Intracellular bio-synthesizing Gold Nanoparticles using bacterial systems and their applications in photothermal therapy (A green approach)
Background: Conventional cancer therapies are heavily constrained by systemic toxicity, off-target side effects, and poor deep-tissue penetration due to the highly heterogeneous tumor microenvironment (TME). Although gold nanoparticles (AuNPs) possess exceptional localized surface plasmon resonance (LSPR) properties ideal for photothermal therapy (PTT), their clinical translation is bottlenecked…
Gold nanoparticles (AuNPs) have shown great potential for photothermal therapy (PTT) in cancer treatment, but their clinical application is limited by systemic toxicity and poor deep-tissue penetration. This study presents a sustainable and biocompatible bio-hybrid platform that utilizes the probiotic E. coli Nissle 1917 (EcN) to create AuNPs through an eco-friendly intracellular green chemistry method.
EcN cultures were grown in Luria-Bertani (LB) medium and exposed to a 1 mM chloroauric acid (HAuCl4) metallic precursor. A room-temperature green synthesis protocol used ascorbic acid (Vitamin C) as a non-toxic co-reductant to induce seed-mediated crystallization of AuNPs onto the bacterial interior.
The resulting bio-hybrid system (EcN::AuNPs) was characterized through visual inspection, UV-Vis spectroscopy, and in vitro PTT assays under continuous-wave near-infrared (NIR) laser irradiation. Upon visual examination, the AuNPs exhibited a deep dark-brownish hue due to the reduction of Au3+ to Au0. UV-Vis spectroscopy confirmed the formation of stabilized, isotropic gold nanostructures (30-60nm) with a broadened surface plasmon resonance (SPR) band at 560nm, which is indicative of the enhanced localization of electromagnetic fields.
Biocompatibility tests showed that the EcN::AuNPs platform caused a significant decrease in cell viability, from 10^8CFU/mL to 10^3CFU/mL, due to trivalent gold heavy-metal toxicity, mechanical disruption of the bacterial cell wall, and metabolic/oxidative stress. However, the surviving bacterial population retained chemotactic capabilities necessary for targeting tumors.
When exposed to 5 minutes of continuous NIR laser irradiation, the EcN::AuNPs bio-hybrid platform demonstrated exceptional concentration-dependent hyperthermia kinetics, causing a thermal increase from 20°C to an absolute peak of 75.4°C. This performance outperformed all control groups (pure EcN, bare HAuCl4, and standalone ascorbic acid).
The engineered EcN::AuNPs bio-hybrid platform represents a promising alternative for targeted oncological interventions, offering a balance between active biological tumor targeting and rapid, localized photothermal ablation while maintaining biosafety and biocompatibility.
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