Cyril Herrier

Capacitive micromachined ultrasonic transducers (CMUTs) are promising gravimetric platforms for volatile organic compound (VOC) detection in clinical environments, yet their deployment is critically hindered by humidity interference: in wound headspace or exhaled breath, rapid relative humidity fluctuations — rather than elevated humidity per se — generate frequency shifts that consistently overshadow ppb–ppm analyte signals. We present a multichannel CMUT sensor array combining peptide surface functionalization with an affinity-based linear humidity correction model. Four bare sensors (S1–S4) and four peptide-functionalized sensors (S5–S8) are operated simultaneously, enabling per-channel decoupling of water-induced and analyte-induced frequency contributions without architectural modification to the chip. Both external and internal humidity referencing strategies are validated against two model analytes — phenylethyl alcohol (PEA) and cis-3-hexenol (Cis3). Internal correction, which uses the bare CMUT sensors themselves as in-situ humidity probes, consistently reduces inter-replicate variability in the extracted VOC affinity coefficients α relative to external referencing, yielding mean values of -3.44 ± 0.52 kHz/ppm for PEA and -0.026 ± 0.003 kHz/ppm for Cis3 across functionalized sensors. The ratio of inter-cluster to intra-cluster distance in PCA space — a metric of analyte class separability — increases from 1.4 to 3.0 upon humidity correction of the full sensor array, confirming that compensation directly improves analyte discriminability. These results establish peptide functionalization coupled with on-chip humidity referencing as a scalable pathway toward miniaturized electronic nose platforms deployable in real-world humid environments.

In this study, we explored the use of surface plasmon resonance (SPR) and Mach–Zehnder interferometry for detecting compounds in complex mixtures separated by supercritical fluid chromatography. Each molecule was individually injected and analyzed by supercritical fluid chromatography (SFC) in a 10% alcoholic solution. The fingerprints obtained via the sensors were then compared to the fingerprints of the same molecules present in a lemon essential oil (EO) at the same dilution. The results show a remarkable correlation between UV sensors and electronic noses (e-nose), enabling compound detection. The obtained signals are normalized and presented as radar charts to visualize the specific olfactory signatures of each molecule. The olfactory profiles of monoterpenes C₁₀H₁₆ such as α-pinene and limonene show notable differences, as do the C₁₀H₁₆O isomers (citral, geranial, and neral). Mach–Zehnder interferometry also allows for the discrimination of limonene enantiomers, a challenging task for current chromatography techniques. Statistical analysis confirms the ability of these technologies to differentiate compounds, including isomers. Even if UV detection is more sensitive than SPR, e-noses (SPR and Mach–Zehnder interferometers) offer the unique advantage of providing specific signatures for each compound, facilitating real-time identification. This study demonstrates the effectiveness of combining e-noses with SFC for rapid, non-destructive detection of volatile compounds. This concept can be extended to other terpenoids and volatile compounds, and hybridization with gas chromatography could be a future potential development.

Headspace analysis of highly humid samples remains a challenge for artificial olfaction. Based on surface plasmon resonance imaging and bio-based sensors, the NeOse Pro olfactive analyzer yields multivariate data and enhances the statistical discrimination capacity of odor patterns. However, the presence of a high background signal, such as water vapor from aqueous samples, may deteriorate its discriminant ability. Recently, miniaturized pre-concentrators packed with hydrophobic adsorbent have been developed to improve the detection limit of gas analysis methods and to enhance their selectivity by reducing the water’s background signal. This work presents, for the first time, the coupling of a miniaturized silicon micro pre-concentration unit (µPC) to a bio-based opto-electronic nose (NeOse Pro). The results showed that the coupling of a silicon µPC with the NeOse Pro led to an improvement in the detection limit of n-nonane by at least a factor of 125. Additionally, principal component analysis (PCA) of eight different flavored waters showed an enhanced discrimination ability of the coupled set-up in highly humid conditions.