Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (F-108) functionalized gold nanoparticles (Au NPs) have been successfully synthesized. During synthesis it is found that an increase in the F-108 concentration contributes to agglomeration in the media, increasing the size of the Au particles, and boosting the curcumin concentration leads to a higher density of functional groups, resulting in smaller Au NPs. FT-IR analysis reveals that the hydroxyl and phenolic groups of curcumin and F-108 are involved during the functionalization of Au surfaces. Enhancement in the fluorescence/RRS intensity is due to the combination of the influence of the shape/size of the Au NPs as well as the extent of curcumin conjugation at the interface of the Au NP surface and F-108. The presence of sugar molecules remarkably boosts the RRS intensity without significantly affecting the fluorescence and surface plasmon absorbance of the Au NPs; in contrast, the RRS intensity of standard CTAB functionalized Au NPs is unaffected by glucose molecules indicating that the functionalization of F-108 at Au surfaces is crucial. Interestingly, no interference from other potential interferents and antioxidant substances like ascorbic acid, creatinine and acetaminophen is observed. This method is simple and fast, and offers a wider linear dynamic range, 0-10 mM, that is applicable under physiological conditions and in serum samples. It is stable and provides an excellent recovery for serum samples, thus, potentially it can be useful in this field due to its low energy consumption, enzyme free assay, fast response time, better selectivity and sensitivity.

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This review expands for the first time the development of curcumin as reducing and stabilizing agent. Curcumin is widely used in food industries, cosmetic domain and the biomedical field. The combination of green synthesis and curcumin to produce nanoparticles has been effective as the amount of toxic waste is highly reduced. Starting with a general introduction about nanoparticles synthesis and curcumin, the use of curcumin as a principal reducing agent and stabilizing compounds in the production of nanoparticles is developed. Consecutively, the preparation of different nanoparticles as gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), copper nanoparticles (Cu NPs), iron nanoparticles (Fe NPs), and manganese and manganese oxide nanoparticles (Mn NPs, MnO NPs) using curcumin is investigated and elaborated. The mechanism of interaction of curcumin with the different metal has also been developed. A concluding section summarizes the advantages of using curcumin as reducing/ stabilizing agent in nanoparticles formation and their analytical applications.

The authors describe the preparation of gold nanoparticles (AuNPs) coated with poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic F-108) by reducing Au to Au using curcumin, a natural and non-toxic food spice, in water of pH ~7 in the presence of F-108 and Ag ion. The coated AuNPs display strong resonance Rayleigh scattering (RRS) and fluorescence that results from the functionalization of the gold surface with curcumin and Pluronic F-108. The molar mass of Pluronic F-108 affects the particle size of the AuNPs formed, and small AuNPs are formed when using low molar weight F-108 that was purified by centrifugation or dialysis. The coated AuNPs were employed in an optical method for the determination of uric acid. The combination of uric acid with the AuNPs boosts both the RRS signal and the fluorescence of the AuNPs. However, higher concentrations of uric acid shift the fluorescence peak to shorter wavelengths. The method is simple, and fluorescence, best measured at excitation/emission wavelengths of 425/534 nm, increases linearly in the 50 μM to 50 mM uric acid concentration range, with a 0.14 μM detection limit which is lower than reported for other methods in the literature. Graphical abstract Pluronic F-108 capped gold nanoparticles prepared by reducing Au to Au using curcumin can estimate uric acid in 50 μM to 50 mM concentration range.

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