In this work, we employed the Raman microscopy to study the internalization kinetics and spatial distribution of small interfering RNA (siRNA)-diatomite nanoparticles (DNPs) complex in human lung epidermoid carcinoma cell line (H1355) up to 72 h. Raman images are compared with confocal fluorescence microscopy results. The Raman analysis provides that the siRNA-DNPs are internalized and co-localized in lipid vesicles within 18 h, after that equilibrium is achieved.
Microneedles are newly developed biomedical devices, whose advantages are mainly in the non-invasiveness, discretion and versatility of use both as diagnostics and as therapeutics tool. In fact, they can be used both for drugs delivery in the interstitial fluids and for the analysis of the interstitial fluid. In this work we present the preliminary results for two devices based on micro needles in PolyEthylene (Glycol). The first for the drugs delivery includes a membrane whose optical reflected wavelength is related to the concentration of drug. Here, we present our preliminary result in diffusion of drugs between the membrane and the microneedles. The second device is gold coated and it works as electrode for the electrochemical detection of species in the interstitial fluid. A preliminary result in detection of glucose will be shown.
Nanostructured photoluminescent materials are optimal transducers for optical biosensors due to their capacity to convert molecular interactions in light signals without contamination or deterioration of the samples. In recent years, nanostructured biosensors with low cost and readily available properties have been developed for such applications as therapeutics, diagnostic and environmental. Zinc oxide nanowires (ZnO NWs) is material with unique properties and due to these they were widely studied in many fields as electronics, optics, and photonics. ZnO NWs can be either grown independently or deposited on solid support, such as glass, gold substrates and crystalline silicon. Vertical aligned ZnO forest on a substrate shows specific advantages in photonic device fabrication. ZnO NWs are typically synthesized by such techniques classified as vapour phase and solution phase synthesis. In particular, hydrothermal methods have received a lot of attention and have been widely used for synthesis of ZnO NWs. This technique shows more crystalline defects than others due to oxygen vacancies, so as the material shows intense photoluminescence emission under laser irradiation. ZnO NWs surface is highly hydrolysed, so it is covered by OH reactive groups, and standard biomodification chemistry can be used in order to bind bioprobes on the surface. In this work, we present our newest results on synthetic nanostructured materials characterization for optical biosensors applications. In particular, we characterize the ZnO NWs structure grown on crystalline silicon by SEM images and the biomodification by photoluminesce technique, fluorescence microscopy, water contact angle and FT-IR measurements.
Sensitive and accurate detection of cancer cells plays a crucial role in diagnosis of cancer and minimal residual disease, so being one of the most hopeful approaches to reduce cancer death rates. In this paper, a strategy for highly selective and sensitive detection of lymphoma cells on planar silicon-based biosensor has been evaluated. In this setting an Idiotype peptide, able to specifically bind the B-cell receptor (BCR) of A20 cells in mice engrafted with A20 lymphoma, has been covalently linked to the sensor active surface and used as molecular probe. The biochip here presented showed a coverage efficiency of 85% with a detection efficiency of 8.5×10<sup>-3</sup> cells/μm<sup>2</sup>. The results obtained suggested an efficient way for specific label-free cell detection by using a silicon-based peptide biosensor. In addition, the present recognition strategy, besides being useful for the development of sensing devices capable of monitoring minimal residual disease, could be used to find and characterize new specific receptor-ligand interactions through the screening of a recombinant phage library.
In this work we have investigated the photoluminescence signal emitted by graphene oxide (GO) nanosheets infiltrated in silanized porous silicon (PSi) matrix. We have demonstrated that a strong enhancement of the PL emitted from GO by a factor of almost 2.5 with respect to GO on crystalline silicon can be experimentally measured. This enhancement has been attributed to the high PSi specific area. In addition, we have observed a weak wavelength modulation of GO photoluminescence emission, this characteristic is very attractive and opens new perspectives for GO exploitation in innovative optoelectronic devices and high sensible fluorescent sensors.
Diatoms are monocellular algae responsible of 20-25% of the global oxygen produced by photosynthetic processes. The protoplasm of every single cell is enclosed in an external wall made of porous hydrogenated silica, the frustule. In recent times, many effects related to photonic properties of diatom frustules have been discovered and exploited in applications: light confinement induced by multiple diffraction, frustule photoluminescence applied to chemical and biochemical sensing, photonic-crystal-like behavior of valves and girdles. In present work we show how several techniques (e.g. digital holography) allowed us to retrieve information on light manipulation by diatom single valves in terms of amplitude, phase and polarization, both in air and in a cytoplasmatic environment. Possible applications in optical microsystems of diatom frustules and frustule-inspired devices as active photonic elements are finally envisaged.
