pH-Responsive Dual-Emitting Hydroxypropyl Methylcellulose-Based Material Containing Fluorescein Isothiocyanate and CaAl2O4:Eu2+,Dy3+ Phosphors

Covalent organic framework-based surface plasmon-enhanced fluorescence sensing for real-time monitoring of cell apoptosis

The complex physiological environment of living organisms is a major hurdle for in situ monitoring of vital cellular activities. Here, we propose that the surface plasmon-coupled emission (SPCE) biointerface sensing system prepared by modifying covalent organic frameworks (COFs) on metal substrates, can be a powerful tool for biointerface sensing. We have successfully developed a novel pH-responsive fluorescent COF nanoprobe, where fluorophores were precisely post-modified into intrinsically enriched chemically reactive sites within the nanoporous structure. A graphene oxide-assisted assembly strategy was employed to facilitate the robust integration of COFs onto the Ag film. Remarkably, the resulting COF-modified biosensing platform achieves a 40-fold directional fluorescence enhancement in directional fluorescence, attributed to the synergistic coupling between the near-field excited fluorophore dipole, Ag nanofilm and π-conjugated graphene oxide. By precisely controlling the penetration depth of the evanescent through angular modulation of incident light, selective detection of the extracellular and intracellular information can be realized. This allows us to construct a stable, fluorescence-enhanced biosensor chip based on surface plasmon coupling for accurate in situ monitoring of extracellular pH changes during apoptosis.

Sustainable and biodegradable polymer packaging: Perspectives, challenges, and opportunities

The escalating environmental impact of non-biodegradable plastic waste has intensified global efforts to seek sustainable alternatives, with biodegradable polymers from renewable sources emerging as a promising solution. This manuscript provides the current perspectives, challenges, and opportunities within the field of sustainable and biodegradable packaging. Despite a significant market presence of conventional non-biodegradable petrochemical-based plastics, there is a growing trend towards the adoption of bio-based polymers from renewable resources driven by environmental sustainability and regulatory measures. However, the transition to biodegradable packaging is fraught with challenges, including scalability, cost-effectiveness, technological limitations, comprehensive waste management systems, and infrastructural needs. The manuscript highlights the intrinsic technological challenges and the need for advancements in material science to enhance the performance and adoption of biodegradable packaging. This paper also supply insights into the development and implementation of biodegradable packaging, offering a comprehensive overview of its role in achieving global sustainability goals.

A pH-responsive fluorescent film with the smartphone-assistance for real-time and visual detection of food freshness

Monitoring food freshness is considerably important for food safety. In this study, a smart pH-responsive fluorescence hydroxypropyl methyl cellulose-κ-carrageenan-fluorescein isothiocyanate-NH2-CaAl2O4 (H-K-F-N) film was prepared. Taking synergetic advantage of the pH-dependent behavior of fluorescein isothiocyanate dye and the luminescence characteristics of calcium aluminate phosphor, the film exhibited a unique strong pH-responsive fluorescence with an exceptional linear relationship (correlation coefficient, R2 = 0.9993) across a wide pH rang of 2.0-12.0. Moreover, the H-K-F-N film, as a smart sensor, could be used to estimate the total volatile basic nitrogen and total viable count through fluorescence intensity based on the partial least squares regression model and support vector machine regression, respectively. Leveraging the relationship between the fluorescent image's digital signals and food freshness indicators, a smartphone-assisted system was developed. These results demonstrated that H-K-F-N film is promising for applications in intelligent food packaging and food safety monitoring.

Preparation of cellulose-based fluorescent aggregations with various morphologies and their microstructure-correlated fluorescence behavior

We provided an efficient method for preparing fluorescent materials with high specificity. Firstly, the cellulose-based aggregations with adjustable morphologies and sizes were obtained by cross-linking copolymerization and self-assembly. Then, after encapsulating the fluorescein isothiocyanate (FITC) into the hydrophobic microregions of the cellulose-based aggregations by ultrasound/dialysis method, a series of cellulose-based fluorescent aggregations with different morphologies was obtained. The flower-like, tentacle-like, microsphere, hollow sphere, coral-like and solid sphere fluorescent aggregations could be obtained by changing the mass ratio of cellulose to gelatin, the degree of alkylation and the length of the alkyl chain. Scanning electron microscope (SEM), Dynamic light scattering (DLS), UV-vis and Zeta potential confirmed the formation of the cellulose-based aggregations with different morphologies and sizes, which provided basis for the successful encapsulation of FITC. The flower-like fluorescent aggregation showed the maximum fluorescence intensity. This was due to the rigid structure of cellulose, electrostatic repulsion, hydrogen bonding, and the larger surface area in flower-like aggregation, which was conducive to inhibiting π-π stacking and hydrogen bonding interaction of FITC, thus promoting the electron radiative transition. Also, cellulose-based fluorescent aggregation could be processed into fluorescent fiber, coating and printing pattern, and had potential applications in information storage, scene warning, and special fiber.

A highly sensitive fluorescent probe based on functionalised ionic liquids for timely detection of trace Hg2+ and CH3Hg+ in food

A novel fluorescent probe was fabricated using fluorescein-based ionic liquids (ILs) to effectively achieve rapid and accurate detection of Hg2+ and CH3Hg+ in food. A probe developed by addition of modified fluorescein into the functionalised ILs presented a promising sensitivity toward Hg2+ and CH3Hg+ at concentrations of 0.4 and 60 nM, respectively. In addition, the novel probe could achieve visual and timely detection of Hg2+ and CH3Hg+ by the naked eyes at concentrations of 0.1 and 1 μM, respectively. The probe could also overcome the interference of potential ions and common organic ligands and detect Hg2+ and CH3Hg+ in real food samples, such as green tea and liquor. The probe could be converted into a paper-based sensor to visually detect Hg2+ and CH3Hg+ at levels as low as 10 nM.

