Standalone operation of an EGOFET for ultra-sensitive detection of HIV

A point-of-care (POC) device to enable de-centralized diagnostics can effectively reduce the time to treatment, especially in case of infectious diseases. However, many of the POC solutions presented so far do not comply with the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment free, and deliverable to users) guidelines that are needed to ensure their on-field deployment. Herein, we present the proof of concept of a self-powered platform that operates using the analysed fluid, mimicking a blood sample, for early stage detection of HIV-1 infection. The platform contains a smart interfacing circuit to operate an ultra-sensitive electrolyte-gated field-effect transistor (EGOFET) as a sensor and facilitates an easy and affordable readout mechanism. The sensor transduces the bio-recognition event taking place at the gate electrode functionalized with the antibody against the HIV-1 p24 capsid protein, while it is powered via paper-based biofuel cell (BFC) that extracts the energy from the analysed sample itself. The self-powered platform is demonstrated to achieve detection of HIV-1 p24 antigens in fM range, suitable for early diagnosis. From these developments, a cost-effective digital POC device able to detect the transition from "healthy" to "infected" state at single-molecule precision, with no dependency on external power sources while using minimal components and simpler approach, is foreseen.

UV crosslinked poly(acrylic acid): a simple method to bio-functionalize electrolyte-gated OFET biosensors

A sensitive EGOFET biosensor fabricated by anchoring bioprobes through a UV crosslinked poly(acrylic acid) coating deposited on an organic semiconductor.

Widely-tunable mid-infrared fiber-coupled quartz-enhanced photoacoustic sensor for environmental monitoring

A compact widely-tunable fiber-coupled sensor for trace gas detection of hydrogen sulfide (H₂S) in the mid infrared is reported. The sensor is based on an external-cavity quantum cascade laser (EC-QCL) tunable between 7.6 and 8.3 μm wavelengths coupled into a single-mode hollow-core waveguide. Quartz-enhanced photoacoustic spectroscopy has been selected as detecting technique. The fiber coupling system converts the astigmatic beam exiting the laser into a TEM(00) mode. During a full laser scan, we observed no misalignment between the optical beam and the tuning fork, thus making our system applicable for multi-gas or broad absorber detections. The sensor has been tested on N₂:H₂S gas mixtures. The minimum detectable H₂S concentration is 450 ppb in ~3 s integration time, which is the best value till now reported in literature for H₂S optical sensors.

QCL-based nonlinear sensing of independent targets dynamics

We demonstrate a common-path interferometer to measure the independent displacement of multiple targets through nonlinear frequency mixing in a quantum-cascade laser (QCL). The sensing system exploits the unique stability of QCLs under strong optical feedback to access the intrinsic nonlinearity of the active medium. The experimental results using an external dual cavity are in excellent agreement with the numerical simulations based on the Lang-Kobayashi equations.

Intrinsic stability of quantum cascade lasers against optical feedback

We study the time dependence of the optical power emitted by terahertz and mid-IR quantum cascade lasers in presence of optical reinjection and demonstrate unprecedented continuous wave (CW) emission stability for strong feedback. We show that the absence of coherence collapse or other CW instabilities typical of diode lasers is inherently associated with the high value of the photon to carrier lifetime ratio and the negligible linewidth enhancement factor of quantum cascade lasers.

Self-mixing in multi-transverse mode semiconductor lasers: model and potential application to multi-parametric sensing

A general model is proposed for a Vertical Cavity Surface Emitting Laser (VCSEL) with medium aspect ratio whose field profile can be described by a limited set of Gauss-Laguerre modes. The model is adapted to self-mixing schemes by supposing that the output beam is reinjected into the laser cavity by an external target mirror. We show that the self-mixing interferometric signal exhibits features peculiar of the spatial distribution of the emitted field and the target-reflected field and we suggest an applicative scheme that could be exploited for experimental displacement measurements. In particular, regimes of transverse mode-locking are found, where we propose an operational scheme for a sensor that can be used to simultaneously measure independent components of the target displacement like target translations along the optical axis (longitudinal axis) and target rotations in a plane orthogonal to the optical axis (transverse plane).

Laser-self-mixing interferometry in the Gaussian beam approximation: experiments and theory

We analyze the laser-self-mixing process in the Gaussian beam approximation and reformulate the expression of the feedback coefficient C in terms of the effective feedback power coupled back into the laser diode. Our model predicts a twenty-fold increase of the ratio between the maximum and the minimum measurable displacements judged against the current plane-wave model. By comparing the interaction of collimated or diverging Gaussian laser beams with a plane mirror target, we demonstrate that diverging beams tolerate larger wobbling during the target displacement and allow for measurement of off-axis target rotations up to the beam angular width. A novel method for reconstructing the phase front of the Gaussian beam by self-mixing scanning measurements is also presented.

Quantum cascade laser-based photoacoustic spectroscopy of volatile chemicals: application to hexamethyldisilazane

The use of photoacoustic spectroscopy and mid-infrared quantum-cascade lasers (QCLs) for the detection of hexamethyldisilazane (HMDS) is reported. A detection limit of 200 parts in 10(9) is found using a Fabry-Perot QCL operated at 8.4 microm in pulsed mode and a photoacoustic cell equipped with four electret microphones. The laser multimode spectrum matches the range of the N-H bending absorption band of HMDS. Further improvements to reach lower detection limits are discussed.

Synthesis and characterization of poly(2,3,5,6-tetrafluoro-1,4-phenylenevinylene)

Poly(2,3,5,6-tetrafluoro-1,4-phenylenevinylene) (PTFPV) was prepared for the first time by the Stille cross-coupling reaction and the resulting material was characterized through MALDI-TOF mass spectrometry, employing a novel sample preparation protocol suitable for insoluble compounds; preliminary optical and electrooptical measurements were performed.

High-Power Infrared (8-Micrometer Wavelength) Superlattice Lasers

A quantum-cascade long-wavelength infrared laser based on superlattice active regions has been demonstrated. In this source, electrons injected by tunneling emit photons corresponding to the energy gap (minigap) between two superlattice conduction bands (minibands). A distinctive design feature is the high oscillator strength of the optical transition. Pulsed operation at a wavelength of about 8 micrometers with peak powers ranging from approximately 0.80 watt at 80 kelvin to 0.2 watt at 200 kelvin has been demonstrated in a superlattice with 1-nanometer-thick AlInAs barriers and 4.3-nanometer-thick GaInAs quantum wells grown by molecular beam epitaxy. These results demonstrate the potential of strongly coupled superlattices as infrared laser materials for high-power sources in which the wavelength can be tailored by design.