Eco-Friendly Silver Nanoparticle Synthesis via Honey and Liposomal Cassyopea®: A Dual-Function System for Enhanced Stability and Antibacterial Efficacy

Silver nanoparticles are recognized for their powerful antimicrobial abilities which makes them a go-to solution in fields ranging from medicine to food preservation. But here’s the problem: the typical methods for creating these nanoparticles often rely on harsh chemicals, which can leave behind toxic residues that pose risks to both human health and the environment. This concern has sparked a major push for more sustainable, eco-friendly ways of producing silver nanoparticles. That’s where honey comes in because it is loaded with antioxidants and works harmoniously with natural biological systems and also can act as a reducing agent, converting silver ions into pure metallic silver without the need for any harsh additives. This is a big advancement forward in green chemistry, but honey alone doesn’t quite solve everything. The nanoparticles it helps create are stable in small lab setups, but over time—and especially when scaled up for larger applications—they can start to lose their structure and effectiveness. Without something to protect them, these silver particles are prone to oxidation or clumping, which greatly limits their practical use. To tackle this, researchers have turned to liposomes—tiny, bubble-like structures made of phospholipids, the same material that forms cell membranes. Liposomes are excellent carriers and can safely encapsulate and deliver various substances, like drugs or nanoparticles. When silver nanoparticles are enclosed within these liposomes, they gain added stability and protection from rapid oxidation. This shielding effect extends the nanoparticles’ lifespan and lowers their toxicity. But there’s a catch: most existing methods require synthesizing the nanoparticles first and then trying to load them into the liposomes, a two-step process that often results in uneven dispersion which compromise stability and performance.

Recognizing these limitations, Professors Gasbarri and Angelini from the University “G .d’Annunzio” of Chieti-Pescara in Italy, set out to simplify things. In their research study published in Colloids and Surfaces A: Physicochemical and Engineering Aspects, they developed a one-step process that merges honey and liposomes from the start. In this method, honey acts as a natural reducing agent, while the liposomes simultaneously encapsulate the silver nanoparticles as they’re being formed. This streamlined approach creates a stable, biocompatible silver nanoparticle housed within a liposome structure called Cassyopea®. The end product is a naturally derived nanoparticle with impressive and enduring antimicrobial power. This novel technique has the potential to pave the way for safer antibacterial treatments and greener production methods across a wide range of industries.

Professors Gasbarri and Angelini started their experiments with a mix of silver nitrate and Acacia honey in water at a basic pH level. When the solution turned a distinctive yellow, it visually confirmed that silver nanoparticles were forming. Later, this color change was backed up by UV–visible spectroscopy, showing a clear plasmonic band at 406 nm—a signature of spherical silver nanoparticles. This showed that the honey had effectively converted silver ions into metallic silver, without the need for any artificial stabilizers. By using tools like field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy and dynamic light scattering, they could see that the nanoparticles were consistently spherical, with a size averaging around 30 nm. According to the authors, not only were these particles well-formed, but they also stayed stable and didn’t clump together, even without synthetic additives.

The researchers then took things a step further by embedding the NewAgNPs® into liposomes to create Cassyopea® aggregates—a new concept where the liposomes acted both as miniature “factories” for synthesizing the particles and as protective containers. The goal was to achieve direct synthesis of AgNPs inside the liposomes, something that hadn’t been tried before. To form Cassyopea®, they hydrated phospholipid films and processed them to form large, single-layer vesicles. Into these vesicles, they introduced the silver nitrate and honey mixture. Once the solution turned yellow again, it signaled that AgNPs were successfully forming inside the Cassyopea®. This was further confirmed through UV–visible spectroscopy, showing a characteristic band at 413 nm. The slight wavelength shift suggested that the liposomal environment subtly influenced the nanoparticles’ optical properties. Dynamic light scattering analysis showed the liposomal structures had an average size of 138 nm, while zeta potential measurements of -69.5 mV indicated high stability because the negative charge prevents the particles from clumping together. To test how well the AgNPs in Cassyopea® could resist oxidation, the authors used a Fenton-like reaction, where hydrogen peroxide (H₂O₂) is applied to trigger the breakdown of metallic silver into silver ions. They exposed both the AgNPs in Cassyopea® and those in plain water to H₂O₂ and tracked the decrease in absorbance at the key wavelengths for AgNPs (406 nm for NewAgNPs® and 413 nm for Cassyopea®) over time. They found that Cassyopea®-encapsulated AgNPs resisted oxidation far better, with a rate constant 21.5 times lower than the NewAgNPs® in water which implies that the liposomal Cassyopea® structure created a barrier that slowed oxidation and effectively shielded the AgNPs from degrading. Further evidence came when the researchers noticed that Cassyopea®’s size increased slightly after H₂O₂ exposure, from 138 nm to about 175 nm, showing that the liposomal membrane allowed H₂O₂ to pass through while keeping its structural integrity and by this protect the particles inside.

The team then examined the antibacterial effectiveness of NewAgNPs® and Cassyopea® against several bacterial strains, both Gram-negative (such as Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (including Staphylococcus aureus and Bacillus cereus). They measured both the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC), yielding some encouraging results. For example, NewAgNPs® showed an MIC of 5.4 μg/mL against E. coli and B. cereus, indicating they could effectively inhibit bacteria at relatively low levels. Cassyopea® also showed strong antibacterial effects, with slightly varying MICs due to the liposomal coating. Interestingly, Cassyopea® achieved lower MIC values for Staphylococcus aureus compared to NewAgNPs®, suggesting that liposomal encapsulation might enhance interaction with specific bacterial types, potentially boosting antibacterial action against Gram-positive strains. In cases like Pseudomonas aeruginosa, Cassyopea® displayed a lower MBC than NewAgNPs®, indicating that the liposomal structure might enable a more potent bactericidal effect at lower doses. These results highlight the potential for tackling infections that are becoming resistant to standard antibiotics.

  In conclusion, the research work of Professors Gasbarri and Angelini stands out for its fresh, sustainable approach to creating nanoparticles and the potential it holds for fields that rely heavily on antimicrobial technology. By using honey as a natural reducing agent and combining it with liposomal carriers, they come up with a method that sidesteps the toxic chemicals typically involved in making nanoparticles. It’s a green, environmentally conscious approach that speaks to growing concerns about the impact of traditional AgNP production on health and the planet. Not only does this method cut down on environmental harm, but it also offers a straightforward and affordable way to produce stable, well-formed nanoparticles. This kind of advancement is bound to catch the attention of industries focused on eco-friendly practices—specially those in healthcare, food safety, and environmental protection. We think one of the most exciting aspects of this work is the Cassyopea® liposome itself, which serves a dual purpose: it’s both a manufacturing environment and a delivery system. The liposomal structure stabilizes the nanoparticles against oxidation, extending their antibacterial effects and keeping them effective over time. This level of stability is key for applications where nanoparticles might otherwise break down quickly, like in medical coatings, drug delivery, or even agricultural treatments. On top of that, the liposomes are biocompatible, meaning they’re safe for use in the body. This opens up possibilities for targeted antimicrobial therapies that need controlled, sustained release without the side effects of traditional metal-based nanoparticles. The potential for Cassyopea® doesn’t stop there—it’s adaptable and could be used for more than just silver nanoparticles. Its protective and stable structure makes it a great candidate for carrying a variety of active compounds, offering a versatile platform for delivering therapeutic agents precisely where they’re needed. This adaptability hints at exciting new avenues for treating infections or diseases tied to oxidative stress, where targeted treatments are critical.