You can use UV spectrophotometry for determination of ssDNA concentration as follows:
at 260 nm, OD value of 1 corresponds to about 40 ug/mL of single-stranded DNA. So from OD at 260 and molecular weight of your oligos you can calculate concentration of your ssDNA in uM: c = OD x 40,000 / M, where M is molecular weight of your oligo in g/mol. You can find many suitable references for this procedure.
RM