Interfaces play a key role in optical biosensor fabrication: biological molecules need to be integrated with inorganic transducers, both electrical and optical, preserving their functions and specificity. Single DNA stands, proteins, enzymes, and antibodies must be blocked on surface by absorption or covalently, depending on different chemistry used. In case of proteins and antibodies, also orientation of biological molecules is very important. In this work, we present our results on a biological passivation procedure that employs hydophobins, small amphiphilic proteins. Since these proteins complex with sugars in nature, we also suggest their utilization as functional layer in optical biosensor for glucose.
A porous silicon (PSi) based microarray has been integrated with a microfluidic system based on polydimethylsiloxane
(PDMS) channels circuit, as a proof of concept device for the optical monitoring of selective label-free DNA-DNA
interaction. Theoretical calculations, based on finite element method, taking into account molecular interactions, are in
good agreement with the experimental results, and the developed numerical model can be used for device optimization.
The functionalization process and the interaction between probe and target DNA has been monitored by spectroscopic
reflectometry for each PSi element in the microchannels.
Porous silicon (PSi) is by far a very useful technological platform for optical monitoring of chemical and biological
substances and due to its peculiar physical and morphological properties it is worldwide used in sensing experiments. On
the other hand, we have discovered a natural material, the micro-shells of marine diatoms, ubiquitous unicellular algae,
which are made of hydrated amorphous silica, but, most of all, show geometrical structures made of complex patterns of
pores which are surprisingly similar to those of porous silicon. Moreover, under laser irradiation, this material is
photoluminescent and the photoluminescence is very sensitive to the surrounding atmosphere, which means that the
material can act as a transducer. Starting from our experience on PSi devices, we explore the optical and photonic
properties of marine diatoms micro-shells in a sort of inverse biomimicry.
Valves of <i>Coscinodiscus wailesii</i> diatoms, monocellular micro-algae characterized by a diameter between 100 and 200
μm, show regular pores patterns which confine light in a spot of few μm<sup>2</sup>. This effect can be ascribed to the
superposition of diffracted wave fronts coming from the pores on the valve surface. We studied the transmission of
partially coherent light, at different wavelengths, through single valves of <i>Coscinodiscus wailesii</i> diatoms. The spatial
distribution of transmitted light strongly depends on the wavelength of the incident radiation. Numerical simulations
help to demonstrate how this effect is not present in the ultraviolet region of the light spectrum, showing one of the
possible evolutionary advantages represented by the regular pores patterns of the valves.
In this work, we have fabricated a porous silicon (PSi) Bragg reflectors microarray using a proper technological process
based on photolithography and electrochemical anodization of silicon. Each element of the array is characterized by a
diameter of 200 μm. The PSi structures have been used as platform to immobilize label-free DNA probe and a simple
optical method has been employed to investigate the interaction between probe-DNA and its complementary target. In
order to confirm the specificity of the DNA hybridization, we have also verified that the reaction of probe-DNA with
non-complementary DNA did not occur.
In this communication, we report some new results obtained in our laboratories in design, fabrication and
characterization of silicon-based optical structures and devices, including metamaterials, raman light amplifiers, and
biomatter-silicon interfaces for sensors and biochips.
Self-assembled monolayers are surfaces consisting of a single layer of molecules on a substrate: widespread examples of chemical and biological nature are alkylsiloxane, fatty acids, and alkanethiolate which can be deposited by different techniques on a large variety of substrates ranging from metals to oxides. We have found that a self-assembled biofilm of proteins can passivate porous silicon (PSi) based optical structures without affecting the transducing properties. Moreover, the protein coated PSi layer can also be used as a functionalized surface for proteomic applications.
In the last few years, silicon photonics has been characterized by a wide range of applications in several fields, from
communications to sensing, from biophotonics to the development of new artificial materials. In this communication,
we report a review of the main results obtained in our laboratories in design, fabrication and characterization of new
silicon-based optical structures and devices, including metamaterials, photodetectors, raman light amplifiers, and
porous silicon based bio-chemical sensors and biochips. Future perspectives in integration of silicon based MEMS
and MOEMS are also presented.
