Amine-responsive cellulose-based ratiometric fluorescent materials for real-time and visual detection of shrimp and crab freshness

Development of dual-channel starch-based film incorporated with betanin@β-cyclodextrin inclusion complex and berberine for indicating shrimp freshness

In this study, the β-cyclodextrin encapsulated betanin (BET@β-CD) with improved thermal stability and retention as well as the berberine (BBR) with aggregate induced luminescence effect were incorporated into corn amylose (CA) biomatrix to develop colorimetric/fluorescent dual-channel smart film. Results shown that the added functional components were uniformly distributed in the film matrix. The high tensile strength (78.87%), low water solubility (31.15%) and water vapor permeability (1.24 × 10-10 g Pa-1 s-1 m-1) of the film predicted its acceptable stability. It was worth mentioning that the film displayed excellent responsiveness to volatile ammonia (0.025-25 mg/mL) with at least 4 times recyclability. Application experiment demonstrated that the film can achieve macroscopic dynamic monitoring of the freshness of shrimps stored at 25 °C, 4 °C, -20 °C under daylight (red to yellow) and UV light (yellow-green to blue-green). Thus, the study suggests an attractive and effective strategy for constructing dual-mode smart packaging materials for food freshness detection.

Nanolignin-containing cellulose nanofibrils (LCNF)-enabled multifunctional ratiometric fluorescent bio-nanocomposite films for food freshness monitoring

Herein, the nanolignin-containing cellulose nanofibrils (LCNF)-enabled ratiometric fluorescent bio-nanocomposite film is developed. Interestingly, the inclusion of LCNF in the cellulose-based film enhances the detecting performance of food freshness, such as high sensitivity to biogenic amines (BAs) (limit of detection (LOD) of up to 1.83 ppm) and ultrahigh discernible fluorescence color difference (ΔE = 113.11). The underlying mechanisms are the fluorescence resonance energy transfer (FRET), π - π interaction, and cation - π interaction between LCNF and fluorescein isothiocyanate (FITC), as well as the increased hydrophobicity due to lignin, which increases the interactions of amines with FITC. Its color stability (up to 28 days) and mechanical property (49.4 Mpa) are simultaneously improved. Furthermore, a smartphone based detecting platform is developed to achieve access to food safety. This work presents a novel technology, which can have a great potential in the field of food packaging and safety.

Using highly water-stable wool keratin/CsPbBr3 nanocrystals as a portable amine-responsive fluorescent test strip for onsite visual detection of food freshness

Perovskite nanocrystals (PNCs) have emerged as promising candidates for fluorescent probes owing to their outstanding photoelectric properties. However, the conventional CsPbBr3 (CPB) NCs are extremely unstable in water, which has seriously limited their sensing applications in water environment. Herein, we present a powerful ligand engineering strategy for fabricating highly water-stable CPB NCs by using a biopolymer of wool keratin (WK) as the passivator and the polyaryl polymethylene isocyanate (PAPI) as the cross-linking agent. In particular, WK with multi-functional groups can serve as a polydentate ligand to firmly passivate CPB NCs by the ligand exchange process in hot toluene; and then the addition of PAPI can further encapsulate CPB NCs by the crosslinking reaction between PAPI and WK. Consequently, the as-prepared CPB/WK-PAPI NCs can maintain ∼ 80 % of their relative photoluminescence (PL) intensity after 60 days in water, and they still maintain ∼ 40 % of their relative PL intensity even after 512 days in the same environment, which is one of the best water stabilities compared previously reported polymer passivation methods. As a proof-of their application, the portable CPB/WK-PAPI NCs-based test strips are further developed as a fluorescent nanoprobe for real-time and visual monitoring amines and food freshness. Among various amine analytes, the as-prepared test strips exhibit higher sensitivity towards conjugated amines, achieving a remarkable detection limit of 18.3 nM for pyrrole. Our research not only introduces an innovative strategy involving natural biopolymers to enhance the water stability of PNCs, but also highlights the promising potential of PNCs for visually and portably detecting amines and assessing food freshness.

Amine response smartphone-based portable and intelligent polyvinyl alcohol films for real-time detection of shrimp freshness

Food freshness monitoring is an important component in ensuring food safety for consumers and the food industry. Therefore, there is an urgent need for a portable, low-cost, and efficient detection method to determine the freshness. In this study, polyvinyl alcohol (PVA) was used as polymer carrier to prepare electrospinning film containing curcumin (Cur) and gardenia blue (GB) as intelligent indicator label on food packaging for real-time nondestructive detection of freshness of shrimp. The detection limit of ammonia response is less than or equal to 20 ppm, and the detection time is about 1 min, indicating that it has a sensitive response effect. At the same time, a smartphone application that can identify amines in response to color changes has been developed, and consumers can understand freshness by scanning the label. This study demonstrates the huge potential of smart indicator labels for food freshness monitoring.

Real-time monitoring of pork freshness using polyvinyl alcohol/modified agar multilayer gas-sensitive labels

Accurate consumer perception of food packages should provide real-time feedback on any changes inside food packaging. Hence, a new multilayer gas-sensitive label (POA-12) was prepared using a layer-by-layer pouring method for simple, visual, and real-time detection of pork's freshness, while the front side was developed by immobilizing red carbon dots and fluorescein isothiocyanate in POA as indicator for volatile nitrogen, and the back side was created using bromothymol blue in POA as pH indicator. The swelling index of the multilayer gas-sensitive labels reduced from 159.19% to 148.36%, and the tensile strength increased from 25.52 MPa to 42.61 MPa. In addition, the POA-12 multilayer label showed a red-to-yellow fluorescence change as TVB-N increased from 6.84 to 31.4 and a yellow-brown-to-blue-green color change as pH increased from 5.74 to 7.24 when detecting pork samples. Thus, it provides dual-indicator monitoring that improves the accuracy and reliability of assessing the freshness of high-protein products.

Dynamically crosslinked chiral optics sensing for ultra-sensitive VOCs detection

Chiroptical sensing with real-time colorimetrical detection has been emerged as quantifiable properties, enantioselective responsiveness, and optical manipulation in environmental monitoring, food safety and other trace identification fields. However, the sensitivity of chiroptical sensing materials remains an immense challenge. Here, we report a dynamically crosslinking strategy to facilitate highly sensitive chiroptical sensing material. Chiral nematic cellulose nanocrystals (CNC) were co-assembled with amino acid by a two-step esterification, of which a precisely tunable helical pitch, a unique spiral conformation with hierarchical and numerous active sites in sensing performance could be trigged by dynamic covalent bond on amines. Such a CNC/amino acid chiral optics features an ultra-trace amount of 0.08 mg/m3 and a high sensitivity of 60 nm/(mg/m3) for formaldehyde gas at a molecule level detection, which is due to the three synergistic adsorption enhancement of dynamic covalent bonded interaction, hydrogen bonded interaction and van der Waals interaction. Meanwhile, an enhancement hierarchical adsorption of CNC/amino acid chiral materials can be readily representative to the precise helical pitch and colorimetrical switch for sensitive visualization reorganization.

