Antonio Qualtieri

Nonclassical emission from single colloidal nanocrystals in a microcavity: a route towards room temperature single photon sources

Secure quantum communication systems (QCS) based on the transmission of crucial information through single photons are among the most appealing frontiers for telecommunications, though their development is still hindered by the lack of cheap and bright single photon sources (SPSs) operating at room temperature (RT). In this paper, we show the occurrence of photon antibunching at RT from single colloidal CdSe/ZnS nanocrystals (NCs) inserted in a vertical microcavity. Moreover, by using high-resolution lithographic techniques, we conceived a general route for positioning single colloidal quantum dots in the microcavity. The findings and the technique presented here can be considered a first step towards the development of SPS devices operating at RT.

Recent advances on single photon sources based on single colloidal nanocrystals

Single colloidal quantum dots (QDs) are increasingly exploited as triggered sources of single photons. This review reports on recent results on single photon sources (SPS) based on colloidal quantum dots, whose size, shape and optical properties can be finely tuned by wet chemistry approach. First, we address the optical properties of different colloidal nanocrystals, such as dots, rods and dot in rods and their use as single photon sources will be discussed. Then, we describe different techniques for isolation and positioning single QDs, a major issue for fabrication of single photon sources, and various approaches for the embedding single nanocrystals inside microcavities. The insertion of single colloidal QDs in quantum confined optical systems allows one to improve their overall optical properties and performances in terms of efficiency, directionality, life time, and polarization control. Finally, electrical pumping of colloidal nanocrystals light emitting devices and of NC-based single photon sources is reviewed.

FILOSE for Svenning: A Flow Sensing Bioinspired Robot

The trend of biomimetic underwater robots has emerged as a search for an alternative to traditional propeller-driven underwater vehicles. The drive of this trend, as in any other areas of bioinspired and biomimetic robotics, is the belief that exploiting solutions that evolution has already optimized leads to more advanced technologies and devices. In underwater robotics, bioinspired design is expected to offer more energy-efficient, highly maneuverable, agile, robust, and stable underwater robots. The 30,000 fish species have inspired roboticists to mimic tuna [1], rays [2], boxfish [3], eels [4], and others. The development of the first commercialized fish robot Ghostswimmer by Boston Engineering and the development of fish robots for field trials with specific applications in mind (http://www.roboshoal. com) mark a new degree of maturity of this engineering discipline after decades of laboratory trials.

Spectral tagging by integrated photonic crystal resonators for highly sensitive and parallel detection in biochips

We propose a technological approach aimed at improving biochips performances, based on an efficient spectral modeling and enhancement of markers fluorescence through the insertion of photonic crystal nanocavities (PhC-NCs) in the readout area of biochips. This strategy univocally associates a specific emission wavelength to a specific bioprobe immobilized on a nanocavity, therefore guaranteeing parallel detection of multiple elements and faster analysis time. Moreover, PhC-NCs significantly enhance the markers fluorescence, thus improving the detection sensitivity.

High-Purcell-factor dipolelike modes at visible wavelengths in H1 photonic crystal cavity

The optimization of H1 photonic crystal cavities for applications in the visible spectral range is reported, with the goal to obtain a versatile photonic platform to explore strongly and weakly coupled systems. The resonators have been realized in silicon nitride and weakly coupled to both organic (fluorophores) and inorganic (colloidal nanocrystals) nanoparticles emitting in the visible spectral range. The theoretical Purcell factor of the two dipolelike modes in the defect has been increased up to approximately 90, and the experimental quality factor was measured to be approximately 750.

