Turning food waste into value-added carbon dots for sustainable food packaging application: A review

Carbon dots and cellulose nanocrystal-incorporated chitosan composite films with enhanced gas selectivity and photodynamic antibacterial properties for fruit preservation

Winter jujube is prone to rapid ripening and deterioration during postharvest storage and transportation. This study developed a multifunctional chitosan (CS) composite film incorporating dialdehyde cellulose nanocrystal (DCNC) and carbon dots (CDs) derived from walnut green husks. DCNC functioned as cross-linking filler, while CDs served as active nanofillers. The CS composite film containing 3 wt% DCNC and 3 wt% CDs (CS/DCNC/CDs-3 %) exhibited significant improvements in UV-blocking, mechanical strength, gas barrier, and thermal stability, attributing to the formation of a dense film structure and synergistic effect of Schiff base and hydrogen bonding interactions among film components. Notably, this composite film demonstrated a high CO2/O2 selectivity of 14.1, facilitating the creation of an ideal atmosphere inside the package. This composite film exhibited remarkable antioxidant activity and displayed potent antibacterial capacity through photocatalytic ROS generation, achieving inhibition rates of 90.8 % against S. aureus and 86.8 % against E. coli. Additionally, this film showed favorable biosafety and biodegradability, addressing food safety and environmental concerns. Postharvest preservation tests confirmed that this film assisted by light exposure effectively regulated physiological metabolism and delayed the ripening of winter jujube, highlighting its potential as an active modified atmosphere packaging material for perishable fruit preservation.

The Use of Carbon Dots for Food Packaging and Preservation: Toxic or Beneficial?

Carbon dots (CDs), which are emerging as versatile nanomaterials, have gained interest in food packaging and preservation due to their sustainable origin and multifunctional characteristics, such as antimicrobial, antioxidant, and UV-protective properties. CDs can be synthesized from biomass and have been proposed as functional additives to packaging material to improve the safety and shelf life of the packaged food. Despite these benefits, concerns are raised about their potential toxicity when leached into foods, especially since they belong to the nanomaterial category. Interestingly, foodborne CDs, which are naturally formed in heat-processed foods and have been consumed by humans for centuries, add a new complexity to the debate. Although there is no definitive evidence linking these endogenous CDs to adverse health effects, some studies suggest their potential to interfere with metabolism in animal models. In addition, the presence of hazardous substances in thermally processed foods, such as polycyclic aromatic hydrocarbons (PAHs), may further complicate safety assessment. This review addresses the paradox of CD from food and packaging sources, highlighting its dual role as both a potentially toxic agent and a beneficial functional material. More extensive research is essential to fully understand the long-term effects of CD on human health and to determine whether its use in food packaging is truly safe or beneficial.

Exploring Sustainable Carbon Dots as UV-Blocking Agents for Food Preservation

Exposure of foods to ultraviolet (UV) radiation during processing, storage, and retail display can result in quality deterioration, reduced shelf life and nutritional value, and potential food safety issues. The use of UV-blocking food packaging is an effective strategy to minimize these harmful effects. Carbon dots (CDs) are a class of carbon-based nanomaterials that have emerged as promising candidates for enhancing the UV-blocking performance of biopolymer-based films and coatings. Their unique advantages of excellent UV absorption ability combined with their low toxicity, biocompatibility, and facile production from sustainable precursors make CDs superior alternatives to traditional UV-blocking agents. Incorporating CDs into biopolymers can significantly enhance UV protection without compromising the transparency of the packaging, thereby maintaining the visual appeal of the packaged product. In addition to UV protection, CDs confer multifunctionality to packaging systems by imparting antioxidant, antimicrobial, and pH-responsive properties, thereby meeting the demand for sustainable and intelligent packaging solutions. These advancements not only protect food from photodegradation but also address broader food safety issues through their active and responsive functions. This review provides an in-depth exploration of the role of CDs as UV-blocking agents in sustainable food packaging. It highlights their mechanisms of action, the advantages they offer over conventional materials, and their contribution to the development of multifunctional and eco-friendly packaging systems.

