Green Synthesis of Mushroom-Derived Glucan Nanosponges for the Templated Growth and Stabilization of Gold Nanoparticles

Gold nanoparticles (AuNPs) have attracted significant scientific attention over the past two decades owing to their remarkable physicochemical properties, including size-dependent optical behavior, high surface-area-to-volume ratio, excellent conductivity, and catalytic efficiency (Daniel & Astruc, 2004; Dreaden et al., 2012). One of the most distinctive features of AuNPs is their localized surface plasmon resonance (LSPR), which arises from collective oscillation of conduction electrons when exposed to electromagnetic radiation, resulting in strong absorption and scattering properties (Link & El-Sayed, 1999). These unique characteristics have enabled extensive applications of AuNPs in diverse fields such as biomedical engineering, drug delivery systems, photothermal therapy, diagnostic imaging, biosensing platforms, environmental monitoring, and heterogeneous catalysis (Jain et al., 2008; Huang et al., 2010).

Conventional chemical and physical synthesis methods for gold nanoparticles typically employ strong reducing agents such as sodium borohydride, hydrazine, or citrate stabilizers, along with organic solvents and surfactants (Turkevich et al., 1951; Brust et al., 1994). Although these approaches allow precise control over nanoparticle size and morphology, they often involve toxic chemicals, high energy consumption, and environmentally hazardous by-products, raising concerns regarding sustainability and biomedical compatibility (Iravani, 2011). Increasing environmental awareness and the principles of green chemistry have therefore encouraged the development of eco-friendly synthesis strategies that minimize toxic reagents and utilize renewable biological resources (Anastas & Warner, 1998).

Green synthesis of nanoparticles employs biological systems such as plant extracts, microorganisms, enzymes, and natural biomolecules as reducing and stabilizing agents (Ahmed et al., 2016; Singh et al., 2018). These biological components contain diverse phytochemicals or biopolymers capable of converting metal ions into nanoparticles under mild reaction conditions. Compared to conventional approaches, green synthesis methods offer advantages including lower toxicity, cost-effectiveness, enhanced biocompatibility, and improved stability of nanoparticles due to natural capping agents (Iravani et al., 2014).

Among biological materials, mushrooms represent an emerging and sustainable source of functional biomolecules for nanomaterial synthesis. Mushroom-derived polysaccharides, particularly β-glucans, have gained considerable attention due to their structural versatility and biological activities such as immunomodulatory, antioxidant, and antimicrobial properties (Wasser, 2010; Zhang et al., 2007). Glucans are polysaccharides composed primarily of glucose monomers connected through β-(1→3) and β-(1→6) glycosidic linkages, forming branched macromolecular networks with high functional group density. Their intrinsic biocompatibility, biodegradability, and non-toxic nature make them highly suitable for biomedical nanotechnology applications (Vetvicka & Vetvickova, 2011).

Importantly, glucan molecules possess abundant hydroxyl and carboxyl functional groups capable of interacting with metal ions, enabling simultaneous reduction and stabilization during nanoparticle synthesis (Sharma et al., 2019). The polymeric architecture of glucans can also serve as a natural template that regulates nucleation and growth processes, thereby influencing nanoparticle size distribution and preventing aggregation (Krabicová et al., 2020). Recent studies have demonstrated that polysaccharide-based nanostructures, including nanosponges, provide porous three-dimensional frameworks that enhance nanoparticle dispersion and improve catalytic performance (Trotta et al., 2012).

In this context, the present study explores a sustainable strategy for synthesizing gold nanoparticles using glucan nanosponges derived from the edible mushroom Agaricus bisporus. The glucan nanosponges are designed to function as multifunctional matrices, offering a porous three-dimensional structure that facilitates efficient adsorption of gold precursor ions and promotes controlled nanoparticle nucleation and growth. The synthesis parameters are optimized to regulate nanoparticle size, morphology, and stability.

Furthermore, the synthesized glucan nanosponges and gold-loaded nanosponges are systematically characterized using advanced analytical techniques to evaluate their structural, optical, and physicochemical properties. By integrating biopolymer self-assembly with green nanotechnology principles, this work aims to develop an environmentally benign and scalable platform for AuNP synthesis.

MATERIALS AND METHODS

Fresh fruiting bodies of Agaricus bisporus (button mushrooms) were purchased from a local market and used as the primary biological source for glucan extraction. Gold(III) chloride trihydrate (HAuCl?·3H?O, purity >99.9%) was obtained from Sigma-Aldrich and used without further purification. All other reagents and solvents were of analytical grade. Deionized water was used throughout the experimental procedures to minimize contamination and ensure reproducibility of results (Sharma et al., 2019).

Extraction and Purification of Mushroom Glucans

Glucans were extracted from Agaricus bisporus following an optimized hot-water extraction method widely used for fungal polysaccharide isolation (Wasser, 2010). Finely chopped mushroom samples were subjected to hot aqueous extraction to solubilize intracellular polysaccharides. The extract was filtered to remove insoluble residues and subsequently precipitated using ethanol, a common approach for polysaccharide recovery (Dubois et al., 1956).

