We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.

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Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

Brain-machine interfaces (BMIs) combine methods, approaches, and concepts derived from neurophysiology, computer science, and engineering in an effort to establish real-time bidirectional links bet...

Brain-Machine Interfaces: From Basic Science to Neuroprostheses and Neurorehabilitation

Neural recording electrode technologies have contributed considerably to neuroscience by enabling the extracellular detection of low-frequency local field potential oscillations and high-frequency action potentials of single units. Nevertheless, several long-standing limitations exist, including low multiplexity, deleterious chronic immune responses and long-term recording instability. Driven by initiatives encouraging the generation of novel neurotechnologies and the maturation of technologies to fabricate high-density electronics, novel electrode technologies are emerging. Here, we provide an overview of recently developed neural recording electrode technologies with high spatial integration, long-term stability and multiple functionalities. We describe how these emergent neurotechnologies can approach the ultimate goal of illuminating chronic brain activity with minimal disruption of the neural environment, thereby providing unprecedented opportunities for neuroscience research in the future.

Novel electrode technologies for neural recordings.

Classical Dynamics of Particles and Systems

The presence and concentration of oxygen in biological systems has a large impact on the behavior and viability of many types of cells, including the differentiation of stem cells or the growth of tumor cells. As a result, the integration of oxygen sensors within cell culture environments presents a powerful tool for quantifying the effects of oxygen concentrations on cell behavior, cell viability, and drug effectiveness. Because microfluidic cell culture environments are a promising alternative to traditional cell culture platforms, there is recent interest in integrating oxygen-sensing mechanisms with microfluidics for cell culture applications. Optical, luminescence-based oxygen sensors, in particular, show great promise in their ability to be integrated with microfluidics and cell culture systems. These sensors can be highly sensitive and do not consume oxygen or generate toxic byproducts in their sensing process. This paper presents a review of previously proposed optical oxygen sensor types, materials and formats most applicable to microfluidic cell culture, and analyzes their suitability for this and other in vitro applications.

Optical oxygen sensors for applications in microfluidic cell culture.

A wireless power management and data telemetry circuit module for high compliance voltage electrical stimulation applications is presented in this paper. The system consists of rectifier, LDOs, DC-DC step-up charge pump and power monitoring circuit for closed loop wireless power management. The system also consists of a clock and data recovery (CDR) circuit and load shift keying (LSK) modulator for bidirectional data telemetry. The system operates at 13.56MHz. The wireless power management block receives AC power through an implantable coil and outputs three DC levels: 1V, 1.8V and 10V. The CDR circuit recovers clock and data from the 13.56MHz RF carrier through the same coil. The power efficiency of the wireless power management system is measured as 42% with 100μA current load connected on each supply output. The forward and backward data rate of the data telemetry achieves 61.5 kbps and 33.3 kbps, respectively. The system is implemented in 0.18μm CMOS process with 24V HV LDMOS option, occupying a core area of 1.8 mm × 1.8 mm.

A wireless power management and data telemetry circuit module for high compliance voltage electrical stimulation applications

A multi-channel biopotential recording analog front-end (AFE) with a fully integrated area-efficient driven-right-leg (DRL) circuit is presented in this paper. The proposed AFE includes 10 channels of low-noise capacitive coupled instrumentation amplifier (CCIA), one shared 10-bit SAR ADC and a fully integrated DRL to enhance the system-level common-mode rejection ratio (CMRR). The proposed DRL circuit senses the common-mode at the CCIA output so that the AFE gain is reused as the DRL loop gain. Therefore, area efficient unit-gain buffer with small averaging capacitors can be used in DRL circuit to reduce the circuit area significantly. The proposed AFE has been implemented in a standard 0.18-μm CMOS process. The DRL circuit achieved more than 85% chip area reduction compared to the state-of-art on-chip DRL circuits and maximum 60 dB enhancement to system-level CMRR. Measurement results show high/low AFE gain of 60 dB/54 dB respectively with 1 μA/channel current consumption under 1.0 V power supply. The measured AFE input-referred noise in 1 Hz − 10k Hz range is 4.2 μVrms and the maximum system-level CMRR is 110 dB.

An Integrated Multi-Channel Biopotential Recording Analog Front-End IC With Area-Efficient Driven-Right-Leg Circuit

Charge balancing is an important task for the stimulators used in chronic electrical stimulation applications. In this paper, a pulse-width-adaptive (PWA) active charge balancing (ACB) circuit with pulse-insertion based residual charge compensation and quantization is proposed to fulfil this task. The proposed circuit dynamically adapts the pulse width (Tc) of counter phase (Φc) over a stimulation pulses train to achieve charge balancing. The adaptation step ΔTc is based on the quantized residual charge (Qres) of the initial stimulation pulse. Pulse insertion technique is used to quantize Qress and perform instant charge balancing after each stimulation pulse. The PWA ACB circuit mainly consists of an auxiliary pulse generator, residual voltage (Vres) monitoring and Qres quantization block, and a digital controller. A successive approximation (SA) algorithm is implemented in the digital controller for fast Tc searching. The proposed circuit is implemented in 0.18μm CMOS process with 24V LDMOS option, occupying a core area of 700μm by 150μm. The functionality and effectiveness of the circuit are verified through bench-top and animal experiments.

A pulse-width-adaptive active charge balancing circuit with pulse-insertion based residual charge compensation and quantization for electrical stimulation applications

Mesoporous materials, such as porous silicon and porous polymer gratings (Bragg structures), offer an attractive platform for the encapsulation of chemical and biological recognition elements. These materials include the advantages of high surface to volume ratio, biocompatibility, functionality with various recognition elements, and the ability to modify the material surface/volume properties and porosity. Two porous structures were used for chemical and biological sensing: porous silicon and porous polymer photonic bandgap structures. Specifically, a new dry etching manufacturing technique employing xenon difluoride (XeF2) based etching was used to produce porous silicon Porous silicon continues to be extensively researched for various optical and electronic devices and applications in chemical and biological sensing are abundant. The dry etching technique to manufacture porous silicon offers a simple and efficient alternative to the traditional wet electrochemical etching using hydrofluoric acid. This new porous silicon material was characterized for its pore size and morphology using top and cross-sectional views from scanning electron microscopy. Its optical properties were determined by angular dependence of reflectance measurements. A new class of holographically ordered porous polymer gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. As an alternative structure and fabrication process, porous polymer gratings that include a volatile solvent as the phase separation fluid was fabricated. Porous silicon and porous polymer materials were used as substrates to encapsulate gaseous oxygen (O2) responsive luminophores in their nanostructured pores. These substrate materials behave as optical interference filters that allow efficient and selective detection of the wavelengths of interest in optical sensors.

Porous silicon and porous polymer substrates for optical chemical sensors

A recording circuit is provided. The recording circuit includes a multiplexing circuit configured to receive a plurality of input signals and to produce a multiplexed output signal including the plurality of input signals, and a plurality of sampling circuits electrically coupled in parallel to each other, each sampling circuit being configured to sample a portion of the multiplexed output signal corresponding to an input signal of the plurality of input signals and the sampling circuits configured to alternately produce an output signal corresponding to the sampled portion.

Lei Yao

Papers

A wireless power management and data telemetry circuit module for high compliance voltage electrical stimulation applications

An Integrated Multi-Channel Biopotential Recording Analog Front-End IC With Area-Efficient Driven-Right-Leg Circuit

A pulse-width-adaptive active charge balancing circuit with pulse-insertion based residual charge compensation and quantization for electrical stimulation applications

Porous silicon and porous polymer substrates for optical chemical sensors

Recording circuit and a method of controlling the same