Micro-ring resonators have been widely employed, in recent years, as wavelength filters, switches and frequency
converters in optical communication circuits, but can also be successfully used as transducing elements in optical sensing
and biosensing. Their operation is based on the optical coupling between a ring-shaped waveguide and one or more
linear waveguides patterned on a planar surface, typically an input and an output waveguide. When incoming light has a
wavelength which satisfies the resonance conditions, it couples into the micro-ring and continuously re-circulates within
it. A fraction of this resonant light escapes the micro-ring structure and couples into the output waveguide. The presence
of a target analyte over the top surface of the micro-ring (i.e. within the evanescent field) changes the effective refractive
index of the mode propagating into the structure, thus causing a shift in resonance wavelength which can be determined
by monitoring the spectrum at the output port. Proper functionalization of the micro-ring surface allows to add selectivity
to the sensing system and to detect specific interaction between a bioprobe and its proper target (e.g. protein-ligand,
DNA-cDNA interactions). We present our preliminary results on the design of micro-ring resonators on silicon-on-insulator
substrate, aimed at selective detection of several biomolecules. The design of the structure has been
accomplished with the help of FDTD 2D numerical simulations of the distribution of the electromagnetic fields inside
the waveguides, the micro-ring and near the micro-ring surface. Furthermore, all the functionalization reactions and the
bio/non-bio interfaces have been studied and modelled by means of spectroscopic ellipsometry.
Diatoms are monocellular micro-algae provided with external valves, the frustules, made of amorphous hydrated silica.
Frustules present patterns of regular arrays of holes, the areolae, characterized by sub-micrometric dimensions. Frustules
from centric diatoms are characterized by a radial disposition of areolae and exhibit several optical properties, such as
photoluminescence, lens-like behavior and, in general, photonic-crystal-like behavior as long as confinement of
electromagnetic field is concerned. In particular, intrinsic photoluminescence from frustules is strongly influenced by
the surrounding atmosphere: on exposure to gases, the induced luminescence changes both in the optical intensity and
peaks positions. To give specificity against a target analyte, a key feature for an optical sensor, a biomolecular probe,
which naturally recognizes its ligand, can be covalently linked to the diatom surface.
We explored the photoluminescence emission properties of frustules of Coscinodiscus wailesii centric species,
characterized by a diameter of about 100-200 μm, on exposure to different vapours and in presence of specific bioprobes
interacting with target analytes. Very high sensitivities have been observed due to the characteristic morphology of
diatoms shells. Particular attention has been devoted to the emission properties of single frustules.
Diatoms are monocellular micro-algae provided with external valves, the frustules, made of amorphous hydrated silica.
Frustules present patterns of regular arrays of holes, the areolae, characterized by sub-micrometric dimensions. In
particular, frustules from centric diatoms are characterized by a radial disposition of areolae and exhibit several optical
properties, such as photoluminescence variations in presence of organic vapors and photonic-crystal-like behaviour as
long as propagation of electromagnetic field is concerned.
We have studied the transmission of coherent light, at different wavelengths, through single frustules of <i>Coscinodiscus
Walesii</i> diatoms, a centric species characterized by a diameter of about 150 μm. The frustules showed the ability to
focalize the light in a spot of a few μm<sup>2</sup>, the focal length depending on the wavelength of the incident radiation. This
focusing effect takes place at the centre of the frustule, where no areolae are present and, as it is confirmed by numerical
simulations, it is probably due to coherent superposition of unfocused wave fronts coming from the surrounding areolae.
Diatoms-based micro-lenses could be used in the production of lensed optical fibers without modifying the glass core
and, in general, they could be exploited with success in most of the optical micro-arrays.
The development of label-free optical biosensors could have a great impact on life sciences as well as on screening
techniques for medical and environmental applications. Peptide nucleic acid (PNA) is a nucleic acid analog in which the
sugar phosphate backbone of natural nucleic acid has been replaced by a synthetic peptide backbone, resulting in an
achiral and uncharged mimic. Due to the uncharged nature of PNA,
PNA-DNA duplexes show a better thermal stability
respect the DNA-DNA equivalents. In this work, we used an optical biosensor, based on the porous silicon (PSi)
nanotechnology, to detect PNA-DNA interactions. PSi optical sensors are based on changes of reflectivity spectrum
when they are exposed to the target analytes. The porous silicon surface was chemically modified to covalently link the
PNA which acts as a very specific probe for its ligand (<i>c</i>DNA).
A direct laser writing process has been exploited to fabricate a high order Bragg grating on the surface of a porous
silicon slab waveguide. The transmission spectrum of the structure, characterized by a pitch of 10 µm, has been
investigated by end-fire coupling on exposure to vapor substances of environmental interest. The analyte molecules
substitute the air into the silicon pores, due to the capillary condensation phenomenon, and the transmitted spectrum of
the grating shifts towards higher wavelengths. The experimental results have been compared with the theoretical
calculations obtained by using the transfer matrix method together with the slab waveguide modal calculation.
