Laser engraving technology is used to embed information code patterns into fluorescent molecules containing hydrogel. Owing to the AIE of such molecules, the embedded patterns will be clearly displayed under ultraviolet light, hence achieving information storage. This novel approach might just turn hydrogel into the next-generation hard drives, achieving massive information storage.

When it comes to a medium for storing information, the first on the mind of most would be a hard drive. The skyrocketing number of pictures and videos that people need to store demands more storage capacity from information storage materials, and adds to the cost. Over the past 50 years, the storage capacity of hard drives has grown from 5MB to terabytes, yet still unable to satiate the thirst for more space. Nowadays, information code, a new type of information storage material that has been gaining attention, could be the solution. Within only a few years, it has not only evolved from one-dimensional code, to two, then three, but also been put into wide application.

According to HUST on October 20, the team led by Professor Ji Xiaofan of its School of Chemistry and Chemical Engineering is working with the team led by Professor Tang Benzhong, Member of the Chinese Academy of Sciences from the Chinese University of Hong Kong (Shenzhen). Together, they have developed a supramolecular hydrogel that can achieve massive information storage. Professor Ji Xiaofan said, “As a new type of information storage material, the hydrogel is anticipated to overcome information code’s bottleneck of only being able to store a single type of information, and can store massive information like a hard drive.” Related papers are published on Advanced Materials.

Read digital information quicker and easier.

As the society and economy develop, so does the demand for information storage. According to Professor Ji Xiaofan, when hard drives were invented in 1956, they could hold no more than 5MB of data. As technology advanced, their storage space grew exponentially, from 30 MB in 1973 to terabytes in 2007. “The rapid expansion of the storage space of hard drives, from minimal to the TBs, has greatly promoted the advancement of a digital society.”

In recent years, information codes, represented by two-dimensional codes, have enjoyed a wide application, from commodity circulation, book management, anti-counterfeiting to ensuring confidentiality, but normally they can only store a single type of information and cannot meet the needs of social development. Can an information code store massive information like a hard drive? Professor Ji told the reporters confidently: “This seemingly unattainable idea is gradually becoming a reality.”

An information code can be divided into three types based on its pattern: one-dimensional code, two-dimensional code, and three-dimensional code. A one-dimensional code is also called a barcode. It consists of many parallel black and white strips of different widths that are lined up in one direction (hence one dimensional) according to a certain coding rule. A two-dimensional code lines up a certain geometric figure both horizontally and vertically (hence two-dimensional) in a specific pattern to form a black and white matrix of barcodes to record data symbols. A three-dimensional code adds different color matrixes based on a typical black and white two-dimensional code to form a unique color pattern.

Although the trio has different principles, they are essentially image codes that convert text (numbers) into images for easy recognition and input by machines (terminals).

Professor Ji explained that compared with traditional information storage materials, information codes are more straightforward, and allow easier and quicker data reading.

“Code in code” may enable multi-layer storage.

To improve the storage capacity of information codes, Professor Ji’s team designed a hydrogel. A source from Ji’s team explained that to let the hydrogel store information, they must find a way to make hydrogel chromogenic, so that the corresponding information pattern can be displayed. However, in the high aggregate state, a typical fluorescent chromophore’s fluorescence will be weakened, or it may not even emit light. This is a phenomenon known as “aggregation-caused quenching” (ACQ).

As early as 2001, Academician Tang Benzhong’s team already discovered another special phenomenon: some fluorescent molecules show stronger fluorescence when aggregated, and they termed this “aggregation-induced emission” (AIE) effect. Subsequently, fluorescent molecules with AIE effect properties have been continuously applied in many fields such as smart sensing materials, liquid crystal or polarized light materials, high-efficiency OLED display and lighting materials, organelle imaging and long-term tracking fluorescent probes.

With the excellent luminescence properties of this fluorescent molecule, Professor Ji Xiaofan’s team designed and prepared 3 kinds of AIE supramolecular hydrogels with different fluorescent colors (red, yellow, and blue). Through the supramolecular assembly of the gel interface, a stable hydrogel assembly is formed, which can be used as a multi-color three-dimensional code to store information. By using laser engraving technology to embed information code patterns into the hydrogel, and relying on the AIE effect exhibited by fluorescent molecules in the hydrogel, the embedded patterns will be clearly shown under ultraviolet light, thereby achieving information storage.

The research team also proposed a “code in code” strategy to embed different types of information codes in AIE supramolecular hydrogels. In doing so, not only would storing massive one-dimensional or two-dimensional information be possible, multi-leveled storage for one, two and three-dimensional information respectively would also be feasible. The “code in code” approach inspired them to design “one-dimensional code in three-dimensional code” and “two-dimensional code in three-dimensional code”, and embed both one and two-dimensional codes into a three-dimensional code concurrently. The result is a great improvement in the information code’s storage capacity.

Large scale application of hydrogel remains to be solved.

“The application of information codes is already prevalent in our daily lives.” Professor Ji Xiaofan further predicted that in the future, information codes would be widely used in many fields such as logistics, health care, tourism, finance, etc., to promote the vigorous development of information storage technology.

However, most of the current researches are based on the independent application of a single type of information code, which can only store one type of information. This makes the breakthrough by Professor Ji’s team even more significant since the team’s new hydrogel-based new information storage material can store multiple types of information.

According to the team’s relevant researchers, the hydrogel’s structure is similar to that of living tissue, and is non-irritating and non-sensitizing. When in contact with human tissues, blood, etc., its ability to adhere to cells and protein is weak. All these properties give it outstanding bio-compatibility. In addition, the hydrogel contains plenty of water and uses water as the solvent, which is environmentally friendly, clean, and easy to obtain. This property also gives this material a significant advantage in the application. In recent years, hydrogel materials have been successfully used as wound dressings, antipyretic patches, and drug carriers. When used as an information storage material, its flexibility and bio-compatibility advantages will bestow it with greater application value in wearable smart devices, flexible devices and other fields.

Compared with information storage technologies such as inorganic silicon and quantum dots, AIE hydrogel is easy to control and process, and is expected to provide an effective solution for a new generation of information storage technology.

“Despite the obvious advantages, technical breakthroughs are still needed.” Professor Ji admitted. In dry environments, hydrogels are prone to rapid moisture-losing and drying-up, while in extremely cold environments it is susceptible to freezing. These shortcomings may result in hydrogel losing some of its functions. Besides, laser engraving technology is needed to embed information codes into the hydrogel when storing information, which undoubtedly adds to the process difficulty.

In the paper, the team’s demonstration of the hydrogel’s information storage effects was limited. “Theoretically, if we embed more information code patterns in each gel unit of the gel assembly, we can store an infinite amount of information.” Professor Ji Xiaofan said. But, this hypothesis faces a practical issue. When a large amount of information is introduced into hydrogel of a certain specification, the number of patterns will greatly increase, while the pattern surface area will be relatively reduced, which puts a stringent demand on the production process. If the massive application is ever to be achieved, the obstacle of the need for more sophisticated equipment remains to be overcome.

Photograph by: Visual China Group

Reported by: Wu Chunxin

Corresponded by: Wang Xiaoxiao

Edited by: Peng Yumeng