Un-functionalized Gold Nanoparticles as a Simple Colorimetric Probe for Sensitive and Selective Detection of Dopamine

Abstract

A dopamine (DA) colorimetric probe based on the growth and aggregation of un-functionalized gold nanoparticles (AuNPs) is reported. Upon addition of AuNPs to dopamine at various concentrations, the shape, size and colour change of the nanoparticles results in spectral shifts to higher wavelengths and hence colour change is the mode of detection. The colour change can be easily observed by the naked eye from as low as 5.0 nM DA, even under sub-optimal conditions. Under optimal pH conditions the calculated limit of detection was 2.5 nM (3ó). The probe was successfully applied to whole blood sample and showed good selectivity and sensitivity towards DA. The simple, sensitive and selective probe could be an excellent alternative for on-site and immediate detection of DA without the use of instrumentation and would thus be useful for rapid diagnostic applications.

Synthesis of Highly Stabilized AuNPs Using 3,5-Dinitrobenzoic Acid and Sodium Acetate as Capping Agents in an Aqueous Solution and their Bioactivity

“…1). No colour change or any aggregation was observed during 6 months and that indicated that Au NPs with time lead to form bigger NPs and confirm the results in this work [19]. Furthermore, the UV-Vis spectra of the DNBA-AuNPs solution at the initial time and after 6 months are shown in Fig.…”

“…Where the intensity steadily increased as a function of time of reaction without any shift in the peak wavelength which confirms what was mentioned in the literature [18]. It is worth mentioning that the stability of AuNPs stable against aggregation was attributed to excess ions of AuCl4and AuCl2which bind to the surface of the AuNPs in the solution during the reduction process of KAuCl4 [19]. UV-Visible spectrum results showed that the SPB of AuNP functionalized by sodium acetate is centred at 536 nm, which is illustrating slightly larger than another ligand that had functionalized AuNPs, which confirm that different ligands were functionalized AuNPs under the same conditions, led to different wavelengths with different stabilities of AuNPs as well.…”

“…the sizes changed of the AuNPs based on results in UV-Vis spectral with (pH above 10 and less than 3.5) shifts to higher wavelengths, also the colour of AuNPs was changed from red to dark purple which can be easily observed by the naked eye through changing of pH conditions. This confirmation was also observed in the research where AuNPs are known to have colours that range from red to purple and blue based on the formation of aggregates, shape, and size of the particles [19]. Because the AuNPs absorb light between 500 and 600 nm, depending on the particle size.…”