Luminescent Hydrogels Research Articles

Emissive glutathione modified sulphur quantum dots for the sensing of lemon yellow and luminescent hydrogels/films

Lemon yellow (LY) is an azo dye which is widely used as food colorant. The continuous consumption can result in the safety concerns for both human and environmental health. This study describes a new sulphur quantum dot (SQD) based fluorescent sensor, which was facilely prepared with oxidized-glutathione (GSSG) as passivator at mild condition of 75 °C. The obtained sulphur quantum dots (GSSG-SQDs) have a relative quantum yield of 0.25, which is 2–5 times that of most SQDs. GSSG-SQDs were used as a sensor for lemon yellow in the concentration range of 0.10–70 μM and the limit of detection of 60 nM. The application was verified with the real sensing of lemon yellow in the soft drinking and tap water, having the standard recovery from 92.5 % to 105 %. Given the great luminescence and photostability, GSSG-SQDs were used as a filler for the preparation of luminescent films and hydrogels as a promising material for a wide range of applications such as information encryption and bioengineering.

Supramolecular Luminescent Hydrogel Based on Glycine/Terbium Complex and Fluorescent Dyes for Visual Temperature Monitoring

AbstractThe development of smart synthetic materials that are sensitive, accurate, and visually responsive to changes in temperature is vital. Herein, a supramolecular luminescent hydrogel based on a glycine/terbium (Gly/Tb) complex, rhodamine B (RB), and gelatin is reported. The hydrogel exhibits responsive luminescence and undergoes a temperature‐induced phase transformation from hydrogel to sol. The electrospray ionization time‐of‐flight mass spectra, Fourier‐transform infrared spectra, and simulation results verifiy the coordination mode of the Gly/Tb complex. The Gly/Tb complex and RB emit green and orange luminescence, respectively. When the Gly/Tb complex and RB are co‐doped into the gel network of gelatin, the obtained Gly/Tb/RB hydrogel displays steady yellow luminescence by virtue of luminescence resonance energy transfer. Subsequently, a luminescent switch is constructed owing to the sensitive and reversible luminescence responsiveness of the Gly/Tb/RB hydrogel to temperature stimuli. Remarkably, the Gly/Tb/RB hydrogel undergoes a visual phase transformation from hydrogel to sol above 35 °C, allowing the ambient temperature variation to be monitored. This study establishes a novel and effective route for the construction of smart optical materials and visual temperature monitors.

Intelligent luminescent microneedle and hydrogel patches for visual monitoring of lactic acid and dopamine

Dopamine (DA) and lactic acid (LA) are vital biochemical indicators of neurotransmitters and tissue oxidation monitoring, which can comprehensively assess the neurological and physical conditions. The combination of fluorescent sensor and artificial intelligence shows great potentials in monitoring and quantizing of human biochemicals. Herein, a Tb3+ functionalized hydrogen-bonded organic framework material (Tb@ME-TPA) is synthesized based on coordination post-synthesis modification, and its sensing mechanism for DA and LA is investigated by experiments and theoretical calculations. For visual detection of DA and LA in actual environment, Tb@ME-TPA is fabricated into PVA films and microneedle patches, which hold the advantages of high efficiency, sensitivity and anti-interference. In addition, microneedles-based probe for minimally invasive sensing of DA in the dermal interstitial fluid along with a portable smartphone platform are designed to monitor with high accuracy. Furthermore, an intelligent back-propagation neural network model based on fluorescence image recognition is constructed, which can combine optical sensing of LA with deep learning by computer, greatly improving the efficiency and accuracy. This work not only presents a novel idea for the integration of fluorescent materials, smartphones and deep learning, but also provides an effective method for the prediction of diseases as well as the real-time monitoring of overall well-being.

Lanthanide conjugated colour-tunable luminescent hydrogels as direct printable inks for anticounterfeiting and forensic applications

Counterfeiting is a global concern that jeopardizes individuals, businesses, and nations, costing trillions of USD annually. To combat this, researchers are continuously developing strong security features to formulate anti-counterfeiting inks. Herein, a novel approach has been adopted to prepare advanced luminescent hydrogel with ligand H3BTC for important applications in authentication of goods and fingerprint detection. In present investigations, Tb3+ and Eu3+ ions conjugated H3BTC hydrogels have been synthesized which emits strong green (542 nm) and red (614 nm) colours under UV lamp (254 nm). Additionally, the colour tunability for intermediate colours i.e. yellow and orange have also been achieved by varying the concentrations of Eu and Tb in H3BTC hydrogel. These hydrogels can be directly printed on any substrate using conventional screen-printing techniques. Moreover, these hydrogels can directly be used for thumb impressions with green and red emissions under 254 nm UV lamp, while appearing white in normal light and making them promising for new alternative solutions to design next-generation security ink for anticounterfeiting and forensic applications.