Transforming Agricultural Waste from Mediterranean Fruits into Renewable Materials and Products with a Circular and Digital Approach

The Mediterranean area is one of the major global producers of agricultural food. However, along the entire supply chain-from farming to food distribution and consumption-food waste represents a significant fraction. Additionally, plant waste residues generated during the cultivation of specific fruits and vegetables must also be considered. This heterogeneous biomass is a valuable source of bioactive compounds and materials that can be transformed into high-performance functional products. By analyzing technical and scientific literature, this review identifies extraction, composite production, and bioconversion as the main strategies for valorizing agricultural by-products and waste. The advantages of these approaches as well as efficiency gains through digitalization are discussed, along with their potential applications in the Mediterranean region to support new research activities and bioeconomic initiatives. Moreover, the review highlights the challenges and disadvantages associated with waste valorization, providing a critical comparison of different studies to offer a comprehensive perspective on the topic. The objective of this review is to evaluate the potential of agricultural waste valorization, identifying effective strategies while also considering their limitations, to contribute to the development of sustainable and innovative solutions in Mediterranean bioeconomy.

Smart packaging films based on gelatin/κ-carrageenan integrated with gromwell root extract rich in shikonin and carbon dots for real-time monitoring of shrimp freshness

Multifunctional pH-responsive gelatin/κ-carrageenan (GC) blend films containing gromwell (Lithospermum erythrorhizon [LE]) root ethanolic extract (LE-EE) rich in shikonin or shikonin rich extract (SRE) and carbon dots (LE carbon dots [LE-CDs]) were prepared and characterized. The hydrothermal method was adopted for the synthesis of LE-CDs, which displayed a blue color under UV light. The obtained LE-CDs possessed exceptional UV barrier, antioxidant and antimicrobial activities. The enhanced activities were recorded when the level of LE-CDs upsurged (p < 0.05). Transmission electron microscopic (TEM) and Fourier transform infrared (FTIR) results revealed the typical morphology and chemical composition of LE-CDs. LE-CDs of 1 and 3% (w/w) were incorporated as the active fillers along with SRE into the GC blend film by the solvent casting method. Developed films showed a slight decrease in tensile and water vapor barrier properties with the inclusion of both additives. Color and opaqueness of the film became darker as the additives were incorporated, whereas the thermal property was greatly enhanced. Film containing 3% LE-CDs blocked UV-A and UV-B by 93.30 and 99.81%, respectively. GC/SRE/3%CD film exhibited strong radical scavenging and antibacterial activities against Listeria monocytogenes and Escherichia coli, in which the growth was terminated after 12 h. Film had a pH-dependent color change, depending on various pH levels (2-12). Shrimp freshness could be monitored as indicated by the shift to bluish color after 48 h. Therefore, this finding indicated that incorporating biomass-derived CDs and natural colorants into biopolymer films, especially GC blend films, could offer diverse strategies for maintaining safety and prolonging shelf life in response to the growing need for smart packaging for food applications.

Carbon dots: synthesis, sensing mechanisms, and potential applications as promising materials for glucose sensors

The disruption of glucose (Glu) metabolism in the human body can lead to conditions such as diabetes and hyperglycemia. Therefore, accurately determining Glu levels is crucial for clinical diagnosis and other applications. Carbon dots (CDs) are a novel category of carbon nanomaterials that exhibit outstanding optical properties, excellent biocompatibility, high water solubility, low production costs, and straightforward synthesis. Recently, researchers have developed various carbon dot sensors for fast and real-time Glu monitoring. In this context, we provide a comprehensive introduction to Glu and CDs for the first time. We categorize the synthetic methods for CDs and the sensing mechanisms, further classifying the applications of carbon dot probes into single-probe sensing, ratiometric sensing, and visual detection. Finally, we discuss the future development needs for CD-based Glu sensors. This review aims to offer insights into advancing Glu sensors and modern medical treatments.

Unlocking the Luminescent Potential of Fish-Scale-Derived Carbon Nanoparticles for Multicolor Conversion

This study introduces a novel approach to addressing environmental issues by developing fish-scale carbon nanoparticles (FSCNPs) with a wide range of colors from discarded fish scales. The process involves hydrothermally synthesizing raw tamban (Sardinella) fish scales sourced from Universal Canning, Inc. in Zamboanga City, Philippines. The optimization of the synthesis was achieved using the response surface methodology with a Box-Behnken design. The resulting FSCNPs exhibited unique structural and chemical properties akin to carbonized polymer dots, enhancing their versatility. The solid-state fluorescence of these nanoparticles can be modulated by varying their concentration in a polyvinylpyrrolidone matrix, yielding colors such as blue, green, yellow, and red-orange with Commission Internationale de l'Eclairage coordinates of (0.23, 0.38), (0.32, 0.43), (0.37, 0.43), and (0.46, 0.48), respectively. An analysis of the luminescence mechanism highlights cross-linking emissions, aggregation-induced emissions, and non-covalent interactions, which contribute to concentration-dependent fluorescence and tunable emission colors. These optical characteristics suggest that FSCNPs have significant potential for diverse applications, particularly in opto-electronic devices.