Sustainable production of cellulosic biopolymers for enhanced smart food packaging: An up-to-date review

Biodegradable and sustainable food packaging (FP) materials have gained immense global importance to reduce plastic pollution and environmental impact. Therefore, this review focused on the recent advances in biopolymers based on cellulose derivatives for FP applications. Cellulose, an abundant and renewable biopolymer, and its various derivatives, namely cellulose acetate, cellulose sulphate, nanocellulose, carboxymethyl cellulose, and methylcellulose, are explored as promising substitutes for conventional plastic in FP. These reviews focused on the production, modification processes, and properties of cellulose derivatives and highlighted their potential for their application in FP. Finally, we reviewed the effects of incorporating cellulose derivatives into film in various aspects of packaging properties, including barrier, mechanical, thermal, preservation aspects, antimicrobial, and antioxidant properties. Overall, the findings suggest that cellulose derivatives have the potential to replace conventional plastics in food packaging applications. This can contribute to reducing plastic pollution and lessening the environmental impact of food packaging materials. The review likely provides insights into the current state of research and development in this field and underscores the significance of sustainable food packaging solutions.

A novel dual-channel cassava starch/polyvinyl alcohol-based film for visual monitoring of shrimp freshness

In this study, the polyvinylpyrrolidone-alizarin nanoparticles (PVP-AZ NPs) with favorable water dispersion and the carbon quantum dots (RQDs) with aggregate induced emission effect were synthesized to construct an eco-friendly film for food freshness monitoring. The introduction of PVP-AZ NPs and RQDs enhanced the network structure and thermal stability of the cassava starch/polyvinyl alcohol film, and reduced its crystallinity and light transmittance via non-covalent binding with the film-forming matrix. The developed film exhibited visually recognizable colorimetric and fluorescent responses to ammonia at 0.025-25 mg/mL, and it can be reused at least 6 times. Practical application experiment proved that the film, as an indicator label, can achieve accurate, real-time, and visual dynamic monitoring of the freshness of shrimp stored at 25 °C, 4 °C, and - 20 °C under daylight (orange yellow to purple) and UV light (red to blue). The integration of multivariate detection technology can eliminate the interference of external factors by self-correction to improve sensitivity and reliability, which provides a reference for the development of other food quality and safety monitoring platforms.

Nelumbo nucifera flower extract incorporated alginate/polyvinyl alcohol films as a sustainable pH indicator for active food packaging applications

In recent years, there has been a growing demand for environmentally friendly smart packaging materials. Therefore, in this study, we developed an eco-friendly pH-sensitive indicator film through the solvent casting process, incorporating alginate, polyvinyl alcohol, garlic, and Nelumbo nucifera flower extract. The effect of extract on the chemical and physical properties of the film were extensively studied using various characterization techniques. XRD and FTIR reveal the strong interaction between the polymers and the extract. The incorporation of the extract influenced various parameters such as swelling behavior, water solubility, and moisture content, while also improving the film's thermal stability, biodegradability, as well as its antioxidant and antimicrobial properties. Interestingly, the film exhibited a color change in response to pH change. During shrimp storage, the film showed a visible transition from purple to green, indicating shrimp spoilage. Additionally, the film's ability to detect freshness was confirmed by measuring total volatile basic nitrogen (TVBN). These findings suggest that the PVA/alginate/garlic/Nelumbo nucifera film shows promise as an intelligent packaging material for real-time food monitoring applications.

Alizarin complexone modified UiO-66-NH2 as dual-mode colorimetric and fluorescence pH sensor for monitoring perishable food freshness

Food prone to spoilage has a huge food safety hazard, threatening people's health, so early detection of food spoilage is a continuous and urgent need. Herein, we developed a dual-mode response sensor, alizarin complexone@UiO-66-NH2, which can accurately detect pH. The sensor demonstrated significant changes in color from pale yellow to deep pink, while the fluorescence shifted from light blue to blue violet. Moreover, both UV absorption and fluorescence intensity showed a linear correlation with pH raging from 4.5 to 7.5. These results indicate that the sensor effectively responds to pH, making it suitable for detecting the freshness of perishable food. To put this into practice, we integrated the sensor with cellulose-based filter paper to determine the freshness of shrimp and beef, which was proved to be effective in assessing freshness. In the future, it can be combined with intelligent colorimetric and fluorescence instruments to achieve visual detection.

Modified halloysite nanotubes as GRAS nanocarrier for intelligent monitoring and food preservation

Conventional "all-in-one" methods for multi-component active packaging systems are not wholly adequate for fresh food. Given the need for multifunctional properties, introducing halloysite nanotubes (HNTs) could be a promising way to achieve controllable release of active ingredients while endowing with pH-sensitive performance. Here, we pioneered a GRAS composite with multifunctional properties, employing natural HNTs as a nanocarrier, citral (Cit) as an active antimicrobial agent, and myricetin (Myr) for monitoring freshness. The Cit-HNTs-Myr had excellent DPPH, ABTS and ·OH radical scavenging capacity, dual-model (contact and fumigant) antibacterial properties, and pH-sensitive performance. Subsequently, a smart tag prepared by dipping cellulose fibers into Cit-HNTs-Myr, which extended the shelf life of shrimp and blueberries, and provided freshness information for the shrimp. These results demonstrate the applicability of Cit-HNTs-Myr in the preservation of perishable goods and freshness monitoring.

Reusable, Green, Portable Ionogels Based on Terpyridine-Imidazole Salt for Visual Monitoring of Pork Spoilage

Ionogels have emerged as a promising approach because they combine the advantageous properties of ionic liquids and gels. Herein, a novel gelator bearing terpyridine and imidazolium salt units was designed and synthesized, which assembled into ionogels in three ionic liquids by a heating-cooling procedure. The properties of ionogels were characterized by FT-IR, UV-vis spectroscopy, POM, XRD, and rheology, and resonance light scattering and opacity measurements were conducted to investigate the gelation kinetics. Furthermore, the ionogels incorporating pH-sensitive dyes (BTB and MR) were exploited as colorimetric sensor to monitor total volatile basic nitrogen (TVB-N) of meat at -4 °C, which can easily and reliably estimate the quality of meat by naked eye recognition, and the results demonstrated a positive correlation between the color variation and TVB-N levels. Notably, the hydrophobic ionogel indicators are more suitable for potential application at high humidity thanks to their antiswelling advantage, which could prevent the inaccurate information produced by hydrogel indicators. In addition, the ionogels could be reused up to three times as colorimetric indicators, suggesting potential applications and competitiveness. Our research sheds new light on the novel application of ionogels in the food industry.

Antibacterial and Antibiofilm Potential of Bacterial Cellulose Hydrogel Containing Vancomycin against Multidrug-Resistant Staphylococcus aureus and Staphylococcus epidermidis

The present study aimed to evaluate the in vitro antibacterial and antibiofilm activity of bacterial cellulose hydrogel produced by Zoogloea sp. (HYDROGEL) containing vancomycin (VAN) against bacterial strains that cause wound infections, such as multidrug-resistant (MDR) Staphylococcus aureus and Staphylococcus epidermidis. Initially, HYDROGEL was obtained from sugar cane molasses, and scanning electron microscopy (SEM) was performed to determine morphological characteristics. Then, VAN was incorporated into HYDROGEL (VAN-HYDROGEL). The antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was assessed using the broth microdilution method to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) against methicillin-sensitive S. aureus (MSSA) ATCC 25923, methicillin-resistant S. aureus (MRSA) ATCC 33591, S. epidermidis INCQS 00016 (ATCC 12228), five clinical isolates of MRSA, and nine clinical isolates of methicillin-resistant S. epidermidis, following the Clinical and Laboratory Standards Institute (CLSI) guidelines. Additionally, the antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was studied using the time-kill assay. Subsequently, the antibiofilm activity of VAN, HYDROGEL, and VAN-HYDROGEL was evaluated using crystal violet and Congo red methods, as well as SEM analysis. VAN and VAN-HYDROGEL showed bacteriostatic and bactericidal activity against MRSA and methicillin-resistant S. epidermidis strains. HYDROGEL did not show any antibacterial activity. Analysis of the time-kill assay indicated that HYDROGEL maintained the antibacterial efficacy of VAN, highlighting its efficiency as a promising carrier. Regarding antibiofilm activity, VAN and HYDROGEL inhibited biofilm formation but did not demonstrate biofilm eradication activity against methicillin-resistant S. aureus and S. epidermidis strains. However, it was observed that the biofilm eradication potential of VAN was enhanced after incorporation into HYDROGEL, a result also proven through images obtained by SEM. From the methods carried out in this study, it was possible to observe that HYDROGEL preserved the antibacterial activity of vancomycin, aside from exhibiting antibiofilm activity and enhancing the antibiofilm effect of VAN. In conclusion, this study demonstrated the potential of HYDROGEL as a candidate and/or vehicle for antibiotics against MDR bacteria that cause wound infections.