A ligand-free hydrogel as a visual fluorescence sensor for detection of rare-earth ions

In this work, a ligand-free luminescent hydrogel is used as a visual ratiometric fluorescence sensor to detect rare-earth (RE) ions for the first time. This hydrogel is easy to be prepared, environmentally friendly, and has high luminescent efficiency. It is found that the fluorescence intensity and emission color of the hydrogel immediately change significantly when solution of active RE3+ ions is added without any treatment. According to the linear relationship between the fluorescence intensity ratio and the concentration of RE3+ solutions, the detection limit is calculated to be as low as 0.94 μM. The detection of RE ions has strong anti-interference to other ions. Therefore, this sensor can be used for preliminary field exploration of RE ores and detection of waste containing small amounts of RE ions.

Multi-stimuli-responsive conductive and luminescent hydrogels for wearable sensors and information encryption transmission

Flexible electronic sensors with optical functions have promising applications in wearable sensing, information storage, encryption and transmission, but realizing multifunctional applications in a single system is still challenging. Herein, the conductive and luminescent hydrogel in a single system was fabricated by non-covalent crosslinked poly(vinyl alcohol) (PVA) network and covalent crosslinked acrylamide (AAm) and [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) network, as well as doping Eu(PDA)3 and glycerol (GL). The acquired PVA0.9/P(AAm-co-SBMA0.5)/Eu(PDA)3/GL (P0.9P0.5EG) hydrogel possesses excellent mechanical properties, adhesion, self-healing capability, water retention ability, anti-freezing property, conductivity, self-powered property, and luminescent properties. Importantly, the hydrogel as a flexible sensor has excellent tensile strain sensitivity (GF = 17.8), pressure sensitivity (S = 1.191 kPa−1), quick response, and stable electrical signals output, which can be used for monitoring multiple movements as well as for information transmission with the help of Morse code. Moreover, the unique luminescent properties and multi-stimuli-responsive behavior also make the hydrogel monitor strain variations via detecting the luminescence signal changes. Notably, the particular process of information encryption transmission was further achieved by converting the luminescence signals to electrical signals. This work provides an alternative strategy for designing and preparing hydrogel sensors for multifunctional applications.

Synthesis and Characterization of Multiple Stimuli-Responsive Fluorescent Polymer Hydrogels Based on Terpyridine and N-Isopropylacrylamide.

A series of stimuli-responsive fluorescent hydrogels were successfully synthesized via micelle radical copolymerization of hydrophilic acrylamide (AM), hydrophobic chromophore terpyridine-based monomer (TPY), and N-isopropylacrylamide (NIPAM). These hydrogels presented blue emissions (423-440 nm) under room temperature, which is caused by the π-π* transition of the conjugated structures. Once the ambient temperature was increased to 55 °C, the fluorescence color changed from blue (430 nm) to pink (575 nm) within 10 min, subsequently to yellow (535 nm), and eventually back to pink. The thermal-responsive properties are attributed to the transition of the TPY units from unimer to dimer aggregation via the intermolecular charge transfer complex at high temperatures. The hydrogels showed pH-responsive properties. The emission peak of the hydrogel exhibited a blue shift of ~54 nm from neuter conditions to acidic conditions, while a 6 nm red shift to an alkaline environment was observed. The hydrogels demonstrated an obvious change in fluorescence intensity and wavelength upon adding different metal ions, which is caused by the coordination between the terpyridine units incorporated on the backbones and the metal ions. As a consequence, the hydrogels presented a sharp quenching fluorescence interaction with Fe2+, Fe3+, Cu2+, Hg2+, Ni2+, and Co2+, while it exhibited an enhanced fluorescence intensity interaction with Sn2+, Cd2+, and Zn2+. The microstructural, mechanical, and rheological properties of these luminescent hydrogels have been systematically investigated.

Metal ion-induced multifunctionality in luminescent hydrogels for information encryption and mercury ion detection

Information security has long been a focal point of research. However, the development of cryptographic hydrogels endowed with both high security and multifunctionality remains a challenge. Herein, we reported a method to construct multifunctional hydrogels using a metal ion-induced strategy. Leveraging Au- induced luminescence, Zn2+- induced shape memory, and Hg2+- induced fluorescence quenching, our method engendered a suite of distinctive properties, including fluorescence, shape memory effects, and ionic conductivity. Tunable fluorescence was utilized for detecting Hg2+ with a detection limit as low as 0.0007 μmol/L. Additionally, a successful design of a multilevel information encryption platform, ranging from 2D to 3D, was achieved by combining the aforementioned properties. The information written using Hg2+ as ink can be protected by the fixed shape of Zn2+, and the encrypted information can only be read under the conditions of shape recovery and UV irradiation. This simple yet effective strategy demonstrates a promising future for the application of this hydrogel in information encryption.

