Instrument firmware is to be updated only by a Thermo Fisher Scientific
representative.
Theory of operation
When DNA samples are prepared for sequencing and fragment analysis on the
instrument, fluorescent dyes are attached to the DNA.
Two calibrations are required to prepare the instrument for sample runs:
• Spatial calibration—Determines the position of the image from each capillary on
the CCD array. For more information, refer to page 104.
• Spectral calibration—Generates a matrix for each capillary that compensates for
dye overlap and is used to convert the 20-color data into 4-, 5-, or 6-dye data. For
more information, refer to “Perform a spectral calibration“ on page 111.
During a run, the instrument:
• Prepares the capillaries by pumping fresh polymer solution under high pressure
from the polymer delivery pump to the waste position in the cathode buffer
container (CBC).
• Electrokinetically injects the sample into the capillaries by briefly applying a low
voltage.
• Washes the capillary tips in the rinse position of the CBC, then returns the
capillary to the buffer position of the CBC.
• Ramps the voltage up to a constant level.
A high electric field is created between the ground end of the anode buffer
container (ABC) and the negative voltage applied to the load header of the
capillary array. This field pulls the negatively charged DNA through the
separation polymer. The smaller fragments migrate faster than the larger
fragments and reach the detector first.
To ensure optimal separation and maintain denaturation of the DNA, the
capillaries are thermally controlled in the oven and in the detection cell. The oven
has a Peltier heat unit and fan-circulated air.
In the detection cell, the dyes attached to DNA are excited by a narrow beam of
laser light. The laser light is directed into the plane of the capillaries from both
the bottom and top. A small amount of laser light is absorbed by the dyes and
emitted as longer wavelength light in all directions.
• Captures the fluorescent light on the instrument optics while blocking the laser
light. The light passes through a transmission grating, which spreads the light
out. The light is imaged onto a cooled CCD array. For each capillary, 20 zones on
the CCD are collected to provide 20-color data for each capillary.
• Converts the 20-color data into multi-dye data for the entire run. For sequencing
applications, 4 different dyes are used to determine the 4 bases A, G, C and T. For
fragment analysis applications, up to 6 dyes can be used in a single run for higher
throughput.
Instrument
firmware
Preparing
samples
Preparing the
instrument
During a run
Chapter 1
Instrument and software description
Theory of operation
1
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3500/3500xL Genetic Analyzer User Guide—Data Collection Software v3.1