Imagine wearing jewellery that emits scents depending on your mood or having a television that provides picture and sound but also the smells associated with what you are watching.

These products may be just around the corner following the patenting of a device that combines electronics and chemicals on a single chip.

The new microchip was developed at the Massachusetts Institute of Technology's Microsystems Technology Laboratory. The work, by Mr John Santini, Professor Michael Cima and Professor Robert Langer and described in a recent issue of Nature, opens the way to self-contained drug delivery systems that could be implanted in a patient to provide automated drug therapies.

The researchers describe it as a possible "pharmacy on a chip" or a "smart tablet". The chip can also be made very cheaply. "We're making them right now in a research lab for about $20 dollars each (€17.75)," Professor Cima said. "With process optimisation and larger batches, I could easily see making them for a few dollars each, or even less."

There is nothing else quite like it, they suggest. The chips are made like any silicon wafer semiconductor device, so the technology is well known, but the researchers added small wells which can be filled with any chemical or substance you like. The tops of the wells are sealed with a thin layer of gold, just 0.3 mm thick, and each has its own circuitry, Mr Santini explained.

If a power supply of no more than one volt is applied, the gold layer dissolves in a matter of seconds, releasing the trapped powder, liquid or gel. The MIT prototype is about the size of an Irish five pence piece and contains 34 reservoirs, each the size of a pinprick. "But there is room for over 1,000 reservoirs, potentially thousands more if you make [the reservoirs] smaller," stated Dr Langer.

Each tiny well contains about 25 nanolitres. If you took a single grain of salt and cut it down into quarters this would represent a volume similar to each reservoir. "The reservoirs and microchips could both be made much larger or smaller, depending on the desired application," Dr Langer said.

With further refinements the device could be completely self contained with its own power supply and a microprocessor to control when each reservoir should be opened. The chip could then be either pre-programmed for the release of chemicals, triggered by remote control or activated by an on-chip biosensor.

Such a device could easily be implanted under the skin or used as a skin surface drug delivery system. Existing implant systems deliver drugs continuously over time, but the new chip would "allow you to control not only the amount of drug released, but also the exact time of delivery", Mr Santini said. Intelligent diagnostics are another possible area. Many tests involve adding precise amounts of chemicals in a specific order to bodily fluids such as blood and saliva, with results available in hours or days. The microchip could be programmed to release a sequence of chemicals over a period allowing faster testing.

More fanciful but achievable uses include jewellery that carries an imbedded chip carrying a variety of scents. The chip could be programmed to respond to body temperature or salinity of the skin.

Professor Langer also suggested a television fitted with a chip that could deliver odours keyed to the images appearing on the screen. A trigger in the broadcast signal could be used to release the smells of a Sunday roast during a gravy advertisement or the pungent scent of dung during a wildlife programme.

The prototype only works when the chip is in solution but the team already has plans for a chip that operates in dry conditions. The prototype took five years to develop and was the subject of Mr Santini's doctoral thesis. It was conceived of by Professor Langer and developed in conjunction with Professor Cima, and the team already has a number of patents protecting the technology.

It was decided early on to develop the technology around existing silicon wafer techniques. This allowed the potential new uses to merge with existing electronic technologies, Mr Santini said. He expected products containing the combination chips to emerge in about two years. "The applications, I think, are unlimited," Professor Langer said. "The question is, which are the best ones." The next stop is to change the prototype into a marketable device. "We want to do the engineering to make this into a real application," Professor Cima said.