Micro-total-analysis-systems and lab-on-chip are more than promises in lot of social interest applications such as clinical
diagnostic or environmental monitoring. There is an increasing demand of new and customized devices with better
performances to be used in very specific applications. Nanostructured Porous silicon is a functional material and a
versatile platform for the fabrication of integrated optical microsystems to be used in biochemical analysis. Our research
activity is focused on the design, the fabrication and the characterization of several photonic porous silicon based
structures, which are used in the sensing of specific molecular interactions. To integrate the porous silicon based optical
transducer in biochip devices we have modified standard micromachining processes, such as anodic bonding and photo-patterning,
in order to make them consistent to the utilization of biological probes.
In this work, we have compared the optical characteristic of two different photonic dielectric multilayers based on the porous silicon technology. We designed and realized two models devices: a Bragg mirror and the S<sub>6</sub> Thue-Morse sequence. Both the structures have the same thickness, the same porosity, and even the same number of the layers but differently spatially ordered. We demonstrate that the two arrangements of the layers influence not only the optical features of these interferometric devices but also their sensitivity when used as optical sensors. We have measured the change of the reflectivity spectra of the devices on exposure to several organic compounds. The experimental results demonstrated that the Thue-Morse aperiodic structure is more sensitive than the Bragg device due to a higher filling capability.
Complex micro- and nano-structured materials for photonic applications are designed and fabricated using top technologies. A completely different approach to engineering systems at the sub-micron-scale consists in recognizing the nanostructures and morphologies that nature has optimized during life's history on earth. In fact, biological organisms could exhibit ordered geometries and complex photonic structures which often overcome the products of the best available fabrication technologies. An example is given by diatoms. They are microalgae with a peculiar cell wall made of amorphous hydrated silica valves, reciprocally interconnected in a structure called the frustule. Valve surfaces exhibit specie-specific patterns of regular arrays of chambers, called areolae, developed into the frustule depth. Areolae range in diameter from few hundreds of nanometers up to few microns, and can be circular, polygonal or elongate. The formation of these patterns can be modeled by self-organised phase separation. Despite of the high level of knowledge on the genesis and morphology of diatom frustules, their functions are not completely understood. In this work, we show that the silica skeletons of marine diatoms, characterized by a photonic crystal-like structure, have surprising optical properties, being capable of filtering and focalizing light, as well as exhibiting optical sensing capabilities.
In this work, an integrated optical microsystems for the continuous detection of flammable liquids has been fabricated
and characterized. The proposed system is composed of a the transducer element, which is a vertical silicon/air Bragg
mirror fabricated by silicon electrochemical micromachining, sealed with a cover glass anodically bonded on its top. The
device has been optically characterized in presence of liquid substances of environmental interest, such as ethanol and
isopropanol. The preliminary experimental results are in good agreement with the theoretical calculations and show the
possibility to use the device as an optical sensor based on the change of its reflectivity spectrum.
The interaction between an analyte and a biological recognition system is normally detected in biosensors by the
transducer element which converts the molecular event into a measurable effect, such as an electrical or optical signal.
Porous silicon microstructures have unique optical and morphological properties that can be exploited in biosensing. The
large specific surface area (even greater than 500 m<sup>2</sup>/cm<sup>3</sup>) and the resonant optical response allow detecting the effect of
a change in refractive index of liquid solutions, which interact with the porous matrix, with very high sensitivity.
Moreover, the porous silicon surface can be chemically modified to link the bioprobe which recognize the target
analytes, in order to enhance the selectivity and specificity of the sensor device. The molecular probe we used was
purified by an extremophile organism, <i>Thermococcus litoralis</i>: the protein is very stable in a wide range of temperatures
even if with different behavior respect to the interaction with the ligand.
It is well known by far that biological organisms could exhibit sophisticated optical system, which compete or overcame the top technology products available. The diatoms are microscopic algae enclosed in intricate amorphous silica cells, called frustules. In this work the optical reflectivity data, infrared spectroscopy, scanning electron microscopy and photoluminescence (PL) characterizations are presented for silica shells of <i>Coscinodiscus wailesii</i>, which is a centric diatom characterized from a diameter that varies in the range between 100 and 500 μm. Preliminary results suggest that the <i>Coscinodiscus wailesii</i> can be used as photonic material and sensor transducer.