3D cell culture resembles tissues better than traditional monolayer cultures, which differ greatly from in vivo models. We use this technique to develop multicellular spheroids from two cell lines: MCF-7 (adenocarcinoma) and U87mg (glioblastoma astrocytoma), by forced-floating method. In this work, we research the spheroid behaviour through two optical techniques: photovoltaic tweezers and laser irradiation. We use photovoltaic tweezers to manipulate spheroids and to explore their electric charge. We also investigate their biological response to laser irradiation depending on wavelength and laser power. Finally, cell viability of the spheroids after undergoing each of these optical/optoelectric treatments has been quantified.
Ferroelectric platforms based on photovoltaic LiNbO3:Fe are a powerful tool for trapping and patterning of micro- and nano-particles. By using this tool, metallic structures have been assembled from Ag and Au nanoparticles on the surface of the ferroelectric crystal. Their plasmonic response has been checked through the measurement of the reflectance extinction spectra. Then, the fluorescence enhancement of relevant biomaterials such as DNA and spermatozoa tagged with a variety of fluorophores such as DAPI, fluorescein, or rhodamine B has been investigated. Relevant plasmonic enhancement extended along the visible spectral range have been obtained, particularly with Ag nanoparticle structures. The results suggest the potential of the obtained metallic structures to improve bio-imaging procedures. Finally, we have found that the metal nanoparticle patterns are able to induce an organization of the sperm cells along the nanoparticle fringe structures.
Ferroelectric crystals generate electric fields under optical and thermal excitation. Recently, photo-induced electric fields generated in photovoltaic ferroelectric crystals have been applied to act on liquid droplets, either to manipulate droplets or to generate tiny droplets from a liquid reservoir. In this work, we investigate the migration of water and aqueous biodroplets under the light-induced electric fields generated in ferroelectric platforms based on iron doped lithium niobate. Different parameters affecting droplet manipulation have been analysed in detail. Light intensity, distance to the photovoltaic substrate and orientation of the polar axis of the active substrate play a key role. The behaviour and analysis of the droplet motion combined with numerical simulations allow to characterize the droplets and, in particular to distinguish between neutral and charged droplets. The results show the potential of this technique in biotechnology and biomedicine for applications such as bio-droplet analysis or sensing.
An overview of the work recently conducted by our group on the development and applications of photovoltaic tweezers is presented. It includes the analysis of the physical basis of the method and the main achievements in its experimental implementation. Particular attention will be paid to the main potential applications and first demonstrations of its use in nano- and bio-technology. Specifically: i) fabrication of metallic nanoestructures for plasmonic applications, ii) development of diffractive components, iii) manipulation and patterning (1D and 2D) of various types of bio-objects (spores or pollen…) and iv) effects of PV fields of LiNbO3 in tumour cells.
The optical damage behaviour of different LiNbO3 optical waveguides has been experimentally studied by measuring the intensity output of a single beam as a function of the intensity input. Parallel measurements of photovoltaic currents have been carried out as a function of the input intensity and they have been correlated with the optical damage data. The following LiNbO3 guides have been studied and compared: proton exchanged (PE) belonging to the phases alpha, beta1, beta2 and reverse proton exchanged (RPE), and Zn in-diffused waveguides. The greatest intensity thresholds for optical damage, about 2x103 times greater than that of the substrate, have been obtained in RPE guides (they support ordinary polarization and have similar nonlinear optic activity as the substrate) and beta2 guides which support extraordinary polarization (they have no nonlinear optic activity). On the other hand, the lowest photovoltaic currents have been measured in beta1,2-phases. As a function of the light intensity, the photovoltaic current exhibits a superlinear behaviour, strong in alpha-phase and weaker in Zn in-diffused and RPE guides. The results for optical damage are discussed in connection with those of photovoltaic currents, paying particular attention to the main mechanisms involved.
Conference Committee Involvement (3)
Optical Methods for Inspection, Characterization, and Imaging of Biomaterials VII
23 June 2025 | Munich, Germany
Optical Methods for Inspection, Characterization, and Imaging of Biomaterials VI
26 June 2023 | Munich, Germany
Optical Methods for Inspection, Characterization, and Imaging of Biomaterials V
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