Project title: Ultra-sensitive sensor system for indoor formaldehyde detection
Acronim: FormalSens
Programme/ Project type: PNCDI IV - Program 5.7.1 – Partnerships for Competitivity, Experimental Demonstration Project (PED)
Contract no. 2⁄ 2025 (PN-IV-P7-7.1-PED-2024-0977)
Project Duration: 08/01/2025 - 31/12/2026
Project Budget: 764.670 lei
Contractor: National Institute of Research and Development in Microtechnologies – IMT Bucharest (www.imt.ro)
Contracting Authority: Executive Agency for Higher Education, Research, Development and Innovation Funding – UEFISCDI (www.uefiscdi.gov.ro)

Project manager: Dr. Angela BARACU (angela.baracu@imt.ro)

Formaldehyde (CH₂O) is a harmful and toxic volatile organic compound, which brings serious concerns regarding the human health and the living environment, due to its carcinogenic effect. Since 2010, formaldehyde is considered a Group 1 carcinogen by the World Health Organization (WHO), and also one of the major indoor air pollutants in the WHO guidelines for indoor air quality, with a very low concentration limit of 80 ppb. Therefore, there is an urgent need for sensitive and selective monitoring methods. The standard analytical techniques currently in use for CH₂O detection (spectrophotometry, chromatography, or polarography) require expensive instrumentation and well-trained operators. The proposed project (FormalSens) will develop a novel approach, integrating resonant SAW devices with graphitic carbon nitride (g-C₃N₄) decorated with zinc oxide (ZnO) nanoparticles, providing high sensitivity, low operating temperature and excellent selectivity. Moreover, the system will allow CH₂O detection in the presence of interfering species (NH₃, NO₂, CO) and different humidity levels (20-80%), making it suitable for real environmental conditions. The method proposed by FormalSens (starting from TRL 2 and advancing to TRL 4) will address the major issues of the formaldehyde indoor air pollution by its efficient monitoring in accordance to the increasingly severe international environmental regulations.

• National Institute for Research and Development in Microtechnologies (IMT-Bucharest)
• ECONIRV SRL

The main scope of the project is to develop and validate a sensitive, selective and room temperature (RT) operating sensor based on Surface Acoustic Wave (SAW) device for the detection of formaldehyde (CH₂O), a toxic and harmful gas in the household indoor environments. The high sensitivity of the gas sensor will be assured both by using resonant-type devices based on SAW structures, and graphitic carbon nitride (g-C₃N₄) sensing film decorated with zinc oxide (ZnO) nanoparticles (NPs), which enhance specific surface areas with more adsorption sites. The excellent selectivity of the new proposed sensors will be provided by adding ZnO NPs in the composite structure, which present high surface areas with a large number of oxygen species available for interactions with the hydrogen atoms in CH₂O molecules through hydrogen bonds. Moreover, by incorporating nanomaterials with SAW devices, the operating temperature of CH₂O sensors is reduced.

The general objectives of the project include:

• Increasing the level of technological maturity by development of an integrated system for the CH₂O detection, including existing SAW microsensors’ technology and the testing platform, by immobilizing a selective nanocomposite thin film on top of the SAW sensing area and data processing;
• Generating new solutions validated in the laboratory for the CH₂O determination in real time, to be offered to economic agents.

Phase 1/2025

In this stage, the fabrication of SAW devices (Surface Acoustic Wave devices) on an ST-cut piezoelectric quartz substrate was carried out using photolithographic techniques. The acoustic delay line configuration was used, which comprises two interdigitated structures and a sensing area placed between them. The SAW structure was manufactured entirely from Cr/Au, with a film thickness of 15/150 nm.
The sensing materials were synthesized by direct calcination of urea, melamine, or cyanuric acid to obtain graphitic carbon nitride (g-C₃N₄), and by the sol-gel method followed by calcination for the preparation of zinc oxide ZnO. These materials were obtained under several conditions, by modifying the raw material in the case of (g-C₃N₄), or the calcination temperature and the carrier gas atmosphere in the case ofZnO. Nanocomposite materials based on (g-C₃N₄) and ZnO were prepared by mixing dispersions containing the individual(g-C₃N₄) and ZnO components, and applying ultrasound to the new dispersion. The volumetric ratio between the two individual component dispersions was varied to obtain different loading degrees of carbon nitride with ZnO particles.
The morpho-structural characterization of the synthesized materials was performed using several analytical techniques (SEM, XRD, and FTIR). SEM images indicated the nanolayer-formed structure of graphitic carbon nitride and the spherical shape of theZnOnanoparticles. Also, the (g-C₃N₄)@ZnO nanocomposite materials showed the two individual components, forming an interconnected network of the two types of particles. XRD analysis confirmed the presence of the crystalline phases of (g-C₃N₄) and ZnO in the synthesized materials, as well as in the (g-C₃N₄)@ZnO nanocomposite materials.
The dissemination of the results was achieved through several papers and communications presented at international conferences in the form of a poster or oral presentation. Furthermore, one paper has been submitted for publication in a prestigious ISI (Q1) journal and is currently under evaluation.

Conferences

1. A. Baracu, O. Simionescu, V. Buiculescu, M. Stoian, C. Obreja, G. Craciun, F. Comanescu, SAW sensors based on nanocrystalline graphite for environmental applications, the 48th edition of the International Semiconductor Conference - CAS 2025, Sinaia, Romania, October 7^th-11^th, 2025 (Poster).
2. Angela Baracu, Marius Stoian, Octavian Simionescu, Cosmin Obreja, Valentin Buiculescu, Raluca Gavrila, Gabriel Craciun, Florin Comanescu, Advanced SAW Sensors Based on Nanocrystalline Graphite for Air Quality Monitoring, IEEE SENSORS 2025, Vancouver, Canada, October 19^th-22^nd,2025 (Lecture).
3. M. Stoian, C. Obreja, V. Buiculescu, A. Dinescu, A. Baracu, Graphitic carbon nitride-based SAW sensor for sensitive detection of formaldehyde, IEEE SENSORS 2025, Vancouver, Canada, October 19-22, 2025 (Poster).
4. A. Baracu, M. Stoian, O. Simionescu, C. Obreja, V. Buiculescu, R. Gavrila, G. Craciun, F. Comanescu, Development of Carbon-Based Sensitive SAW Sensors for Air Pollution Monitoring, the 17th International Conference on Physics of Advanced Materials (ICPAM-17), Hamamatsu, Japan, November 16^th – 23^rd, 2025 (Lecture).
5. M. Stoian, C. Obreja, V. Buiculescu, A. Dinescu, A. Baracu, Graphitic carbon nitride-based material integrated in a SAW device for the detection of formaldehyde, 17th International Conference on Physics of Advanced Materials (ICPAM-17), Hamamatsu, Shizuoka, Japan, November 16-23, 2025 (Poster).
6. M. Stoian, A. Baracu, C. Romanitan, O. Brincoveanu, A. Radoi, Synthesis of cobalt oxide and cobalt hexacyanoferrate nanoparticles for electrode development with energy storage applications, 8th Autumn School on Physics of Advanced Materials (PAMS-8), Hamamatsu, Shizuoka, Japan, November 16–23, 2025 (Poster).

ISI Journals

1. Marius C. Stoian, Cosmin Alexandru Obreja, Dana G. Popescu, Bogdan Trica, Raluca Gavrila, Valentin Buiculescu, Angela Mihaela Baracu, Surface acoustic wave sensor based on molecularly imprinted polymer for highly sensitive detection of glyphosate, Applied Materials Today APMT-S-23-02750 (under evaluation lucrare trimisă spre evaluare).