Comment made by 'Anonymous Monk' is incorrect.

$bio_seq is infact a Bio::Seq::RichSeq object
This object is an input sequence from a rich sequence database such as GenBank, SwissProt and EMBL.
You can create such an object using the following code snippet (code pulled from cpan docs):

$seq    = Bio::Seq::RichSeq->new( -seq => 'ATGGGGGTGGTGGTACCCT',
                                  -id  => 'human_id',
                                  -accession_number => 'AL000012',
          );
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There is documentation available for Bio::Tools::SiRNA here

Hope this is useful!!