In pursuit of the Sustainable Development Goals,
An article titled : " Medical applications of colloidal nanomaterials produced by laser ablation "
By dr Raad Shaker Alnayli
Abstract:
The fabrication of metallic nanomaterials is a vital field in materials science due to their unique properties that fundamentally differ from their bulk counterparts. Among the various techniques employed for their synthesis, Laser Ablation stands out as a promising method, particularly for producing high-purity and precisely controlled nanoparticles. This article reviews the fundamental principles of the laser ablation process, focusing on the underlying physical mechanisms of metallic nanomaterial formation in different media (liquid and gas). It also discusses the key factors influencing the properties of the produced materials and highlights their prominent applications, with a particular emphasis on the biomedical field. Finally, the paper addresses current challenges and future prospects for this promising technology.
Keywords: Nanomaterials, Laser Ablation, Metallic Nanoparticles, Nanofabrication, PLAL, Biomedical Applications.
1. Introduction
The past few decades have witnessed a tremendous evolution in the field of nanomaterials, defined as materials possessing at least one dimension within the 1-100 nanometer range [1]. These nanoscale dimensions bestow unique physical and chemical properties upon the materials, distinctly different from their bulk counterparts. Such properties include enhanced surface area-to-volume ratio, quantum mechanical effects, and improved optical and electronic characteristics [2]. This uniqueness has opened doors to unprecedented applications across diverse fields, including medicine, energy, electronics, environmental science, and catalysis [3].
Numerous methods exist for nanomaterial synthesis, generally categorized into two main approaches: Bottom-Up, which builds nanostructures from atoms and molecules (e.g., chemical and physical vapor deposition), and Top-Down, which starts from bulk materials and reduces their dimensions to the nanometer scale (e.g., milling and laser ablation) [4].
Laser Ablation has emerged as an effective and sustainable physical technique for producing metallic nanomaterials. This method is characterized by its ability to synthesize high-purity nanoparticles without the need for reducing agents or complex chemical reagents, making it particularly appealing for biologically sensitive applications [5]. This article aims to provide a comprehensive overview of the laser ablation process for metallic nanomaterial production, with a specific focus on their biomedical relevance.
2. Principles of Laser Ablation
Laser ablation is a physical process involving the removal of material from a solid or liquid surface using a high-intensity, high-energy laser beam. When the laser beam strikes the target material, its energy is absorbed by electrons, leading to rapid heating of the material, followed by melting, vaporization, and the formation of a laser-induced plasma [6]. This plasma consists of high-energy atoms, ions, and electrons.
The precise ablation mechanism largely depends on the laser characteristics (such as wavelength, pulse duration, and fluence) and the target material properties. For long-pulse lasers (nanoseconds), multiphoton absorption and thermal interactions lead to plasma formation. In contrast, for ultrashort-pulse lasers (femtoseconds or picoseconds), the process is primarily non-thermal, where material removal occurs through direct vaporization or plasma disintegration, leading to what is often referred to as "cold ablation" [7].
3. Mechanisms of Metallic Nanomaterial Production
The production of metallic nanomaterials by laser ablation can be broadly categorized into two main approaches: Pulsed Laser Ablation in Liquid (PLAL) and Gas Phase Laser Ablation.
3.1. Pulsed Laser Ablation in Liquid (PLAL)
In PLAL, the metallic target material is submerged in a liquid (often deionized water, organic solvents, or ionic solutions). When a laser pulse strikes the metal surface through the liquid, a laser-induced plasma forms within the liquid. This p
lasma rapidly cools and condenses due to the presence of the surrounding liquid, leading to the formation of nanoparticles. The mechanism can be summarized as follows [8]:
* Laser Absorption and Plasma Formation: The laser strikes the target, creating a luminous plasma plume.
* Plasma Expansion and Cooling: The plasma rapidly expands and collides with the surrounding cold liquid, leading to rapid cooling and condensation of atoms and ions to form nanoparticle nuclei.
