Electronic detection of DNA by its intrinsic molecular charge

Abstract

We report the selective and real-time detection of label-free DNA using an electronic readout. Microfabricated silicon field-effect sensors were used to directly monitor the increase in surface charge when DNA hybridizes on the sensor surface. The electrostatic immobilization of probe DNA on a positively charged poly-L-lysine layer allows hybridization at low ionic strength where field-effect sensing is most sensitive. Nanomolar DNA concentrations can be detected within minutes, and a single base mismatch within 12-mer oligonucleotides can be distinguished by using a differential detection technique with two sensors in parallel. The sensors were fabricated by standard silicon microtechnology and show promise for future electronic DNA arrays and rapid characterization of nucleic acid samples. This approach demonstrates the most direct and simple translation of genetic information to microelectronics. Awide range of techniques for detecting nucleic acids is based on their hybridization to DNA probes on a solid surface (ref. 1, entire issue, and ref. 2). In the methods used most routinely, the physical nature of the readout requires the attachment of reporter molecules such as fluorescent, chemiluminescent, redox, or radioactive labels (1, 3, 4). Although labeldependent methods achieve the highest sensitivities (5-7), eliminating the labeling steps has the advantage of simplifying the readout and increasing the speed and ease of nucleic acid assays, which is especially desirable for characterizing infectious agents, scoring sequence polymorphisms and genotypes, and measuring mRNA levels during expression profiling. The development of label-independent methods that can monitor hybridization in real time and that are simple and scalable is still in its infancy (8-11). Here we describe a label-free method for electronically detecting DNA by its intrinsic molecular charge using microfabricated field-effect sensors.The field-effect sensor is based on an electrolyte-insulator-silicon (EIS) structure. Variations in the insulator-electrolyte surface potential, which arise from the binding of charged molecules (e.g., nucleic acids) to the insulator surface ( Fig. 1 a and b), modify the charge distribution in the silicon below the electrolyte. Surface charge and surface potential at this interface are related according to the Grahame equation (12). The surface potential can be measured by changes in conductivity (13) or capacitance (14) in the silicon part of the EIS structure. We have chosen to measure the capacitance, because it requires only one electrical connection to the silicon. The measured capacitance between the silicon and counter electrode in the electrolyte solution is dominated by the insulator capacitance and the capacitance of the charge-depleted region in the silicon. These two capacitances appear in series, and only the silicon depletion capacitance is modulated by the insulator surface potential. The capacitance-versus-voltage dependence of EIS structures (15) is similar to that of metal-oxide-semiconducto...

Label‐Free Impedance Biosensors: Opportunities and Challenges

“…are the canonical examples [6], but similar mechanisms operate in semiconducting nanowires [7], semiconducting carbon nanotubes [8], electrolyte-insulator-semiconductor structures [9][10][11][12], suspended gate thin film transistors [13], and light-addressable potentiometric sensors [14,15]. These field-effect sensors rely on the interaction of external charges with carriers in a nearby semiconductor and thus exhibit enhanced sensitivity at low ionic strength where counterion shielding is reduced; this is explained in a recent review [16] and evidenced by the low salt concentrations often used (e.g., [7,10]). Even though the response of field-effect sensors can be characterized by channel conductance or capacitance of the electrolyte-insulator-semiconductor interface, we restrict this review to cases in which the impedance of the biological layer itself is measured.…”

An integrated semiconductor device enabling non-optical genome sequencing

“…Although a variety of electrochemical detection methods have been studied 24,25 , the ion-sensitive field-effect transistor (ISFET) 26,27 was most applicable to our chemistry and scaling requirements because of its sensitivity to hydrogen ions, and its compatibility with CMOS processes [28][29][30][31] . Previous attempts to detect both single-nucleotide polymorphisms (SNPs) 32 and DNA synthesis 33 as well as sequence DNA electronically 34 have been made.…”

p H sensors based on hydrogenated diamond surfaces

“…Ion-sensitive field effect transistors ͑ISFETs͒ have been combined with biological receptors ͑enzymes, oligonucleotides, and cells͒, and can be considered as a basic building block of microelectronic biosensors. [3][4][5] So far, there have only been a few reports investigating the applicability of diamond-based IS-FET devices. [6][7][8] The p-type conductive layer which is induced at the diamond surface by a hydrogen termination has been suggested as a very promising sensing system to be used in a liquid electrolyte environment.…”