University Oral Examination- Evan Thrush (Aug. 31, 1:30pm)

Evan Thrush ethrush at
Mon Aug 23 09:48:09 PDT 2004

University Oral Examination


"Semiconductor Integrated Fluorescence Sensor"


Evan Thrush

Department of Electrical Engineering

Stanford University


1:30pm, Tuesday, August 31, 2004

Packard 101

(Refreshments served at 1:15 in Packard 102)





Fluorescence sensing is one of the most commonly used methods to study
biological systems.  Unfortunately, conventional fluorescence detection
systems typically use bulky and discrete components which are expensive and
non-portable.  The goal of this work is to create an integrated fluorescence
sensing solution by capitalizing on optoelectronics developed for
telecommunications.  By building upon technology used for
telecommunications, it is believed that huge cost reductions are possible
when compared to other integrated approaches and may open a wide range of
interesting applications.  Potential applications of such a sensor are
numerous and include portable and disposable medical diagnostics, highly
parallel research instrumentation and biological implants.


In this work, all the components of a conventional fluorescence sensing
system (laser, photodetector and optical filter) are monolithically
integrated on GaAs.  The integration is achieved through a simple
modification to a vertical-cavity surface-emitting laser (VCSEL) to create a
PIN photodetector and optical filter.  These optoelectronic components and
their interaction are characterized.  By bringing the laser and
photodetector together in such close proximity (* 50mm), laser background
sources are created that limit sensitivity.  Laser background sources are
studied, and design solutions are proposed and implemented to reduce laser
background.  With integrated metal optical blocks, greater than 106 optical
isolation between the photodetector and laser is achieved, which shows that
highly sensitive detection is possible despite the monolithic integration


The sensor is integrated with microfluidic channels to test sensitivity.
The experimental and theoretical limits of detection of IR-800 dye are
determined to be 250nM and 40nM respectively.  These detection limits are
sufficient for certain applications such as immunology.  Large increases in
sensor sensitivity are possible through the systematic reduction of the
laser background and will enable more applications.  Results suggest that
order of magnitude increases in sensitivity will be possible by improving
the performance of the optical filter and increasing spatial filtration.  It
is believed that this technology holds great potential to reach sub-nM
detection limits and compete against bulk optic approaches.


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