Your research team is working on a pluripotent cell line 3T3…

Your research team is working on a pluripotent cell line 3T3L1 that was previously modified by CRISPR. The cells, over time, can differentiate into special tissue types after certain inducing treatment. In your experiment, you did the inducing treatment on Day1 (d1) and collected the sample on Day8 (d8). You conducted Northern blotting, looking at a gene called PPAR. All the samples in the right panel were taken from the same mouse. You also included 18S rRNA as a positive control. The gel result is shown as a separate  gel with the opposite coloring scheme (dark background, bright band). When designing a detecting probe in a Northern blot, what is the most critical characteristic the probe must possess?