Blueberry Anthocyanin Functionalized CaMoO4:Tb3+ Nanophosphors for Dual-Mode pH Sensing

A series of green phosphors, Ca1-y%MoO4:y%Tb3+ (where y = 0.1, 0.5, 1, 2, 3, 4, and 5) were successfully prepared via hydrothermal synthesis. The pH levels were used to modulate the luminescent of CMO:Tb. To confirm the potential application of proposed phosphors, Blueberry anthocyanin (BBA) was loading onto CMO:Tb surface to form a luminescence probe. The synthesized phosphors and probes were characterized using X-ray diffraction (XRD), FT-IR spectra, transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). As a proof-of-concept, the constructed probes were adopted to evaluate the acidity of solution. The results showed that luminescence emission intensity at 546 nm increased with pH value increasing in the range of 2-12. Meanwhile, the color of the sensor solution changed from bright red to pink, then to purple, and finally to yellow as the pH varies between 2 and 12. The above results indicated that the proposed probe could evaluate the acidity of solution via the dual-mode luminescence detecting and naked eye to obtain accurate results. This proposed strategy gives an insight to design the efficient probes to precisely and sensitively evaluate the acidity in complex samples.

A time-multiplexed self-erasing nanopaper for water induced information transmission

The progressive presentation of multilevel information enhances the security level of information storage and transmission. Here, a time-multiplexed self-erasing nanopaper was developed by integrating cellulose nanofiber (CNF)-stabilized gold nanoclusters and CNF-modified long afterglow materials. The orange fluorescence of gold nanoclusters on nanopaper was regulated by the reversible swelling and shrinking of CNF induced by water solution, while the cyan fluorescence of micron-long afterglow remained stable and acted as the background signal. It was noteworthy that the fluorescence colour and intensity of the nanopaper could be freely adjusted between orange and cyan on the time scale. Therefore, the array information on the nanopaper could be encoded by a water solution, iterated variation as the step-by-step solvent volatilized on the time scale measured by the time of the afterglow duration. This work provides a new approach for constructing time-multiplexed self-erasing nanopaper for confidential information storage and transmission.

Recent studies on proteins and polysaccharides-based pH-responsive fluorescent materials

Polymer-based pH-responsive fluorescent materials have the characteristics of fast response, real-time monitoring, visualisation, and easy forming. Consequently, they have attracted widespread attention in wound healing, sweat monitoring, security and anti-counterfeiting, freshness detection of aquatic products, metal-ion sensing and bioimaging. This paper analyses the preparation principles and characteristics of pH-responsive fluorescent materials based on cellulose, chitosan and proteins. It then outlines the fluorescence properties, environmental response mechanisms and applications of various luminescent materials. Next, the research indicates that amines, N-heterocyclic rings, carboxyl groups and amino plasmonic groups on the fluorescent molecule structure and polymer skeleton appear to change the degree of ionisation under acid or alkali stimulation, which affects the light absorption ability of chromophore electrons, thus producing fluorescence changes in fluorescent materials under different pH stimuli. On this basis, the challenges and growth encountered in the development of proteins and polysaccharides-based pH-responsive fluorescent materials were prospected to provide theoretical references and technical support for constructing pH-responsive fluorescent materials with high stability, high sensitivity, long-lasting pH-response and wide detection range.

Fabrication of stable solid fluorescent starch materials based on Hantzsch reaction

In this paper, a series of fluorescent starches were prepared simply and effectively by Hantzsch multi-component reaction (MRC). These materials showed bright fluorescence emission. Notably, due to the existence of polysaccharide skeleton, starch molecules can effectively inhibit the common aggregation induced quenching effect caused by the aggregation of conjugated molecules in traditional organic fluorescent materials. Meanwhile, the stability of this material is so excellent that the fluorescence emission of the dried starch derivatives would not destroy after boiling at a high temperature in some common solvents, and even brighter fluorescence can be stimulated in alkaline solution. In addition to fluorescence, starch was also endowed with hydrophobic property by one-pot method connecting long alkyl chains. Compared with native starch, the contact angle of fluorescent hydrophobic starch increased from 29° to 134°. Furthermore, the fluorescent starch can be prepared into film, gel and coating by different processing methods. The preparation of these Hantzsch fluorescent starch materials provide a new way for the functional modification of starch materials and has great application potential in detecting, anti-counterfeiting, security printing and other related fields.

Recent advances in determination applications of emerging films based on nanomaterials

Sensitive and facile detection of analytes is crucial in various fields such as agriculture production, food safety, clinical diagnosis and therapy, and environmental monitoring. However, the synergy of complicated sample pretreatment and detection is an urgent challenge. By integrating the inherent porosity, processability and flexibility of films and the diversified merits of nanomaterials, nanomaterial-based films have evolved as preferred candidates to meet the above challenge. Recent years have witnessed the flourishment of films-based detection technologies due to their unique porous structures and integrated physical/chemical merits, which favors the separation/collection and detection of analytes in a rapid, efficient and facile way. In particular, films based on nanomaterials consisting of 0D metal-organic framework particles, 1D nanofibers and carbon nanotubes, and 2D graphene and analogs have drawn increasing attention due to incorporating new properties from nanomaterials. This paper summarizes the progress of the fabrication of emerging films based on nanomaterials and their detection applications in recent five years, focusing on typical electrochemical and optical methods. Some new interesting applications, such as point-of-care testing, wearable devices and detection chips, are proposed and emphasized. This review will provide insights into the integration and processability of films based on nanomaterials, thus stimulate further contributions towards films based on nanomaterials for high-performance analytical-chemistry-related applications.