

Why is formaldehyde dangerous to humans?

At its core, formaldehyde is a toxic and widely used industrial chemical.² It is a gas at room temperature, and it is widely used in the development of household products, such as pressed-wood products, glues and adhesives, and certain insulation materials, to name a few.³ It is also found naturally on some food items because it is added as a food preservative.³

People are exposed to formaldehyde in several ways. It can be inhaled, absorbed through the skin, or consumed via foods or liquids.³ While a small amount of formaldehyde exposure is not harmful to humans, abundant quantities of exposure can be damaging to human health. For example, formaldehyde exposure has been linked to increased risk of leukemia and cancer of the nasal sinuses.³

Because of these associated health risks, researchers have looked at how they can use fluorescent sensors to detect and quantify the presence of formaldehyde in the environment and in water. The challenge that researchers encountered when using CQDs with new sensors is that CQDs could not provide a visual signal readable without laboratory instrumentation, making them poorly suited for field deployment.¹

Does the probe that the researchers developed using carbon quantum dots address this limitation?

The short answer is yes, and that the probe's sensitivity and visual readout suggest potential for on-site water quality monitoring. However, further validation is still needed before it can be deployed in practical applications. When formaldehyde concentration rises from zero to 80 mM, the probe's fluorescence, which was observed under 365 nm ultraviolet excitation, shifts progressively through white, blue, cyan, green, and yellow.¹ This color gradient gives operators a visible, qualitative read of contamination severity without specialized equipment, while quantitative analysis remains possible for laboratory settings.¹

The researchers synthesized and compared four CQD formulations in their study: undoped; urea-doped; o-phenylenediamine-doped; and the dual-nitrogen co-doped version. The co-doped variant outperformed the others on sensitivity by roughly an order of magnitude.¹ The team also characterized how nitrogen doping alters the physical morphology, chemical structure, and optical properties of the quantum dots, and proposed a mechanistic explanation for how each probe interacts with formaldehyde.¹

Using industrial waste wood as the carbon feedstock keeps material costs low and offers a potential use case for a byproduct that is otherwise discarded.

This study in full was published in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy.¹

References

1. Li, Y.; Fang, L.; Gao, S.; et al. From Spruce Packaging Waste to Fluorescent Carbon Quantum Dots/Formaldehyde Detection Probe: Performance and Mechanism. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2026, 361, 128070. DOI: 10.1016/j.saa.2026.128070
2. Owen, B. A.; Dudney, C. S.; Tan, E. L.; Easterly, C. E. Formaldehyde in Drinking Water: Comparative Hazard Evaluation and an Approach to Regulation. Regul. Toxicol. Pharmacol. 1990, 11 (3), 220–236. DOI: 10.1016/0273-2300(90)90023-5
3. American Cancer Society, Formaldehyde and Cancer Risk. Cancer.org. https://www.cancer.org/cancer/risk-prevention/chemicals/formaldehyde.html (accessed 2026-05-26).