Packaged europium/fluorescein-based hydrogen bond organic framework as ratiometric fluorescent probe for visual real-time monitoring of seafood freshness

The freshness of sea food has always been the focus of attention from consumers, and food-safety issues are in urgent need of efficient approaches. A HOF-based ratiometric fluorescence probe (HOF-FITC/Eu) featuring superior amine-response, offers the real-time and visual detection of seafood freshness. Via intermolecular hydrogen bond interaction to form hydrogen-bonded organic frameworks (HOFs), which serve as a structural basis for the conjugate loading of pH-sensitive fluorescein (5-FITC) and coordination doping of lanthanide Eu3+. Amine vapors stimulate the dual-wavelength (525 nm and 616 nm) characteristic fluorescence of HOF-FITC/Eu with an inverse trend, resulting in an increase of the ratio of I525 to I616 accompanied by a distinct color transition from red to green. Prepared HOF-FITC/Eu featuring sensitive red-green color change characteristics of amine response are readily dripped into composite films of filter paper through integrated smartphone and 254 nm UV lamp as mobile observation devices to on-site monitor the freshness of raw fish and shrimp samples. The intelligent food probe HOF-FITC/Eu opens a novel material assembly type for fluorescence sensing and a potential pathway for other functional materials in the field of investigational food.

High-Performance Room Temperature Ammonia Sensors Based on Pure Organic Molecules Featuring B-N Covalent Bond

Exploring organic semiconductor gas sensors with high sensitivity and selectivity is crucial for the development of sensor technology. Herein, for the first time, a promising chemiresistive organic polymer P-BNT based on a novel π-conjugated triarylboron building block is reported, showcasing an excellent responsivity over 30 000 (Ra/Rg) against 40 ppm of NH3, which is ≈3300 times higher than that of its B-N organic small molecule BN-H. More importantly, a molecular induction strategy to weaken the bond dissociation energy between polymer and NH3 caused by strong acid-base interaction is further executed to optimize the response and recovery time. As a result, the BN-H/P-BNT system with rapid response and recovery times can still exhibit a high responsivity of 718, which is among the highest reported NH3 chemiresistive sensors. Supported by in situ FTIR spectroscopy and theoretical calculations, it is revealed that the N-H fractions in BN-H small molecule promoted the charge distribution on phenyl groups, which increases charge delocalization and is more conducive to gas adsorption in such molecular systems. Notably, these distinctive small molecules also promoted charge transfer and enhanced electron concentration of the P-BNT sensing polymer, thus achieving superior B-N-containing organic molecules with excellent sensing performance.

A water quality assessment model involving novel fluorescence technology

The reasonable utilization of water resources and real-time monitoring of water pollution are the core tasks of current world hydrological and water conservancy work. Novel technologies and methods for monitoring water pollution are important means to ensure water health. However, the absence of intuitive and simple analysis methods for the assessment of regional pollution in large-scale water bodies has prevented scientists from quickly grasping the overall situation of water pollution. In this study, we propose a strategy based on the unique combination of fluorescence technology and simple kriging (SK) interpolation (FL-SK) for the first time. This strategy could present the relative magnitude and distribution of the physicochemical indicators of a whole natural lake intuitively and accurately. The unique FL-SK model firstly offers a simple and effective water quality method that provides the pollution index of different sampling points in lakes. The macroscopic evaluation of large-scale water bodies by the FL-SK model primarily relies on the fluorescence response of the RDM-TPE to the comprehensive indicators of the water body, as experimental results have revealed a good correlation between fluorescent responses and six normalized physicochemical indicators. Multiple linear regression and fluorescence response experiments on RDM-TPE indicate that to some extent, the fluorescence signals of the FL-SK model may originate from a certain type of sulfide in the water body. Pattern discovery could enable the analysis of pollution levels in other ecosystems and promote early pollution assessment in the future.

Selective fluoride sensing by a novel series of lanthanide-based one-dimensional coordination polymers through intramolecular proton transfer

A novel series of one-dimensional coordination polymers (CPs) is achieved via a facile one-pot synthesis strategy employing the nitrate salts of trivalent lanthanides, a pentadentate chelating ligand, and triphenylphosphine oxide at a controlled stoichiometry under ambient conditions. All the CPs are characterized comprehensively using spectroscopic, X-ray crystallographic and magnetometric studies. The CPs are found to be thermally stable up to a significantly high temperature and resistant to water for an indefinite time. They are photoactive and exhibit selective fluoride ion (F-) sensing with excellent efficiency both colorimetrically and fluorimetrically in the solid-state as well as in solution. The presence of F- concomitantly sensitizes the photoluminescence enhancement and visual decolourization of the CPs in solution owing to the ground-state intra-molecular proton transfer. The photophysical response of the CPs to F- in solution was found to be instantaneous (<30 s). The sensitivity of detection is observed to be significantly high over a wide range of F- concentrations, covering the beneficial and detrimental domains of F- concentrations in drinking water. The limit of detection (LoD) under ambient conditions was found to be in the micromolar (μM) range-the best being 0.22 μM found using UV-vis spectrometry and 7.5 μM using fluorimetry. In comparison, the USEPA standard cut-off for the upper limit of F- concentration in drinking water is 211 μM, and the LoD of measuring F- concentration using the USEPA standard method using a fluoride-selective electrode is 26.3 μM. The CPs display markedly high selectivity toward F- with negligible-to-no interference from the commonly abundant ions (Cl-, Br-, I-, CH3CO2-, CO32-, SO42-, HPO42-, NH4+, Na+, K+, Mg2+, and Ca2+) in terms of UV-vis spectral change. Moreover, they also exhibit solid-state IR-spectrometric sensitivity towards F- under ambient conditions.

Manipulating Crystal Growth and Secondary Phase PbI2 to Enable Efficient and Stable Perovskite Solar Cells with Natural Additives

In perovskite solar cells (PSCs), the inherent defects of perovskite film and the random distribution of excess lead iodide (PbI2) prevent the improvement of efficiency and stability. Herein, natural cellulose is used as the raw material to design a series of cellulose derivatives for perovskite crystallization engineering. The cationic cellulose derivative C-Im-CN with cyano-imidazolium (Im-CN) cation and chloride anion prominently promotes the crystallization process, grain growth, and directional orientation of perovskite. Meanwhile, excess PbI2 is transferred to the surface of perovskite grains or formed plate-like crystallites in local domains. These effects result in suppressing defect formation, decreasing grain boundaries, enhancing carrier extraction, inhibiting non-radiative recombination, and dramatically prolonging carrier lifetimes. Thus, the PSCs exhibit a high power conversion efficiency of 24.71%. Moreover, C-Im-CN has multiple interaction sites and polymer skeleton, so the unencapsulated PSCs maintain above 91.3% of their initial efficiencies after 3000 h of continuous operation in a conventional air atmosphere and have good stability under high humidity conditions. The utilization of biopolymers with excellent structure-designability to manage the perovskite opens a state-of-the-art avenue for manufacturing and improving PSCs.

