High specificity THz metamaterial-based biosensor for label-free transcription factor detection in melanoma diagnostics.

In this work, we present a promising diagnostic tool for melanoma diagnosis. With the proposed terahertz biosensor, it was possible to selectively and sensitively detect the early growth response protein 2, a transcription factor with an increased activity in melanoma cells, from a complex sample of cellular proteins. Fundamentally, the sensor belongs to the frequency selective surface type metamaterials and consists of a two-dimensional array of asymmetrically, doubly split ring resonator unit cells. The single elements are slits in a metallic layer and are complemented by an undercut etch. This allows a selective functionalization of the active area of the sensor and increases the sensitivity towards the target analyte. Hereby, specific detection of a defined transcription factor is feasible.

Graphene-Based Optoelectronic Mixer Device for Time-of-Flight Distance Measurements for Enhanced 3D Imaging Applications.

A large and growing number of applications benefit from innovative and powerful 3D image sensors. Graphene photodetectors can achieve 3D sensing functionalities by intrinsic optoelectronic frequency mixing due to the nonlinear output characteristics of the sensor. In first proof of principle distance measurement demonstrations, we achieve modulation frequencies of 3.1 MHz, signal-to-noise ratios of ∼40 dB, distance detection up to at least 1 m, and a mean accuracy of 25.6 mm. The scalable More than Moore detector approach enables geometrical fill factors close to 100% and can easily complement powerful functionalities by simple back-end integration on top of CMOS electronics.

Imaging the Terahertz Nanoscale Conductivity of Polycrystalline CsPbBr3 Perovskite Thin Films.

Terahertz (THz) radiation is a valuable tool to investigate the electronic properties of lead halide perovskites (LHPs). However, attaining high-resolution information remains elusive, as the diffraction-limited spatial resolution (∼300 µm) of conventional THz methods prevents a direct analysis of microscopic effects. Here, we employ THz scattering scanning near-field optical microscopy (THz-sSNOM) for nanoscale imaging of cesium lead bromide (CsPbBr3) thin films down to the single grain level at 600 GHz. Adopting a scattering model, we are able to derive the local THz nanoscale conductivity in a contact-free fashion. Increased THz near-field signals at CsPbBr3 grain boundaries complemented by correlative transmission electron microscopy-energy-dispersive X-ray spectroscopy elemental analysis point to the formation of halide vacancies (VBr) and Pb-Pb bonds, which induce charge carrier trapping and can lead to nonradiative recombination. Our study establishes THz-sSNOM as a powerful THz nanoscale analysis platform for thin-film semiconductors such as LHPs.

High-speed nonlinear focus-induced photoresponse in amorphous silicon photodetectors for ultrasensitive 3D imaging applications.

A large and growing number of applications benefit from simple, fast and highly sensitive 3D imaging sensors. The Focus-Induced Photoresponse (FIP) can achieve 3D sensing functionalities by simply evaluating the irradiance dependent nonlinear sensor response in defect-based materials. Since this advantage is intricately associated to a slow response, the electrical bandwidth of present FIP detectors is limited to a few [Formula: see text] only. The devices presented in this work enable modulation frequencies of 700 kHz and beat frequency detection up to at least 3.8 MHz, surpassing the bandwidth of reported device architectures by more than two orders of magnitude. The sensors achieve a SNR of at least [Formula: see text] at [Formula: see text] and a DC FIP detection limit of 0.6 µW/mm2. The mature and scalable low-temperature a-Si:H process technology allows operating the device under ambient air conditions waiving additional back-end passivation, geometrical fill factors of [Formula: see text] and tailoring the FIP towards adjustable 3D sensing applications.

Correlation of electrical and structural properties of single as-grown GaAs nanowires on Si (111) substrates.

We present the results of the study of the correlation between the electrical and structural properties of individual GaAs nanowires measured in their as-grown geometry. The resistance and the effective charge carrier mobility were extracted for several nanowires, and subsequently, the same nano-objects were investigated using X-ray nanodiffraction. This revealed a number of perfectly stacked zincblende and twinned zincblende units separated by axial interfaces. Our results suggest a correlation between the electrical parameters and the number of intrinsic interfaces.

Long-range guided THz radiation by thin layers of water.

We propose a novel method to guide THz radiation with low losses along thin layers of water. This approach is based on the coupling of evanescent surface fields at the opposite sides of the thin water layer surrounded by a dielectric material, which leads to a maximum field amplitude at the interfaces and a reduction of the energy density inside the water film. In spite of the strong absorption of water in this frequency range, calculations show that the field distribution can lead to propagation lengths of several centimeters. By means of attenuated total reflection measurements we demonstrate the coupling of incident THz radiation to the long-range surface guided modes across a layer of water with a thickness of 24 µm. This first demonstration paves the way for THz sensing in aqueous environments.

Design of an LED-based sensor system to distinguish human skin from workpieces in safety applications.

Commercial light curtains use a technique known as muting to differentiate between work pieces and other objects (e.g., human limbs) based on precise model knowledge of the process. At manually fed machinery (e.g., bench saws), such precise models cannot be derived due to the way the machinery is used. This paper presents a multispectral scanning sensor to classify an object's surface material as a new approach for the problem. The system is meant to detect the presence of limbs and therefore optimized for human skin detection. Evaluation on a test set of skin and (wet) wood samples showed a sufficiently high reliability with respect to safety standards.

High signal-to-noise-ratio electro-optical terahertz imaging system based on an optical demodulating detector array.

We present a 64x48 pixel 2D electro-optical terahertz (THz) imaging system using a photonic mixing device time-of-flight camera as an optical demodulating detector array. The combination of electro-optic detection with a time-of-flight camera increases sensitivity drastically, enabling the use of a nonamplified laser source for high-resolution real-time THz electro-optic imaging.

Ultrahigh-quality-factor silicon-on-insulator microring resonator.

The development of ultrahigh-quality-factor (Q) silicon-on-insulator (SOI) microring resonators based on silicon wire waveguides is presented. An analytical description is derived, illustrating that in addition to low propagation losses the critical coupling condition is essential for optimizing device characteristics. Propagation losses as low as 1.9 +/- 0.1 dB/cm in a curved waveguide with a bending radius of 20 microm and a Q factor as high as 139.000 +/- 6.000 are demonstrated. These are believed to be the highest values reported for a curved SOI waveguide device and for any directly structured semiconductor microring fabricated without additional melting-induced surface smoothing.

Integrated planar terahertz resonators for femtomolar sensitivity label-free detection of DNA hybridization.

A promising label-free approach for the analysis of genetic material by means of detecting the hybridization of polynucleotides with electromagnetic waves at terahertz (THz) frequencies is presented. Using an integrated waveguide approach, incorporating resonant THz structures as sample carriers and transducers for the analysis of the DNA molecules, we achieve a sensitivity down to femtomolar levels. The approach is demonstrated with time-domain ultrafast techniques based on femtosecond laser pulses for generating and electro-optically detecting broadband THz signals, although the principle can certainly be transferred to other THz technologies.