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Colloidal gold nanoparticles (AuNPs) were prepared from two different liquid precursors (gold (III) acetate and gold (III) chloride), using the Ultrasonic Spray Pyrolysis (USP) process. The STEM characterisation showed that the AuNPs from gold chloride are spherical, with average diameters of 57.2 and 69.4 nm, while the AuNPs from gold acetate are ellipsoidal, with average diameters of 84.2 and 134.3 nm, according to Dynamic Light Scattering (DLS) measurements. UV/VIS spectroscopy revealed the maximum absorbance band of AuNPs between 532 and 560 nm, which indicates a stable state. Colloidal AuNPs were used as starting material and were mixed together with acrylic acid (AA) and acrylamide (Am) for the free radical polymerization of polyacrylate-AuNPs’ composites, with the purpose of using them for temporary cavity fillings in the dental industry. SEM characterisation of polyacrylate-AuNPs’ composites revealed a uniform distribution of AuNPs through the polymer matrix, revealing that the AuNPs remained stable during the polymerization process. The density measurements revealed that colloidal AuNPs increase the densities of the prepared polyacrylate-AuNPs’ composites; the densities were increased up to 40% in comparison with the densities of the control samples. A compressive test showed that polyacrylate-AuNPs’ composites exhibited lower compressive strength compared to the control samples, while their toughness increased. At 50% compression deformation some of the samples fracture, suggesting that incorporation of colloidal AuNPs do not improve their compressive strength, but increase their toughness significantly. This increased toughness is the measured property which makes prepared polyacrylate-AuNPs potentially useful in dentistry.

In this paper, we present Nanotechnology, which is a branch of science and engineering focused on materials with at least one dimension below 100 nm. It involves the understanding of materials or processes on the "nano" scale. Nanomaterials, in the form of nanoparticles, nanotubes, nanopyramids, etc., have different properties compared to materials with ordinary dimensions. They have altered physical and chemical properties, which come from the large surface-to-volume ratio. This is reflected in their high surface activity and, because of this, they are useful in various fields (Electronics, Chemistry, Biotechnology, Medicine). Based on this fact, Nanotechnology is a broad term that covers many areas of science, research and technology.

Gold nanoparticles (GNPs) were synthesised by the Ultrasonic Spray Pyrolysis (USP) process and collected in deionised water with the addition of a stabiliser, i.e. PVP (0.1 wt.%). With the use of a rotary evaporator, a highly concentrated GNPs' suspension was achieved (600 ppm concentration of GNPs), which was used directly as novel nano gold ink for inkjet printing. The physical and chemical characteristics of such prepared nano gold ink were explained in detail by the use of Zeta (ζ) Potential, ATR-FTIR spectroscopy, UV/VIS spectroscopy, and nanoparticle size was identified through SEM. With nano gold ink the chosen pattern was printed onto photo paper, which was characterised for confirming the presence of gold with optical and SEM/EDX observations. The observations revealed that the tested printed nano gold ink on the paper provided a new route for the fabrication of paper-based electrochemical immunosensors, colorimetric sensors and nanometallic biomedical sensors.