Federico Thei

Parallel Recording of Single Ion Channels: A Heterogeneous System Approach

The convergence of integrated electronic devices with nanotechnology structures on heterogeneous systems presents promising opportunities for the development of new classes of rapid, sensitive, and reliable sensors. The main advantage of embedding microelectronic readout structures with sensing elements is twofold. On the one hand, the SNR is increased as a result of scaling. On the other, readout miniaturization allows organization of sensors into arrays. The latter point will improve sensing accuracy by using statistical methods. However, accurate interface design is required to establish efficient communication between ionic-based and electronic-based signals. This paper shows a first example of a concurrent readout system with single-ion channel resolution, using a compact and scalable architecture. An array of biological nanosensors is organized on different layers stacked together in a mixed structure: fluidics, printed circuit board, and microelectronic readout. More specifically, an array of microholes machined into a polyoxymethylene homopolymer (POMH or Delrin) device coupled with ultralow noise sigma-delta converters current amplifiers, is used to form bilayer membranes within which ion channels are embedded. It is shown how formation of multiple artificial bilayer lipid membranes (BLMs) is automatically monitored by the interface. The system is used to detect current signals in the pA range, from noncovalent binding between single, BLM-embedded ¿-hemolysin pores and ß-cyclodextrin molecules. The current signals are concurrently processed by the readout structure.

20.5 A Sub-pA ΔΣ Current Amplifier for Single-Molecule Nanosensors

Current readout has been a known technique since the inception of electronic sensors and is widely used, for example, in radiation detectors, impedance spectroscopy, and mechanical sensors. Recently, new challenges have emerged for current sensing in the upcoming era of nanosensors. Nanowires, carbon nanotubes and nanopores are emerging devices that have been proven to be effective in sensing ultra-low concentrations of target molecules [1]. For those devices, current sensing becomes challenging since outputs consist of signals in the pA range or less, in the kHz band. To measure these values, very low-noise front-end amplifiers are needed such as the one in [2]. It achieves a noise floor as low as 20fArms at 1kHz and it is designed for electrophysiology experiments, such as in patch clamp techniques, where single-ion channel recordings from cell membranes are required. However, the instrument is bulky and needs a cooled headstage to boost performance. An integrated solution offering quad current-input 20b analog-to-digital converters is reported in [3]. However, its measured equivalent input noise is above 700fArms at 1kHz.

A Distributed Amplifier System for Bilayer Lipid Membrane (BLM) Arrays With Noise and Individual Offset Cancellation

Lipid bilayer membrane (BLM) arrays are required for high throughput analysis, for example drug screening or advanced DNA sequencing. Complex microfluidic devices are being developed but these are restricted in terms of array size and structure or have integrated electronic sensing with limited noise performance. We present a compact and scalable multichannel electrophysiology platform based on a hybrid approach that combines integrated state-of-the-art microelectronics with low-cost disposable fluidics providing a platform for high-quality parallel single ion channel recording. Specifically, we have developed a new integrated circuit amplifier based on a novel noise cancellation scheme that eliminates flicker noise derived from devices under test and amplifiers. The system is demonstrated through the simultaneous recording of ion channel activity from eight bilayer membranes. The platform is scalable and could be extended to much larger array sizes, limited only by electronic data decimation and communication capabilities.

A nanosensor interface based on delta-sigma Arrays

An emerging area of biosensors is based on the use of structures provided by recent advances of Nanotechnology such as nanowires, nanotubes and nanopores. Among them, the integration of natural nanopores such as ion channels with electronics is a promising approach to develop rapid, sensitive and reliable biosensors able to detect low concentration of target molecules or DNA sequencing. This paper presents a compact and low-cost system able to readout, process and record current in the pA range, provided by biological or synthetic nanopores. The approach is based on the idea that by processing the outputs of a large amount of single-molecule nanosensors would result in a significant increase of resolution and signal-to-noise ratio. The approach consists of an electronic interface able to detect current-based array of nanosensors, where the management of very large amount of data is critical for the readout process. As working example, we acquired the single molecule signals derived from non-covalent bindings between single a-hemolysin pores, embedded into an artificial lipid bilayer, and β-cyclodextrin molecules. The system embeds the electronic readout with the microfluidic where is placed the nanosensor array. The electronic interface is a 0.5mm2 current amplifier based on an array of ΣΔ converters. Then the high rate data streams are processed and downsampled by a DSP that communicates with a PC via a USB interface for data processing and storage.

Concurrent Acquisition Approach for High Resolution Sensor Arrays

An increasing amount of sensor applications require multiple data acquisition with high resolution in truly parallel fashion. This requirement is particularly useful in the field of Nanotechnology where concurrent acquisition is required to understand the correlation between weak stochastic events. In this paper, we will propose a sensor array readout approach where synchronous sigma-delta converters are interfacing each sensing point and whose outputs are concurrently downsampled by dedicated hardware for decimation processing. The approach shows the following advantages: on the one hand the sigma-delta conversion ensures high resolution and linearity (>12 bits), on the other, the 1-bit output allows easier routing access to the array. The approach is particularly useful in the presence of very low signals where direct raster-mode switching access to the array would compromise the signal-to-noise ratio of the readout process. As a proof of this concept, the approach is applied to an array of lipid bilayer membranes (BLMs) permitting to acquire and display single molecule event data by means of a PC-based graphical user interface (GUI).

Solvent Free Bilayer Recordings using a Novel All-In-One Miniaturized Amplifier

We present a new minaturized all-in-one Amplifier suitable to perform high-quality electrophysiology measurements. The instrument has been evaluated on a platform where ion channel proteins are reconstituted in solvent-free bilayers and multiple corresponding experimental data sets are shown.Characterization of reconstituted ion channels is still challenging as low noise current measurements in the pA range have to be combined with a large bandwidth of tens of kilohertz. Traditional transimpedance amplifiers use resistive or capacitive feedback to generate an analog output which needs to be digitized for further processing and display, resulting in complex, bulky and expensive systems. The amplifier shown here uses a switched capacitor gain stage combined with a sigma-delta digitizer which directly produces a digital signal. The actual layout is completely done in one silicon die (ASIC). This novel approach allows the integration of a multiple gain stage, filters, signal conditioning circuitry, digitizer and USB interface into the size of a pack of cigarettes while noise performance (≈100fA rms @ 1KHz) and bandwidth (up to 100kHz) are comparable to state-of-the-art patch clamp amplifiers.Combined with an already established platform using planar glass chips for semi-automatic formation of solvent-free BLMs an integrated and easy-to-use system has been set up offering students and researches an easy entry to high level electrophysiology research.