Incorporation of carbon dots into polyvinyl alcohol/corn starch based film and its application on shiitake mushroom preservation

Developing eco-friendly edible packaging films with multi-functional properties is highly required. This study involved synthesizing carbon dots (CDs) from dragon fruit, then incorporating them into a composite film based on polyvinyl alcohol (PVA)/corn starch (CS) to create a functional package to extend the shelf life of fresh shiitake mushrooms. Functional composite films with varying levels of CDs were formulated. The films' characteristics of morphology, mechanical properties, antioxidant properties, etc. were then determined, as well as their preservation effect on the fresh shiitake mushrooms. The results showed that the PVA/CS/CDs composite film showed excellent mechanical property, Ultraviolet (UV) barrier capability, antioxidant and antimicrobial properties. Specifically, addition of 8 mg/mL CDs in the composite films reduced weight loss of shiitake mushrooms by 30.74 %, decreased the decline in soluble solids content by 10.48 %, and halved the reduction in total sugar content after a 7-day storage period compared to films without added CDs. Furthermore, the films effectively lowered the respiratory intensity and browning of the mushrooms. This research demonstrates that CDs can serve as an effective component for the development of eco-friendly edible packaging films, as well as for their application in food preservation.

Edible coating using carbon quantum dots for fresh produce preservation: A review of safety perspectives

Fresh produce deteriorates and spoils after harvest due to its perishable nature. Deterioration in quality over time has become a major problem for the food industry, placing an undue burden on the economy and agriculture. Food scientists have developed various methods and technologies to prevent spoilage of fruits and vegetables during storage and logistics. Utilizing carbon quantum dots (CQDs) in the form of active packaging and coatings has been a popular strategy recently. CQDs have recently attracted attention as sustainable and functional nanomaterials. CQDs are popular among food scientists due to their easy and economical synthesis, sustainability, non-toxicity, biocompatibility, edibility, UV protection, and antibacterial and antioxidant activities. Although many studies have been conducted and reviewed on the utilization of CQDs in the manufacture of flexible active packaging materials, relatively few studies have investigated the use of CQDs in edible coating formulations for fresh produce. The main reasons for this are concerns about the potential toxicity and edibility of CQDs if they are coated directly on fresh produce. Therefore, this review aims to address these issues by investigating the dose-dependent non-toxicity and biocompatibility of sustainable CQDs along with other important properties from a food packaging perspective. Additionally, this review focuses on the studies performed so far on the direct coating of CQD-based formulations on fresh and fresh-cut fruits and vegetables and discusses the important impact of CQDs on the quality of coated agricultural products. This review is intended to provide food packaging researchers with confidence and prospects for utilizing sustainable CQDs in direct coating formulations for food.

Green synthesis of non-isocyanate hydroxyurethane and its hybridization with carboxymethyl cellulose to produce films

Non-isocyanate polyurethanes (NIPUs) have attracted increasing attention as a sustainable alternative to conventional isocyanate-based polyurethanes. This study synthesized non-isocyanate hydroxyurethanes (NIHUs) through an addition reaction between propylene carbonate (PC) and 1,2-ethylenediamine (EDA). The resulting NIHU was then hybridized with carboxymethyl cellulose (CMC) to investigate its hybridization potential. Structural analysis through FTIR, NMR, and XRD confirmed the crystalline nature of NIHU, featuring urethane bonds and abundant hydroxyl groups. It was found that NIHU and CMC interacted by forming hydrogen bonds between hydroxyl groups of NIHU and carboxyl groups of CMC, resulting in a dense CMC/NIHU hybrid structure. NMR and XRD analyses revealed changes in the hybrids' chain mobility, the Young's modulus of the hybrid with 30 % NIHU content decreased from 1627 MPa to 502 MPa relative to CMC, and the elongation at break increased from 4.44 % to 17.2 %. Increasing the concentration of NIHU in CMC reduced the hydrophobicity, in terms of water contact angle, from 70° to 41.7°. The simplicity of the synthesis method for NIHU, coupled with the desirable structure, strength, and balanced flexibility of CMC/NIHU hybrids, is expected to facilitate the production of NIHU-rich hybrids and increase their application in packaging.

