Nanodisk Codes

December 27, 2007 By Laura Mgrdichian feature
Nanodisk Codes
Physical binary codes formed by nanodisks carved out of nanorods. Image courtesy Chad Mirkin.

Researchers at Northwestern University have devised a way to use billionth-of-a-meter-sized disks to create codes that could be used to encrypt information, serve as biological labels, and even tag and track goods and personnel.

The nanodisks can form a physical pattern, similar in concept to a barcode, as well as a spectroscopic code, meaning it can exhibit a specific, unique response to electromagnetic radiation, or light, depending on the type of molecule (or molecules) attached to the disks—in other words, how the disks are “functionalized.”

Nanostructures can be ideal for encoding. Their small size allows them to be hidden easily in a variety of materials and objects, and scientists' ability to easily tailor their physical and chemical properties makes it possible to design nanostructures for specific coding functions.

In a paper describing this work, published in a recent edition of Nano Letters, the researchers, led by Northeastern chemist Chad Mirkin, describe how the nanodisks can form physical binary codes. The group started with nanorods made of gold and nickel and, using a method they developed, carved disks out of each rod. The disks are created in twos, with up to five pairs created per rod.

Each of the five disk-pair locations along the rod can correspond to a “0” or a “1,” depending on whether that location is occupied by a disk pair. For example, if only one disk pair is present, and it is situated at the third location, that code is read as 00100. If two disk pairs are present, at the fourth and fifth locations, the code is 00011.

“This is a rapid, low cost way of making many unique nanostructures that can identified and read based upon high sensitivity spectroscopic techniques,” Mirkin said to “It's a beautiful example of how the ability to shape and control the size and surface composition of a nanostructure can translate into significant technological advantages.”

The group has made nanodisk arrays as long as 12 micrometers (millionths of a meter), which can support as many as 10 disk pairs, yielding 287 physical nanodisk codes.

The researchers increased the codes' usefulness by functionalizing them with a class of dye molecules called chromophores. This makes the codes spectroscopically active, allowing each to emit a unique light spectrum when illuminated by an exterior light source, typically a laser beam.

Due to the physical and spectroscopic codes they can exhibit, the nanodisks are particularly suited for biological tagging, a method of tracking and detecting individual biological materials, such as DNA. The researchers proved this by attaching pieces of single-stranded DNA to the surfaces of the nanodisks in a 11011 code. Each of these strands was complementary to half of a “target” DNA strand—the strand being tagged. The other half of the target strand was complementary to a “reporter” strand, rendered spectroscopically active with dye. The overall structure formed a three-strand “sandwich,” with the target strand in the middle.

The group also created a similar sandwich structure using a different reporter strand and a 10101 code, and then mixed the two samples. They were able to successfully detect and distinguish between the unique spectrums emitted by both reporter molecules.

Citation: Nano Lett., 7 (12), 3849-3853, 2007

Copyright 2007
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of

Explore further: Gene on-off switch works like backpack strap: Team unravels how loops form in genome

Related Stories

A new single-molecule tool to observe enzymes at work

September 28, 2015

A team of scientists at the University of Washington and the biotechnology company Illumina have created an innovative tool to directly detect the delicate, single-molecule interactions between DNA and enzymatic proteins. ...

DNA molecules can detect pathogens, deliver drugs

May 20, 2009

( -- First, Cornell researchers created DNA "bar codes" -- strands of the genetic material that quickly identify the presence of different molecules by fluorescing. Now, they have created new DNA molecules that ...

Recommended for you

Mathematicians identify limits to heat flow at the nanoscale

November 24, 2015

How much heat can two bodies exchange without touching? For over a century, scientists have been able to answer this question for virtually any pair of objects in the macroscopic world, from the rate at which a campfire can ...

New sensor sends electronic signal when estrogen is detected

November 24, 2015

Estrogen is a tiny molecule, but it can have big effects on humans and other animals. Estrogen is one of the main hormones that regulates the female reproductive system - it can be monitored to track human fertility and is ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Dec 30, 2007
I think physorg messed up this story.. check out this related blog post: http://1stedition...k-codes/
not rated yet Jan 02, 2008
How do you figure 287 possible codes?
1 / 5 (1) Jan 10, 2008
10 disk pairs equates to 20 "flags" each corresponding to 1 or 0.

last time I checked,

2^20 = 1024^2 = 1,048,576

unique combinations.

In any case, it is binary, and 287 is absolutely the wrong number no matter how many discs are possible.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.