Syringes are a set of items you will use to treat infected patients. Upon activating your Clinic, the chest within it will contain a syringe mold. If this breaks you can craft one using various metals on the Machining Mill, in your clinic's lab space. You can use this mold to craft empty syringes in your Injection Molder. Use the empty syringes to take blood samples from your infected patients. Do not stick multiple patients with the same syringe. If you do, you will ruin that sample. Keep in mind patients don't like to be stuck with needles multiple times and they won't tolerate it for long. Once you have a blood sample from an infected patient, you can create a treatment in the Bioreactor.