Gianluca Valentini

• MS
• Professor (Full) at Politecnico di Milano

A number of applications require methods to detect with high spatial resolution and chemical specificity microplastics (MPs) extracted from different matrices. Here we introduce a wide-field hyperspectral Fourier transform Raman microscope for the rapid detection and identification of MPs. The instrument, based on a common-path birefringent interfe...

Remote sensing in thermal infrared bands (TIR) is largely dominated by cumbersome dispersive-type hyperspectral imagers, which usually require expensive and cryo-cooled quantum detectors to make up for their low optical throughput. Here, we present a compact and low-cost TIR hyperspectral camera based on the Fourier-transform approach. It combines...

Hyperspectral imaging (HSI) is a very powerful tool to study artworks in a non-contact way. Nevertheless, typical HSI systems, which rely on spatial-scanning and dispersive spectrometers, suffer from high-light losses and are difficult to operate for analysing complex artworks. Here we review the capabilities of a HSI system based on TWINS, an inno...

This work introduces a novel method to multivariate analysis applied to fused hyperspectral datasets in the field of Cultural Heritage (CH). Hyperspectral Imaging is a well-established approach for the non-invasive examination of artworks, offering insights into their composition and conservation status. In CH field, a combination of hyperspectral...

This paper introduces a novel multimodal optical microscope, integrating Raman and laser-induced photoluminescence (PL) spectroscopy for the analysis of micro-samples relevant in Heritage Science. Micro-samples extracted from artworks, such as paintings, exhibit intricate material compositions characterized by high complexity and spatial heterogene...

Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique for studying biological processes. There exists a growing interest in developing strategies to enhance throughput and reduce acquisition time of FLIM systems, which commonly employ laser scanning excitation and time-correlated single-photon counting (TCSPC) detection. In this w...

Hyperspectral imaging (HSI) has emerged as an effective tool to obtain spatially resolved spectral information of artworks by combining optical imaging with spectroscopy. This technique has proven its efficacy in providing valuable information both at the large and microscopic scale. Interestingly, the macro scale has yet to be thoroughly investiga...

Significance The reprojection setup typical of oblique plane microscopy (OPM) limits the effective aperture of the imaging system, and therefore its efficiency and resolution. Large aperture system is only possible through the use of custom specialized optics. A full-aperture OPM made with off the shelf components would both improve the performance...

A single-pixel camera combined with compressive sensing techniques is a promising fluorescence microscope scheme for acquiring a multidimensional dataset (space, spectrum, and lifetime) and for reducing the measurement time with respect to conventional microscope schemes. However, upon completing the acquisition, a computational step is necessary f...

A class of hyperspectral imaging systems operating on an extremely wide spectral range has been developed based on a new compact and reliable interferometer. The systems are portable and feature high throughput and low noise.

A system for high throughput fluorescence lifetime imaging based on single-pixel camera and compressed-sensing is presented. Moreover, a fast fitting algorithm for multidimensional data set is proposed and experimentally validated.

The ability to observe traces of biological material on buildings and stone artworks is of particular importance in understanding how to best deal with them and maybe, in the future, even make use of biofilms for conservation science. We have identified hyperspectral imaging as a viable method for the efficient analysis of such biological materials...

Diffuse Raman spectroscopy (DIRS) extends the high chemical specificity of Raman scattering to in-depth investigation of thick biological tissues. We present here a novel approach for time-domain diffuse Raman spectroscopy (TD-DIRS) based on a single-pixel detector and a digital micromirror device (DMD) within an imaging spectrometer for wavelength...

UV–Vis-induced luminescence techniques are commonly employed by conservators and restorers to examine cultural heritage objects in a non-invasive manner. Many chemical components in artworks show luminescent emission, which can be used for both diagnostic and conservative purposes. The emission spectrum and lifetime are precious indicators of the f...

Heterogeneity investigation at the single-cell level reveals morphological and phenotypic characteristics in cell populations. In clinical research, heterogeneity has important implications in the correct detection and interpretation of prognostic markers and in the analysis of patient-derived material. Among single-cell analysis, imaging flow cyto...

The synthesis of ultrashort pulses with simultaneously tailored spatial and temporal properties opens new horizons in multimode photonics, especially when the spatial degree of freedom is controlled by robust topological structures. Current methods to shape space–time beams with correlations between their topological charges and spectral components...