Luminescent Supramolecular Metallogels: Drug Loading and Eu(III) as Structural Probe.

Supramolecular metallogels combine the rheological properties of gels with the color, magnetism, and other properties of metal ions. Lanthanide ions such as Eu(III) can be valuable components of metallogels due to their fascinating luminescence. In this work, we combine Eu(III) and iminodiacetic acid (IDA) into luminescent hydrogels. We investigate the tailoring of the rheological properties of these gels by changes in their metal:ligand ratio. Further, we use the highly sensitive Eu(III) luminescence to obtain information about the chemical structure of the materials. In special, we take advantage of computational calculations to employ an indirect method for structural elucidation, in which the simulated luminescent properties of candidate structures are matched to the experimental data. With this strategy, we can propose molecular structures for different EuIDA gels. We also explore the usage of these gels for the loading of bioactive molecules such as OXA, observing that its aldose reductase activity remains present in the gel. We envision that the findings from this work could inspire the development of luminescent hydrogels with tunable rheology for applications such as 3D printing and imaging-guided drug delivery platforms. Finally, Eu(III) emission-based structural elucidation could be a powerful tool in the characterization of advanced materials.

Hybrid MPA-CdSe quantum dots-based luminescent hydrogel: White light emission regulation and Cu2+ recognition

In this study, a novel CdSe@PEI-PVP luminescent hydrogel was constructed by using MPA-CdSe quantum dots (QDs) as a single emitter and hydrogen bond cross-linking network between highly branched polyethyleneimine (PEI) and polyvinylpyrrolidone (PVP) as a hydrogel skeleton, in which PEI also works as a passivation ligand for MPA-CdSe quantum dots. Utilizing the dual emission of MPA-CdSe quantum dots and adjusting the surface state of MPA-CdSe with PEI and Cd2+, CdSe@PEI-PVP hydrogel can emit bright white light as a whole. Furthermore, CdSe@PEI-PVP shows specific recognition for Cu2+, luminescent color changes from bright white to orange when Cu2+ is added, which enables CdSe@PEI-PVP hydrogel to serve as a fluorescent probe for ion detection. The luminescent hydrogel has great self-healing ability and reversible morphological thermal responsiveness, existing as a white luminescent hydrogel at room temperatures and transforming into a pale green luminescent solution at high temperatures.

Multifunctional chitosan-based lanthanide luminescent hydrogel with stretchability, adhesion, self-healing, color tunability and antibacterial ability

Lanthanide luminescent hydrogels have broad application prospects in various fields. However, most of lanthanide hydrogels possess relatively simple functions, which is not conducive to practical applications. Therefore, it is becoming increasingly urgent to develop multifunctional hydrogels. Herein, a multifunctional chitosan-based lanthanide luminescent hydrogel with ultra-stretchability, multi-adhesion, excellent self-healing, emission color tunability, and good antibacterial ability was prepared by a simple one-step free radical polymerization. In this work, our designed lanthanide complexes [Ln(4-VDPA)3] contain three reaction sites, which can be copolymerized with N-[tris(hydroxymethyl) methyl] acrylamide (THMA), acrylamide (AM), and diacryloyl poly(ethylene glycol) (DPEG) to form the first chemical crosslinking network, while hydroxypropyltrimethyl ammonium chloride chitosan (HACC) interacts with the hydroxyl and amino groups derived from the chemical crosslinking network through hydrogen bonds to form the second physical crosslinking network. The structure of the double network as well as the dynamic hydrogen bond and lanthanide coordination endow the hydrogel with excellent stretchability, adhesion and self-healing properties. Moreover, the introduction of lanthanide complexes and chitosan makes the hydrogel exhibit outstanding luminescence and antibacterial performances. This research not only realizes the simple synthesis of multifunctional luminescent hydrogels, but also provides a new idea for the fabrication of biomass-based hydrogels as intelligent and sustainable materials.