* Nanoparticle Growth and Aggregation: These nuclei grow through aggregation or agglomeration to form stable nanoparticles, which then disperse in the liquid to form a colloidal solution.
This method is distinguished by its ability to produce exceptionally clean nanoparticles, free from capping agents or chemical impurities, making it ideal for biomedical and biological applications.
3.2. Gas Phase Laser Ablation
In this method, the ablation process occurs in a vacuum chamber or an inert gas atmosphere (e.g., argon). The target is heated by the laser, and the material vaporizes to form a plasma plume. This plume then expands and cools, and the ejected atoms condense to form nanoparticles or nanostructured thin films on a substrate placed in the path of the ablated material [9]. This technique is sometimes referred to as Pulsed Laser Deposition (PLD) when used for thin film fabrication. This method allows for precise control over the thickness and composition of the nanolayers.
4. Factors Influencing the Properties of Produced Nanomaterials
The properties of metallic nanomaterials produced by laser ablation (such as size, shape, and distribution) are influenced by several key factors [10]:
* Laser Parameters:
* Fluence: Directly affects the amount of ablated material and the size of the produced nanoparticles; higher fluence typically leads to larger particles.
* Pulse Duration: Femtosecond and picosecond lasers generally produce smaller nanoparticles with a more uniform size distribution compared to nanosecond lasers, due to the non-thermal ablation mechanisms.
* Laser Wavelength (\lambda): Influences material absorption of energy and plasma formation.
* Repetition Rate: Affects the production rate and can influence particle size through successive laser-plasma interactions.
* Medium Parameters:
* Liquid Type (in PLAL): Influences rapid plasma quenching, nanoparticle stability, and prevention of agglomeration. Water, alcohols, or organic solvents can be used.
* Gas Pressure (in Gas Phase Ablation): Affects plasma expansion and particle formation.
* Target Material Properties: The purity and hardness of the target material influence the ablation efficiency and the quality of the produced materials.
5. Properties and Characterization of Produced Metallic Nanomaterials
Metallic nanomaterials produced by laser ablation exhibit unique properties characterized using advanced techniques [11]:
* Morphological Analysis: Using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM), the size and shape of nanoparticles can be determined. Particles produced are often spherical, but shape can be controlled to produce other structures (e.g., rods or plates) under specific conditions.
* Dispersibility Analysis: Dynamic Light Scattering (DLS) measurements provide information about the hydrodynamic size distribution of particles in colloidal solutions.
* Crystalline Analysis: X-ray Diffraction (XRD) reveals the crystalline structure of the particles, with most metallic nanoparticles being crystalline.
* Optical Properties: UV-Vis Spectroscopy is used to determine the optical properties of the particles, such as the Localized Surface Plasmon Resonance (LSPR) for gold and silver nanoparticles, which is highly dependent on size and shape.
* Chemical and Surface Analysis: X-ray Photoelectron Spectroscopy (XPS) can determine the surface chemical composition of the materials, confirming the high purity of nanoparticles produced by laser ablation.
6. Biomedical Applications of Laser-Ablated Metallic Nanomaterials
The metallic na
nomaterials produced by laser ablation hold a broad spectrum of promising biomedical applications due to their unique properties, especially their high purity and tuneable characteristics [12]:
* Drug Delivery: Nanoparticles (e.g., gold and silver) are extensively used as carriers for targeted drug delivery, enabling precise delivery of therapeutic agents to specific cells or tissues, thereby minimizing side effects. Their biocompatibility and ease of surface functionalization make them ideal for this purpose.
* Bioimaging: The distinct optical properties of metallic nanoparticles, such as LSPR in gold and silver, make them excellent contrast agents for various bioimaging techniques, including optical coherence tomography, photoacoustic imaging, and surface-enhanced Raman scattering (SERS) imaging, allowing for high-resolution visualization of biological structures.
