Silver nanoparticles loaded carbon-magnetic nanocomposites: A nanozyme for colorimetric detection of dopamine

Dopamine (DA) is catecholamine neurotransmitters that play an important role in the central nervous system. In recent years people started to intentionally add DA to animal feed to enhance muscle development and increase their profit margin. Human consumption of the residual DA from animal tissues has been reported to be associated with the development of such diseases as Parkinson's disease, epilepsy, senile dementia, and schizophrenia and pose serious human health risks. These require development of rapid, cheap, and sensitive methods for detection of DA from animal tissue. Compared to other techniques that require access to expensive instruments, skilled human power, and tiresome routine procedures, colorimetric methods provide cheap and reliable options for detection of DA. Here we report a colorimetric method based on the peroxidase-mimic activity of Fe₃O₄@C@AgNPs for the detection of DA. A simple wet chemical method was employed to synthesize AgNPs on hydrophilic carbon coated Fe₃O₄. The produced nanocomposites were characterized by transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR), and surface-enhanced Raman spectroscopy (SERS). The detection of DA was done based on inhibition of the peroxidase-like activity of Fe₃O₄@C@AgNPs using 3, 3', 5, 5'-tetramethylbenzidine (TMB) as a substrate. In the presence of DA, however, the peroxidase-like activity started to decrease. The decrease in activity was concentration dependent showing a linear relationship in the range of 0.5-80 µM. In this linear range, the limit of detection (LOD) was computed and found to be as low as 0.12 µM. Therefore, we propose that the peroxidase-like activity of Fe₃O₄@C@AgNPs could be used for quantitative detection of DA from different samples.