Influence of the Gold Nanoparticle Size on the Colorimetric Detection of Histamine.

Histamine is a well-known biogenic amine (BA) that is often associated with allergic reactions and is a significant cause of foodborne illnesses resulting from the consumption of spoiled food. Detecting histamine is essential for maintaining food safety standards and preserving the quality. In this work, we developed a simple, low-cost, and rapid colorimetric method for detecting histamine. Gold nanoparticles (AuNPs) of different sizes (16, 25, and 40 nm) were synthesized by using the citrate reduction method. The particle size was controlled by adjusting the precursor molar ratio (MR), with smaller ratios leading to larger particles and a red-shift in the surface plasmon resonance (SPR) peak (520, 524, and 528 nm). The nanoparticles were allowed to interact with increasing concentrations of histamine (ranging from 1 to 100 ppm), and the changes in the absorbance spectra and color of the solution were monitored. AuNP aggregation was induced by interaction with histamine through amino and imidazole groups that will coordinate with the AuNP's surface via electrostatic and hydrogen-bonding interactions, causing the solution to turn blue from red. The size variations of AuNPs significantly affected the colorimetric response to histamine. Among the varied sizes, 25 nm AuNPs exhibited the lowest detection limit of 0.72 µM and a linear detection range of 1-10 ppm. Notably, this sensor offered rapid detection (under 1 min) and a remarkable selectivity toward histamine analyte, highlighting its potential for practical applications.

Dopamine-Functionalized Gold Nanoparticles for Colorimetric Detection of Histamine.

Histamine, a primary biogenic amine (BA) generated through the decarboxylation of amino acids, concentration increases in protein-rich foods during deterioration. Thus, its detection plays a crucial role in ensuring food safety and quality. This study introduces an innovative approach involving the direct integration of dopamine onto gold nanoparticles (DCt-AuNP), aiming at rapid histamine colorimetric detection. Transmission electron microscopy revealed the aggregation of uniformly distributed spherical DCt-AuNPs with 12.02 ± 2.53 nm sizes upon the addition of histamine to DCt-AuNP solution. The Fourier-transform infrared (FTIR) spectra demonstrated the disappearance of the dicarboxy acetone peak at 1710 cm-1 along with the formation of well-defined peaks at 1585 cm-1, and 1396 cm-1 associated with the N-H bending modes and the aromatic C=C bond stretching vibration in histamine molecule, respectively, confirming the ligand exchange and interactions of histamine on the surface of DCt-AuNPs. The UV-vis spectra of the DCt-AuNP solution exhibited a red shift and a reduction in surface plasmon resonance (SPR) peak intensity at 518 nm along with the emergence of the 650 nm peak, signifying aggregation DCt-AuNPs with increasing histamine concentration. Notably, color transitions from wine-red to deep blue were observed in the DCt-AuNP solution in response to histamine, providing a reliable colorimetric signal. Dynamic Light Scattering (DLS) characterization showed a significant increase in the hydrodynamic diameter, from ∼15 to ∼1690 nm, confirming the interparticle cross-linking of DCt-AuNPs in the presence of histamine. This newly developed DCt-AuNP sensor provides colorimetric results in less than a minute that exhibits a remarkable naked-eye histamine detection threshold of 1.57 µM and a calculated detection limit of 0.426 µM, making it a promising tool for the rapid and sensitive detection of histamine.

In vitro studies of solution precursor plasma-sprayed copper-doped hydroxyapatite coatings with increasing copper content.

In this present study, in vitro characterization on bioactivity and biocompatibility of the copper-doped hydroxyapatite (Cu-HA) coatings deposited onto Ti6Al4V alloy with increasing copper content obtained using solution precursor plasma spray process were evaluated under simulated body fluid (SBF) and cytotoxicity tests. The growth of flake-like structures was observed at the coatings' surface after 7 days of immersion in SBF. Elemental composition analysis showed a calcium-deficient carbonate-containing apatite for the grown layer. Broadening of the HA peaks were also observed in the X-ray diffraction patterns and infrared absorption spectra of the immersed coatings associated with the possible formation of an amorphous layer at the surface of the coatings. Copper incorporation does not alter the bioactivity of HA but only slowed down for 10 mol% copper content. Cytotoxicity evaluation using MTT assays showed that 3 mol% Cu-HA coating was not toxic under in vitro characterizations.