Lucia Cavigli

Multimodal imaging and optical treatment technologies face significant ethical and financial constraints associated with animal use during early-stage validation. A hierarchical manufacturing strategy for anatomical phantoms is introduced to replicate key structural and biophysical features, such as lung porosity and skin tones. This approach provides a cost-effective, reproducible platform for benchmarking imaging modalities and developing AI-driven diagnostic solutions, reducing reliance on animal models while promoting ethical and scalable research practices.

We introduce a hierarchical manufacturing method for creating anatomical phantoms using water-in-elastomer micro-emulsions. This approach addresses the cost, ethical, and technical limitations of animal models, providing a reliable alternative for multimodal imaging and artificial intelligence development, particularly in photoacoustic imaging.

Seed-borne pathogens pose a significant threat to global food security. This study focuses on Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), a quarantine plant pathogen causing bacterial wilt of common beans. Despite its global spread and economic impact, effective control measures are limited. Existing diagnostic methods, such as PCR, are time-consuming, destructive, and challenging for large-scale screening. This study explores the potential of photoacoustic techniques as a non-destructive, rapid, and high-throughput alternative. These techniques leverage the photoacoustic effect to measure optical absorption, offering high sensitivity and accuracy. Cff colonies exhibit distinct pigmentation, suggesting their suitability for photoacoustic detection. We characterised the optical properties of Cff and developed an in vitro model to simulate conditions within Cff-infected bean seeds. The results demonstrate the efficiency of the photoacoustic technique in detecting Cff in a mimicked-bean seed and indicate the potential discrimination of different coloured Cff strains. This study paves the way for a novel, non-invasive approach to the early detection of Cff and other seed-borne pathogens, contributing to improve crop health and food security.

Optical microresonators based on Whispering Gallery Modes have been extensively investigated as unique tools for fundamental studies and as core components in several applications. Specifically, microbubbles resonators (MBR) made from glass capillaries combine high optical and mechanical Q-factors together with intrinsic microfluidics, and in this work we demonstrate them as unique platforms for photoacoustic (PA) detection and photothermal (PT) spectroscopy. In a first configuration, we employed a MBR as an optical transducer to detect the PA signal generated by a suspension of gold nanorods (GNRs) placed within the MBR, demonstrating all-optical PA detection and high sensitivity towards nanoparticles optical absorption. The MBR acts both as the ultrasound sensor and as the microvial, enabling the inspection of submicroliter samples without the need for impedance-matching media. We then present a flow cytometry experiment where the GNRs run through the MBR, and we estimate PA intensity by a Fourier analysis of the read-out signal. The sharp MBR mechanical eigenmodes allowed to easily decouple the environmental noise from the PA contributions. In a second proof-of-concept experiment using a similar setup, we implemented the MBR transducer to reconstruct the GNRs absorption spectrum through the photothermal conversion. The high sensitivity of the MBR towards temperature variations allowed for the interrogation of small samples while using a low-intensity beam for their excitation. This thermal detection produces spectra that are insensitive towards light scattering in the sample, as proved experimentally by comparing the spectra of aqueous GNR suspensions in the presence or absence of milk powder.

We present a proof-of-concept experiment where the absorbance spectra of suspensions of plasmonic nanoparticles are accurately reconstructed through the photothermal conversion that they mediate in a microbubble resonator. This thermal detection produces spectra that are insensitive towards light scattering in the sample, as proved experimentally by comparing the spectra of acqueos gold nanorods suspensions in the presence or absence of milk powder. In addition, the microbubble system allows for the interrogation of small samples (below 40 nl) while using a low-intensity beam (around 20 µW) for their excitation. In perspective, this system could be implemented for the characterization of turbid biological fluids through their optical absorption, especially when considering that the microbubble resonator naturally interfaces to a microfluidic circuit and may easily fit within portable or on-chip devices.

Plasmonic particles as gold nanorods have emerged as powerful contrast agents for critical applications as the photoacoustic imaging and photothermal ablation of cancer. However, their unique efficiency of photothermal conversion may turn into a practical disadvantage, and expose them to the risk of overheating and irreversible photodamage. Here, we outline the main ideas behind the technology of photoacoustic imaging and the use of relevant contrast agents, with a main focus on gold nanorods. We delve into the processes of premelting and reshaping of gold nanorods under illumination with optical pulses of a typical duration in the order of few ns, and we present different approaches to mitigate this issue. We undertake a retrospective classification of such approaches according to their underlying, often implicit, principles as: constraining the initial shape; or speeding up their thermal coupling to the environment by lowering their interfacial thermal resistance; or redistributing the input energy among more particles. We discuss advantages, disadvantages and contexts of practical interest where one solution may be more appropriate than the other.

We present different approaches to improve the photostability of plasmonic nanoparticles, either by constraining their initial shape, or by enhancing their thermal coupling to the environment by lowering the corresponding interfacial resistance.