Isomeric Benzenediol-Linked Organophosphonates as a Handy Reusable Emitting Platform: Diversity in Polyamine Vapor Detection

This work introduces metal/column-free facile quantitative access to conformationally twisted catechol-linked organophosphonate (CAP) as a blue-emitting solid that could reversibly detect only 1,3-diaminopropane (DAP) and 1,2-ethylenediamine (EDA) vapors, belonging to industrially and pharmaceutically abundant crucial diamines. In CAP, two adjacent hydroxy groups in a benzene ring facilitate selective diamine-dihydroxy (amine-phenol type) interactions in the solid phase, leading to a quenched emission with selectively smaller aliphatic PAs, that is, DAP and EDA. The disparity was noticed with an isomeric resorcinol-linked emitter (RAP), detecting various polyamine vapors with superior sensitivity. A one-carbon-away placed hydroxy group in RAP can only generate a monoamine-hydroxy complex, not diamine-dihydroxy. The more acidic nature of resorcinol would prefer ionizing the amines and, consequently, creating amine/hydroxy interactions. More systematic investigations reveal an exciting role of amine-hydroxy realization for the catechol analog in the solid phase with a syn-anti conformation for CAP. Unlike CAP, RAP's available crystal void space creates considerable room in which to come closer and facilitates amine-phenol interactions. The role of phosphonates in the selective detection of PAs is also examined. Observed outcomes are substantiated by FT-IR, single-crystal X-ray diffraction, SEM, XPS, and mass spectroscopic studies. The proposed amine-hydroxy interactions are further supported by DFT-optimized molecular structures.

Machine Learning-Assisted Portable Microplasma Optical Emission Spectrometer for Food Safety Monitoring

To meet the needs of food safety for simple, rapid, and low-cost analytical methods, a portable device based on a point discharge microplasma optical emission spectrometer (μPD-OES) was combined with machine learning to enable on-site food freshness evaluation and detection of adulteration. The device was integrated with two modular injection units (i.e., headspace solid-phase microextraction and headspace purge) for the examination of various samples. Aromas from meat and coffee were first introduced to the portable device. The aroma molecules were excited to specific atomic and molecular fragments at excited states by room temperature and atmospheric pressure microplasma due to their different atoms and molecular structures. Subsequently, different aromatic molecules obtained their own specific molecular and atomic emission spectra. With the help of machine learning, the portable device was successfully applied to the assessment of meat freshness with accuracies of 96.0, 98.7, and 94.7% for beef, pork, and chicken meat, respectively, through optical emission patterns of the aroma at different storage times. Furthermore, the developed procedures can identify beef samples containing different amounts of duck meat with an accuracy of 99.5% and classify two coffee species without errors, demonstrating the great potential of their application in the discrimination of food adulteration. The combination of machine learning and μPD-OES provides a simple, portable, and cost-effective strategy for food aroma analysis, potentially addressing field monitoring of food safety.

Integration of lanthanide MOFs/methylcellulose-based fluorescent sensor arrays and deep learning for fish freshness monitoring

Preserving fish meat poses a significant challenge due to its high protein and low fat content. This study introduces a novel approach that utilizes a common type of lanthanide metal-organic frameworks (Ln-MOFs), EuMOFs, in combination with 5-fluorescein isothiocyanate (FITC) and methylcellulose (MC) to develop fluorescent sensor arrays for real-time monitoring the freshness of fish meat. The EuMOF-FITC/MC fluorescence films were characterized with excellent fluorescence response, ideal morphology, good mechanical properties, and improved hydrophobicity. The efficacy of the fluorescence sensor array was evaluated by testing various concentrations of spoilage gases (such as ammonia, dimethylamine, and trimethylamine) within a 20-min timeframe using a smartphone-based camera obscura device. This sensor array enables the real-time monitoring of fish freshness, with the ability to preliminarily identify the freshness status of mackerel meat with the naked eye. Furthermore, the study employed four convolutional neural network (CNN) models to enhance the performance of freshness assessment, all of which achieved accuracy levels exceeding 93 %. Notably, the ResNext-101 model demonstrated a particularly high accuracy of 98.97 %. These results highlight the potential of the EuMOF-based fluorescence sensor array, in conjunction with the CNN model, as a reliable and accurate method for real-time monitoring the freshness of fish meat.

Highly selective and sensitive histamine and tryptamine analysis using SiO2@AuNPs@PDA molecularly imprinted polymer coupled with SALDI-TOF MS

A combination of SiO2@AuNPs@PDA molecularly imprinted and surface-assisted laser desorption/ionization-time-of-flight mass spectrometry (SALDI-TOF MS) was devised as a method for highly specific and ultrasensitive detection of two biogenic amines-histamine (HIS) and tryptamine (TRP)-in real samples. In this strategy, AuNPs modified amino-abundant silica nanospheres (SiO2@AuNPs). The prepared SiO2@AuNPs were used as a substrate to synthesize a molecularly imprinted polymer (MIP) through in situ dopamine self-polymerization with HIS and TRP as the template molecules (SiO2@AuNP@PDA-MIP). The as-prepared MIP structure, properties, and target-analyte identification conditions were characterized and optimized and it was used as the matrix for MS. Compared to the case of nonimprinted materials, the imprinting function endowed the matrix with a higher selectivity for capturing the target molecules. The enriched analytes were directly and rapidly identified using SALDI-TOF MS without elution. Meanwhile, the proposed method has low background interference, good reproducibility and stability, high salt tolerance, and satisfactory linearity (R2 > 0.99), and it enables ultrasensitive detection of HIS and TRP (limits of detection for HIS and TRP were 0.2 and 0.1 ng mL-1, respectively). Moreover, the proposed method was applied to analyze samples of real beer, sausage, and chicken, and the results agreed with those obtained via liquid chromatography-MS, suggesting that the method has excellent practical applications in the field of food safety.

A paper-based ratiometric fluorescent sensor for NH3 detection in gaseous phase: Real-time monitoring of chilled chicken freshness

A ratiometric fluorescence sensor platform with easy-to-use and accurate is nanoengineered for NH3 quantitative detection and visual real-time monitoring of chicken freshness using smartphones. The ratiometric fluorescent probe formed by combining the zinc ion complex and carbon dots has a double-emitted fluorescence peak. The fluorescence intensity of the complex changed can be clearly observed with the increase of the concentration of ammonia solution under 365 nm wavelength excitation. In order to detect NH3 concentration in gaseous phase, a portable paper-based sensor was designed. The sensor had a good linear relationship with NH3 concentration ranging from 10.0 to 90.0 μmol/L and the LOD value was 288 nM. This fluorescent paper-based sensor was used to check the freshness of chicken breast refrigerated at 4 °C, revealed observable shifts from blue to green. The fluorescent paper-based sensor can detect NH3 concentration in real time and simplify the monitoring process of meat freshness while ensuring accuracy and stability.

