Mei-Yu Yeh

Hydrazine is a highly toxic, potentially carcinogenic compound widely used in industry, necessitating sensitive detection. Meanwhile, latent fingerprint identification requires high-contrast, high-resolution imaging. Both demand rapid and visually discernible signals, motivating the development of integrated materials for simultaneous chemical sensing and forensic imaging. Herein, we report a rationally designed imidazole-based fluorophore, DPI–DCN, that integrates reaction-based hydrazine sensing with high-resolution latent fingerprint (LFP) visualization. By incorporating a strongly electron-withdrawing dicyanovinyl unit, DPI–DCN establishes an efficient donor–acceptor framework, leading to enhanced intramolecular charge transfer (ICT) and pronounced bathochromic shifts relative to its ester analogue, DPI–DET. These photophysical characteristics are supported by density functional theory calculations, which reveal a reduced HOMO–LUMO gap and favorable orbital separation. DPI–DCN exhibits excellent selectivity toward hydrazine, displaying a distinct fluorescence “turn-off” response with a low detection limit of 1.94 μM. Mechanistic investigations using 1H NMR and mass spectrometry confirm that nucleophilic addition of hydrazine to the dicyanovinyl moiety disrupts π-conjugation and suppresses ICT, accounting for the observed optical changes. Beyond solution-phase sensing, DPI–DCN functions as an effective solid-state fluorescent powder for LFP development, enabling high-contrast imaging across diverse substrates, including aged fingerprints. Notably, multilevel fingerprint features up to level III are clearly resolved, demonstrating its capability for detailed forensic analysis. This work establishes a direct structure–property–function relationship and presents a versatile molecular platform that bridges chemical sensing and forensic imaging, offering new opportunities for integrated analytical and security applications.

Hydrogels are highly hydrated cross-linked polymer networks whose composition and structure can be engineered to achieve desirable mechanical properties, adhesion, and biocompatibility for biomedical, functional material, and environmental applications. In this study, acrylamide (AAM) was employed as the primary backbone monomer to construct the fundamental polymer network. Methacrylated lysine (LysMA), methacrylated poly(vinyl alcohol) (PVAMA), and carboxymethyl cellulose (CMC) were incorporated as functional comonomers, while N,N'-methylenebis(acrylamide) (MBAA) served as the chemical cross-linker to establish a stable and tunable three-dimensional structure. The multiple intermolecular interactions of the amine and carboxyl groups provided by LysMA effectively enhanced interfacial adhesion. Meanwhile, PVAMA and CMC synergistically reinforced the network toughness and maintained overall mechanical integrity through hydrogen bonding and chain entanglement effects. After optimizing the compositional ratios, the hydrogel exhibited significantly enhanced mechanical performance, with the tensile stress increasing by approximately 680.2% and the toughness improving by 393.5% compared to the control group without PVAMA, indicating a markedly improved ability to withstand deformation and effectively absorb and dissipate mechanical energy. In terms of adhesion performance, the optimized hydrogel achieved a maximum adhesion strength of 213.63 kPa on aluminum substrates, which is markedly superior to most previously reported systems. Notably, the optimized formulation not only balanced high adhesion strength and enhanced mechanical performance, but also exhibited good fatigue resistance and biocompatibility, confirming its stability and safety under long-term application scenarios. These findings highlight a rational molecular design and compositional optimization strategy for developing high-performance functional hydrogels with broad cross-disciplinary application potential.

Conductive hydrogels are functional materials that combine soft, highly hydrated properties with electrical signal transmission capabilities. Their conductivity arises from ionic or electronic pathways, and the key design challenge is achieving good conductivity and long-term stability without compromising mechanical performance and biocompatibility. Among various conductive components, conductive polymers have attracted considerable attention due to their tunable mechanical properties, high electrical conductivity, good biocompatibility, and facile synthesis routes. In this study, a series of conductive hydrogels were rationally designed and fabricated by copolymerizing acrylamide and N,N′-methylenebisacrylamide with functionalized poly(vinyl alcohol) (PVA) and poly(3,4-ethylenedioxythiophene-co-thiophene) [P(EDOT-co-Th)]. The functionalized PVA provided multiple dynamic hydrogen-bonding sites, significantly enhancing the toughness of the hydrogel and its adhesion to various substrates, while the P(EDOT-co-Th) copolymer imparted good and stable electrical conductivity. By systematically adjusting the amount of functionalized PVA, the mechanical strength, adhesiveness, and durability of the conductive hydrogels were effectively optimized. The optimized hydrogel exhibited robust adhesion to a wide range of surfaces, excellent fatigue resistance, and long-term stability under repeated mechanical deformation. Moreover, the combination of mechanical resilience and good conductivity enabled precise and reliable signal transduction, highlighting its strong potential as a next-generation material for wearable strain and pressure sensors.

