After performing PCR, I ran electrophoresis, but on agarose the results showed some rather blurred samples. I wanted to know the cause and how to fix this situation. Please note that the chemicals and dyes are normal because the positive control shows a clear band.
A picture would help but if the diffuse band is less than 100bp it is probably primer dimer in samples that do not amplify well. If they are larger than this then try leaving the gel tocool for longer ( the edges may have cooled quicker than the centre so the control may look better if it is an edge sample) and also run at a lower voltage to minimise heating of the gel while the samples are running
For some samples with clear bands, I tried diluting the DNA concentration before PCR. The result is blurred bands. However, the DNA quality of some samples after separation is quite low.
How many cycles of pcr are you running and how much dna (ng) are you amplifying in each pcr reaction?
Diluting the starting DNA is a good way to reduce the concentration of molecules that can inhibit PCR.
The blur might be from failed amplification.
Maybe try diluting the DNA for the other blurry samples & try again.
Can you share a picture of the gel? Keep in mind that even blurry bands can be fine data. Unless you are planning to publish the gel image (or put it on a poster), the bands might be good enough to get the information you need.
For example, colony PCR often gives slightly blurry bands due to the starting material having cells etc. in it.
As others have mentioned above, diluting your template can help out. If your starting material is purified DNA, it might have salt, ethanol, secondary metabolites etc. that can lead to blurred bands.
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