Novel soft materials should comprise multiple supramolecular nanostructures whose responses (for example, assembly and disassembly) to external stimuli can be controlled independently. Such multicomponent systems are present in living cells and control the formation and break-up of a variety of supramolecular assemblies made of proteins, lipids, DNA and RNA in response to external stimuli; however, artificial counterparts are challenging to make. Here, we present a hybrid hydrogel consisting of a self-sorting double network of nanofibres in which each network responds to an applied external stimulus independent of the other. The hydrogel can be made to change its mechanical properties and rates of release of encapsulated proteins by adding NaSO or bacterial alkaline phosphatase. Notably, the properties of the gel depend on the order in which the external stimuli are applied. Multicomponent hydrogels comprising orthogonal stimulus-responsive supramolecular assemblies would be suitable for designing novel adaptive materials.
Nanoscale measurements provide insight into the nano world. For instance, nanometric spatiotemporal distribution of intracellular pH is regulated by and regulates a variety of biological processes. However, there is no general method to fabricate nanoscale pH sensors. Here, we, to endow pH-sensing functions, tailor the surface properties of a fluorescent nanodiamond (FND) containing nitrogen-vacancy centers (NV centers) by coating the FND with an ionic chemical layer. The longitudinal relaxation time T 1 of the electron spins in the NV centers inside a nanodiamond modified by carboxyl groups on the particle surface was found to depend on ambient pH between pH 3 and pH 7, but not between pH 7 and pH 11. Therefore, a single particle of the carboxylated nanodiamond works as a nanometer-sized pH meter within a microscopic image and directly measures the nanometric local pH environment. Moreover, the pH dependence of an FND was changed by coating it with a polycysteine layer, which contains a multitude of thiol groups with higher pK a. The polycysteine-coated nanodiamond obtained a pH dependence between pH 7 and pH 11. The pH dependence of the FND was also observed in heavy water (D2O) buffers. This indicates that the pH dependence is not caused by magnetic noise induced by 1H nuclear spin fluctuations, but by electric noise induced by ion exchanges. Via our method, the sensitive pH range of the nanodiamond pH sensor can potentially be controlled by changing the ionic layer appropriately according to the target biological phenomena.
Living cells exhibit sophisticated functions because they contain numerous endogenous stimuli-responsive molecular systems that independently and cooperatively act in response to an external circumstance. On the other hand, artificial soft materials containing multiple stimuli-responsive molecular systems are still rare. Herein, we demonstrate a unique multicomponent hydrogel composed of a self-sorting double network prepared through a post-assembly fabrication (PAF) protocol. The PAF protocol allowed the construction of a well-ordered hydrogel with a dual-biomolecule response to two important biomolecules (adenosine triphosphate (ATP) and sarcosine). Such a hydrogel could not be prepared through a one-step mixing protocol. The resultant multicomponent hydrogel responded to ATP and sarcosine through gel–sol transition behavior programmed in an AND logic gate fashion. Finally, we applied the multicomponent hydrogel to the controlled release of an antibody.
Hydrogelators are small, self-assembling molecules that form supramolecular nanofiber networks that exhibit unique dynamic properties. Development of supramolecular hydrogels that degrade in response to various biomolecules could potentially be used for applications in areas such as drug delivery and diagnostics. Here we provide a synthetic procedure for preparing redox-responsive supramolecular hydrogelators that are used to create hydrogels that degrade in response to oxidizing or reducing conditions. The synthesis takes ∼2-4 d, and it can potentially be carried out in parallel to prepare multiple hydrogelator candidates. This described solid-phase peptide synthesis protocol can be used to produce previously described hydrogelators or to construct a focused molecular library to efficiently discover and optimize new hydrogelators. In addition, we describe the preparation of redox-responsive supramolecular hydrogel-enzyme hybrids that are created by mixing aqueous solutions of hydrogelators and enzymes, which requires 2 h for completion. The resultant supramolecular hydrogel-enzyme hybrids exhibit gel degradation in response to various biomolecules, and can be rationally designed by connecting the chemical reactions of the hydrogelators with enzymatic reactions. Gel degradation in response to biomolecules as triggers occurs within a few hours. We also describe the preparation of hydrogel-enzyme hybrids arrayed on flat glass slides, enabling high-throughput analysis of biomolecules such as glucose, uric acid, lactate and so on by gel degradation, which is detectable by the naked eye. The protocol requires ∼6 h to prepare the hydrogel-enzyme hybrid array and to complete the biomolecule assay.
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