Amine vapor-responsive ratiometric sensing tag based on HPTS/TPB-PVA fluorescent film for visual determination of fish freshness

In this study, amine vapor-sensitive films with ratiometric fluorescence attributes were developed. The pH-sensitive fluorescein 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and its tetraphenylethylene derivative (TPB) were selected as ratiometric indicators and incorporated into a polyvinyl alcohol (PVA) matrix to produce HPTS/TPB-PVA films. The films responded well to amine vapors, and the interference of aromatic vapors did not substantially affect the fluorescence signals of the films. Under UV light at a wavelength of 365 nm, the fluorescence of the films changed from dark pink to light pink and finally to yellow when the freshness of the fish was visually checked during storage. In addition, the color difference values of the films showed a positive correlation with the total volatile basic nitrogen (TVB-N), ranging from 12.7 to 24.8 mg/100 g at 25 °C and 8.4 to 25.6 mg/100 g at 4 °C, respectively. This indicates that fluorescent films have good potential for quantifying fish freshness in the near future when connected to an automatic data processing system based on color differences.

A ratiometric fluorescence platform for on-site screening meat freshness

Meat freshness is related to food safety and human health. Developing a simple and effective method for on-site detection of meat freshness is essential to ensure food safety. This study aimed to explore a ratiometric fluorescence platform for on-site screening of meat freshness. We synthesized a series of benzothiazole-based fluorescent compounds (BM, BHM and BTH), each with different recognition groups for detecting meat freshness biomarkers cadaverine (Cad) and putrescine (Pte). The optimized 2-(2'-hydroxyphenyl-3-aldehyde-5-1,3-indanedione) benzothiazole (BTH) demonstrated a noticeable color and fluorescence change, a fast response (<15 min), and high selectivity and sensitivity (LOD = 70 nM) to Cad. Portable test strips based on BTH were prepared for rapid visual detection of meat freshness, which exhibited visible color and fluorescen color changes to Cad and Pte. Furthermore, a portable smartphone-based fluorescence device integrated with a self-programmed Python program was fabricated and used on-site to monitor Cad and Pte within 5 min. The BTH-loaded portable test strips were successfully employed as low-cost, high-contrast, fast-response, and smartphone-adaptable fluorescent labels for detecting Cad and Pte in meat samples under different temperatures (25 °C, 4 °C, and -20 °C). This enabled consumers and food supply chain stakeholders to quickly and visually monitor the meat freshness in real beef, chicken, and pork products.

Integrated Fruit Ripeness Assessment System Based on an Artificial Olfactory Sensor and Deep Learning

Artificial scent screening systems, inspired by the mammalian olfactory system, hold promise for fruit ripeness detection, but their commercialization is limited by low sensitivity or pattern recognition inaccuracy. This study presents a portable fruit ripeness prediction system based on colorimetric sensing combinatorics and deep convolutional neural networks (DCNN) to accurately identify fruit ripeness. Using the gas chromatography-mass spectrometry (GC-MS) method, the study discerned the distinctive gases emitted by mango, peach, and banana across various ripening stages. The colorimetric sensing combinatorics utilized 25 dyes sensitive to fruit volatile gases, generating a distinct scent fingerprint through cross-reactivity to diverse concentrations and varieties of gases. The unique scent fingerprints can be identified using DCNN. After capturing colorimetric sensor image data, the densely connected convolutional network (DenseNet) was employed, achieving an impressive accuracy rate of 97.39% on the validation set and 82.20% on the test set in assessing fruit ripeness. This fruit ripeness prediction system, coupled with a DCNN, successfully addresses the issues of complex pattern recognition and low identification accuracy. Overall, this innovative tool exhibits high accuracy, non-destructiveness, practical applicability, convenience, and low cost, making it worth considering and developing for fruit ripeness detection.

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.

Design of Highly Efficient Electronic Energy Transfer in Functionalized Quantum Dots Driven Specifically by Ethylenediamine

The exploration of emerging functionalized quantum dots (QDs) through modulating the effective interaction between the sensing element and target analyte is of great significance for high-performance trace sensing. Here, the chromone-based ligand grafted QDs (QDs-Chromone) were initiated to realize the electronic energy transfer (EET) driven specifically by ethylenediamine (EDA) in the absence of spectral overlap. The fluorescent and colorimetric dual-mode responses (from red to blue and from colorless to yellow, respectively) resulting from the expanded conjugated ligands reinforced the analytical selectivity, endowing an ultrasensitive and specific response to submicromolar-liquid of EDA. In addition, a QDs-Chromone-based sensing chip was constructed to achieve the ultrasensitive recognition of EDA vapor with a naked-eye observed response at a concentration as low as 10 ppm, as well as a robust anti-interfering ability in complicated scenarios monitoring. We expect the proposed EET strategy in shaping functionalized QDs for high-performance sensing will shine light on both rational probe design methodology and deep sensing mechanism exploration.

Ratiometric Imaging of Catecholamine Neurotransmitters with Nanosensors

Neurotransmitters are important signaling molecules in the brain and are relevant in many diseases. Measuring them with high spatial and temporal resolutions in biological systems is challenging. Here, we develop a ratiometric fluorescent sensor/probe for catecholamine neurotransmitters on the basis of near-infrared (NIR) semiconducting single wall carbon nanotubes (SWCNTs). Phenylboronic acid (PBA)-based quantum defects are incorporated into them to interact selectively with catechol moieties. These PBA-SWCNTs are further modified with poly(ethylene glycol) phospholipids (PEG-PL) for biocompatibility. Catecholamines, including dopamine, do not affect the intrinsic E11 fluorescence (990 nm) of these (PEG-PL-PBA-SWCNT) sensors. In contrast, the defect-related E11* emission (1130 nm) decreases by up to 35%. Furthermore, this dual functionalization allows tuning selectivity by changing the charge of the PEG polymer. These sensors are not taken up by cells, which is beneficial for extracellular imaging, and they are functional in brain slices. In summary, we use dual functionalization of SWCNTs to create a ratiometric biosensor for dopamine.

Programmable Dynamic Information Storage Composite Film with Highly Sensitive Thermochromism and Gradually Adjustable Fluorescence

The development of an integrated material system capable of effectively organizing and combining multisource information, such as dynamic pigmentary, structural, and fluorescent colors, is significant and challenging. Achieving such programmable dynamic information storage can considerably enhance the diversity and security of information deliveries. Here, a polymer-stabilized cholesteric liquid crystal system with highly temperature-sensitive structural color and light-sensitive pigmentary and fluorescence colors is presented. The prepared cholesteric liquid crystals (clcs) can reversibly change their structural color from red to blue within variational 3 °C near room temperature, and exhibit a gradually adjustable fluorescence which can transform from blue to pink and finally to bright red. All this dynamic information is programmable and tailored, hundreds of thousands of (>540 000) pattern combinations can easily be achieved by optical writing with a "bagua" pattern photomask. Therefore, if the corresponding code combinations to the pattern are assigned particular meanings, encrypted transmission of information with very high security can be achieved by utilizing applicable information encoding tables and decryption rules.

Bacterial cellulose/gelatin-based pH-responsive functional film for food freshness monitoring

Food safety is related to public health and environmental safety. Therefore, it is necessary to develop accurate and effective detection methods to assess food quality and safety. In this study, a pH-responsive functional film (BC/GA/FITC/PCA) was generated for the real-time and visual monitoring of shrimp freshness. Bacterial cellulose /Gelatin (BC/GA) was used as a film-forming matrix, and fluorescein isothiocyanate (FITC) and red cabbage (PCA) were used as the response signals. The addition of FITC and PCA increased the shading capacity (< 30 %) and antioxidant properties (22.8 %) of the films. WCA (82.73 ± 0.95°), WVP (1.48 × 10-11 g·cm/cm2·s·Pa) and OTR (2.42 × 10-15 cm3·cm/cm2·s·Pa) indicated that the film possessed water resistance and oxygen barrier properties. When exposed to daylight, the film underwent a color transition from purple to green as the ammonia concentration increased. In addition, the blue-green fluorescence of the films gradually increased and the detection limit was low (170 ppb). In particular, the change in film color caused by shrimp spoilage corresponded to the TVBN value. This study work provides a new strategy for controlling and monitoring food safety and has a wide range of applications in the fields of food-active packaging and smart packaging.

