Graphene displays properties that make it appealing for neuroregenerative medicine, yet its interaction with peripheral neurons has been scarcely investigated. Here, we culture on graphene two established models for peripheral neurons: PC12 cells and DRG primary neurons. We perform a nano-resolved analysis of polymeric coatings on graphene and combine optical microscopy and viability assays to assess the material cytocompatibility and influence on differentiation. We find that differentiated PC12 cells display a remarkably increased neurite length on graphene (up to 27%) with respect to controls. Notably, DRG primary neurons survive both on bare and coated graphene. They present dense axonal networks on coated graphene, while they form cell islets characterized by dense axonal bundles on uncoated graphene. These findings indicate that graphene holds potential for nerve tissue regeneration and might pave the road to novel concepts of active nerve conduits.

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Peripheral Neuron Survival and Outgrowth on Graphene

The pinned photodiode is the primary photodetector structure used in most CCD and CMOS image sensors. This paper reviews the development, physics, and technology of the pinned photodiode.

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A Review of the Pinned Photodiode for CCD and CMOS Image Sensors

This paper investigates terahertz detectors fabricated in a low-cost 130 nm silicon CMOS technology. We show that the detectors consisting of a nMOS field effect transistor as rectifying element and an integrated bow-tie coupling antenna achieve a record responsivity above 5 kV/W and a noise equivalent power below 10 pW/Hz(0.5) in the important atmospheric window around 300 GHz and at room temperature. We demonstrate furthermore that the same detectors are efficient for imaging in a very wide frequency range from ~0.27 THz up to 1.05 THz. These results pave the way towards high sensitivity focal plane arrays in silicon for terahertz imaging.

Broadband terahertz imaging with highly sensitive silicon CMOS detectors

Single-photon avalanche diode (SPAD) arrays are solid-state detectors that offer imaging capabilities at the level of individual photons, with unparalleled photon counting and time-resolved performance. This fascinating technology has progressed at a very fast pace in the past 15 years, since its inception in standard CMOS technology in 2003. A host of architectures have been investigated, ranging from simpler implementations, based solely on off-chip data processing, to progressively "smarter" sensors including on-chip, or even pixel level, time-stamping and processing capabilities. As the technology has matured, a range of biophotonics applications have been explored, including (endoscopic) FLIM, (multibeam multiphoton) FLIM-FRET, SPIM-FCS, super-resolution microscopy, time-resolved Raman spectroscopy, NIROT and PET. We will review some representative sensors and their corresponding applications, including the most relevant challenges faced by chip designers and end-users. Finally, we will provide an outlook on the future of this fascinating technology.

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Single-photon avalanche diode imagers in biophotonics: review and outlook

We introduce a 512 × 424 time-of-flight (TOF) depth image sensor designed in a TSMC 0.13 μm LP 1P5M CMOS process, suitable for use in Microsoft Kinect for XBOX ONE. The 10 μm × 10 μm pixel incorporates a TOF detector that operates using the quantum efficiency modulation (QEM) technique at high modulation frequencies of up to 130 MHz, achieves a modulation contrast of 67% at 50 MHz and a responsivity of 0.14 A/W at 860 nm. The TOF sensor includes a 2 GS/s 10 bit signal path, which is used for the high ADC bandwidth requirements of the system that requires many ADC conversions per frame. The chip also comprises a clock generation circuit featuring a programmable phase and frequency clock generator with 312.5-ps phase step resolution derived from a 1.6 GHz oscillator. An integrated shutter engine and a programmable digital micro-sequencer allows an extremely flexible multi-gain/multi-shutter and multi-frequency/multi-phase operation. All chip data is transferred using two 4-lane MIPI D-PHY interfaces with a total of 8 Gb/s input/output bandwidth. The reported experimental results demonstrate a wide depth range of operation (0.8–4.2 m), small accuracy error ( $ 1%), very low depth uncertainty ( $ 0.5% of actual distance), and very high dynamic range ( $>$ 64 dB).

