Emily B. Cooper

Electronic detection of DNA by its intrinsic molecular charge.

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.

Terabit-per-square-inch data storage with the atomic force microscope

An areal density of 1.6 Tbits/in.2 has been achieved by anodically oxidizing titanium with the atomic force microscope (AFM). This density was made possible by (1) single-wall carbon nanotubes selectively grown on an AFM cantilever, (2) atomically flat titanium surfaces on α-Al2O3 (1012), and (3) atomic scale force and position control with the tapping-mode AFM. By combining these elements, 8 nm bits on 20 nm pitch are written at a rate of 5 kbit/s at room temperature in air.

High-resolution micromachined interferometric accelerometer

We demonstrate a promising type of microfabricated accelerometer that is based on the optical interferometer. The interferometer consists of surface-micromachined interdigital fingers that are alternately attached to a proof mass and support substrate. Illuminating the fingers with coherent light generates a series of diffracted optical beams. Subangstrom displacements between the proof mass and frame are detected by measuring the intensity of a diffracted beam. The structure is fabricated with a two-mask silicon process and detected with a standard laser diode and photodetector. We estimate that the minimum detectable acceleration is six orders of magnitude below the acceleration of gravity, i.e., 2 μg/Hz in a 1 Hz bandwidth centered at 650 Hz.

Fabric computing interfaces

This paper presents a series of physical computer interfaces and computational devices that are constructed from electronic fabrics and conducting threads. We introduce two types of textile keyboards, a piecework switch matrix and a capacitive embroidered keypad. We discuss these fabric sensors in a variety of applications. We give examples of computational clothing using this technology. This clothing shows how digital technology can be imbedded into the world around us. We argue that creating computational devices with new and unexpected materials gives designers the creative freedom to radically change the appearance and “feeling” of such devices.

Microvolume field-effect pH sensor for the scanning probe microscope

A pH sensitive scanning probe is realized by integrating a micron-sized field-effect sensor onto a cantilever designed for an atomic force microscope. The hybrid device, called a scanning probe potentiometer (SPP), is capable of measuring pH gradients over a sample surface. The device was used to profile the pH across a reservoir of laminar streams created by fluid flow in an array of microfluidic channels of varying pH. When a single SPP scanned, a 1.5 mm reservoir in a 10-channel array, the pH profile was measured in less than 1 min with a spatial resolution of 10 μm and sensitivity of less than 0.01 pH units.

Experimental and theoretical results of room-temperature single-electron transistor formed by the atomic force microscope nano-oxidation process

The single-walled carbon-nanotube (SWNT) was grown directly onto the top of the conventional Si atomic force microscopy (AFM) cantilever. This SWNT AFM cantilever was introduced into the AFM nano-oxidation process, which oxidized the titanium (Ti) metal film on the atomically flat α-Al2O3 substrate and formed the ultranarrow oxidized titanium (TiOx) line of 5 nm width. This TiOx line was used as the tunnel junction of the single-electron transistor (SET), and the SET fabricated by this process showed room-temperature Coulomb oscillation with periods of 1 V. It was determined by three-dimensional simulation that the tunnel-junction capacitance shows only weak dependence on the tunnel-junction width.