In Situ Optical Detection of Amines at a Parts-per-Quadrillion Level by Severing the Through-Space Conjugated Supramolecular Domino

Conventional fluorophores suffer from low sensitivity and selectivity in amine detection due to the inherent limitations in their "one-to-one" stoichiometric sensing mechanism. Herein, we propose a "one-to-many" chain reaction-like sensing mechanism by creating a domino chain consisting of one fluorescent molecule (e.g., PTF1) and up to 40 nonemissive polymer chains (pPFPA) comprising over thousand repeating units (PFPA). PTF1 (the domino trigger) interacts with adjacent PFPA units (the following blocks) through polar-π interactions and initiates the domino effect, creating effective through-space conjugation along pPFPA chains and generating amplified yellow fluorescent signals through charge transfer between PTF1 and pPFPA. Amine exposure causes rapid dismantling of the fluorophore-pPFPA-based domino chain and significantly reduces the amplified emissions, thus providing an ultrasensitive method for detecting amines. Relying on the above merits, we achieve a limit of detection of 177 ppq (or 1.67 × 10-12 M) for triethylamine, which is nearly 4 orders lower than that of previous methods. Additionally, the distinct reactivity of pPFPA toward different amines allows for the discrimination of primary, secondary, and tertiary amines. This study presents a "domino effect" sensing mechanism that has not yet been reported and provides a general approach for chemical detection that is beyond the reach of conventional methods.

Modulation of Deep-Red to Near-Infrared Room-Temperature Charge-Transfer Phosphorescence of Crystalline "Pyrene Box" Cages by Coupled Ion/Guest Structural Self-Assembly

Organic cocrystals obtained from multicomponent self-assembly have garnered considerable attention due to their distinct phosphorescence properties and broad applications. Yet, there have been limited reports on cocrystal systems that showcase efficient deep-red to near-infrared (NIR) charge-transfer (CT) phosphorescence. Furthermore, effective strategies to modulate the emission pathways of both fluorescence and phosphorescence remain underexplored. In this work, we dedicated our work to four distinct self-assembled cocrystals called "pyrene box" cages using 1,3,6,8-pyrenetetrasulfonate anions (PTS4-), 4-iodoaniline (1), guanidinium (G+), diaminoguanidinium (A2G+), and hydrated K+ countercations. The binding of such cations to PTS4- platforms adaptively modulates their supramolecular stacking self-assembly with guest molecules 1, allowing to steer the fluorescence and phosphorescence pathways. Notably, the confinement of guest molecule 1 within "pyrene box" PTSK{1} and PTSG{1} cages leads to an efficient deep-red to NIR CT phosphorescence emission. The addition of fuming gases like triethylamine and HCl allows reversible pH modulations of guest binding, which in turn induce a reversible transition of the "pyrene box" cage between fluorescence and phosphorescence states. This capability was further illustrated through a proof-of-concept demonstration in shrimp freshness detection. Our findings not only lay a foundation for future supramolecular designs leveraging weak intermolecular host-guest interactions to engineer excited states in interacting chromophores but also broaden the prospective applications of room-temperature phosphorescence materials in food safety detection.

Rare Earth -MOFs: From Synthesis to Their Deployment for Amine-Sensing Application in Aqueous Media

The pursuit of developing sensors, characterized by their fluorescence-intensity enhancement or "turn-on" behavior, for accurately detecting noxious small molecules, such as amines, at minimal levels remains a significant challenge. Metal-organic frameworks (MOFs) have emerged as promising candidates as sensors as a result of their diverse structural features and tunable properties. This study introduces the rational synthesis of a new highly coordinated (6,12)-connected rare earth (RE) alb-MOF-3, by combining the nonanuclear 12-connected hexagonal prismatic building units, [RE9(μ3-O)2(μ3-X)12(OH)2(H2O)7(O2C-)12], with the 6-connected rigid trigonal prismatic extended triptycene ligand. The resulting Y-alb-MOF-3 material is distinguished by its high microporosity and Brunauer-Emmett-Teller surface area of approximately 1282 m2/g, which offers notable hydrolytic stability. Remarkably, it demonstrates selective detection capabilities for primary aliphatic amines in aqueous media, as evidenced by fluorescence turn-on behavior and photoluminescence (PL) titration measurements. This work emphasizes the potential of MOFs as sensors in advancing their selectivity and sensitivity toward various analytes.

A three-in-one versatile sensor for concise detecting biogenic amines and beef freshness

Biogenic amines (BAs), as important indicators for evaluating food spoilage caused by fermentation processes or microbial activities, present significant risks of food safety. Consequently, the development of a simple, sensitive, and selective detection method for amines is of great importance. In this study, we proposed a three-in-one sensor 3,6-bis(dimethylamino)-9-(ethylthio)xanthylium (PSE) for high sensitivity and selectivity detecting BAs with multimodal responses, including olfactory, colorimetric, and fluorescent signals, thus facilitating convenient real-time detection of BAs. Mechanism study indicated that the nucleophilic substitution of PSE with BAs induced such rapid multi-responses with a low detection limit (LOD = 0.03 μM). We further fabricated PSE loaded paper for portable detection of BAs vapors. And the accurate determination of BAs levels is achieved through analyzing the RGB color mode. Finally, we successfully applied these test strips for non-destructive assessing meat beef freshness with the assistance of a smartphone in on-site scenarios.

Magnetically-activated, nanostructured cellulose for efficient capture of circulating tumor cells from the blood sample of head and neck cancer patients

In this report, the relative efficiency of cellulose nanocrystals (CNCs) and nanofibers (CNFs) to capture circulating tumor cells (CTCs) from the blood sample of head and neck cancer (HNC) patients was evaluated. Detection and enumeration of CTCs are critical for monitoring cancer progression. Both types of nanostructured cellulose were chemically modified with Epithelial Cell Adhesion Molecule (EpCAM) antibody and iron oxide nanoparticles. The EpCAM antibody facilitated the engagement of CTCs, promoting entrapment within the cellulose cage structure. Iron oxide nanoparticles, on the other hand, rendered the cages activatable via the use of a magnet for the capture and separation of entrapped CTCs. The efficiency of the network structures is shown in head and neck cancer (HNC) patients' blood samples. It was observed that the degree of chemical functionalization of hydroxyl groups located within the CNCs or CNFs with anti-EpCAM determined the efficiency of the system's interaction with CTCs. Further, our result indicated that inflexible scaffolds of nanocrystals interacted more efficiently with CTCs than that of the fibrous CNF scaffolds. Network structures derived from CNCs demonstrated comparable CTC capturing efficiency to commercial standard, OncoDiscover®. The output of the work will provide the chemical design principles of cellulosic materials intended for constructing affordable platforms for monitoring cancer progression in 'real time'.