A 0.13 μm CMOS System-on-Chip for a 512 × 424 Time-of-Flight Image Sensor With Multi-Frequency Photo-Demodulation up to 130 MHz and 2 GS/s ADC

A new architecture for PET photodetectors based on small-area SiPMs (mini-SiPMs) with individual SPAD digitization and in-pixel data compression is presented The main goal of this architecture is to reduce the electronics area occupation per SPAD and thus improve the fill factor Two compression schemes are described, spatial and temporal compression, and a combination of both is implemented in the pixel Our first chip using this architecture is described, where each pixel contains a mini-SiPM with 32 SPADs, a 4-bit digital counter and individual SPAD SRAMs for disabling high DCR devices The sensor contains a 14 × 10 pixel array for a total of 4480 SPADs, and the achieved fill factor is about 29% The sensor also contains column-level TDCs, which acquire the time of arrival of the first photon in each column The expected compression response of this sensor is presented

A CMOS mini-SiPM detector with in-pixel data compression for PET applications

We present a Montecarlo simulator developed in Matlab® for the analysis of a Single Photon Avalanche Diode (SPAD)-based Complementary Metal-Oxide Semiconductor (CMOS) flash Light Detection and Ranging (LIDAR) system. The simulation environment has been developed to accurately model the components of a flash LIDAR system, such as illumination source, optics, and the architecture of the designated SPAD-based CMOS image sensor. Together with the modeling of the background noise and target topology, all of the fundamental factors that are involved in a typical LIDAR acquisition system have been included in order to predict the achievable system performance and verified with an existing sensor.

https://www.mdpi.com/1424-8220/20/18/5203/pdf

Numerical Model of SPAD-Based Direct Time-of-Flight Flash LIDAR CMOS Image Sensors.

Recent technology surveys identified flash light detection and ranging technology as the best choice for the navigation and landing of spacecrafts in extraplanetary missions, working from single-point altimeter to range-imaging camera mode. Among all available technologies for a 2D array of direct time-of-flight (DTOF) pixels, CMOS single-photon avalanche diodes (SPADs) represent the ideal candidate due to their rugged design and electronics integration. However, state-of-the-art SPAD imagers are not designed for operation over a wide variety of scenarios, including variable background light, very long to short range, or fast relative movement.

6.5 A 64×64-pixel digital silicon photomultiplier direct ToF sensor with 100Mphotons/s/pixel background rejection and imaging/altimeter mode with 0.14% precision up to 6km for spacecraft navigation and landing

We report on room temperature THz detection by means of antenna-coupled field effect transistors fabricated by using epitaxial graphene grown on silicon carbide substrate. Two independent detection mechanisms are found: plasma wave assisted-detection and thermoelectric effect, which is ascribed to the presence of junctions along the FET channel. The superposition of the calculated functional dependence of both the plasmonic and thermoelectric photovoltages on the gate bias qualitatively well reproduces the measured photovoltages. Additionally, the sign reversal of the measured photovoltage demonstrates the stronger contribution of the plasmonic detection compared to the thermoelectric mechanism. Although responsivity improvement is necessary, these results demonstrate that plasmonic detectors fabricated by epitaxial graphene on silicon carbide are potential candidates for fast large area imaging of macroscopic samples.

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THz detection with epitaxial graphene field effect transistors on silicon carbide

The Abbe–Rayleigh diffraction limit constrains spatial resolution for classical imaging methods. Quantum imaging exploits correlations between photons to reproduce structures with higher resolution. Quantum-correlated N-photon states were shown to potentially surpass the classical limit by a factor of 1/N, corresponding to the Heisenberg limit, using a method known as optical centroid measurement (OCM). In this work, the theory of OCM is reformulated for its application in imaging. Using entangled photon pairs and a recently developed integrated time-resolving detector array, OCM is implemented in a proof-of-principle experiment that demonstrates the expected enhancement. Those results show the relevance of entanglement for imaging at the Heisenberg limit.

Matteo Perenzoni

Papers

A CMOS mini-SiPM detector with in-pixel data compression for PET applications

Numerical Model of SPAD-Based Direct Time-of-Flight Flash LIDAR CMOS Image Sensors.

6.5 A 64×64-pixel digital silicon photomultiplier direct ToF sensor with 100Mphotons/s/pixel background rejection and imaging/altimeter mode with 0.14% precision up to 6km for spacecraft navigation and landing

THz detection with epitaxial graphene field effect transistors on silicon carbide

Super-resolution quantum imaging at the Heisenberg limit