Temperature-adaptive coloration hydrogels, which mimic the thermally responsive color-changing abilities of animals such as chameleons and certain fish species, can reversibly adjust their optical appearance in response to temperature changes. This dynamic responsiveness is vital for applications in smart sensing, dynamic camouflage, and anti-counterfeiting technologies. In this study, we developed a multifunctional hydrogel (AP-β-Py) that exhibits temperature-responsive color modulation alongside outstanding mechanical performance. The hydrogel was synthesized via the copolymerization of acrylamide (AAM) and a fluorescent monomer, pyrene-functionalized 2-hydroxyethyl methacrylate (Py-HEMA), and structurally reinforced through supramolecular host–guest interactions, where β-cyclodextrin (β-CD) served as the host and dialdehyde-functionalized polyethylene glycol (DF-PEG) acted as the guest. This design enables the hydrogel to form a dynamic yet robust polymer network with tunable fluorescence, mechanical strength, self-recovery properties, and superior adhesion to various surfaces. Additionally, the AP-β-Py hydrogel exhibits extraordinary mechanical properties, including high elongation (>1000%), excellent puncture resistance, and the ability to recover its original properties after stretching, twisting, and being subjected to high-load conditions. These attributes ensure its structural integrity and functionality, even under extreme deformation. The AP-β-Py hydrogel represents a novel material platform with immense potential for use in smart sensors, biological imaging, anti-counterfeiting applications, and next-generation robotic skin.

Conductive hydrogels hold great promise for biomedical and electronic applications. However, their practical use is often limited by poor self-healing capability, which can affect long-term stability and durability. To address this, we developed alginate/polyacrylamide-based conductive hydrogels incorporating FeCl₃ and AlCl₃, named CH-Fe and CH-Al, respectively. We systematically studied the influence of metal cations on the hydrogels’ mechanical and electrical properties. CH-Al showed the most optimized performance, with a 329% increase in tensile strength and a 323% improvement in conductivity compared to the blank hydrogel. Additionally, CH-Al demonstrated excellent self-healing ability, with nearly 100% recovery after damage. The introduction of Al³⁺ improved conductivity by forming dynamic electron-conductive pathways through interactions with the polymer network. The self-healing behavior arises from reversible metal–ligand coordination bonds, which enable rapid recovery of the hydrogel’s structure after mechanical disruption. This study successfully developed a conductive hydrogel that combines high electrical conductivity, robust mechanical strength, and an intrinsic self-healing ability, offering significant potential for applications in bioelectronic devices, flexible sensors, and implantable medical technologies.

Hydrogels are extensively utilized in biomedical fields because of their remarkable properties, including biocompatibility, high water content, flexibility, and elasticity. However, despite substantial progress in hydrogel research, creating a hydrogel adhesive that integrates high stretchability, fatigue resistance, and reversible adhesion continues to pose significant challenges. In this study, we aimed to address these challenges by preparing hydrogels using a combination of acrylic acid, acrylamide, carboxymethylcellulose methacrylate, thiol-functionalized polyhedral oligomeric silsesquioxane, and poly(ethylene glycol) dimethacrylate (PEGDM). By systematically varying the molecular weight of PEG, we were able to precisely adjust the mechanical and adhesive properties of the hydrogels. Our research revealed that a PEG molecular weight of 2000 (resulting in P1 hydrogel) provided a notable adhesive strength of 717.2 kPa on glass surfaces. This performance is particularly impressive given the challenges associated with achieving high adhesive strength while maintaining other desirable hydrogel properties. Beyond its strong adhesive capabilities, the P1 hydrogel also demonstrated exceptional stretchability, support, and fatigue resistance. These characteristics are crucial for applications where the adhesive needs to endure repeated stress and deformation without losing effectiveness. The successful development of P1 hydrogel underscores its potential as a multifunctional adhesive material with a broad range of applications. The ability to tailor the properties of hydrogels through molecular weight adjustments offers a promising approach to creating advanced adhesive solutions that meet the demanding requirements of modern biomedical and industrial applications.

Smart hydrogels, known for their stimuli-responsive properties in drug delivery, tissue engineering, and sensors, are typically created using a top-down approach, which limits precise molecular control. In this study, we employ a bottom-up strategy to achieve greater molecular precision, enabling the development of innovative, multi-stimuli-responsive hydrogels. We designed and synthesized asymmetric cyanine amphiphiles incorporating diphenylimidazole as the donor and indole as the acceptor to create molecules with intramolecular charge transfer characteristics. These diphenylimidazole-indole amphiphiles, DPIIH and DPIIF, differ in that DPIIH lacks a fluorine atom at the indole terminal, while DPIIF includes this substitution. Additionally, diphenylimidazole reveals nonplanar conformations and twisted dihedral angles between the phenyl rings at the 4,5-position of imidazole, giving it aggregation-induced emission properties. In contrast to DPIIH, DPIIF can self-assemble into a hydrogel in water, probably due to the hydrogen bonding interactions between DPIIF and water molecules. Through detailed exploration of DPIIF, it was found to exhibit a reversible photochromic effect in polar solvents and can undergo reversible acid–base reactions. The photoisomerization and pH stimulus-response behaviors of DPIIF can be observed via colorimetric and fluorescence changes, making it suitable for applications such as invisible ink and pH sensors. In its hydrogel state, DPIIF reveals reversible photoswitching and pH-switching features, enabling reversible sol–gel transitions. These properties suggest potential applications in both cell culture (gel state) and cell recovery (solution state), offering versatile functionality in biomedical and research settings. Furthermore, the fluorescent properties of the hydrogel can be used to study and visualize cell–material interactions in detail, providing valuable insights for various biological studies.