Two-Photon Polymerization Lithography and Laser Doppler Vibrometry of a SU-8-Based Suspended Microchannel Resonator

We present the optical realization and characterization of complex suspended microchannel resonator (SMR) for biomechanical sensing applications. We exploit the flexibility of two-photon direct laser writing to optimize a highly versatile fabrication strategy based on a shell-writing procedure with the aim to reduce fabrication time of big inlet/outlet sections compatible with most microfluidic systems for lab-on-chip. Compared with standard microfabrication techniques, requiring several technological steps to obtain suspended hollow structures, this method allows to fabricate complex SMR sensors in only one fabrication step by virtue of its intrinsically 3-D nature. The realized resonant structure was characterized by laser doppler vibrometry, showing good agreement with finite-element methods simulations and an experimental quality factor of the fundamental mode of ~60.

Parylene conformal coating encapsulation as a method for advanced tuning of mechanical properties of an artificial hair cell

A soft Parylene conformal coating encapsulation is demonstrated to be an efficient method to control the mechanical and sensory properties of a bioinspired artificial hair cell, tuning the mechanoreceptive responsivity from a sub-linear to a super-linear behaviour such as hair cells adapt to a natural environment.

A bio-inspired real-time capable artificial lateral line system for freestream flow measurements

To enhance todays artificial flow sensing capabilities in aerial and underwater robotics, future robots could be equipped with a large number of miniaturized sensors distributed over the surface to provide high resolution measurement of the surrounding fluid flow. In this work we show a linear array of closely separated bio-inspired micro-electro-mechanical flow sensors whose sensing mechanism is based on a piezoresistive strain-gauge along a stress-driven cantilever beam, mimicking the biological superficial neuromasts found in the lateral line organ of fishes. Aiming to improve state-of-the-art flow sensing capability in autonomously flying and swimming robots, our artificial lateral line system was designed and developed to feature multi-parameter freestream flow measurements which provide information about (1) local flow velocities as measured by the signal amplitudes from the individual cantilevers as well as (2) propagation velocity, (3) linear forward/backward direction along the cantilever beam orientation and (4) periodicity of pulses or pulse trains determined by cross-correlating sensor signals. A real-time capable cross-correlation procedure was developed which makes it possible to extract freestream flow direction and velocity information from flow fluctuations. The computed flow velocities deviate from a commercial system by 0.09 m s(-1) at 0.5 m s(-1) and 0.15 m s(-1) at 1.0 m s(-1) flow velocity for a sampling rate of 240 Hz and a sensor distance of 38 mm. Although experiments were performed in air, the presented flow sensing system can be applied to underwater vehicles as well, once the sensors are embedded in a waterproof micro-electro-mechanical systems package.

Label-Free

Immunosensors are devices that exploit immobilized antibodies to promote the binding of specific analytes related to diseases of medical importance, such as cancer or cardiac dysfunctions. Label-free immunosensors have an important role, due to their simplicity and fast read-out. Here, the proof of concept for an immunosensor based on a 2-D photonic crystal silicon nitride membrane is presented. The device has been fabricated by means of a well-tuned nanofabrication protocol, achieving a high-quality photonic pattern on a large-area membrane (1 mm × 1 mm), and it has been tested for the detection of interleukin-6, getting protein detection at pg/mL concentrations.

\hbox{Si}_{3}\hbox{N}_{4}

Parylene C is a polymer well-known for its inertness and chemical resistance, thus ideal for covering and sealing 3D substrates and structures by conformal coating. In the present study, the Parylene C surface is modified by functionalization with pH-responsive poly(methacrylic acid) microgels either over the whole surface, or in a pattern through a poly(dimethylsiloxane) stamp. The surface functionalization consists of two phases: first, an oxygen plasma treatment is used to make the surface superhydrophilic, inducing the formation of polar functional groups and surface topography modifications; then, the plasma-treated samples are functionalized by drop casting a solution of pH-responsive microgels, or in a pattern via microcontact printing of the same solution. While both techniques, namely, drop casting and microcontact printing, are easy to use, fast, and cheap, the microcontact printing was found to provide a more homogeneous functionalization and to be applicable to any shape of substrate. The functionalization effectiveness was tested by the repeated uptake and release of a fluorescent labeled monoclonal CD4 antibody at different pH values, thus suggesting a new sensing approach.