Green Fluorescent Carbon Dots with Critically Controlled Surface States: Make Silk Shine via Feeding Silkworms

Feeding silkworms with functional materials as additives to produce naturally modified silk is a facile, diverse, controllable, and environmentally friendly method with a low cost of time and investment. Among various additives, carbon dots (CDs) show unique advantages due to their excellent biocompatibility and fluorescence stability. Here, a new type of green fluorescent carbon dots (G-CDs) is synthesized with a high oil-water partition ratio of 147, a low isoelectric point of 5.16, an absolute quantum yield of 71%, and critically controlled surface states. After feeding with G-CDs, the silkworms weave light yellow cocoons whose green fluorescence is visible to the naked eye under UV light. The luminous silk is sewn onto the cloth to create striking patterns with beautiful fluorescence. Such G-CDs have no adverse effect on the survival rate and the life cycle of silkworms and enable their whole bodies to glow under UV light. Based on the strong fluorescence, chemical stability, and biological safety, G-CDs are found in the digestive tracts, silk glands, feces, cocoons, and even moth bodies. G-CDs accumulate in the posterior silk glands where fibroin protein is secreted, indicating its stronger combination with fibroin than sericin, which meets the requirements for practical applications.

Carboxymethyl cellulose-based multifunctional film integrated with polyphenol-rich extract and carbon dots from coffee husk waste for active food packaging applications

Sustainable carboxymethyl cellulose (CMC)-based active composite films were developed through the addition of polyphenol-rich extract from coffee husk (CHE) and carbon dots (CDs) prepared using the biowaste residue of CHE extraction. The influences of various CDs contents on the physicochemical and functional characteristics of composite films have been researched. The 6% (w/w) CHE and 3% (w/w) CDs were uniformly dispersed within the CMC matrix to produce a homogenous film with enhanced mechanical properties. The CMC/CHE/CDs3% film exhibited outstanding UV-light blocking, improved water and gas barriers, potent antioxidant activity with above 95% DPPH and ABTS scavenging rates, and effective antibacterial capabilities against L. monocytogenes and E. coli. The food packaging experiment demonstrated that this active composite film slowed the rotting of fresh-cut apples and extended their shelf-life to 7 days at 4 °C storage. Therefore, the obtained multifunctional film showed promise as an environmentally friendly food packaging material.

Biomass-derived carbon dots as emerging visual platforms for fluorescent sensing

Biomass-derived carbon dots (CDs) are non-toxic and fluorescently stable, making them suitable for extensive application in fluorescence sensing. The use of cheap and renewable materials not only improves the utilization rate of waste resources, but it is also drawing increasing attention to and interest in the production of biomass-derived CDs. Visual fluorescence detection based on CDs is the focus of current research. This method offers high sensitivity and accuracy and can be used for rapid and accurate determination under complex conditions. This paper describes the biomass precursors of CDs, including plants, animal remains and microorganisms. The factors affecting the use of CDs as fluorescent probes are also discussed, and a brief overview of enhancements made to the preparation process of CDs is provided. In addition, the application prospects and challenges related to biomass-derived CDs are demonstrated.

Fluorescent Nanocarbons: From Synthesis and Structure to Cancer Imaging and Therapy

Nanocarbons are emerging at the forefront of nanoscience, with diverse carbon nanoforms emerging over the past two decades. Early cancer diagnosis and therapy, driven by advanced chemistry techniques, play a pivotal role in mitigating mortality rates associated with cancer. Nanocarbons, with an attractive combination of well-defined architectures, biocompatibility, and nanoscale dimension, offer an incredibly versatile platform for cancer imaging and therapy. This paper aims to review the underlying principles regarding the controllable synthesis, fluorescence origins, cellular toxicity, and surface functionalization routes of several classes of nanocarbons: carbon nanodots, nanodiamonds, carbon nanoonions, and carbon nanohorns. This review also highlights recent breakthroughs regarding the green synthesis of different nanocarbons from renewable sources. It also presents a comprehensive and unified overview of the latest cancer-related applications of nanocarbons and how they can be designed to interface with biological systems and work as cancer diagnostics and therapeutic tools. The commercial status for large-scale manufacturing of nanocarbons is also presented. Finally, it proposes future research opportunities aimed at engendering modifiable and high-performance nanocarbons for emerging applications across medical industries. This work is envisioned as a cornerstone to guide interdisciplinary teams in crafting fluorescent nanocarbons with tailored attributes that can revolutionize cancer diagnostics and therapy.