This code produces the answer - you should be able to incorporate the idea into your code.

perl -e '@x=qw| 28 8a 1c 59 cc 85|;
         my $o="";
         for (my $i=0; $i<$#x; $i+=2){
               $o.=$x[$i].$x[$i+1]."."}
        chop $o;
        print "$o\n"'
288a.1c59.cc85
[download]

Update: Fixed typo in code above, to produce right answer.

There are other, slightly more elegant methods (using natatime from List::MoreUtils), but to use those, you will need to use CPAN modules.

Here is another option (Has trailing "."):

perl -e '@x=qw| 28 8a 1c 59 cc 85|; 
    while ($_=shift @x){
    print "$_" .shift (@x) . "."}'
[download]

Note -: This one destroys the source array.