* Photothermal Therapy (PTT): Gold nanoparticles, in particular, are capable of efficiently absorbing near-infrared (NIR) laser light and converting it into heat. This localized heat generation can selectively ablate cancerous cells while minimizing damage to healthy tissues, offering a non-invasive cancer treatment option.
* Antimicrobial Agents: Silver nanoparticles are well-known for their potent antimicrobial, antibacterial, and antifungal properties. Nanoparticles produced by PLAL offer an advantage due to the absence of chemical residues, reducing potential toxicity in biomedical applications. They are used in wound dressings, medical devices, and antimicrobial coatings.
* Biosensors: The large surface area and unique electronic properties of metallic nanoparticles enhance the sensitivity and selectivity of biosensors for detecting various biological molecules, pathogens, and biomarkers, facilitating early disease diagnosis.
* Diagnostic Tools: Beyond imaging and sensing, these nanoparticles can be engineered for various in vitro and in vivo diagnostic applications, including rapid diagnostic tests and molecular diagnostics.
Conclusion
Laser ablation is a powerful and versatile method for the production of metallic nanomaterials. This technique is distinguished by its ability to synthesize high-purity nanoparticles with precisely controllable properties, opening vast possibilities for their applications, especially in the biomedical field, as well as in catalysis and energy. Despite current challenges related to production rate and cost, continuous advancements in laser technology and the understanding of ablation mechanisms indicate a promising future for this technique in advanced nanomaterial fabrication.
9. References
[1] M. C. Roco, "Nanotechnology: Convergence with modern biology and medicine," Current Opinion in Biotechnology, vol. 14, no. 3, pp. 337-346, 2003.
[2] A. M. El-Sayed, "Surface plasmon resonance of metal nanoparticles: from a nanoparticle to a nanorod," Pure and Applied Chemistry, vol. 74, no. 11, pp. 1957-1967, 2002.
[3] G. Cao and Y. Wang, Nanostructures and Nanomaterials: Synthesis, Properties, and Applications, World Scientific, 2011.
[4] K. S. Suslick, "Ultrasound in Materials Chemistry," Annual Review of Materials Science, vol. 29, pp. 295-326, 1999.
[5] J. H. Park et al., "Pulsed laser ablation in liquid for nanoparticles synthesis," Chemical Society Reviews, vol. 42, no. 10, pp. 4323-4339, 2013.
[6] S. Amoruso et al., "Ablation of metals by ultrashort laser pulses: Electron-phonon coupling and thermal relaxation," Applied Physics A, vol. 77, no. 7, pp. 817-822, 2003.
[7] P. Schaaf, "Laser ablation for the synthesis of nanoparticles," Materials Science and Engineering: A, vol. 495, no. 1-2, pp. 1-16, 2008.
[8] F. F. He et al., "Synthesis of gold nanoparticles by pulsed laser ablation in liquid," Journal of Alloys and Compounds, vol. 605, pp. 222-227, 2014.
[9] D. B. Chrisey and G. K. Hubler, Pulsed Laser Deposition of Thin Films, Wiley, 1994.
[10] S. S. Chahal et al., "Factors influencing the synthesis of nanoparticles by pulsed laser ablation in liquid," Materials Science and Engineering: B, vol. 277, p. 115609, 2022.
[1
1] M. A. Shah et al., "Characterization of metal nanoparticles synthesized by laser ablation," Applied Sciences, vol. 8, no. 11, p. 2092, 2018.
[12] N. V. Dinh et al., "Applications of laser ablation in liquid for noble metal nanoparticle synthesis," Journal of Science: Advanced Materials and Devices, vol. 5, no. 3, pp. 320-330, 2020.
[13] T. G. S. I. Nanayakkara et al., "Scale-up production of nanoparticles by pulsed laser ablation in liquid," Journal of Materials Science, vol. 56, no. 14, pp. 8916-8933, 2021
_______
Almustaqbal University is the first university in Iraq.