Carbon nanotubes (CNTs), are safe, biocompatible, bioactive, and biodegradable materials, and have sparked a lot of attention due to their unique characteristics in a variety of applications, including medical and dye industries, paper manufacturing and water purification. CNTs also have a strong film-forming potential, permitting them to be widely employed in constructing sensors and biosensors. This review concentrates on the application of CNT-based nanocomposites in the production of electrochemical sensors and biosensors. It emphasizes the synthesis and optimization of CNT-based sensors for a range of applications and outlines the benefits of using CNTs for biomolecule immobilization. In addition, the use of molecularly imprinted polymer (MIP)-CNTs in the production of electrochemical sensors is also discussed. The challenges faced by the current CNTs-based sensors, along with some the future perspectives and their future opportunities, are also briefly explained in this paper. Graphical Abstract

This paper presents an overview of the fundamentals and state of the-art in noninvasive physiological monitoring instrumentation with a focus on electrode and optrode interfaces to the body, and micropower-integrated circuit design for unobtrusive wearable applications. Since the electrode/optrode-body interface is a performance limiting factor in noninvasive monitoring systems, practical interface configurations are offered for biopotential acquisition, electrode-tissue impedance measurement, and optical biosignal sensing. A systematic approach to instrumentation amplifier (IA) design using CMOS transistors operating in weak inversion is shown to offer high energy and noise efficiency. Practical methodologies to obviate 1/f noise, counteract electrode offset drift, improve common-mode rejection ratio, and obtain subhertz high-pass cutoff are illustrated with a survey of the state-of-the-art IAs. Furthermore, fundamental principles and state-of-the-art technologies for electrode-tissue impedance measurement, photoplethysmography, functional near-infrared spectroscopy, and signal coding and quantization are reviewed, with additional guidelines for overall power management including wireless transmission. Examples are presented of practical dry-contact and noncontact cardiac, respiratory, muscle and brain monitoring systems, and their clinical applications.

This paper presents a fully integrated resonant regulating rectifier (IR ³ ) with an on-chip coil used to wirelessly power mm-sized implants. By combining rectification and regulation in a single stage, and controlling this stage via a hybrid pulse-width modulation and pulse-frequency modulation (PFM) feedback scheme, the IR ³ avoids efficiency-limiting cascaded losses while enabling tight voltage regulation with low dropout and ripple. The IR ³ is implemented in 0.078 mm ² of active area in 180-nm Silicon oxide insulator (SOI) CMOS, and achieves a 1.87% AV _DD /V _DD power supply regulation ratio with a 1-nF decoupling capacitor despite a tenfold load current variation from 8 to 80 μA. A 0.8-V V _DD is maintained at a 8-kΩ load for 144-MHz RF inputs ranging from 0.98 to 1.5 V. At 1-V regulation, the voltage conversion efficiency is greater than 92% with less than 5.2-mVpp ripple, while the power conversion efficiency is 54%. The measured overall wireless power transfer system efficiency, from the primary coil to VDD output of the IR ³ , is 2% at 160-μW load, and reaches 5% at 700 μW.

We present a telemetry IC with a new data modulation scheme for efficient simultaneous transfer of power and backward data over a single inductive link. Data-driven synchronized single-cycle shorting of the secondary LC tank conserves reactive energy while inducing an instantaneous voltage change on the primary side. Contrary to conventional load shift keying modulation, the recovery time of the secondary LC oscillation after shorting improves asymptotically with increasing quality factor of the secondary LC tank. Since quality factor does not reduce the data rate, the LC tank can be simultaneously optimized for power and data telemetry, obviating the conventional tradeoff between power transfer efficiency and data rate. Cyclic ON-OFF keying time-encoded symbol data mapping of the shorting cycle allows transmission of two data bits per four carrier cycles while supporting simultaneous power delivery during at least six nonshorting out of eight half cycles. All timing control signals for rectification and data transmission are generated from a low-power clock recovery comparator and a phased-locked loop. The 0.92 mm ² 65 nm CMOS IC delivers up to 11.5 mW power to the load and simultaneously transmits 6.78 Mb/s data while dissipating 64 μW power. A bit error rate of ≤9.9 × 10 ^-8 was measured over a single 1 cm 13.56 MHz inductive link at a data rate of 6.78 Mb/s with a 10 mW load power.

Recent demand and initiatives in brain research have driven significant interest toward developing chronically implantable neural interface systems with high spatiotemporal resolution and spatial coverage extending to the whole brain. Electroencephalography-based systems are noninvasive and cost efficient in monitoring neural activity across the brain, but suffer from fundamental limitations in spatiotemporal resolution. On the other hand, neural spike and local field potential (LFP) monitoring with penetrating electrodes offer higher resolution, but are highly invasive and inadequate for long-term use in humans due to unreliability in long-term data recording and risk for infection and inflammation. Alternatively, electrocorticography (ECoG) promises a minimally invasive, chronically implantable neural interface with resolution and spatial coverage capabilities that, with future technology scaling, may meet the needs of recently proposed brain initiatives. In this paper, we discuss the challenges and state-of-the-art technologies that are enabling next-generation fully implantable high-density ECoG interfaces, including details on electrodes, data acquisition front-ends, stimulation drivers, and circuits and antennas for wireless communications and power delivery. Along with state-of-the-art implantable ECoG interface systems, we introduce a modular ECoG system concept based on a fully encapsulated neural interfacing acquisition chip (ENIAC). Multiple ENIACs can be placed across the cortical surface, enabling dense coverage over wide area with high spatiotemporal resolution. The circuit and system level details of ENIAC are presented, along with measurement results.

We present a 65k-neuron integrate-and-fire array transceiver (IFAT) for spike-based neural computation with low-power, high-throughput connectivity. The internally analog, externally digital chip is fabricated on a 4×4 mm ² die in 90 nm CMOS and arranged in 4 quadrants of 16k parallel addressable neurons. Each neuron circuit serves input spike events by dynamically instantiating conductance-based synapses onto four local synapse circuits over two membrane compartments, and produces output spike events upon reaching a threshold in integration over one of the membrane compartments. Fully asynchronous input and output spike event data streams are mediated over the standard address event representation (AER) protocol. To support full event throughput at large synaptic fan-in, a two-tier micro-pipelining scheme parallelizes input events along neural array cores, and along rows of each core. Measured results show sustained peak synaptic event throughput of 18.2 Mevents/s per quadrant, at 22 pJ average energy per synaptic input event and 25 μW standby power.