How to create a string including a number in scientific or engineering form

[kaihans (Kai Hansen)]

For example:

u=1.0 10^-8
v="u: "<>u

u = 1.0 10^-8;
v = "u= " <> u;
v

StringJoin::string: String expected at position 2 in u= <>1.*10^-8. >>
"u= " <> 1.*10^-8

This is not what I want
I want:
u=1.0*10^-8

Thanks

[nma (Nasser M. Abbasi)]

u = 1.0*10^(-8);
v = "u = " <> ToString@TraditionalForm[u];
v

Head[v]
(*String*)