Raman microscopy is a powerful analytical technique for materials and life sciences that enables mapping the spatial distribution of the chemical composition of a sample. State-of-the-art Raman microscopes, based on point-scanning frequency-domain detection, have long ( ${\sim}1\;{\rm s}$ ) pixel dwell times, making it challenging to acquire images...

Multispectral imaging and time-resolved imaging are two common acquisition schemes in fluorescence microscopy, and their combination can be beneficial to increase specificity. The multidimensionality of the dataset (space, time, and spectrum) introduces some challenges, such as the acquisition of big datasets and long measurement times. In this wor...

In this chapter, we will describe several analysis and imaging techniques that are transportable to the artwork. Section 1 describes a steady-state and time-resolved laser-induced fluorescence that can be used for the identification of painting materials, such as dyes and some pigments. Section 2 adds another layer of information by adding mapping...

Fourier-plane microscopy is a powerful tool for measuring the angular optical response of a plethora of materials and photonic devices. Among them, optical microcavities feature distinctive energy-momentum dispersions, crucial for a broad range of fundamental studies and applications. However, measuring the whole momentum space (k-space) with suffi...

Structured Illumination Microscopy (SIM) is a key technology for high resolution and super-resolution imaging of biological cells and molecules. The spread of portable and easy-to-align SIM systems requires the development of novel methods to generate a light pattern and to shift it across the field of view of the microscope. Here we show a miniatu...

Three-dimensional fluorescence microscopy is a key technology for inspecting biological samples, ranging from single cells to entire organisms. We recently proposed a novel approach called spatially modulated Selective Volume Illumination Microscopy (smSVIM) to suppress illumination artifacts and to reduce the required number of measurements using...

Structured Illumination Microscopy (SIM) is a key technology for high resolution and super-resolution imaging of biological cells and molecules. The spread of portable and easy-to-align SIM systems requires the development of novel methods to generate a light pattern and to shift it across the field of view of the microscope. Here we show a miniatu...

Scientific investigation in the cultural heritage field is generally aimed at the characterization of the constituent materials and the conservation status of artworks. Since the 1990s, reflectance spectral imaging proved able to map pigments, reveal hidden details and evaluate the presence of restorations in paintings. Over the past two decades, h...

Here we present an interferometric wide field hyperspectral microscope based on a common-path birefringent interferometer with translating wedges, to measure photoluminescence emission from two-dimensional semiconductors. We show diffraction-limit hyperspectral photoluminescence microscopy from two-dimensional materials across millimiter areas, pro...

We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation led to plasma generation with a characteristic spectral line emission at 391 nm. By following the emitted signal...

Physical methods to control pest arthropods are increasing in importance, but detailed knowledge of the effects of some of these methods on the target organisms is lacking. The aim of this study was to use light sheet fluorescence microscopy (LSFM) in anatomical studies of blood-sucking arthropods in vivo to assess the suitability of this method to...

We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation leads to plasma excitation with a characteristic spectral line emission at 391 nm. By following the emitted signa...

We present wide-field hyperspectral microscopy images of photoluminescence from two-dimensional semiconductors. The microscope exploits Fourier-transform spectroscopy and uses a common-path birefringent interferometer. Our hyperspectral microscope is a fast tool to characterize 2D materials.

We present the application of a novel hyperspectral camera, based on the Fourier-transform approach, to study the photoluminescence emission from artworks at different spatial scales and emission timescales. The hyperspectral system relies on an innovative wide-field, compact and ultra-stable interferometer coupled to different excitation and detec...

In multi-view fluorescence microscopy, each angular acquisition needs to be aligned with care to obtain an optimal volumetric reconstruction. Here, instead, we propose a neat protocol based on auto-correlation inversion, that leads directly to the formation of inherently aligned tomographies. Our method generates sharp reconstructions, with the sam...

Compressed sensing (CS) is a signal processing approach that solves ill-posed inverse problems, from under-sampled data with respect to the Nyquist criterium. CS exploits sparsity constraints based on the knowledge of prior information, relative to the structure of the object in the spatial or other domains. It is commonly used in image and video c...