Dual-channel MIRECL portable devices with impedance effect coupled smartphone and machine learning system for tyramine identification and quantification

We designed a novel, portable, and visual dual-potential molecularly imprinted ratiometric electrochemiluminescence (MIRECL) sensor for tyramine (TYM) detection based on smartphone and deep learning-assisted optical devices. Molecularly imprinted polymer-Ce2Sn2O7 (MIP-Ce2Sn2O7) layers were fabricated by in-situ electropolymerization method as the capture and signal amplification probe. Oxygen vacancies in Ce2Sn2O7 not only enhance the electrochemical redox capability but also accelerate the energy transfer, thereby enhancing the luminescence of cathode ECL. Under optimal conditions, the ECL signals of MIP-Ce2Sn2O7 at the cathode and the anode response of Ru(bpy)32+ was reduced, thus a wide linear range from 0.01 μM to 1000 μM with the detection limit as low as 0.005 μM. Interestingly, combined with an artificial intelligence image recognition algorithm and the principle of optical signal reading by smartphone, the developed MIRECL sensor has been applied to the portable and visual determination of TYM in aquatic samples, and its practicability has been satisfactorily verified.

Fluorescence turn-on mode of Eu3+ complex nanocomposite to detect histamine for seafood freshness

Biogenic amines (BAs), which naturally occur as chemicals in seafood, are indicators of food freshness and quality. High concentrations of BAs can cause an undesirable inflammatory response. However, traditional detection methods cannot meet the needs of rapid analysis nowadays. It is essential to explore a simple and valid method to monitor the food quality. Herein, we design and prepare a nanoclay-based turn on fluorescent material with BAs response, which could be used for the real-time and visual detection of raw fish freshness. As the concentration of BAs increase, the sensor of the fluorescence signal is significantly enhanced. The sensor demonstrated wonderful response and sensitivity which showed a detection limit of 0.935 mg/L for typical BAs histamine within a linear range of 2-14 mg/L in an aqueous solution. More importantly, we developed a responsive BAs device by doping the sensor into polyvinyl alcohol (PVA), which is well applied as a rapid-responsive fluorescent marker for visual monitoring the freshness of raw fish.

Mechanistic insight into homogeneous catalytic crosslinking behavior between cellulose and epoxide by explicit solvent models

Inspired by recent advances on functional modification of cellulosic materials, the crosslinking behaviors of epoxide with cellulose under the catalysis of different homogeneous catalysts including H2O, Brønsted acid, Brønsted base, Lewis acid and neutral salt were systematically investigated using density functional theory (DFT) methods with hybrid micro-solvation-continuum approach. The results showed that catalytic activity, reaction mechanism and regioselectivity are determined by the combined effect of catalyst type, electronic effect and steric hindrance. All the homogeneous catalysts have catalytic activity for the crosslinking reaction, which decreases in the order of NaOH > HCl > NCl3 > MCl2 > CH3COOH > NaCl (N = Fe3+, Al3+; M = Zn2+, Ca2+). Upon the catalysis of NaOH, hydroxyl group of cellulose is firstly deprotonated to form a carbanion-like intermediate which will further attack the less sterically hindered C atom of epoxide showing excellent regioselectivity. Acidic catalysts readily cause epoxide protonated, which suffers from nucleophilic attack of cellulose and forms the carbocation-like intermediate. Brønsted acid exhibits poor regioselectivity, however, Lewis acid shows an interesting balance between catalytic activity and regioselectivity for the crosslinking reaction, which may be attributed to the unique catalysis and stabilization effects of its coordinated H2O on the transition state structure.

Two dimensional iron metal-organic framework nanosheet with peroxidase-mimicking activity for colorimetric detection of hypoxanthine related to shrimp freshness

Two dimensional iron metal-organic framework nanosheet (2D Fe MOF) was facilely synthesized at room temperature by simple stirring of iron salts and terephthalic acid ligand in a mixed solution containing triethylamine. Its morphology and structure were fully characterized by TEM, AFM, XPS and TEM element mapping. Then, its peroxidase-mimicking activity was studied by using H2O2 and 3, 3', 5, 5'- tetramethylbenzidine as substrate. Km and Vmax of 2D Fe MOF towards H2O2 were 0.02 mM and 2.08 × 10-8 M s-1, respectively. Through the formation of cascade reaction between xanthine oxidase and 2D Fe MOF, a visual method for hypoxanthine (Hx) detection was constructed to evaluate aquatic products freshness. After effective validation, this method presented wide linear range (5.0-500.0 μM), low limit of detection (3.29 μM), satisfied accuracy (recovery of 94.78-99.85%), and good selectivity. By using this method, Hx content in shrimp samples at different storage time were determined.

Cellulose/amylose derivatives bearing bulky substituents as reversible fluorescent sensors for detection of Fe3

Two novel cellulose and amylose derivatives bearing bulky tris(2-benzothienylformate) pendants (Cel-3 and Amy-3) were expeditiously prepared by one-step esterification. The fluorescent sensing performance of six polysaccharide derivatives, including Cel-3/Amy-3, and other four previously prepared benzothienyl- or benzofuranyl-phenylcarbamates of cellulose and amylose (Cel-1/Amy-1, Cel-2/Amy-2), were carefully evaluated using eight metal ions, including Co2+, K+, Na+, Li+, Hg2+, Ni2+, Ca2+ and Fe3+. All six derivatives exhibited excellent fluorescence quenching property to Fe3+ ions with high sensitivity and selectivity. Especially, the limit of detection of Amy-2 with benzofuranylphenylcarbamates for Fe3+ was 3.0 μM, much lower than the maximum contaminant level for Fe3+ in the drinking water. Additionally, the six bulky derivatives displayed the interesting fluorescence "turn-off" and "turn-on" observation, indicating a desirable reversibility for Fe3+ detection. The high anti-interference ability was also observed for detection of Fe3+ on the benzothienyl/benzofuranyl derivatives of cellulose and amylose in the combined system containing Co2+, K+, Na+, Li+, Hg2+, Ni2+ and Ca2+. It suggested that the obtained polysaccharide derivatives with bulky chromophores possessed good potentials for detection of Fe3+ as high-efficient fluorescent sensors in diverse applications. The sensing mechanism for detection of Fe3+ was further proposed based on the Stern-Volmer plots and fluorescence titration analysis.

A comprehensive review of the spoilage of shrimp and advances in various indicators/sensors for shrimp spoilage monitoring

Shrimp is a popular internationally traded shellfish due to its unique taste, texture, and nutritional value. Shrimp is highly perishable because it has enough free amino acids, high moisture levels, non-nitrogenous compounds used for microbial growth, and melanosis. Shrimp spoilage after death is caused by various reasons, like autolysis (endogenous proteinases actions during shrimp storage), growth of spoilage microorganisms, ATP degradation, melanin formation, and lipid peroxidation. A microbial byproduct, total volatile basic nitrogen, is one of the major reasons for the generation of foul odors from shrimp spoilage. Shrimp freshness monitoring is crucial for market sellers and exporters. Traditional methods for estimating shrimp freshness are expensive and inaccessible to the general public. Sensors are rapid, sensitive, selective, and portable food toxins' detection tools, devoid of expensive instruments, skilled people, sample pretreatment, and a long detection time. This review addresses shrimp spoilage causes. The mechanisms of different stages of shrimp spoilage after death, like rigor mortis, dissolution of rigor mortis, autolysis, and microbial spoilage mechanisms, are discussed. This review highlights the last five years' advances in shrimp freshness detection sensors and indicators like colorimetric pH indicators, fluorescence sensors, electronic noses, and biosensors, their working principles, and their sensitivities. Commercially available indicators and sensors for shrimp spoilage monitoring are also discussed. A review highlighting the applications of the different sensors and indicators for monitoring shrimp freshness is unavailable to date. Challenges and future perspectives in this field are explained at the end.

