A microchip that lets you 'stop and smell the roses'

Strap yourself in for the next wave of smart devices: jewelry that emits aromas to match your mood, televisions that give off a cheese smell during a pizza commercial, and pills and implants that dispense drugs in carefully measured doses.

An experimental microchip from the Massachusetts Institute of Technology in Cambridge promises all that and more. The new chip is the first silicon semiconductor to be able to store and release a variety of different chemicals in precise amounts at specific times from tiny, built-in reservoirs. And it has no moving parts: the chemicals are released when a small electric current dissolves a thin gold cap covering each reservoir. Future versions might be made of new, biodegradable materials with biosensors.

"The applications are almost unlimited," said Robert Langer, co-developer of the chip and professor of chemical and biomedical engineering at MIT. "The chips can be made larger or smaller. They can have all kinds of chemicals in them. And they can be integrated with microprocessors to make them smart."

Professor Langer, Michael Cima, a ceramic processing professor at MIT, and John Santini, a chemical engineering graduate student at MIT, spent five years developing the chip. Their research, funded in part by the National Science Foundation, appears in today's issue of Nature.

The first products using MIT's controlled-release chemical microchip technology could appear in a few years, Langer says. The manufacturing technology already exists, but the chip is only in prototype form now. It needs to be improved and refined for particular applications.

Langer and his colleagues become animated when they talk about future uses of the chip, spouting a new application with each sentence. They envision more life-like entertainment systems that can unleash an almost unprecedented assault on the senses.

Imagine a movie theater screen that sprays pine scent during a nature film to complement the stereo surround-sound crackling of brush in the forest and the digital video variations of green in fir tree branches. New cars will waft lemon to enliven stale air. And chemists will use hand-held probes with reagent-laden chips for medical diagnostics or detection of polluting chemicals.

Graduate student Santini said other scientists are experimenting with a similar idea: integrating smell into virtual-reality goggles via tubes carrying scents.

Existing silicon microchips for electronic devices can think to some degree and store in memory the details of our lives. The MIT microchip adds to this the sense of smell. And a new type of chip, the DNA chip, marries biochemistry and computer technology to read genetic material in people.

The MIT microchip adds to that the ability to dispense stored chemicals on demand. MIT already holds a patent on the chip's concept, and two more patents are pending.

"The microchip is unique. There are potentially lots of uses in consumer products and drug-delivery systems," said Mark Saltzman, professor of biomedical engineering at Cornell University in Ithaca, N.Y. Professor Saltzman saw a demonstration of the chip. "And you can deliver the fluids by dissolving a membrane, so you don't need small micro-pumps."

The current dime-sized chip has 34 reservoirs etched into it. Each reservoir can hold a different liquid, gel, or solid chemical about the size of a grain of salt. The chemicals can be released one at a time or in combinations at predetermined times and amounts. Future chips might have 1,000 or more reservoirs.

In the current test chip, each reservoir has a wire connecting it to an external power source. A reservoir is opened by a small current applied between its thin gold cover (the anode) and another gold structure (the cathode). The cathode remains intact, but the anode is dissolved by an electrochemical reaction between it and the salt solution in which it sits. This in turn releases the chemical in the reservoir.

Langer and his colleagues say it should be possible to make an autonomous microchip without the wires or salt bath by using a small battery and a microprocessor. This also would allow the chip to be pre-programmed to release chemicals, to be activated by an on-chip biosensor, or to be triggered by remote control.

In electronics applications, a remote device could prompt a television to emit scents keyed to an advertisement or scene. Much engineering work needs to be done, they say, before consumers can buy an earring with an aroma chip that releases scent to match the wearer's mood.

Cima expects the chip, which can be made using today's silicon chip manufacturing processes, to cost only a few dollars over time. It now costs about $20 to make each prototype.

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