I have a page stuck to the bulletin board next to my desk covered with haphazard ideas I've had regarding Mad Science and the potential profitabilities therein.
This is another thing I spend too much valuable time thinking about - so why not make the time wastage more thorough, and post this stuff here.
I have 4 categories of Mad Science. In order of increasing profitability:
1. Mad Science
Octopuses are remarkably intelligent, but females practice semelparous reproduction: they die after tending their once-a-lifetime batch of offspring to independence. What could be done with a female who survives reproduction, with her mind and instincts uncluttered by the urge to procreate?
Fusion power generation is a widely-held dream. I'm not talking about industrial or commercial applications of Tokamak reactors and the like. I'm talking about the automobile-mounted, anything-for-fuel device displayed at the end of the first Back-to-the-Future movie. Seriously, how much fun would it be to dump cheap beer, the can it came in, and banana peels into your fuel system? I'd probably end up using my car's fuel tank as a garbage can - just because.
Immortality is probably impossible, and may be unpleasant besides. But the urge to be remembered always is strong in our species. It's been suggested in science fiction; we have the technology. After you die, your corpse is placed in a stable solar orbit - where it will remain until the sun goes Red Giant, in some 5 billion or more years.
Really Big Laser
I know little about lasers, but they are frickin' cool. I'm sure there is fun galore to be had with a truly large laser.
Really Big Railgun
Again, a topic much beyond my ken. But also again, I am certain that fun could be found.
Rocket propulsion, built on Newton's Third Law, works better the faster the fuel-mass is thrown away. The fastest possible fuel-mass is in the form of protons. Besides, a flashlight powerful enough to push a ship is a dangerous thing. See Larry Niven's Angel's Pencil spacecraft in the first Man-Kzin wars book.
2. Wealthy Biochemist
Seastars have tubefeet, which they use to stick to rocks, prey, and anything else they want to grab. The force of attraction exerted by the tubefeet is only partly due to water pressure - mostly it's from a sticky glue. The animal also secretes an unglue, which removes the glue when it wants to let go. This system of glue-unglue is infinitely repeateable, with no apparent drop in efficiency. I would think there are industrial applications to such a pair of substances.
Echinoderm Mutable Collagenous Tissue
Another trick of the seastars, and their con-phylumers (I made that word up), is a material named mutable collagenous tissue. It goes from flexible to rigid and back to flexible with changes in Calcium ion concentration. Once again, this system is infinitely repeatable.
A no-brainer, really. It's much stronger than steel, and lighter.
Not as hard as many other materials, but made from the same molecular subunits (glucose) as wood-pulp cellulose. I'd like plates made of this, anyway.
Some (most?) slugs produce a mucous with an interesting property - the coefficient of friction is different for forces applied in different directions. That's freaky-weird, and must be useful in many, many places
Yes, yes, we already have some flame-resistant materials. Many of them are either nasty toxic or degrade to become nasty toxic things. Many pinecones, and the eggs of some insects, are capable of withstanding forest fires - without poisoning the embryos within.
3. Possible within an arbitrary timescale
We've been 20 years from Fusion Power for about 50 years, I think. Sooner or later we will have it (I hope), and whoever gets there first will be rich.
Spider Robinson, in an article in a book (or perhaps it was one of his Globe and Mail columns), once stated (paraphrasing) "Want to be rich? Mine the metals of the asteroid belt. Everyone on earth can get 10 Billion Dollars!"
If he's even partly correct, mining for iron, nickel, gold, etc in the asteroids is the way to go.
My personal favourite, since, as far as I know, I invented the concept. With that in mind, I'll keep it a secret, for now.
Metals from the Oceans
Either by chemistry-based robots, or by genetic engineering marine microbes, someone could extract arbitrary quantities of pretty much anything from the global ocean. Water is the closest we've ever found to the Universal Solvent, and the oceans have been estimated to carry every chemical and element yet described at some non-zero concentration.
4. Totally Unlikely
Invent this (or probably just discover the working principles), and retire. And allow your great-to-the-nth grandchildren retire whenever they want.
Now you have access to an extremely large thing - exactly how large depends on the limitations (speed, range, available destinations) of your FTL drive.
Even if Time is inviolate, you'd still get fantastically, unimaginably wealthy off of this one.