Nanoscatterer-Assisted Fluorescence Amplification Technique

Weak fluorescence signals, which are important in research and applications, are often masked by the background. Different amplification techniques are actively investigated. Here, a broadband, geometry-independent and flexible feedback scheme based on the random scattering of dielectric nanoparticles allows the amplification of a fluorescence signal by partial trapping of the radiation within the sample volume. Amplification of up to a factor of 40 is experimentally demonstrated in ultrapure water with dispersed TiO2 nanoparticles (30 to 50 nm in diameter) and fluorescein dye at 200 μmol concentration (pumped with 5 ns long, 3 mJ laser pulses at 490 nm). The measurements show a measurable reduction in linewidth at the emission peak, indicating that feedback-induced stimulated emission contributes to the large gain observed.

Machine Learning-Assisted High-Throughput Strategy for Real-Time Detection of Spermine Using a Triple-Emission Ratiometric Probe

In this study, we designed and fabricated a spermine-responsive triple-emission ratiometric fluorescent probe using dual-emissive carbon nanoparticles and quantum dots, which improve the sensor's accuracy and reduce interfering environmental effects. The probe is advantageous for the proportionate detection of spermine because it has good emission resolution, and the maximum points of the two emission peaks differ by 95 nm. As a proof of concept, cuvettes and a 96-well plate were combined with a smartphone and YOLO series algorithms to accomplish real-time, visual, and high-throughput detection of seafood and meat freshness. In addition, the reaction mechanism was verified by density functional theory and fundamental characterizations. Upon exposure to different amounts of spermine, the intensity of the fluorescent probe changed linearly, and the fluorescent color shifted from yellow-green to red, with a limit of detection of 0.33 μM. To enable visual identification of food-originated spermine, a hydrogel-based visual sensing platform was successfully developed utilizing the triple-emission fluorescent probe. Consequently, spermine could be identified and quantified without complicated equipment.

Construction of self-propelled micromotor for "hunting bacteria"

The inherent migration behavior of bacteria has inevitably impacted the advancement of the antibacterial treatment technology. Hunting bacteria, especially those with flagellates, requires self-propelled materials, which could kill bacteria autonomously. Herein, we designed and synthesized a self-propelled micromotor (SPM) tailed with poly(thiazole) to yield bimetallic organic frameworks (BiOFs), in which the assembly of BiOFs are similar to the "Newman projection". The moving speed of the obtained SPM was 238.6 μm s-1 and presented excellent antibacterial activity; more than 90% bacteria were hunted and killed in flowing water. Its minimum inhibitory concentration (MIC) against E. coli and S. aureus was 3.2 and 0.4 mg mL-1, respectively, and its antibacterial activity was still retained after recycling for 5 times. Its antibacterial mechanism along with the contribution of the active units and flow rate was investigated. In summary, a novel self-propelled material for hunting bacteria was synthesized by an unprecedented and efficient strategy. This approach is anticipated to create huge possibilities for its applications in the fields of antibacterial, disinfection, and microdevices.

Integrated portable food safety testing pipette based on a color-switchable fluorescence probe for rapid visual discrimination of mild food deterioration

A sensitive, portable, easy-to-operate, directly-readable food freshness monitoring device has been developed for rapid visual identification of mild food spoilage.

Recent Development of Polymer Nanofibers in the Field of Optical Sensing

In recent years, owing to the continuous development of polymer nanofiber manufacturing technology, various nanofibers with different structural characteristics have emerged, allowing their application in the field of sensing to continually expand. Integrating polymer nanofibers with optical sensors takes advantage of the high sensitivity, fast response, and strong immunity to electromagnetic interference of optical sensors, enabling widespread use in biomedical science, environmental monitoring, food safety, and other fields. This paper summarizes the research progress of polymer nanofibers in optical sensors, classifies and analyzes polymer nanofiber optical sensors according to different functions (fluorescence, Raman, polarization, surface plasmon resonance, and photoelectrochemistry), and introduces the principles, structures, and properties of each type of sensor and application examples in different fields. This paper also looks forward to the future development directions and challenges of polymer nanofiber optical sensors, and provides a reference for in-depth research of sensors and industrial applications of polymer nanofibers.

Exopolysaccharide riclin and anthocyanin-based composite colorimetric indicator film for food freshness monitoring

Food freshness monitoring is vital to ensure food safety. Recently, packaging materials incorporating pH-sensitive films have been employed to monitor the freshness of food products in real time. The film-forming matrix of the pH-sensitive film is essential to maintain the desired physicochemical functions of the packaging. Conventional film-forming matrices, such as polyvinyl alcohol (PVA), have drawbacks of low water resistance, poor mechanical properties, and weak antioxidant ability. In this study, we successfully synthesise PVA/riclin (P/R) biodegradable polymer films to overcome these limitations. The films feature riclin, an agrobacterium-derived exopolysaccharide. The uniformly dispersed riclin conferred outstanding antioxidant activity to the PVA film and significantly improved its tensile strength and barrier properties by forming hydrogen bonds. Purple sweet potato anthocyanin (PSPA) was used as a pH indicator. The intelligent film with added PSPA provided robust surveillance of volatile ammonia and changed its color within 30 s in the pH range of 2-12. This multifunctional colorimetric film also engendered discernible color changes when the quality of shrimp deteriorated, demonstrating its great potential as an intelligent packaging material to monitor food freshness.

Cellulose levulinate ester as a robust building block for the synthesis of fully biobased functional cellulose esters

Facile modification of cellulose or cellulosic derivatives is one of the important strategies to prepare materials with targeted properties, multifunctionality, thus extending their applications in various fields. Cellulose levulinate ester (CLE) has the structural advantage of acetyl propyl ketone moiety pendant, on which fully biobased cellulose levulinate ester derivatives (CLEDs) have been successfully designed and prepared via aldol condensation reaction of CLE with lignin-derived phenolic aldehydes catalyzed by DL-proline. The structure of CLEDs are featured by a phenolic α,β-unsaturated ketone structure, thus endowing them with good UV absorption properties, excellent antioxidant activity, fluorescence properties and satisfactory biocompatibility. The utility of this aldol reaction strategy, together with the facile tunable substitution degree of cellulose levulinate ester and the diversity of aldehydes, can provide potentially a large spectrum of structurally diverse functionalized cellulosic polymers and create new avenues to advanced polymeric architectures.

Recent advances in meat freshness "magnifier": fluorescence sensing

To address the serious waste of meat resources and food safety problems caused by the decrease in meat freshness due to the action of microorganisms and enzymes, a low-cost, time-saving and high-efficiency freshness monitoring method is urgently needed. Fluorescence sensing could act as a "magnifier" for meat freshness monitoring due to its ability to sense characteristic signal produced by meat spoilage. Here, the magnification mechanism of meat freshness via sensing the water activity, adenosine triphosphate, hydrogen ion, total volatile basic nitrogen, hydrogen sulfide, bioamines was comprehensively analyzed. The existing "magnifier" forms including paper chips, films, labels, arrays, probes, and hydrogels as well as the application in livestock, poultry and aquatic meat freshness monitoring were reviewed. Future research directions involving innovation of principles, visualization and quantification capabilities for various meats freshness were provided. By critically evaluating the potential and limitations, efficient and reliable meat freshness monitoring strategies wish to be developed for the post-epidemic era.