Biagio Mandracchia

Endowing a plain fluidic chip with micro-optics: a holographic microscope slide

Lab-on-a-Chip (LoC) devices are extremely promising in that they enable diagnostic functions at the point-of-care. Within this scope, an important goal is to design imaging schemes that can be used out of the laboratory. In this paper, we introduce and test a pocket holographic slide that allows digital holography microscopy to be performed without an interferometer setup. Instead, a commercial off-the-shelf plastic chip is engineered and functionalized with this aim. The microfluidic chip is endowed with micro-optics, that is, a diffraction grating and polymeric lenses, to build an interferometer directly on the chip, avoiding the need for a reference arm and external bulky optical components. Thanks to the single-beam scheme, the system is completely integrated and robust against vibrations, sharing the useful features of any common path interferometer. Hence, it becomes possible to bring holographic functionalities out of the lab, moving complexity from the external optical apparatus to the chip itself. Label-free imaging and quantitative phase contrast mapping of live samples are demonstrated, along with flexible refocusing capabilities. Thus, a liquid volume can be analyzed in one single shot with no need for mechanical scanning systems.

Label-free quantification of the effects of lithium niobate polarization on cell adhesion via holographic microscopy

The surface of a c- cut ferroelectric crystal at room temperature is characterized by the so-called screening surface charges, able to compensate the charge due to the spontaneous polarization. Recently, these charges inspired the investigation of the interaction affinity of live cells with lithium niobate and lithium tantalate crystals. However, different knowledge gaps still remain that prevent a reasonable application of these materials for biological applications. Here, a label-free holographic total internal reflection microscopy is shown; the technique is able to evaluate quantitatively the contact area of live fibroblast cells adhering onto the surface of a ferroelectric lithium niobate crystal. The results show values of contact area significantly different between cells adhering onto the positive or negative face of the crystal. This reinforces the reasons for using the polarization charge of these materials to study and/or control cellular processes and, thus, to develop an innovative platform based on polar dielectric functional substrates.

Twofold Self-Assembling of Nanocrystals Into Nanocomposite Polymer

In this paper, we introduce a single-step self-assembling process aimed at forming two-dimensional (2-D) array microstructures made from a nanocomposite polymer layer in which are dispersed CdSe-CdS nanocrystals. The novelty of the process reported here is that it operates simultaneously as a two-fold process where the liquid polymer matrix is self-shaped by electrohydrodynamic pressure as a 2-D array of microstructures, while at the same time, the nanocrystals are self-assembled by dielectrophoretic forces. The proposed approach could inspire future smart fabrication techniques for producing self-assembled lensed nanocomposite layers. In principle, the method is scalable down to diameter lens up to few micrometers.

Mapping electric fields generated by microelectrodes using optically trapped charged microspheres

In this work, we show a new technique to measure the direction and amplitude of the electric field generated by microelectrodes in a liquid environment, as often used in microfluidic devices. The method is based on the use of optical tweezers as a force transducer. A trapped, charged particle behaves as a probe. With this technique, it is possible to obtain a detailed map of the electric field, even for very complex electrode structures with a resolution below a micrometre and with a sensitivity as low as a few hundreds of V m(-1).

Interferometric measurement of film thickness during bubble blowing

In this paper, we propose digital holography in transmission configuration as an effective method to measure the time-dependent thickness of polymeric films during bubble blowing. We designed a complete set of experiments to measure bubble thickness, including the evaluation of the refractive index of the polymer solution. We report the measurement of thickness distribution along the film during the bubble formation process until the bubble‘s rupture. Based on those data, the variation range and variation trend of bubble film thickness are clearly measured during the process of expansion to fracture is indicated.

Recent Advancements and Perspective About Digital Holography: A Super-Tool in Biomedical and Bioengineering Fields

Digital holographic microscopy (DHM) has become a technique utilized widely for sample inspection, having many applications in different fields of science and technology. The capability for recovering the complex amplitude distribution scattered by the sample permits numerical refocus after acquisition and quantitative phase imaging. These are two of the features that make DHM a very versatile microscopy technique. The standard DHM system is based on a Mach–Zehnder interferometer that can be configured for operating in transmission or reflection modes, working in either the in-line or off-axis architecture. With the benefit of such special characteristics, DHM is used in basic research as much in the industry. Here we review some of the recent advancements for the label-free inspection of biological samples and the study of thin films.

Wavefront division off-axis digital holography microscopy on chip

We designed, realized, and tested a pocket module that allows performing off-axis Digital Holography microscopy with no need for an interferometer setup. A commercial plastic chip is engineered for the scope. Our strategy is moving complexity from the reconstruction algorithms and the external imaging apparatus to the chip itself, using custom optical components. We functionalized the chip with a photoresist grating and polymer lenses, to avoid the need for a reference arm as well as external optical components. Thanks to the single beam scheme, the system is robust against vibrations and the stability of fringe patterns implies enhanced portability.

Detection and sorting of microplastics in marine environment by new imaging tools

Digital holographic microscopy (DHM) has proved to be a powerful imaging tool for identifying, analysing and reconstructing the 3D shape of cells and small organisms in their natural environment. In fact, DHM has the advantage, compared to other imaging techniques, to be a non-intrusive, non-destructive and label-free method for in situ measurements. This makes holography the most suitable tool for underwater imaging, where many of the species under investigation are very fragile and can be damaged. In particular, we built up an optofluidic platform based on DHM able to perform such analysis in microfluidic environment, i.e. in dynamic conditions and also in case of a turbid medium. In this work, we take advantage of this technique to identify, sort and reconstruct the morphology of different classes of microplastics (e.g. PVC, PET, PP, etc.) dispersed in water, which are among the major pollutants in the ocean, and to provide an effective assessment of their abundance. By adopting special algorithms for numerical processing of the acquired images, we try to separate the plastics from other materials, such as organic debris (shell fragments, animals parts, diatoms, etc.) and other items (metal paint coatings, tar, glass, etc.).

Easy Printing of High Viscous Microdots by Spontaneous Breakup of Thin Fibers

Electrohydrodynamic jetting is emerging as a successful technique for printing inks with resolutions well beyond those offered by conventional inkjet printers. However, the variety of printable inks is still limited to those with relatively low viscosities (typically <20 mPa s) due to nozzle clogging problems. Here, we show the possibility of printing ordered microdots of high viscous inks such as poly(lactic-co-glycolic acid) (PLGA) by exploiting the spontaneous breakup of a thin fiber generated through nozzle-free pyro-electrospinning. The PLGA fiber is deposited onto a partially wetting surface, and the breakup is achieved simply by applying an appropriate thermal stimulation, which is able to induce polymer melting and hence a mechanism of surface area minimization due to the Plateau-Rayleigh instability. The results show that this technique is a good candidate for extending the printability at the microscale to high viscous inks, thus extending their applicability to additional applications, such as cell behavior under controlled morphological constraints.

Through-the-objective holographic surface plasmon resonance imaging for quantitative measurement of thin film thickness

We built and tested a Holographic Surface Plasmon Resonance (HoloSPR) objective-based microscope for simultaneous amplitude-contrast and phase-contrast Surface Plasmon Resonance imaging (SPRi). SPRi is a widely spread tool for label-free detection of changes in refractive index and concentration, as well as mapping of thin films. However, to obtain quantitative data of thin film thickness, usually scanning techniques have to be employed. Thanks to the simultaneous detection of amplitude and phase, we show that HoloSPRi provides a versatile imaging tool for high-throughput SPR detection, which yields, moreover, the possibility of non-scanning quantitative measurements of thin film thickness.