Acid-responsive polydiacetylene-Na+ assemblies with unique red-to-blue color transition.

Polydiacetylenes (PDAs), conjugated and stimuli-responsive polymers, are of interest for colorimetric sensing technologies. Commercially available PDAs with carboxylic headgroup do not show any colorimetric response to acid. To achieve acid-responsive property, the headgroups of PDAs are often modified with some functional moieties, involving complicated synthetic processes. This contribution presents a facile approach to develop acid-responsive materials via co-assembly of PDA and excess sodium hydroxide (NaOH). After low-temperature incubation and photopolymerization, the mixtures of 10,12-tricosadiynoic acid (TCDA) and NaOH develop into red-phase poly (TCDA-Na+) assemblies. A unique red-to-blue color transition occurs when the poly (TCDA-Na+) assemblies are exposed to hydrogen chloride (HCl) acid both in aqueous solution and gas phase. Increasing the concentrations of NaOH and TCDA monomer during the self-assembly process affects the molecular organization and morphologies of the resultant poly (TCDA-Na+) assemblies, which in turn govern the sensitivity to acid. The results of this study offer a simple and inexpensive method for developing acid-responsive PDAs, extending their colorimetric sensing applications.

A Color-Detectable Vitamin C Controlled-Release System Fabricated Using Electrospinning.

This study develops a vitamin C controlled-release system, trackable via color changes as a function of vitamin C release. The system is composed of coaxial microfibers prepared via coaxial electrospinning, with a core of poly(ethylene oxide) (PEO) incorporating vitamin C, and a shell composed of polycaprolactone (PCL) containing polydiacetylene (PDA) as the color-changing material. The shell thickness is controlled by adjusting the amount of PCL ejected during electrospinning, allowing regulation of the release rate of vitamin C. When vitamin C added to PEO penetrates the PCL layer, the color of PDA changes from blue to red, indicating a color change. The results of this study can be applied to devices that require immediate detection of vitamin C release levels.

Inkjet Printing of Nanoscale Functional Patterns on 2D Crystalline Materials and Transfer to Soft Materials.

Nanometer-scale control over surface functionality is important in applications ranging from nanoscale electronics to regenerative medicine. However, approaches that provide precise control over surface chemistry at the nanometer scale are often challenging to use with higher throughput and in more heterogeneous environments (e.g., complex solutions, porous interfaces) common for many applications. Here, we demonstrate a scalable inkjet-based method to generate 1 nm-wide functional patterns on 2D materials such as graphite, which can then be transferred to soft materials such as hydrogels. We examine fluid dynamics associated with the inkjet printing process for low-viscosity amphiphile inks designed to maximize ordering with limited residue and show that microscale droplet fluid dynamics influence nanoscale molecular ordering. Additionally, we show that scalable patterns generated in this way can be transferred to hydrogel materials and used to create surface chemical patterns that induce adsorption of charged particles, with effects strong enough to overcome electrostatic repulsion between a charged hydrogel and a like-charged nanoparticle.

Sub-10 µm Soft Interlayers Integrating Patterned Multivalent Biomolecular Binding Environments.

Designing surfaces that enable controlled presentation of multivalent ligand clusters (e.g., for rapid screening of biomolecular binding constants or design of artificial extracellular matrices) is a cross-cutting challenge in materials and interfacial chemistry. Existing approaches frequently rely on complex building blocks or scaffolds and are often specific to individual substrate chemistries. Thus, an interlayer chemistry that enabled efficient nanometer-scale patterning on a transferrable layer and subsequent integration with other classes of materials could substantially broaden the scope of surfaces available for sensors and wearable electronics. Recently, we have shown that it is possible to assemble nanometer-resolution chemical patterns on substrates including graphite, use diacetylene polymerization to lock the molecular pattern together, and then covalently transfer the pattern to amorphous materials (e.g., polydimethylsiloxane, PDMS), which would not natively enable high degrees of control over ligand presentation. Here, we develop a low-viscosity PDMS formulation that generates very thin films (<10 µm) with dense cross-linking, enabling high-efficiency surface functionalization with polydiacetylene arrays displaying carbohydrates and other functional groups (up to 10-fold greater than other soft materials we have used previously) on very thin films that can be integrated with other materials (e.g., glass and soft materials) to enable a highly controlled multivalent ligand display. We use swelling and other characterization methods to relate surface functionalization efficiency to the average distance between cross-links in the PDMS, developing design principles that can be used to create even thinner transfer layers. In the context of this work, we apply this approach using precision glycopolymers presenting structured arrays of N-acetyl glucosamine ligands for lectin binding assays. More broadly, this interlayer approach lays groundwork for designing surface layers for the presentation of ligand clusters on soft materials for applications including wearable electronics and artificial extracellular matrix.

Light-Induced Self-Assembled Polydiacetylene/Carbon Dot Functional "Honeycomb".

The design of functional supramolecular assemblies from individual molecular building blocks is a fundamental challenge in chemistry and material science. We report on the fabrication of "honeycomb" films by light-induced coassembly of diacetylene derivatives and carbon dots. Specifically, modulating noncovalent interactions between the carbon dots, macrocyclic diacetylene, and anthraquinone diacetylene facilitates formation of thin films exhibiting a long-range, uniform pore structure. We show that light irradiation at distinct wavelengths plays a key role in the assembly process and generation of unique macro-porous morphology, by both initiating interactions between the carbon dots and the anthraquinone moieties and giving rise to the topotactic polymerization of the polydiacetylene network. We further demonstrate utilization of the macro-porous film as a photocatalytic platform for water pollutant degradation and as potential supercapacitor electrodes, both applications taking advantage of the high surface area, hydrophobicity, and pore structure of the film.

Macrocyclic Diacetylene / Sulfonate Fluorophore Hierarchical Multifunctional Nanotoroids.

Functional supramolecular materials exhibit important features including structural versatility and versatile applications. Here, this study reports the construction of unique hierarchically organized nanotoroids exhibiting fluorescence, photocatalytic, and sensing properties. The nanotoroids comprise of macrocyclic diacetylenes (MCDA) and 8-anilino-1-naphthalene sulfonate (ANS), a negatively charged aromatic fluorescent dye. This study shows that the hierarchical structure of the nanotoroids consist of MCDA nanofibers formed by stacked diacetylene monomers as the basic units, which are further bent and aligned into toroidal organization by electrostatic and hydrophobic interactions with the ANS molecules. The amine moieties on the nanotoroids surface are employed for deposition of gold nanostructures - Au nanoparticles or Au nanosheets - which constitute effective platforms for photocatalysis and surface enhanced Raman scattering (SERS)-based sensing.

Spray-On Colorimetric Sensors for Distinguishing the Presence of Lead Ions.

Sprayable stimuli-responsive material coatings represent a new class of detection system which can be quickly implemented to transform a surface into a color-responsive sensor. In this work, we describe a dipicolylamine-terminated diacetylene-containing amphiphile formulation for spray coating on to a simple paper substrate to yield disposable test strips that can be used to detect the presence of lead ions in solution. We find the response to be very selective to only lead ions and that the sensitivity can be modulated by altering the UV curing time after spraying. Sensitive detection to at least 0.1 mM revealed a clear color change from a blue to red phase. This represents the first demonstration of a spray-on sensor system capable of detection of lead ions in solution.