By borrowing a page from the genomics revolution, University at Buffalo chemists have taken a major step toward placing hundreds, and possibly even thousands, of reusable chemical sensors in an area smaller than a dime.
Their work, published in the March 1 issue of Analytical Chemistry, could transform sensor technology by providing agricultural, clinical, environmental and pharmaceutical laboratories with a small, fast and portable methodology for simultaneously detecting numerous chemicals in a sample a hundred or a thousand times smaller than a drop of water.
A provisional patent has been filed.
The research overcomes a key obstacle in exploiting high-tech materials, called xerogels, into which the UB team has pioneered investigations as the basis of new chemical sensors.
Xerogels are porous glasses, developed through sol-gel processing techniques in which a special solution reacts to form a porous polymer. The resulting xerogel is a rigid material, like a glass, only it consists of an intricate network of nanoscopic pores. In past work, the UB group has developed innovative ways to stabilize and trap proteins within the xerogels. These proteins then can be put to work to signal the presence of important chemicals in a sample.
‘We now understand very well the chemistry involved in making good xerogels that contain active proteins,’ said Frank V. Bright, Ph.D., co-author and associate chair and professor in the Department of Chemistry in UB’s College of Arts and Sciences.
The problem with traditional xerogel-based sensors, he explained, is that they are large and designed to detect only one chemical species. The UB researchers wanted to shrink down all of the sensor technology so they could place multiple sensors in a small area and obtain information on the presence of many chemicals in a single, small sample.
‘The process of having to analyse for different molecules one at a time is amazingly time-consuming, and it turns out to waste a whole lot of the sample,’ said Bright.
Initially, Bright and Eun Jeong Cho, lead author and doctoral candidate in the UB Department of Chemistry, micromachined wells that were on the order of 1/25,000th of an inch in diameter on top of a light emitting diode (LED), a tiny, inexpensive chip made of semiconducting materials that can turn electrical energy into light.
‘Using our xerogels in these wells on a LED was a great idea on paper, but the volume of a well turns out to be fairly small, about a billionth of a quart,’ said Bright. ‘Trying to fill the wells turned out to be a nightmare.’
But then Cho suggested pin-printing, a technology widely used in genomics in which an extremely thin pin point sucks up by capillary action small volumes of solution and deposits or prints them onto microscope slides.
Using a commercial pin-printer, just like those hard at work in DNA microarray facilities, the UB team had suddenly conquered the problem.
‘Pin-printing is like taking a tiny quill pen, dipping it into a solution and instead of filling wells, we contact-print the sol-gel solution onto the surface directly to form an array of xerogel-based sensors; we no longer need wells at all,’ Bright said.
‘Because the volume delivered by these pin-printers is less than a trillionth of a quart, the sensors are very small, so we can cram many different sensors in a small footprint and, in principle, detect hundreds or even thousands of chemical species simultaneously.’
Bright and his team are now working on pin-printing chemical sensors onto the top of an LED to form a fully self-contained sensor array platform.
The work was funded by the US National Science Foundation.