Luminescent carbon dots-rooted polysaccharide crosslinked hydrogel adsorbent for sensitive determination and efficient removal of Cu2+

In this study, a novel luminescent carbon dot-rooted polysaccharide hydrogel (CDs@CCP hydrogel) was prepared by crosslinking cellulose, chitosan (CS), and polyvinyl alcohol (PVA) for simultaneous fluorescent sensing and adsorption of Cu2+. The crosslinking of these low-cost, polysaccharide polymers greatly enhance the mechanical strength of the composite hydrogel while making the polysaccharide-based adsorbent easy to reuse. This composite hydrogel exhibited an excellent adsorption capacity (124.7 mg∙g−1) for residual Cu2+ in water, as well as a sensitive and selective fluorescence response towards Cu2+ with a good linear relationship (R2 > 0.97) and a low detection limit (LOD) of 0.02 μM. The adsorption isotherms, adsorption kinetics, and thermodynamics studies were also conducted to investigate the adsorption mechanism. This composite hydrogel offers an efficient tool for simultaneous monitoring and treatment of Cu2+ from wastewater.

Background-Free and Reversible Upconversion Hydrogel Sensing Platform for Visual Monitoring of Sulfite.

Excessive sulfite usage in food and pharmaceutical production causes respiratory and neurological diseases, underscoring the need for a sensitive and rapid quantification strategy. The portable sensing platform based on a luminescent hydrogel sensor is a powerful tool for the on-site, real-time detection of sulfite ions. However, the lack of recyclability in almost all reaction-based hydrogel sensors increases the application cost. This study constructed a reversible and upconversion nanoprobe combining upconversion nanoparticles (UCNPs) and pararosaniline (PAR) for sulfite detection. The upconversion nanoprobe was further encapsulated in a three-dimensional polyacrylamide hydrogel matrix to create a background-free, reversible hydrogel sensor. The near-infrared excitation of UCNPs avoids the autofluorescence in the hydrogel and real samples. Meanwhile, PAR serves as a specific recognition unit for sulfite ions. After the addition of sulfites, a specific reaction occurs between PAR and sulfites, leading to the recovery of characteristic emission at 540 nm, achieving sensitive detection of sulfite ions. Importantly, this specific reaction is reversible under thermal treatment, allowing the hydrogel sensor to return to its initial state and thus enabling reversible detection of sulfite ions. Furthermore, a portable sensing platform is developed to realize point-of-care, real-time quantitative detection of sulfite ions. The proposed upconversion reversible hydrogel sensor provides a new sensing strategy for the detection of hazardous substances in food and offers new insights into the preparation of reversible, highly sensitive hydrogel sensors.

Lanthanide coordinated multicolor luminescent polymeric hydrogels

A review of lanthanide coordinated multicolor luminescent polymeric hydrogels (LPHs) based on the synthetic strategies.

A dual encapsulation strategy to generate anion-responsive luminescent lanthanide hydrogels.

We report a new method to generate ion-responsive luminescent hydrogels, involving encapsulation of a luminescent lanthanide probe within crosslinked amphiphilic polymer particles and subsequent entrapment within a hydrogel. The resulting hydrogels are capable of reversible bicarbonate sensing, exhibit no leaching, and can be tuned for a range of sensing applications.

Fabrication of a novel dual-emission fluorescence covalent organic framework and its luminescent hybrid hydrogel material: Application in the detection and adsorption of eriochrome azo anionic dyes

Herein, a novel fluorescent covalent organic framework (COF) and its luminescent sodium alginate based hybrid hydrogel were synthesized and applied to detect and adsorb eriochrome azo anionic dyes. Firstly, by optimizing a series of conditions affecting the crystallinity, a dual-emission fluorescence COF (TD-COF) with high crystallinity was synthesized at room temperature for the first time. TD-COF yielded remarkable fluorescence and adsorption properties; thus it can be employed as a dual platform for fluorescence sensing and adsorption of eriochrome black T, eriochrome blue-black R and eriochrome blue SE. The platform showed good linearity in fluorescence detection of three dyes from 0 to 100 μg mL−1 and the maximum adsorption capacities ranged from 89.28 to 228.64 mg g−1. Subsequently, TD-COF had a Thiol-ene "click" reaction with thiolated sodium alginate to produce a sort of luminescent hybrid hydrogel material (GelTSA@TD-COF), which improved the maximum adsorption capacities of eriochrome blue-black R (6410.06 mg g−1) and eriochrome blue SE (106.79 mg g−1). Due to the blocky appearance of GelTSA@TD-COF, it is more portable and practical compared to powdered TD-COF, and can be used for on-site fluorescent visualization of dyes. Finally, the detection and adsorption effect of dyes in water samples further verified the practical application value of TD-COF and GelTSA@TD-COF.

