Francesca Carpignano

The refractive index of cells provides insights into their composition, organization and function. Moreover, a good knowledge of the cell refractive index would allow an improvement of optical cytometric and diagnostic systems. Although interferometric techniques undoubtedly represent a good solution for quantifying optical path variation, obtaining the refractive index of a population of cells non-invasively remains challenging because of the variability in the geometrical thickness of the sample. In this paper, we demonstrate the use of infrared low-coherence reflectometry for non-invasively quantifying the average refractive index of cell populations gently confined in rectangular glass micro-capillaries. A suspension of human red blood cells in plasma is tested as a reference. As a use example, we apply this technique to estimate the average refractive index of cell populations belonging to epithelial and hematological families.

The use of patterned light for three-dimensional (3D) imaging and movement tracking has been in the last decade object of experimental investigations for industrial, scientific, and consumer applications. In this paper, we demonstrate the functionality of a compact silicon microsystem for patterned light generation suitable for 3D imaging. It incorporates a single-axis torsional MEMS mirror for steering a near-infrared beam on a diffractive silicon microstructure that projects light patterns on the target. We, here, report images, acquired with a CMOS camera, of the detected light patterns realized with different diffractive elements. As an example of application, we have illuminated 3D objects with a generated line pattern and then detected the deformation of the projected lines with the same camera. By image processing, from the line deformation, we have estimated the object depth that was found in agreement with the geometrical size.

We report the application of an all-fiber setup for spectral reflectivity measurements on rectangular glass microcapillaries, in view of their application as micro-opto-fluidic devices for detection of solution concentration. We tested two kind of capillaries, both with 50 μm × 500 μm cross section but different wall thickness, respectively equal to 35 μm and 50 μm. Optical readout was provided by a broadband light source with λc = 1.55 μm. We here compare the results obtained on the two different devices in terms of sensitivity and limit of detection when tested with Glucose solutions in water.

In recent years the development of silicon micromachining technologies has required more efforts in research to find non-contact measurement techniques for in-depth, non-destructive inspection of layered and microstructured samples. In this work, we apply a optical low-coherence reflectometry for in-plane and out-of-plane measurements aimed at detecting the optical path between hidden interfaces of several silicon devices with characteristic distance in the range 3 - 17 μm. The implemented configuration is based on a fiberoptic Michelson interferometer and it used infrared broadband radiation in the wavelength range of 1.2 - 1.7 μm, exhibiting a coherence length shorter than 2 μm. Out-of-plane measurements were performed to detect the optical pathlength of the main structural layers of a MEMS gyroscope. Moreover, in-plane measurements on vertical periodic silicon/air microstructures allowed us to detect the optical path among several silicon/air interfaces. Arrays with different spatial period were tested and the optical distance between hidden interfaces was obtained with high in-depth resolution. The results were in good agreement with the design parameters of the specific device. The proposed spot optical technique is a powerful and highly versatile diagnostic tool for non-destructive testing of silicon devices.

We investigated the capacity of tumour cells to populate the gaps of three-dimensional microstructures (3D-SMS) formed by periodic arrays of parallel 3-μm-thick silicon walls separated by 5-μm-wide, 50 μm-deep air gaps. To evaluate a possible correlation between this feature and cell aggressiveness, we tested eight human tumour cell lines with a well known different aggressive potential. The qualitative analysis performed by fluorescence microscopy revealed that some tumour cell lines populate the narrow gaps of the microstructure due to their greater plasticity and enhanced aggressiveness; on the other hand, cells with low aggressive potential are less prone to colonise the gaps. Image analysis of fluorescence microscopy fields allowed the quantification of the fraction of cells inside the gaps over the total cell number. Our results suggest that tumour cell plasticity could be considered as a biomarker of aggressiveness of tumour cells grown in an innovative 3D micro-device characterised by a well-defined and highly reproducible geometrical layout.

We recently employed three-dimensional (3D) silicon microstructures (SMSs) consisting in arrays of 3 μm-thick silicon walls separated by 50 μm-deep, 5 μm-wide gaps, as microincubators for monitoring the biomechanical properties of tumor cells. They were here applied to investigate the in vitro behavior of HT1080 human fibrosarcoma cells driven to apoptosis by the chemotherapeutic drug Bleomycin. Our results, obtained by fluorescence microscopy, demonstrated that HT1080 cells exhibited a great ability to colonize the narrow gaps. Remarkably, HT1080 cells grown on 3D-SMS, when treated with the DNA damaging agent Bleomycin under conditions leading to apoptosis, tended to shrink, reducing their volume and mimicking the normal behavior of apoptotic cells, and were prone to leave the gaps. Finally, we performed label-free detection of cells adherent to the vertical silicon wall, inside the gap of 3D-SMS, by exploiting optical low coherence reflectometry using infrared, low power radiation. This kind of approach may become a new tool for increasing automation in the drug discovery area. Our results open new perspectives in view of future applications of the 3D-SMS as the core element of a lab-on-a-chip suitable for screening the effect of new molecules potentially able to kill tumor cells.

Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.