Multispectral/hyperspectral fluorescence lifetime imaging microscopy ( $\lambda$ FLIM) is a promising tool for studying functional and structural biological processes. The rich information content provided by a multidimensional dataset is often in contrast with the acquisition speed. In this work, we develop and experimentally demonstrate a wide-fi...

In multi-view fluorescence microscopy, each angular acquisition needs to be aligned with care to obtain an optimal volumetric reconstruction. Here, instead, we propose a neat protocol based on auto-correlation inversion, that leads directly to the formation of inherently aligned tomographies. Our method generates sharp reconstructions, with the sam...

We introduce a Fourier-transform hyperspectral microscope based on an ultrastable interferometer. It enables wide-field acquisition with broad spectral coverage, tunable spectral resolution and high sensitivity. We provide examples of applications for fluorescence and Raman imaging. © 2021 The Author(s)

The historical knowledge inherited from house paint documents and the experimental research on synthetic pigments show that production methods have an important role in the performance of paint. In this regard, this work investigates the links existing between the optical emission, crystal defects and photocatalytic activity of zinc white pigment f...

Cadmium yellows are a class of inorganic pigments introduced during the middle of the 19th c. and widely employed by modern painters. Recent research has reported the degradation of cadmium yellow paints in important artworks such as The Scream by Edward Munch, raising questions about its triggering factors. To address this issue, we investigated,...

Crystalline solids can exhibit photoluminescence when properly excited by sufficiently energetic light radiation. Following excitation, different radiative and non-radiative recombination pathways can occur that are informative of the energetic structure of the material as well as of the presence of crystal defects and impurities. Usually, the char...

Optical Projection Tomography (OPT) is a powerful three-dimensional imaging technique used for the observation of millimeter-scaled biological samples, compatible with bright-field and fluorescence contrast. OPT is affected by spatially variant artifacts caused by the fact that light diffraction is not taken into account by the straight-light propa...

Luminescent emission from artworks is usually employed by conservators and restorers as a visual and quick method for assessing the presence of protective varnishes and restoration materials, as well to evaluate the painting conservation status. Besides these mere qualitative observations, the analysis of both spectral and temporal features of the...

The painting object of the present work, currently exposed in the Museum of Colle del Duomo in Viterbo (Italy), has been dated back by art historians to the 16th century and it owes its relevance to a still discussed attribution to Michelangelo Buonarroti. For this reason, art historians and the responsible curator of the Museum commissioned scient...

Colorants are present in trace concentration in objects made of plastic and their identification is a methodological and analytical challenge. In conservation, the identification of colorants may allow a better understanding of colorant degradation (such as color change and fading) and provide information about the historical development, productio...

We present a systematic characterization of the optical properties (µa and µs’) of nine representative ex vivo porcine tissues over a broadband spectrum (650-1100 nm). We applied time-resolved diffuse optical spectroscopy measurements for recovering the optical properties of porcine tissues depicting a realistic representation of the tissue heterog...

Modern pigments have been synthetically produced starting from the 19th century. Frequently, achievements in the synthesis technology have changed the physical characteristics of these inorganic pigments in order to improve their stability and coloring power. A clear example of this trend is represented by titanium white (TiO2) that evolved from th...

Arabidopsis thaliana glutamate receptor-like (GLR) channels are amino acid-gated ion channels involved in physiological processes including wound signaling, stomatal regulation, and pollen tube growth. Here, fluorescence microscopy and genetics were used to confirm the central role of GLR3.3 in the amino acid-elicited cytosolic Ca ²⁺ increase in Ar...

We introduce a wide field hyperspectral microscope using the Fourier-transform approach. The interferometer is based on the translating-wedge-based identical pulses encoding system, a common-path birefringent interferometer which combines compactness, intrinsic interferometric delay precision, long-term stability, and insensitivity to vibrations. W...

Time-resolved photoluminescence spectroscopy (TRPS) shows potential as a sensitive, non-destructive, high throughput, label-free laser-based spectroscopy technique capable of analysing low concentrations of organic species adsorbed on and within zeolite pores. Here we report the results from a study that uses TRPS to characterise photoluminescence...

Time-resolved cameras with high temporal resolution (down to ps) enable a huge set of novel applications ranging from biomedicine and environmental science to material and device characterization. In this work, we propose, and experimentally validate, a novel detection scheme for time-resolved imaging based on a compressed sampling approach. The pr...

