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During the interpretation of gel electrophoresis results, a protective glass plate was utilized to shield the UV transilluminator, and exposure time to UV light was minimized to mitigate potential DNA damage.
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The desired DNA band was precisely excised from the gel using a sterile razor blade, ensuring cuts were made as close as possible to the band to minimize the volume of co-excised agarose.
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The excised gel slice was then transferred into a pre-weighed microcentrifuge tube. Subsequently, the tube containing the gel slice was weighed to determine the exact mass of the agarose, which is crucial for calculating the appropriate volume of solubilization buffer required in the following step.
Dissolve the Gel Slice
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A 3:1 volume ratio of solubilization buffer to excised gel slice (e.g., 300 µL of buffer for a 100 mg gel slice) was added to the microcentrifuge tube.
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The mixture was then inverted for fragments smaller than 5 kb or gently vortexed for larger fragments, with periodic mixing every few minutes to facilitate complete dissolution of the agarose.
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The tube was subsequently incubated at 50-60°C for approximately 5 minutes, or until the gel slice was entirely dissolved.
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A pH indicator was employed to confirm that the solution maintained a yellow color, signifying the optimal pH for efficient DNA binding. If necessary, a pH-adjusting solution was added to achieve the desired pH.
Bind the DNA to the Spin Column
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A spin column was inserted into a collection tube, and the entire dissolved gel mixture was carefully transferred to the spin column.
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The column was then centrifuged at 13,000-17,000 x g for 1 minute to facilitate DNA binding to the silica membrane.
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Following centrifugation, the flow-through was discarded, and the spin column was re-inserted into the collection tube.
Wash the DNA:
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Approximately 500-750 µL of wash buffer was added to the spin column, and the column was centrifuged again at 13,000-17,000 x g for 1 minute.
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The flow-through was discarded. Depending on the sensitivity of subsequent applications to residual salts, an additional wash step with wash buffer was performed.
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A final centrifugation step was executed at maximum speed (≥17,000 x g) for 1 minute to ensure complete drying of the silica membrane and to remove any residual ethanol, which is known to inhibit downstream enzymatic reactions.
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The spin column was then carefully removed from the collection tube, which was subsequently discarded along with any residual flow-through.
Elute the DNA
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The spin column was meticulously transferred to a new, sterile microcentrifuge tube.
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30-50 µL of Elution Buffer (pre-warmed to 50°C for enhanced yield) was dispensed directly onto the center of the column membrane, taking care to avoid contact with the pipette tip.
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The column was then allowed to sit at room temperature for 1-2 minutes, providing sufficient time for the DNA to rehydrate and dissociate from the membrane.
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Finally, the column was centrifuged at 13,000-17,000 x g for 1 minute to collect the purified DNA into the clean microcentrifuge tube.
Quantify and Store the Purified DNA
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The concentration and purity of the eluted DNA were assessed using a spectrophotometer.
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The purified DNA was stored at 4°C for short-term experimental use or at -20°C for long-term preservation.