Brian N. Johnson

Advances in on-chip photodetection for applications in miniaturized genetic analysis systems

Microfabrication techniques have become increasingly popular in the development of next generation DNA analysis devices. Improved on-chip fluorescence detection systems may have applications in developing portable hand-held instruments for point-of-care diagnostics. Miniaturization of fluorescence detection involves construction of ultra-sensitive photodetectors that can be integrated onto a fluidic platform combined with the appropriate optical emission filters. We have previously demonstrated integration PIN photodiodes onto a microfabricated electrophoresis channel for separation and detection of DNA fragments. In this work, we present an improved detector structure that uses a PINN+ photodiode with an on-chip interference filter and a robust liquid barrier layer. This new design yields high sensitivity (detection limit of 0.9 ng µl−1 of DNA), low-noise (S/N ~ 100/1) and enhanced quantum efficiencies (>80%) over the entire visible spectrum. Applications of these photodiodes in various areas of DNA analysis such as microreactions (PCR), separations (electrophoresis) and microfluidics (drop sensing) are presented.

A Microfabricated Fluidic Reaction and Separation System for Integrated DNA Analysis

In recent years, there has been increasing interest in developing a complete, highvolume, DNA analysis system using microfabrication techniques. Such analysis systems require components for injection, pumping, mixing, reaction, separation and detection. Over the past decade, many researchers have demonstrated that micromachined fluidic devices are capable of performing many of the required functions of chemical analysis. In addition, coupling the individual analysis steps onto a single microfabricated device significantly simplifies the process, minimizes human intervention, reduces the risk of contamination, and could lead to the realization of hand-held ‘Lab-on-a-chip’ devices. We are presently developing a fluidic handling, reaction and separation system for integrated DNA analysis. The current generation of our system contains an injection system based on selective hydrophobic patterning, air driven/thermocapillary fluid pump, a temperature controlled reaction chamber and a high-resolution electrophoresis and detection system. Since all the components are fabricated on the same wafer and use a similar channel design, the entire device could potentially function as one unit. We have successfully used these devices to perform a variety of DNA analysis techniques including constant temperature amplification using Strand Displacement Amplification (SDA) and gel-electrophoresis.

Toroidal inductors for integrated radio frequency and microwave circuits

A toroidal inductor has been developed that confines flux and eliminates eddy currents. A printed circuit and micromachined RFIC-compatible implementations of the inductor are presented.A toroidal inductor has been developed that confines flux and eliminates eddy currents. A printed circuit and micromachined RFIC-compatible implementations of the inductor are presented.

On-Line Detection of Electrophoretic Separations on A Microchip by Raman Spectroscopy

Capillary electrophoresis has advantages of high efficiency, high-speed separations, instrumental simplicity and wide applicability. Separations of molecules ranging from herbicides to DNA have been described in the capillary format.1,2 Separations on a microchip have been the subject of intense research, particularly for electrophoretic separations. The microchip format allows development of complex channel geometries with opportunities for automated, compact multistep separations. Additionally, the microchip offers excellent heat dissipation that enables rapid separation by use of high electric fields.

Advances in On-Chip Fluorescence Detection for DNA Analysis Systems

Developing an on-chip fluorescence detection involves construction of ultrasensitive photodetectors that can be integrated onto a fluidic platform. In this work, we report a novel doping and construction of a P-I-N-N + photodiode with an on-chip interference filter and a robust liquid barrier layer. This new design yields a highly sensitive, low-noise photodiode and its applications in several areas of DNA analysis are presented.

An 8.5 GHz SiGe-based amplifier using fully self-aligned double mesa SiGe HBTs

We report an 8.5 GHz fully integrated SiGe amplifier developed using a novel fully self-aligned double mesa HBT process technology. The common-base HBT demonstrates a G/sub max/ > 14 dB and an f/sub max/ > 37 GHz. At 8.5 GHz, the small-signal gain of the amplifier is better than 4 dB, with input and output return loss of -10 dB and -5 dB, respectively. The amplifier is also shown to be unconditionally stable.

High yield reduced process tolerance self-aligned double mesa process technology for SiGe power HBTs

Two novel high yield reduced process tolerance process technologies were developed for double mesa SiGe power HBT. DC and RF results from both 10 and 20 finger devices were presented. A reduced tolerance process is essential in the further development of MMICs using these transistors.