Federico Mecarini

Bacterial ratchet motors

Self-propelling bacteria are a nanotechnology dream. These unicellular organisms are not just capable of living and reproducing, but they can swim very efficiently, sense the environment, and look for food, all packaged in a body measuring a few microns. Before such perfect machines can be artificially assembled, researchers are beginning to explore new ways to harness bacteria as propelling units for microdevices. Proposed strategies require the careful task of aligning and binding bacterial cells on synthetic surfaces in order to have them work cooperatively. Here we show that asymmetric environments can produce a spontaneous and unidirectional rotation of nanofabricated objects immersed in an active bacterial bath. The propulsion mechanism is provided by the self-assembly of motile Escherichia coli cells along the rotor boundaries. Our results highlight the technological implications of active matter’s ability to overcome the restrictions imposed by the second law of thermodynamics on equilibrium passive fluids.

Nano-patterned SERS substrate: application for protein analysis vs. temperature.

We have illustrated the fabrication of nano-structures as a surface enhanced Raman scattering (SERS) substrate using electro-plating and electron-beam lithography techniques to obtain an array of gold nanograin-aggregate structures of diameter ranging between 80 and 100 nm with interstitial gap of 10-30 nm. The nanostructure based SERS substrate permits us to have better control and reproducibility on generation of plasmon polaritons. The calculation shows the possible detection of myoglobin concentration down to attomole. This SERS substrate is used to investigate the structural changes of different proteins; lysozyme, ribonuclease-B, bovin serum albumin and myoglobin in the temperature range between -65 and 90 degrees C. The in-depth analysis even for small conformational changes is performed using 2D Raman correlation analysis and difference Raman analysis in order to gain straightforward understanding of proteins undergoing thermodynamical perturbation.

Superhydrophobic Surfaces as Smart Platforms for the Analysis of Diluted Biological Solutions

The aim of this paper is to expound on the rational design, fabrication and development of superhydrophobic surfaces (SHSs) for the manipulation and analysis of diluted biological solutions. SHSs typically feature a periodic array or pattern of micropillars; here, those pillars were modified to incorporate on the head, at the smallest scales, silver nanoparticles aggregates. These metal nanoclusters guarantee superior optical properties and especially SERS (surface enhanced Raman scattering) effects, whereby a molecule, adsorbed on the surface, would reveal an increased spectroscopy signal. On account of their two scale-hybrid nature, these systems are capable of multiple functions which are (i) to concentrate a solution, (ii) to vehicle the analytes of interest to the active areas of the substrate and, therefore, (iii) to measure the analytes with exceptional sensitivity and very low detection limits. Forasmuch, combining different technologies, these devices would augment the performance of conventional SERS substrates and would offer the possibility of revealing a single molecule. In this work, similar SHSs were used to detect Rhodamine molecules in the fairly low atto molar range. The major application of this novel family of devices would be the early detection of tumors or other important pathologies, with incredible advances in medicine.

In Situ X-ray Scattering Studies of Protein Solution Droplets Drying on Micro- and Nanopatterned Superhydrophobic PMMA Surfaces

Superhydrophobic poly(methyl methacrylate) surfaces with contact angles of ∼170° and high optical and X-ray transparencies have been fabricated through the use of optical lithography and plasma etching. The surfaces contain either a microscale pattern of micropillars or a random nanofibrillar pattern. Nanoscale asperities on top of the micropillars closely resemble Nelumbo nucifera lotus leaves. The evolution of the contact angle of water and lysozyme solution droplets during evaporation was studied on the micro- and nanopatterned surfaces, showing in particular contact-line pinning for the protein solution droplet on the nanopatterned surface. The microstructural evolution of lysozyme solution droplets was studied on both types of surfaces in situ under nearly contact-free conditions by synchrotron radiation microbeam wide-angle and small-angle X-ray scattering revealing the increasing protein concentration and the onset of precipitation. The solid residuals show hollow sphere morphologies. Rastermicrodiffraction of the detached residuals suggests about a 1/3 volume fraction of ≥17 nm lysozyme nanocrystalline domains and about a 2/3 short-range-order volume fraction. About 5-fold larger nanocrystalline domains were observed at the attachment points of the sphere to the substrates, which is attributed to particle growth in a shear flow. Such surfaces represent nearly contact-free sample supports for studies of inorganic and organic solution droplets, which find applications in biochips.

Water soluble nanoporous nanoparticle for in vivo targeted drug delivery and controlled release in B cells tumor context.

Multitasking nanoparticles are gaining great attention for smart drug delivery systems. The exploration of the nano-scale opens new concrete opportunities for revealing new properties and undiscovered cell-particle interactions. Here we present a biodegradable nanoporous silicon nanoparticle that can be successfully employed for in vivo targeted drug delivery and sustained release. The bare nanoporous nanocarriers can be accurately designed and fabricated with an effective control of porosity, surface chemistry and particle size, up to a few nm. The proposed nanoparticles exhibit several remarkable features including high payload, biodegradability, no toxicity, and multiple loading in water without the need of additional chemical reagents at room temperature. The targeting strategy is based on phage display technology that was successfully used to discover cell surface binding peptide for murine B lymphoma A20 cell line. The peptide used in combination with the nanoporous nanoparticles allows an efficient in vivo targeting, a sustained release and a sensible therapeutic effect.

