Ditulis oleh:

In the ongoing fight against bacterial infections, a surprising new ally has emerged from nature: the humble lichen. Often overlooked, these resilient organisms are now central to "green" nanotechnology. Specifically, research highlights how the lichen species Parmotrema praesorediosumcan be utilized to synthesize silver nanoparticles, a tiny metallic structures with potent antibacterial properties against stubborn bacterial foes.

The Dawn of Green Nanotechnology

Traditionally, the synthesis of silver nanoparticles (AgNPs) involved harsh chemicals, high temperatures, and significant energy consumption, making the process far from eco-friendly. This led to the rise of "Green Chemistry," a movement dedicated to replacing toxic industrial processes with natural, sustainable alternatives. By leveraging plants and natural resources, the biocompatible nanoparticles produced are safer for pharmaceutical and biomedical applications (Gilaki, 2010). Lichens, being a symbiotic partnership between a fungus and green algae, offer a unique chemical toolkit of metabolites like polysaccharides and phenolic compounds. These compounds can naturally reduce silver ions into solid, functional nanoparticles, making lichens particularly fascinating for this purpose.

Characterizing the "Micro-Shields"

To ensure the effectiveness of the synthesized nanoparticles, their size and shape were meticulously characterized using advanced techniques such as Transmission Electron Microscopy (TEM) and X-ray diffraction. These analyses revealed that the silver nanoparticles are predominantly spherical, with an average size of 19 nm. They exhibit a face-centered cubic crystal structure, one of characteristic of pure metallic silver.

Crucially, the lichen extract not only facilitates the creation of these particles but also acts as a natural stabilizer (Mie at al, 2014). It effectively coats the silver nanoparticles, preventing agglomeration and maintaining their stability for over a month. This inherent stabilizing property is vital for their potential application in various fields.

The Fight Against Bacteria

The ultimate validation for these "green" nanoparticles lies in their ability to combat pathogenic bacteria. The AgNPs underwent rigorous testing against eight distinct bacterial strains, encompassing both Gram-negative (e.g.,Salmonella typhi) and Gram-positive (e.g., MRSA).

The evaluation employed the "disk diffusion method," a standard microbiological technique. In this method, paper disks impregnated with the nanoparticles are placed on Petri dishes inoculated with bacterial cultures. The presence of a "zone of inhibition", a clear area devoid of bacterial growth around the disk, serves as a direct measure of the nanoparticles' antibacterial potency.

Results: Potent Activity Against Gram-Negative Bacteria

The findings unequivocally demonstrate that these lichen-based silver nanoparticles exhibit particularly strong efficacy against Gram-negative bacterial strains. Figure 2 shows that the original lichen extract (C) and distilled water (B) showed no significant antibacterial activity on Salmonella typhi, proving it is the synthesized silver nanoparticles (A) doing the work.

How Do They Work?

Why are these tiny silver spheres can be deadly to bacteria? While the exact mechanism is a subject of ongoing study, the prevailing theory is that their small size provides a massive surface area to interact with the bacterial cell membrane. They may even penetrate the bacteria entirely, disrupting the internal machinery that the microbes need to survive (Kim et al, 2007). The specific structure of Gram-negative cell walls may make them particularly vulnerable to this silver-based breach.

Why This Matters

This work was the first report of using a lichen species to successfully reduce silver ions into functional AgNPs. It proves that, there is no toxic industrial processes to create high-tech medical tools. As antibiotic resistance continues to be a global threat, these lichen-grown nanoparticles offer a path toward potent, cost-effective, and environmentally friendly antibacterial agents. The humble lichen, once just a quiet part of the forest, is now a cornerstone of modern nanomedicine.

References:

1. Gilaki M. Biosynthesis of silver nanoparticles using plant extracts. Journal of Biological Sciences. 2010;10:465–467. 

2. Krishnaraj C, Jagan EG, Rajasekar S, Selvakumar P, Kalaichelvan PT, Mohan N. Synthesis of silver nanoparticles using Acalypha indica leaf extracts and its antibacterial activity against water borne pathogens. Colloids Surf B Biointerfaces. 2010;76:50–56.

3. Ropisah Mie, Mohd Wahid Samsudin, Laily Din, Azizan Ahmad, Nazlina Ibrahim & Siti Nor Adnalizawati Adnan. Synthesis of silver nanoparticles with antibacterial activity using the lichen Parmotrema praesorediosum. International Journal of Nanomedicine 2014; 9 : 121-127. 

4. Kim JS, Kuk E, Yu KN, Kim JH, Park SJ, Lee HJ, Kim SH, Park YK, Park YH, Hwang CY, Lee YS, Jeong DH, & Cho MH. Antimicrobial effects of silver nanoparticles. Nanomedicine Nanotechnology Biology and Medicine. 2007;3:95–101.