How do we indicate a volume fraction like 0.05 in procedure descriptions?

I'm translating a Russian biotech text, and there's this sentence with a number without measurement units:



> 
> The contents of the wells were discarded; the wells were washed three times with 200 µL of Buffer containing **0.05 of Tween 20**.
> 
> 
> 


I was told that this figure indicates a volume fraction, and is dimensionless, hence no units after it. Will this be understood by the native speaker of English as-is, without any units, as in my quote?


Or is it better to write it down as:



> 
> The contents of the wells were discarded; the wells were washed three times with 200 µL of Buffer containing **5% (v/v) of Tween 20**.
> 
> 
> 


Or maybe like this:



> 
> The contents of the wells were discarded; the wells were washed three times with 200 µL of Buffer containing **5 vol% of Tween 20**.
> 
> 
> 


Is there a way to retain **0.05** and somehow indicate that this is a volume fraction? 




I think it would be wise to include units, because how would you distinguish between mass and volume fractions? Options 2 and 3 that you present are both seen in the scientific literature and text books. My opinion is that option 3 is the least ambiguous way to present both the numeric value and the context (i.e. the units).


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