Special Issue on the Chemometrics-assisted Spectroscopic Methods of Analysis

Abstract

Green nanotechnology offers immense opportunities as it applies principles of green chemistry for synthesis of nanomaterial for various applications. Green gold nanoparticles (AuNPs) provide eco-friendly materials at low cost and toxicity, high chemical and thermal stability, enhanced degradation activity for environmental remediation and used in numerous biomedical fields. For biomedical application, the toxic chemical agents used for synthesis via conventional methods are a major deterrent. To address this, green synthesized of gold nanoparticles (AuNPs) were extensively studied. Continuous efforts have been focused on facile, low cost, pure, non-toxic and environment friendly approach for their synthesis. Their biocompatibility, photonic properties and their possible solubility in aqueous phases enabled the assimilation of AuNPs in diverse biomedical field. Different biological resources normally existing in the environment have been used for biosynthesis of biogenic nanoparticles that include bacteria, fungi, algae, yeast, cyanobacteria, actinomycetes, viruses and plants This review provides a comprehensive overview of synthesis and characterization of biogenic AuNPs with their broad applications in biomedical fields have also been elucidated along with their future prospects.

Introduction

NPs: Nanoparticles; nm: Nanometer; sp.: Species; EPS: Exopolysaccharides; DNA & RNA: Deoxy-Ribonucleic Acid/ Ribonucleic Acid; UV-vis: UV-Visible Spectroscopy; XRD: X-ray diffraction; FTIR: Fourier Transform Infrared Spectroscopy; GCMS: Gas Chromatography-Mass Spectrometry; HPLC: High Performance Liquid Chromatography; EDS: Energy Dispersive Spectroscopy; DLS: Dynamic Light Scattering; SEM: Scanning Electron Microscopy; TEM: Transmission Electron Microscopy; AFM: Atomic Force Microscopy; SPR: Surface Plasmon Resonance; ZP: Zeta Potentials; mV: Milli Volts; SAED: Selected Area Electron Diffraction; pH: Potential of Hydrogen; ROS: Reactive Oxygen Species; MIC: Minimum Inhibitory Conc.; CFU: Colony Forming Unit; LPS: Lipopolysaccharides; JAK/STAT: Janus Kinase/Signal Transducers And Activators of Transcription; NF-kB: Nuclear Factor Kappa-Light-Chain-Enhancer of Activated B Cells; GFP: Green Fluorescent Protein; RME: Receptor-Mediated Endocytosis; MRI: Magnetic Resonance Imaging; CT scan: Computer Tomography Scan; LOD: Limit of Detection; LOQ: Limit of Quantification

Materials and Methods

Collectively, this review highlights the recent trends in the fundamental processes and mechanisms of biogenic synthesis AuNPs by using various biological systems (plants, algae, bacteria, fungus and etc). Consequently, till date, no detailed analyses and comprehend of the rationale factors affecting the green synthesis of AuNPs and their characterization has been studied.Further, we exclusively update the context of various factors affecting the biogenic synthesis of AuNPs and different characterization techniques used to determine the physiochemical properties of synthesized NPs and offer a deep understanding of NPs and their potential biomedical application in modern technology and in green environmental technology. The imminent applications of green AuNPs in the biomedical fi eld involves anti-microbial agents, drug delivery agents, therapeutic agents, bio-sensing agents, and removal of environmental pollutants are also elaborated meticulously.

