The α-helix is the most prevalent conformation in proteins. However, formation of the α-helical conformation remains a challenge for short peptides with less than 5 amino acids. We demonstrated in this study that enzyme-instructed self-assembly (EISA) provides a unique pathway to assist the self-assembly of peptides into the α-helical conformation, while a heating–cooling process leads to a conformation more similar to a β-sheet. The same peptide with different conformations self-assembled into different nanostructures. The peptide with α-helical conformation self-assembled into stable nanofibers and hydrogels, while the other one assembled into an unstable nanoparticle suspension. The nanofiber solution exhibited better stability against proteinase K digestion and an enhanced cellular uptake compared to the nanoparticle solution. Therefore, the nanomedicine formed by the α-helical peptide showed a better inhibition capacity against cancer cells in vitro and significantly inhibited tumor growth in vivo compared to the one formed by the β-sheet peptide. Our study demonstrates the unique advantages of EISA to assist peptide folding and self-assembly into biofunctional nanomaterials.

We showed in this study that enzymatic triggering is a totally different pathway for the preparation of self-assembling nanomaterials to the heating–cooling process. Because the molecules were under lower energy levels and the molecular conformation was more ordered during the enzymatic triggeration under mild conditions, nanomaterials with higher supramolecular order could be obtained through biocatalytic control. In this study, nanoparticles were obtained by an enzymatic reaction and nanofibers were observed through the heating–cooling process. We observed a distinct trough at 318 nm from the CD spectrum of a particle sample but not a fiber sample, suggesting the long range arrangement of molecules and helicity in the nanoparticles. The nanoparticles with higher supramolecular order possessed much better potency as a protein vaccine adjuvant because it accelerated the DC maturation and elicited stronger T-cells cytokine production than the nanofibers. Our study demonstrated that biocatalytic triggering is a useful method for preparing supramolecular nanomaterials with higher supramolecular order and probably better bioactivity.

Fluorescence probes have been widely applied for the detection of important analytes with high sensitivity and specificity. However, they cannot be directly applied for the detection in samples with autofluorescence such as blood. Herein, we demonstrated a simple but effective method of surface-induced self-assembly/hydrogelation for fluorescence detection of an enzyme in biological fluids including blood and cell lysates. The method utilizes an attracting glass surface to induce self-assembly of an enzyme-generating fluorescent probe. After removing the upper solution, the fluorescence turn-on at the glass surface can therefore be used for the detection of enzyme activity. By judging the thickness and color depth of hydrogels at the surface of the glass plates, we could also estimate the enzyme activity by naked eyes. Our study not only expands the application of molecular self-assembly but also provides a useful method that can be applied for direct detection of enzyme activity in complex biological samples such as blood and cell lysates.

We report in this study on optimized ratiometric fluorescent probes by peptide self-assembly. The resulting self-assembled nanoprobes show extraordinary stability in aqueous solutions and extremely low background fluorescence in buffer solutions. Our optimized probes with much bigger ratiometric fluorescence ratios also show an enhanced cellular uptake, lower background noise, and much brighter fluorescence signal in the cell experiment. Our study provides a versatile and very useful strategy to design and produce fluorescent probes with better performance.

We reported in this study a versatile method to prepare multi-responsive supramolecular hydrogels for drug delivery application.

