I used Naphtol, fast red violet LB salt, N,N dimethylfirmamide, 0.1M sodium actate buffer (pH-5). I mixed these for ~30mins. After that, I filtered the soluion with 40um filter. After adding these filtered solution into the well of the plate, I found a lot of junks on the cell surface even after rinsing with DW several times. I tried to filter with filter paper. But, it didn't work either. Can you give any suggestion to this problem? The junk on the cell surface as shown in the attached photo. Thanks in advance.