An Electronic Approach for Stochastic Sensing

In recent years, we have assisted to an ever-increasing capability of electronic systems to detect extremely small signals in noisy environments. Following this trend, the capability to electronically detect single molecular binding events could bring to a new, high performance class of biosensors. One of the best transducers coding single molecule event into an electric signal is already existing in nature and widely used by cells for interacting with the external environment: the ligand-gated ion channel. The biological cell is filled with all types of ion channels that control the trafficking of ions and molecules in and out of the cell and among the subcellular structures. However, the signaling derived by ion channels upon molecular binding is intrinsically stochastic, due to the thermal agitation of the physical system at molecular scale. Properties of their gating are strongly influenced by binding between receptive sites located on the channel surface and specific target molecules. In this paper we propose to use signals deriving from ligand-gated ion channels for realizing quantitative sensors, able to detect specific chemical species in fluid mixtures. Following this goal, we have implemented an electronic system, able to record ionic currents derived by single gated ion channels having hundreds of femto-amperes of resolution. Additionally, we propose a statistical approach for processing the electrical information, in order to estimate the concentration value of the target molecules. The proposed algorithm was tested using a Monte Carlo simulator and a simple channel model taken from literature

A Compact System for Single Ion Channel Recording

The integrated use of ion channels and electronics is a promising approach to develop rapid, sensitive and reliable biosensors able to detect low concentration of target molecules, with applications that range from pharmacology to diagnostic tools. Several reports on stochastic sensors have been published [2-4], however all are based on bulky and expensive instruments. This paper presents a compact (two credit cards size) and low-cost integrated system able to record and process signals in the typical single-channel recording bandwidths. To test the approach, we used signals derived from non-covalent bonds between single α-hemolysin pores, embedded into an artificial lipid bilayer, and β-cyclodextrin molecules. The system is based on a ∆Σ converter implemented on a PCB using discrete components technology to readout ion currents in the order of pA. The digitized output is sent to a DSP for decimation and filtering and then to a PC for storage, visualization and stochastic data processing