Results and Discussion

Similarly, plants can also be utilized for nanoparticles synthesis using bio reduction reactions. Numerous parts of plant such as stem, barks, leaves, roots, seeds, latex, secondary metabolites, twigs, peels, fruits, seedlings, essential oils, tissues. etc. are rich source of plant phytochemical (polyphenols, flavonoids, sugars, enzymes, and proteins) readily involved in synthesis process acting as reducing and stabilizing agents [22]. Such biogenic synthesis can reduce the high cost of chemicals, environmental risk of being exposed to hazardrous chemicals, and can be used in developing “environmentally-friendly” nanofertilizers, nanopesticides, and nanoherbicides etc. However, the detailed description of mechanistic events is not yet well understood reflecting involvement of diverse phyto-constituents from plant extract working synergistically in the synthesis process mainly being polyphenols, organic acids, and proteins that are acting as main reducing agents [22,23]. Plant dependent synthesis of biogenic nanoparticles begins with plant-based extraction of phytochemicals and plant extract preparation. Here, the process of extraction is very critical as it is involved in parting the desired plant metabolites from the raw plant source in presence of specific solvents with no chemical modification and easy extraction method. It depends on extraction period, type of solvent, specific temperature, pH, solvent/ sample ratio, and particulate size of plant raw materials etc. Further effectiveness of the extraction methods that are being employed in biogenic nanoparticles synthesis relies on easy laboratory practices, timely and cost-effective production process. There are different extraction methods that are known for this purpose such as (a) solvent extraction (b) microwave dependent extraction (c) maceration extraction (d) ultrasound-assisted extraction [24,25]. The utilization of eco-friendly reagents and solvents, reducing high energy expenditure methods, employing non-toxic biomolecules, such as nucleic acids (DNA & RNA), enzymes, carbohydrates and proteins, as well as plant extracts, permit synthesizing biocompatible metallic NPs by depleting metal ions in aqueous solutions [26,27]. Effective role of different part of plants in extract form for biosynthesis of gold nanoparticles is in form of sequential steps; initial is activation phase, formation of reduced form of precursor metal salt to metal ion occur, this is followed by nucleation reaction involving its further reduction to metal atoms. In growing phase smaller nanoparticles impulsively coalesce into large nanoparticles size (a process commonly known as Ostwald ripening), amplifying the thermodynamic stability of synthesised gold nanoparticles. The duration of this growth phase is vital factor to be considered as aggregation of nanoparticles might lead to nanoparticles surface irregularities forming nanotubes, nanohexahedrons etc. with this it is entering into termination phase where energetically stable conformation is now finally confirmed. Such as case of nanotriangles which are known to have high surface energy and less stable configuration, but after stabilisation is provided in form of plant extract it might acquire a more stable truncated morphology hence, minimize the Gibbs free energy [28]. The advantages of plant-based approach on other green approach are contaminant free large-scale production of biogenic nanoparticles with definite shape, size and morphology along with desired fabrication [29]. Kamaraj, et al has worked on AuNPs that were synthesised from Gracilaria crassa (seaweed) using pre-prepared aqueous extract. During this ecological, rapid, and one step synthetic approach the nanoparticles has acquired spherical morphology, with nanodiameter of 32.0 nm ± 4.0 nm, NPs were highly stable and had a polycrystalline nature. However, its biological application against Anopheles stephensi larvae was also studies and was found to be very ecotoxic on exposure to different concentrations of prepared nanoparticles. Therefore, shedding radiance on its ecotoxicological potential of the prepared nanoparticles with enhance potential overcoming risk to aquatic biota [30]. The limitation associated with this method is raw materials nature that is responsible for restraining its production to the favourable conditions thus impact NPs formation Table 1.

Conclusion

In green technology, the quality of nanoparticles to be formed are also influencing by incubation time of the reaction required for the production of AuNPs [89]. In the same way, we can alter the characteristics of nanoparticles with alteration of time duration of light exposure and storage conditions, etc. [90] and these variations in the time may resulting aggregation of particles for longer storage; it may decrease or increase their size during storage, their shelf life, and other factors which affects the efficacy potential [91]. Noruzi and colleague investigated that biosynthesis of AuNPs by Rosa hybrid petal was rapid and completed their reaction within 5 min [92] on the other hand, Dwivedi and Gopal [Dwivedi and Gopal, 2010] reported that AuNPs and AgNPs synthesis by Chenopodium album leaf started the reactions in 15 min. They also observed that with increasing contact time is strongly responsible for the sharpening of the intensity peaks in both AuNPs and AgNPs. In additions, some of the reports also suggested that there are changes in the size and shape of the NPs with the increase of their reaction time [93]. Apart from this incubation and reaction time, time required for centrifugation is also an important factor. To stop the reaction and also for eliminating the unwanted components, duration of centrifugations plays a major role. Balasubramanian et al., investigated the size of prepared nanoparticles which shows distinct variation with a duration of 5min- 3 hrs of centrifugation process [94].

Special Issue on the Chemometrics-assisted Spectroscopic Methods of Analysis

Abstract

Introduction

Materials and Methods

Results and Discussion

Conclusion

References