The crude glucan fraction was purified through repeated dialysis against deionized water to remove salts, proteins, and low-molecular-weight impurities (Zhang et al., 2013). The carbohydrate content and purity of the extracted glucan were confirmed using the phenol–sulfuric acid colorimetric method, a standard assay for total polysaccharide quantification (Dubois et al., 1956).

Formation of Glucan Nanosponges

Purified glucan polymers were converted into nanosponges through aqueous self-assembly. A defined concentration of glucan was dissolved in deionized water under continuous stirring to obtain a homogeneous solution. Sonication was applied to promote intermolecular hydrogen bonding and nanoscale aggregation, facilitating the formation of porous nanosponge structures (Trotta et al., 2012).

The resulting nanosponges were isolated by centrifugation and freeze-dried via lyophilization to obtain stable nanosponge powders suitable for nanoparticle templating applications (Krabicová et al., 2020).

Synthesis of Gold Nanoparticles

Gold nanoparticles (AuNPs) were synthesized through an in-situ green reduction process using glucan nanosponges as both reducing and stabilizing agents. Pre-formed nanosponges were dispersed in deionized water to create a uniform suspension, followed by the addition of aqueous HAuCl?·3H?O solution under continuous stirring. The reaction mixture was maintained at controlled temperature conditions to allow glucan functional groups (hydroxyl and polysaccharide moieties) to reduce Au(III) ions into metallic gold nanoparticles while stabilizing their growth (Iravani, 2011; Ahmed et al., 2016). The synthesized Au-loaded nanosponges were washed repeatedly with deionized water and lyophilized for further analysis.

Figure 1. Purified Glucan and Synthesis of Gold Nanospong.

RESULTS AND DISCUSSION

Characterization of Mushroom Glucans and Nanosponges

The extracted polysaccharide obtained from Agaricus bisporus was systematically characterized to confirm its chemical composition and nanoscale structural organization. Quantitative carbohydrate analysis using the phenol–sulfuric acid method revealed a high carbohydrate content dominated by glucose residues, confirming the successful isolation of β-glucan polymers consistent with previously reported fungal polysaccharides (Dubois et al., 1956; Wasser, 2010).

The purification process effectively removed proteins, salts, and low-molecular-weight contaminants, resulting in structurally uniform glucan suitable for nanosponge fabrication. The formation of glucan nanosponges through aqueous self-assembly was confirmed using scanning electron microscopy (SEM) and dynamic light scattering (DLS).

Figure 2. SEM image of mushroom-derived glucan nanosponges.

SEM images showed porous spherical architectures, indicating successful nanosponge formation driven by intermolecular hydrogen bonding among glucan chains. These structures exhibited interconnected cavities capable of acting as nanoreactors or templating matrices. DLS measurements showed a relatively narrow particle size distribution, confirming homogeneous nanoscale aggregation with an average hydrodynamic diameter within the nanometer range.

Table 1. Size distribution and zeta potential of mushroom-derived glucan nanosponges.

Zeta potential analysis revealed a negative surface charge, attributed primarily to hydroxyl and residual carboxyl functional groups present on the glucan backbone. The negative potential contributes significantly to colloidal stability by generating electrostatic repulsion between particles and also enhances affinity toward positively charged metal ions such as Au³?. Similar stabilization mechanisms have been reported for polysaccharide-based nanostructures (Zhang et al., 2013).

Collectively, these results confirm that mushroom-derived glucans successfully self-assemble into stable nanosponges possessing structural and surface properties suitable for nanoparticle synthesis.

Green Synthesis and Stabilization of Gold Nanoparticles

Upon addition of aqueous HAuCl? solution to the glucan nanosponge suspension, a rapid color transition from pale yellow to dark ruby red was observed, indicating the formation of colloidal gold nanoparticles (AuNPs). This color change arises from localized surface plasmon resonance (SPR), a phenomenon characteristic of nanoscale gold particles (Iravani, 2011).

UV–Visible spectroscopy confirmed nanoparticle formation. The synthesized Au-loaded glucan nanosponges displayed a pronounced absorption peak centered near 530 nm, corresponding to spherical AuNPs with sizes typically between 10–30 nm (Ahmed et al., 2016).

(Graph showing SPR band around 530 nm)

Figure 3. UV–Vis spectra of Au-loaded glucan nanosponges synthesized at different concentrations of gold precursor.

The intensity increase of the SPR band with precursor concentration indicates progressive nanoparticle formation without significant aggregation, suggesting efficient stabilization by the glucan matrix.

Transmission electron microscopy (TEM) further validated nanoparticle morphology and spatial distribution. TEM images revealed uniformly dispersed AuNPs embedded within the porous nanosponge network. The particles were predominantly spherical with an average diameter of approximately 20 nm.

High-resolution TEM (HRTEM) analysis displayed distinct lattice fringes corresponding to the (111) crystallographic planes of face-centered cubic (FCC) gold, confirming crystalline nanoparticle formation.

Figure 4. TEM image of Au-loaded glucan nanosponges.

