Supercharged biomacromolecules can maintain their reordered structures induced, for example, by a fingertip touch

May 14, 2018, Wiley
Supercharged biomacromolecules can maintain their reordered structures induced, for example, by a fingertip touch
Credit: Wiley

Stimuli-sensitive materials can respond to physical forces with structural phase transitions. This also applies to biopolymer–surfactant mixtures, a study by German and Chinese scientists now reports. Surprisingly, the newly adopted phases persist after removal of the stress and can be detected by a simple optical read-out technology. Biometric fingerprint detection is an attractive application for this technology. The results are published in the journal Angewandte Chemie.

Liquid crystals are shape-anisotropic molecules that can adopt distinct ordered phases, depending on the physical conditions. Temperature, pressure, or charge can produce color shifts, dark–light switches, or a birefractive appearance, all of which represent changes in the molecular order. Such transitions can also occur in gels, and even in soaps with micellar transitions. The chemical system developed by Andreas Herrmann at the University of Groningen, the Netherlands, and colleagues at the Chinese Academy of Sciences, is a complex of a supercharged polypeptide with a cationic surfactant. The viscous liquid adopted birefringence patterns after simply being touched, to reveal details such as those of a fingerprint.

Seeking to explore the behavior of biological fluids, the scientists designed a series of supercharged polypeptides that form biological soft materials with interesting properties when paired with molecules supplying the opposite charge. The supercharged polypeptides consisted of five amino acid repeating units with one or two negatively charged glutamic acid residues within each unit. As the cationic surfactant, the researchers designed an aromatic azobenzene with a positive charge on one side and a hydrophobic chain on the other. Added together, the polypeptide and the surfactant formed a water-rich polypeptide liquid droplet with an orange hue. In this liquid the scientists found no molecular order, birefringence, or diffraction pattern, and merely an isotropic viscous fluid.

A shear force stimulated a different response. Flowing water or the touch of a finger made the sample birefringent, and ordered patterns were evident, the authors reported. These ordered structures resembled the long-range lyotropic liquid crystalline phases typical for surfactant-containing mixtures. Surprisingly, that order persisted, even after removing the shear. A polarized optical microscope detected birefringence patterns that sensitively recorded the texture of the shear-applying tool. In other words, the minutiae, the ridges and lines on the fingertip that make up a fingerprint, were well-represented in the polarization micrographs.

This remarkable discovery suggests that the supercharged fluid could, in principle, be used for biometric detection. Whereas modern day fingerprint sensors that are not based on ink printing rely on finely adjusted electronics, the scientists present a different setup with microscopic birefringence read-out. However, the exact conditions for the phase transitions in the material and the underlying mechanisms have yet to be explored, the authors remark.

Explore further: Sulfur improves birefringence for developing liquid crystalline molecules

More information: Lei Zhang et al. Genetically Engineered Supercharged Polypeptide Fluids: Fast and Persistent Self-Ordering Induced by Touch, Angewandte Chemie International Edition (2018). DOI: 10.1002/anie.201803169

Related Stories

Scientists make huge strides in imaging science

June 2, 2014

(Phys.org) —University scientists have developed a rapid new technique involving X-ray imaging that allows clear images to be obtained displaying the orientational properties of molecules in solid materials.

Scientists print all-liquid 3-D structures

March 27, 2018

Scientists from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a way to print 3-D structures composed entirely of liquids. Using a modified 3-D printer, they injected threads ...

Recommended for you

Field-responsive mechanical metamaterials (FRMMs)

December 11, 2018

In a recent study published in Science Advances, materials scientists Julie A. Jackson and colleagues presented a new class of materials architecture called field-responsive mechanical metamaterials (FRMM). The FRMMs exhibit ...

CRISPR method for conditional gene regulation

December 11, 2018

A team of engineers at the University of Delaware has developed a method to use CRISPR/Cas9 technology to set off a cascade of activities in cells, a phenomenon known as conditional gene regulation. Their method, described ...

Researchers develop smartphone-based ovulation test

December 11, 2018

Investigators from Brigham and Women's Hospital are developing an automated, low-cost tool to predict a woman's ovulation and aid in family planning. Capitalizing on advancements in several areas, including microfluidics, ...

0 comments

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.