The combination of an environment-sensitive fluorophore, 4-nitro-2,1,3-benzoxadiazole (NBD), and peptides have yielded supramolecular nanofibers with enhanced cellular uptake, brighter fluorescence, and significant fluorescence responses to external stimuli. We had designed and synthesized NBD-FFYEEGGH that can form supramolecular nanofibers and emit brighter than its counterpart of NBD-EEGGH without the self-assembling property. The nanofibers of NBD-FFYEEGGH could specifically bind to Cu2+, leading to the formation of fluorescence quenched elongated nanofibers. This fluorescence quenching property was enhanced in self-assembling nanofibers and could be applied for detection of Cu2+ in vitro and within cells. In a further step, an enzyme-cleavable DEVD peptide was placed between NBD-FFY and the copper binding tripeptide GGH. The resulting self-assembling peptide NBD-FFFDEVDGGH also showed strong fluorescence quenching to Cu2+. Upon the enzymatic cleavage to remove the Cu2+-binding GGH tripeptide from the peptide, the fluorescence was restored. The cellular uptake of nanofibers was better than that of free molecules because of endocytosis. The supramolecular nanofibers with fluorescence turn-on property could therefore be applied for detection of caspase-3 activity in vitro and within cells. We believe that the combination of environment-sensitive fluorescence and fast responses of supramolecular nanostructures would lead to a useful platform to detect many important analytes.

We report on a peptide-based hydrogel that can stimulate the growth of the bacterium Delftia.

In addition to the widely used polymeric hydrogels, molecular hydrogels are also emerging as promising biomaterials. However, molecular hydrogels typically suffer from poor mechanical properties and relatively low in vivo stability. Here we report on the preparation of two hybrid hydrogels (Hgel I and Hgel II) by the combination of two molecular hydrogelators and alginate, respectively. First, the molecular hydrogelator and sodium alginate were dissolved in water, and then a hydrogel was formed upon triggering by enzymes or reductants. Afterward the resulting hydrogel was soaked in calcium ion solution to form the hybrid hydrogel. The preparation process was easy and mild which allowed the resulting hybrid hydrogels to act as carriers for biomacromolecules such as enzymes. Both Hgel I and Hgel II had better stabilities and mechanical properties than the calcium alginate gel (CAgel) alone. Hgel I had exceptional stability compared with Hgel II and CAgel. The reason we propose is that molecular hydrogelators in Hgel I interacted with alginate more strongly than molecular hydrogelators in Hgel II according to the fluorescence results of these gels. Unlike the porous microstructure of molecular hydrogels, the microstructure of two hybrid hydrogels was almost the same as that of CAgel (film-like morphology) except with some nanofibers embedded. We found that Hgel I was an ideal carrier for enzyme immobilization with high recyclable properties and excellent preservation of enzyme activities due to its good mechanical strength. However, Hgel II was not suitable as a carrier for immobilized lactase probably due to poor affinity between Hgel II and the substrate. Combining the advantages of molecular hydrogels and polymeric hydrogels would broaden the applications of both kinds of hydrogels in the future.

We report on molecular hydrogelators based on peptoid–peptide conjugates with good biocompatibility to different cells and superior stability against proteinase K digestion.

It is well known that the saccharides forming the intricate sugar coat that surrounds the cells play important biological roles in intercellular communication and cell differentiation. Therefore, it is worthwhile developing saccharide-based hydrogels for cell culture study. In this study, three novel saccharide-based compounds were designed and synthesized. It was found that one of them could form hydrogels efficiently, while the other two precipitated from water. The stability of the resulting hydrogel was tested, and the supramolecular nanofiber with fiber diameters in the range of 80–300 nm was characterized as the structural element by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fluorescence microscopy revealed that extensive hydrogen bonds between sugar rings assisted the formation of efficient π–π stacking between aromatic naphthalene groups, thus resulting in the formation of a stable hydrogel in aqueous solution. When the gel was applied for mouse embryonic fibroblast (NIH 3T3), human hepatocellular carcinoma (HepG2), AD293 and HeLa cells culture in two dimensional environments, all of them showed a very good adhesion and good proliferation rate on the top of the hydrogel. These results indicates that the biocompatible hydrogel reported here has a potential to be developed into useful materials for in vitro cell culture, drug delivery, and tissue engineering.A fluorescent saccharide-based supramolecular hydrogel was found to be bioactive for HepG2, AD293, NIH 3T3, and HeLa cell culture in two dimensional environments.

We reported in this study a versatile method to prepare multi-responsive supramolecular hydrogels for drug delivery application.