the most common of the -cones used in shine serum is silicone, which is synthetic in origin. There are more natural things that also add shine, like silk amino acids for instance.  I read this book called the curly girl handbook, and they warn against using silicone and other things that end in -cone, saying that it isn't good for your strands.  You're better off sticking with natural things.  Even extra virgin olive oil, coconut oil, or any other kind of natural oil could be used as a shine serum, and it's less expensive!  You could even add some essential oils to a portion of it to give it a nice scent.