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madras 09-13-2018 10:06 AM

NaOH denaturation with large volumen of low conc library
I am doing targeted sequencing using a <15000 kb panel, and because I consequently get rather low library conc (and try to limit the no of PCR cycles) I often use a somewhat large volumen of my library pools for the NAOH denaturation step prior flow cell loading (Nextseq 500 mid).
For rutine library pools the protocol says:
1. Dilute library pool to 2 nM in a 0.1% Tween buffer
2. Denature 5 uL hereof with 5 uL 0.2 M NaOH, neutralize with 5 uL 0.2 M Tris-HCl
3. Do this for all pools to be loaded.
4. Add to each pool HT1 loading buffer to a total volumen (for all pools) of 1 mL.
5. Load onto flowcell.

For the 15k panel:
1. Skip step 1 since the conc is below 2 nM
2. Denature 10 - 50 uL (depending on the conc of the library pool) in 0.2 M NaOH, neutralize with same amount of 0,2 M NaCl.
3-5. Same.

The thing is that it seems as if the cluster generation some times is very inefficient (measured as cluster density per library copies). I suspect that it could have something to do with the larger ratio of (Library+NaOH+Hcl) / HT1 compared to the rutine protocol. In a rutine setup for 4 library pools it would be 4 pools * 5 uL* 3 = 60 uL Library+NaOH+Hcl and 940 uL HT1. The same numbers for 4 40 uL pools in the alternative protocol is 4*40*3 = 360 uL and 640 uL HT1 buffer.

Some concerns could be :
1. A higher amount of Na Cl .
2. Lower molarity of the HT1 constituents
3. Insuffucient buffer capacity with less HT1 (pH is not optimal).

Does anyone have experience with low conc / high vol setup ?


gabrieltw 09-14-2018 04:18 AM

Try to search older threads. There are a few talking about using low concentration library.

madras 09-14-2018 06:14 AM

Yeah thanks.
I did look through these, e.g. this one. They seem to be somewhat old. My main concern I think is whether HT1 buffer need to be almost "undiluted" - i.e. constitute the majority of the volumen loaded.

Kodavali 10-22-2018 05:21 AM


I recently ran Nextseq, I have observed that the cluster density and the total number of reads was very low when compare to the other experiments. Qscore was 97%, Cluster passing filter was above 95% but cluster density K/mm2 was around 94 and the total number of reads for 4 lanes was around 200 million reads. For my previous experiments usually I will get above 180 K/mm2 and around 400 to 500 million reads. I have just followed the same as previous experiments, but not sure where went wrong to get low cluster density and reads.

I have denatured the sample with 0.2 N NaOH, is it the sample that is behaving or something wrong with the preparation?

I used 4nM sample conc with 1.8 loading concentration.


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