Novel plasmonic nanodevices for few/single molecule detection

This paper reports the fabrication of two reproducible surface enhanced Raman scattering devices using; a) nanoPillar coupled with PC cavity by means of FIB milling and electron beam induced deposition techniques (Device 1), and b) plasmonic gold nanoaggregate structures using electro-plating and e-beam lithography techniques (Device 2). Device 1 consists of photonic crystal cavity as an optical source to couple the incident laser with a metallic tapered nanolens. Exploiting such approach it is possible to overcome the difficulties related to scattering and diffraction phenomena when visible laser (514 nm) illuminates nanostructures. The nanostructure is covered with HMDS and is selectively removed leaving HMDS polymer on nanoPillar only. A clear Raman scattering enhancement has been demonstrated for label-free detection of molecule in sub-wavelength regime. On the other hand, myoglobin protein is deposited on Device 2 using drop coating deposition method and is estimated that the substrate is able to detect the myoglobin concentration down to attomole.

Photonic Crystals for Plasmonics: From Fundamentals to Superhydrophobic Devices

In the last couple of decades we have been witnessing an enormous technological advancement in the field of micro-technology to the extent that nowadays we talk about nanotechnology. Faster computers, LCD based mobiles, nanoparticles for UV absorption in suntan lotions are just few of many examples where nanotechnology plays a fundamental role. The merit of this is mainly in the advance of the fabrication methods. Present techniques such as Focused Ion Beam (FIB) lithography guarantee a resolution of less than 10 nanometers which is about five times more precise than ten years before. Also Photonic Crystals (PhCs), among the others, take advantage from this extremely high resolution level allowing a downscale that permits the realization of structures which in principle can work at vey high energy. Historically PhCs were known as Bragg mirrors and only in 1987 (Yablonovitch, 1987; Sajeev, 1987) with the works of Yablonovitch and Sajeev the term Photonic Crystals was introduced. Nowadays, besides their natural application as filters in particular under full band gap conditions, PhCs see a number of applications: optical fibers (Birks et al., 1997; Zhao et al., 2010), vertical cavity surface emitting lasers (Yokouchi et al., 2003), high reflection coatings, temperature sensors (Song et al., 2006), high efficiency solar cells (Bermel et al., 2007), electric field detectors (Song & Proietti Zaccaria, 2007), non-linear analysis (Malvezzi et al., 2002; Malvezzi et al., 2003), just to name a few. Many are the techniques for the fabrication of PhCs, for example by means of focused-ion beam (Cabrini et al., 2005), two-photon fabrication (Deubel et al., 2004), laser-interference (Proietti Zaccaria et al., 2008a) or waver-fusion techniques (Takahashi et al., 2006). Here we shall focus on the role that PhCs can play for another exciting discipline known as Plasmonics. It refers to the capability of some devices of sustaining an optical surface mode, namely an electromagnetic wave travelling at the interface between two different materials such as a dielectric and a metal. Such a wave originates from the coupling of incident photons on the interface with

Low Concentration Protein Detection Using Novel SERS Devices

We report, herein, novel processes of nanofabrication techniques for few molecules detection by generating surface plasmons, thus giving a giant electric field in a controllable and reproducible manner. Surface enhanced Raman scattering (SERS) measurements are performed for different proteins, namely, lysozyme, ribonuclease-B, bovin serum albumin, ferritin, and myoglobin in the temperature range between –65°C and 90°C, using “Device1”, which is fabricated by means of e-beam and electro-plating technique. The calculation shows the possible detection of myoglobin concentration down to attomole. The in-depth analysis even for small conformational changes is performed using 2D Raman correlation analysis and difference Raman analysis in order to gain straightforward understanding of proteins undergoing thermodynamical perturbation. “Device2” is fabricated by e-beam and metal electroless techniques to investigate the Rhodamine 6G (R6G) of different concentrations. Modifying this device by using bimetal (Ag and Au) electroless deposition permits us the further enhancement in Raman signal and better durability.

Adiabatic focusing of surface plasmon polaritons for label free detection of few molecules by means of Raman scattering

Here we report the design, the fabrication and measurement of a photonic-plasmonic device that is fully compatible with AFM microscopy and surface enhanced Raman spectroscopy. The physical mechanism exploited is the adiabatic compression of Surface Plasmon Polaritons which propagate along a silver nanocone generating a very high electric field at the tip end. A photonic crystal cavity is employed to efficiently couple the external laser radiation with the nanocone. The reported measurements demonstrate the accumulation of the electric field at the tip of the nanocone that allow the detection of a few molecules located near the tip end. The estimated Raman enhancement factor is about 106 with respect to a standard configuration. The present results open a good perspective for the development of an integrated Raman-AFM microscopy able to perform both topography and chemical mapping in label free condition with a spatial resolution comparable to the tip end.

Spectroscopy nanofabrication and biophotonics

This paper reports on the fabrication of reproducible surface enhanced Raman scattering (SERS) device based on nanoPillar coupled with PC cavity by means of FIB milling and electron beam induced deposition techniques (Device 1): In addition to this device, another SERS device using e-beam lithography and electroless metal deposition techniques (Device 2) is fabricated in order to have planar geometry particularly useful for future nanoarray architectures SERS device. Various measurements have been performed for the monolayer of different materials showing extremely promising SERS based device. It is revealed that the Rhodamine6G is clearly evidenced in Raman 2D mapping spectrum, showing a very high enhancement in SERS signal in the order of 1012 (theoretically) with respect to the normal Raman measurements. We estimate the number of Rhodamine6G molecule detected is about 100-150.