Take my advice with a grain of salt because I'm still a student, but I'd join the company. You don't really need large amounts of money just after graduating, and besides, most people in other majors probably end up making even less. On the other hand, working for a small startup would probably be more interesting and exciting, especially if you like the founders. Then, if it doesn't pan out, you would probably have no problem finding a job at a bigger company for a sufficiently high salary. So maybe you'd make less money overall in the event of a the biotech company's failure, but you'd still have enough to not worry and a more interesting experience.

Also, your risk tolerance as a fresh grad is much higher than it will be in the future. You (probably) don't have an expensive lifestyle or a family, and you can live pretty cheaply yourself. So you have much less reason to be leery of equity than somebody older and more established.

I personally think that the best time to work for a small startup is just after graduating, and that it's definitely worth doing at some point in your life. So I would go for it in your position.