A General Purpose Lock-In Amplifier Enabling Sub-ppm Resolution

A novel architecture for digital lock-in amplifiers (LIAs) able to overcome the resolution limit of standards implementations is proposed. The slow gain fluctuations of both the DAC and ADC of the generation and acquisition stages of the LIA are compensated using two ADCs alternately acquiring the signal coming from the device under test (DUT) and the stimulus (STIM) signal. Experimental results demonstrate a resolution enhancement of more than an order of magnitude with respect to state of art LIAs, enabling sub-ppm resolution measurements with an instrument working up to 5 MHz without imposing any constraint to the DUT or to the experimental setup

An open-source high-frequency lock-in amplifier

We present characterization of a lock-in amplifier based on a field programmable gate array capable of demodulation at up to 50 MHz. The system exhibits 90 nV/sqrt(Hz) of input noise at an optimum demodulation frequency of 500 kHz.The passband has a full-width half-maximum of 2.6 kHz for modulation frequencies above 100 kHz. Our code is opensource and operates on a commercially available platform

Integrated platform for detecting pathogenic DNA via magnetic tunneling junction-based biosensors

In recent years, the development of portable platforms for performing fast and point-of-care analyses has drawn considerable attention for their wide variety of applications in life science. In this framework, tools combining magnetoresistive biosensors with magnetic markers have been widely studied in order to detect concentrations of specific molecules, demonstrating high sensitivity and ease of integration with conventional electronics. In this work, first, we develop a protocol for efficient hybridization of natural DNA; then, we show the detection of hybridization events involving natural DNA, namely genomic DNA extracted from the pathogenic bacterium Listeria monocytogenes, via a compact magnetic tunneling junction (MTJ)-based biosensing apparatus. The platform comprises dedicated portable electronic and microfluidic setups, enabling point-of-care biological assays. A sensitivity below the nM range is demonstrated. This work constitutes a step forward towards the development of portable lab-on-chip platforms, for the multiplexed detection of pathogenic health threats in food and food processing environment

Advances in High-Resolution Microscale Impedance Sensors

Sensors based on impedance transduction have been well consolidated in the industry for decades. Today, the downscaling of the size of sensing elements to micrometric and submicrometric dimensions is enabled by the diffusion of lithographic processes and fostered by the convergence of complementary disciplines such as microelectronics, photonics, biology, electrochemistry, and material science, all focusing on energy and information manipulation at the micro- and nanoscale. Although such a miniaturization trend is pivotal in supporting the pervasiveness of sensors (in the context of mass deployment paradigms such as smart city, home and body monitoring networks, and Internet of Things), it also presents new challenges for the detection electronics, reaching the zeptoFarad domain. In this tutorial review, a selection of examples is illustrated with the purpose of distilling key indications and guidelines for the design of high-resolution impedance readout circuits and sensors. The applications span from biological cells to inertial and ultrasonic MEMS sensors, environmental monitoring, and integrated photonics

Spin decoherence in nanodiamond and digital signal processing for quantum sensing and magnetometry

This thesis presents research into the characteristics necessary for diamond and nanodiamond in the application of optically detected magnetic resonance (ODMR) for sensitive magnetic field detection, magnetocardiography, quantum computing and fundamental physics research and also addresses digital signal processing requirements for some of these applications. Firstly, an open source, high frequency lock-in amplifier is presented, along with characterisation that demonstrates a sensitivity of 90 n V/√Hz and a maximum demodulation frequency of 50 MHz. This device is compared with a commercial alternative, and its suitability for diamond magnetometry in magnetocardiography is discussed. Secondly, confocal fluorescence microscopy measurements of nitrogen vacancy centres in high purity nanodiamond are presented, along with a discussion of the nanoparticles' suitability for fundamental physics experiments. T2 spin-spin decoherence times of up to 120 µs are reported, achieved using the spin echo method, twenty times longer than previous research using high yield nanodiamonds. These experiments were performed on nanodiamonds deposited on a custom designed silicon substrate marked with a simple grid for location enabling the measurement of specific nanodiamonds not only in confocal fluorescence but also under scanning electron microscopy. Finally, progress is made towards optical trapping of these nanodiamonds for the investigation of the macroscopicity of particles in a spatial quantum superposition. Trapping frequencies of 220 kHz using an aspheric lens were achieved, and a three-axis Helmholtz coil was constructed and thermally tested in aid of applying ODMR to trapped nanodiamonds