X-ray diffraction (XRD) analysis provided additional structural confirmation. Diffraction peaks observed at 38.2°, 44.4°, 64.6°, and 77.5° correspond to the (111), (200), (220), and (311) planes of FCC gold, respectively. The absence of impurity peaks indicates high phase purity.

Figure 5. XRD pattern of Au-loaded glucan nanosponges.

Fourier transform infrared (FTIR) spectroscopy was used to evaluate functional group participation during nanoparticle synthesis.

Figure 6. FTIR spectra of (a) purified glucan nanosponges and (b) Au-loaded glucan nanosponges.

The pristine glucan nanosponges exhibited characteristic absorption bands:

Following AuNP formation, shifts and intensity reductions in hydroxyl-related bands were observed, indicating involvement of these groups in Au³? reduction and nanoparticle stabilization. These spectral changes strongly support a biomediated reduction mechanism.

Mechanisms of Reduction and Stabilization

The experimental observations suggest a dual functional role of glucan nanosponges as both reducing agents and stabilizing scaffolds. Hydroxyl groups present along the polysaccharide backbone donate electrons to Au³? ions, reducing them to metallic Au?. Reduction preferentially occurs within nanosponge pores where metal ions accumulate through electrostatic interactions.

Physical confinement within the porous polymeric network prevents uncontrolled aggregation, leading to narrow particle size distribution. This templated growth mechanism represents a defining advantage of green polysaccharide-mediated synthesis compared with conventional chemical reduction methods.

Stability and Catalytic Properties

The Au-loaded glucan nanosponges demonstrated remarkable colloidal stability, remaining dispersed in aqueous media for prolonged periods without aggregation or sedimentation. This stability arises from a combination of steric shielding by glucan chains and electrostatic repulsion due to surface functional groups. Catalytic activity was evaluated using the model reduction reaction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of a reducing agent. The reaction progress was monitored spectrophotometrically through the decrease in absorbance of 4-NP and simultaneous formation of 4-AP. The AuNP-embedded nanosponges exhibited rapid catalytic conversion, indicating that immobilization within the glucan matrix does not hinder active surface accessibility. Instead, the porous architecture enhances reactant diffusion while preventing nanoparticle aggregation, thereby improving catalytic efficiency and reusability.

CONCLUSION

The present study successfully demonstrated a sustainable and green approach for the synthesis of glucan nanosponges derived from Agaricus bisporus and their application as bio-templates for the formation and stabilization of gold nanoparticles (AuNPs). The optimized hot-water extraction followed by ethanol precipitation and dialysis produced highly purified glucan polymers rich in carbohydrate content, confirming efficient isolation of fungal polysaccharides as previously reported for mushroom-derived glucans (Wasser, 2010; Zhang et al., 2013). Self-assembly of purified glucans under controlled aqueous conditions, assisted by sonication, resulted in the formation of nanosponge structures with spherical morphology and nanoscale dimensions. SEM and DLS analyses verified uniform particle distribution, while the observed negative zeta potential indicated the presence of surface hydroxyl and carboxyl functional groups contributing to colloidal stability through electrostatic repulsion (Trotta et al., 2012). These physicochemical properties highlight the suitability of glucan nanosponges as biocompatible nanostructured scaffolds. The glucan nanosponges efficiently mediated the green synthesis of gold nanoparticles through an in-situ reduction mechanism without the need for toxic chemical reducing agents. The formation of AuNPs was confirmed by the characteristic surface plasmon resonance (SPR) band around 530 nm in UV–Vis spectroscopy, consistent with spherical nanoparticles within the 10–30 nm size range (Iravani, 2011; Ahmed et al., 2016). TEM and HRTEM analyses further confirmed the uniform dispersion and crystalline nature of AuNPs embedded within the nanosponge matrix, while XRD patterns verified the face-centered cubic (FCC) structure of metallic gold.

FTIR spectral shifts demonstrated the active participation of glucan functional groups, particularly hydroxyl moieties, in both reduction of Au(III) ions and stabilization of the formed nanoparticles. These findings support the dual functionality of glucan nanosponges as reducing as well as capping agents, a defining feature of green nanotechnology approaches (Ahmed et al., 2016). Moreover, the Au-loaded glucan nanosponges exhibited remarkable colloidal stability and retained catalytic activity, effectively facilitating the reduction of 4-nitrophenol to 4-aminophenol. The enhanced catalytic efficiency can be attributed to the high surface area, porous nanosponge architecture, and uniform immobilization of AuNPs, which ensured accessibility of active catalytic sites (Krabicová et al., 2020). Overall, this study establishes mushroom-derived glucan nanosponges as an eco-friendly, renewable, and multifunctional platform for nanoparticle synthesis and stabilization. The integration of natural polysaccharides with nanotechnology offers significant potential for applications in catalysis, environmental remediation, biomedical systems, and green materials science. The developed methodology provides a scalable and sustainable alternative to conventional nanoparticle synthesis routes, aligning with current principles of green chemistry and bio-nanotechnology.

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