Light sheet fluorescence microscopy has become one of the most widely used techniques for three-dimensional imaging due to its high speed and low phototoxicity. Further improvements in 3D microscopy require limiting the light exposure of the sample and increasing the volumetric acquisition rate. We hereby present an imaging technique that allows vo...

We introduce a wide field hyperspectral microscope using the Fourier-transform approach. The interferometer is based on the Translating-Wedge-Based Identical Pulses eNcoding System (TWINS) [Opt. Lett. 37, 3027 (2012)], a common-path birefringent interferometer which combines compactness, intrinsic interferometric delay precision, long-term stabilit...

Zinc oxide (ZnO), used as a pigment since the 19th C., is highly reactive when mixed with drying oils. Indeed, the combination of metal-based pigments and drying oils may react to form metal complexes in paint, which may lead to the aggregation of metal carboxylates or soaps. Whereas the mechanism and chemistry behind metal soap formation has been...

SM related to "Monitoring metal ion leaching in oil-ZnO paint systems with a paramagnetic probe"

The formation and growth of metal soaps is of interest in heritage science, as soaps have been linked to a range of alteration and degradation phenomena potentially affecting works of art. However, current approaches detect metal soaps mainly in an invasive way or only at a late formation stage when the metal soaps are formed on the surface of the...

We introduce a high-performance hyperspectral camera based on the Fourier-transform approach, where the two delayed images are generated by the Translating-Wedge-Based Identical Pulses eNcoding System (TWINS) [Opt. Lett. 37, 3027 (2012)10.1364/OL.37.003027], a common-path birefringent interferometer that combines compactness, intrinsic interferomet...

We demonstrate a Fourier-transform hyperspectral microscope based on an ultrastable birefringent interferometer. As an application example, we obtained fluorescence image from a cancer tissue biopsy.

In conservation science, the identification of painting materials is fundamental for the study of artists' palettes, for dating and for understanding ongoing degradation phenomena. For these purposes, the study of stratigraphic micro-samples provides unique information on the complex heterogeneity of the pictorial artworks. In this context , we pro...

The first detailed analysis of FLIM applications for Mg cell imaging is presented. We employed the Mg-sensitive fluorescent dye named DCHQ5, a derivative of diaza-18-crown-6 ethers appended with two 8-hydroxyquinoline groups, to perform fluorescence lifetime imaging in control and Mg deprived SaOS-2 live cells, which contain different concentration...

Paints based on cadmium sulfide (CdS) were popular among artists beginning in the mid-19th century. Some paint formulations are prone to degrade, discoloring and disfiguring paintings where they have been used. Pablo Picasso’s Femme (Époque des “Demoiselles d’Avignon”) (1907) includes two commercial formulations of CdS: one is visibly degraded and...

Calcium imaging in plants requires a high-resolution microscope, able to perform volumetric acquisition in a few seconds, inducing as low photobleaching and phototoxicity as possible to the sample. Light sheet fluorescence microscopy offers these capabilities, with the further chance to mount the sample in vertical position, mimicking the plant's g...

In painting conservation the examination of cross-sections is fundamental, especially when dealing with aged samples where the presence of deterioration products located within the paint stratigraphy and at the surface must be considered. The use of an epifluorescence microscope equipped with a UV light source is particularly advantageous for the e...

Recent studies have shown that modern pigments produced after the Second Industrial Revolution are complex systems characterized by a high level of heterogeneities. Therefore, it is fundamental to adopt a multi-analytical approach and highly-sensitive methods to characterize the impurities present within pigments. In this work we propose time-resol...

Diffuse Optical Tomography (DOT)is a powerful tool for the reconstruction of optical properties inside a diffusive medium, such as biological tissues. In particular, in the last years, techniques based on structured light illumination and compressive sensing detection have been developed. In this work a time-resolved system based on structured ligh...

The time-resolved photoluminescence (PL) in the nanosecond time scale of TiO2 materials undoped or co-doped with nitrogen and fluorine (N,F-doping) and modified by noble metals (NM, i.e. Au or Pt) nanoparticles (NPs) photodeposition has been systematically investigated in relation to their photocatalytic activity in hydrogen production. Main aim of...