Aristotelianism sees the immaterialism of knowledge as any relation to another as symbol or even as signaling. He saw it clearly in animals, but it’s become clear that plants are capable of this too. The advances of the sciences make it clear that even molecules can signal each other, or code information and execute algorithms for themselves. And so Aristotelianism leads to a bona fide immaterialism all the way down, even on the elemental level (or, minimally, on hte level of any living thing). Being nothing more than an act in an environment requires the sort of presence of the intelligible form of another that Aristotle counts as knowledge.
But though something deserving the name of knowledge arises in any actual thing, truth only arises for those knowers with retorsive cognition – where knowledge in one and the same order is capable of being its own object. This does not happen in sensation: we cannot taste that we taste, or even have a vision of our own vision.
Knowledge is thus present somehow in any actuality but truth cannot be explained as a feature or a physical cognitive organ: i.e. a sense organ, or whatever it is that trees or DNA uses to detect signals. We can explain any number of things about our knowledge by pointing to an essentially physical cognitive component (say, a nervous system) but we can’t explain why the knowledge is true or false.*
*or “unknowable” in the relevant sense, which indicates something that, though falling within the ambit of the true and false, is such that we cannot determine which side it falls on. The past is unknowable in this sense, the future is not.