“Cancer treatments have hit a wall,” says chemist Michael J. Sailor of the University of California at San Diego. Today’s chemotherapy drugs leave the body too quickly, and both chemo and radiation kill healthy cells indiscriminately, he explains. So he has developed “nanoworms,” strings of iron-oxide particles that could swim through your blood to kill nascent cancerous tumors—and nothing else.

Its a drizzly morning on New Yorks Upper East Side, and Rockefeller University microbiologist David Thaler is sipping a double espresso amid the retro-hippie pillows and dangling paper stars of Java Girl, a favorite haunt of the neighborhoods brainiac Nobel laureates, aging poets and famous entertainers. Thaler somehow manages to embody all three—a long, graying ponytail curling down the middle of his back, wire-frame glasses askew over expansive brown eyes, and a schnozz to rival an Einstein, Ginsberg or Allen. Thaler is one of the leading cheerleaders for a new field of biotechnology aimed at engineering the bacteria inside us to deliver drugs, destroy tumors, actively fight infection, and even vaccinate against their disease-causing kin.