Designing energy transfer-based color-tunable, information-encrypting, luminous hydro-gels, and latent fingerprint detection systems using BaLa2ZnO5:Tb3+, Bi3+ nanophosphors

Synthesizing cost-effective blue-green emitting BaLa2ZnO5:Tb3+, Bi3+ nanophosphors (BLZO:Tb3+, Bi3+ NPs) through an eco-friendly urea-aided combustion method. Thorough examination of phase purity, structure, surface characteristics, and luminescent properties of the resulting products reveals a robust blue-green emission linked to the 5D4 → 7F5 transition of Tb3+ under 365 nm UV excitation, as well as evident energy transfer from Bi3+ to Tb3+ within the co-doped BLZO, discussed in detail. Optimal doping concentrations are determined to be 5 mol% for Tb3+ and 0.3 mol% for Bi3+ in BLZO phosphor, with non-radiative transition mechanisms explaining concentration quenching. BLZO:Tb3+ NPs emits green light, while co-doping with Bi3+ shifted to the blue-green region. The optimized phosphor is employed for latent fingerprint (LFP) development on porous, semi-porous, and non-porous surfaces, with clear visualization under 365 nm UV light. The generated fingerprints (FPs) display level I–III ridge features with exceptional sensitivity, selectivity, and contrast. The luminescent hydro-gels exhibit outstanding photo-stability, chemical stability, and long-term durability, making them ideal for anti-counterfeiting (AC) applications. Furthermore, BLZO:Tb3+, Bi3+ NPs demonstrate the ability to mitigate oxidative stress and thrombosis, evidenced by their DPPH scavenging activity and their capacity to normalize stress indicators in Red Blood Cells (RBC) exposed to NaNO2-induced oxidative stress. These NPs also reduce ADP-induced platelet aggregation. Collectively, these results highlight the effective utilization of the optimized phosphor in display devices, advanced forensics, anti-counterfeiting measures, and biomedical applications.

Lanthanides-based invisible multicolor luminescent hydrogels and films for anti-counterfeiting

Developing high-level luminescent anti-counterfeiting materials with simple preparation and portability is still challenging. Herein, the luminescent anti-counterfeiting hydrogels were acquired via the coordination of 1,2,4,5-benzene tetracarboxylic acid (H4BTC) to Tb(NO3)3 and/or Eu(NO3)3 in water. Multicolor luminescence from green to yellow, orange, and red can be easily obtained by controlling the molar ratio of Tb(NO3)3 to Eu(NO3)3. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the coordination between H4BTC and lanthanides. Emission spectra and optical images confirmed that luminescent hydrogels could be functionalized as luminescent inks for painting and writing with the help of a writing brush. Importantly, the information fabricated by hydrogels cannot be seen under daylight and can only be seen under UV light. Noteworthy, multicolor luminescence can be designed to encode information in multiple ways, resulting in increasing the complexity of information decryption. It can prevent the tampering and forging of information effectively. Moreover, the inks have good stability and adhesion. And the H4BTC-Ln hydrogels can be dried to powders for storage and recovered to hydrogels by adding water. Meanwhile, the multicolor luminescent films were easily prepared by dispersing the corresponding powders of H4BTC-Ln into polyacrylamide (PAAm) matrix. The acquired films have high transmittance as well as good luminescent properties and excellent mechanical properties. They were applied as luminescent anti-counterfeiting labels. This work provides a simple and convenient method for preparing high-level lanthanides-based luminescent anti-counterfeiting materials.

Thermal responsive smart lanthanide luminescent hydrogel actuator

Among stimuli-responsive soft materials, thermal responsive hydrogels are the most attractive one because temperature is the most easily regulated external stimuli. We here report a thermal responsive bilayer smart luminescent hydrogel actuator with tough mechanical strength and thermal reversible deformation behavior. The bilayer hydrogel is composed of Poly(N-isopropylacrylamide)-Laponite-Tb complex (PNIPAM-Lap-Tb·L3) layer and Poly(N,N-dimethylacrylamide)-Laponite-Eu complex (PDMA-Lap-Eu·L3) layer. Upon alternative heating and cooling, the PNIPAM-Lap-Tb·L3 layer undergoes reversible shrink and expansion, while the PDMA-Lap-Eu·L3 layer is not affected, leading to asymmetric deformation behavior. The luminescent intensity of the bilayer hydrogel was enhanced by heating, and the maximum bending angle was 371° in 15 min. By processing the bilayer hydrogel into complex 2D and 3D structure, we further demonstrate their great potential as smart soft actuators.

Cellulose Luminescent Hydrogels Loaded with Stable Carbon Dots for Duplicable Information Encryption and Anti-counterfeiting

Cellulose Luminescent Hydrogels Loaded with Stable Carbon Dots for Duplicable Information Encryption and Anti-counterfeiting