Synthesis, Chemical-Physical Characterization, and Biomedical Applications of Functional Gold Nanoparticles: A Review

Abstract

Relevant properties of gold nanoparticles, such as stability and biocompatibility, together with their peculiar optical and electronic behavior, make them excellent candidates for medical and biological applications. This review describes the different approaches to the synthesis, surface modification, and characterization of gold nanoparticles (AuNPs) related to increasing their stability and available features useful for employment as drug delivery systems or in hyperthermia and photothermal therapy. The synthetic methods reported span from the well-known Turkevich synthesis, reduction with NaBH₄ with or without citrate, seeding growth, ascorbic acid-based, green synthesis, and Brust-Schiffrin methods. Furthermore, the nanosized functionalization of the AuNP surface brought about the formation of self-assembled monolayers through the employment of polymer coatings as capping agents covalently bonded to the nanoparticles. The most common chemical-physical characterization techniques to determine the size, shape and surface coverage of AuNPs are described underlining the structure-activity correlation in the frame of their applications in the biomedical and biotechnology sectors.

Keywords: drug delivery; gold nanoparticles; nanomaterials synthesis; photothermal activity.

Figure 1

Scheme of the synthesis, characterization, and application of AuNPs.

Figure 2

Colloidal gold nanoparticle (AuNP) formation process.

Figure 3

Multi–functional modification of AuNPs surface.

Figure 4

Representation scheme of the surface functionalization method through (a) a place exchange and (b) coupling reaction.

Figure 5

General procedure of synthesis of AuNP@N-thio-alkylcarbazoles [125].

Figure 6

Various mechanism of antimicrobial activity of AuNP@antibiotics/antibacterial coatings.

Figure 7

UV–Vis spectra for gold nanoparticles of different shapes.

Figure 8

Hyperthermia cancer treatment using AuNPs. Nanoparticles carry a specific binder of the tumor, interacting with abnormal cells due to the implemented permeability of the vessels surrounding the cancer cells. Laser illumination of the AuNPs generates heat production.

Figure 9

Functioning scheme of the AuNPs used in a bio-barcode. (a) Complex formed by a magnetic nanoparticle carrying specific antibodies and a target molecule, attracted on a magnetic substrate. (b) AuNPs bearing a double-stranded DNA and an antibody. (c) The double-stranded DNA washed away by water moves and interacts with a polynucleotide fixed to a chip. (d) Added AuNPs are functionalized by a complementary polynucleotide. (e) Finally, silver deposition allows the amplification of the detection signal.