ABSTRACT
Caffeine (CAF) is a psychostimulant present in many beverages and with rapid bioabsorption. For this reason, matrices that effectuate the sustained release of a low amount of CAF would help reduce the intake frequency and side effects caused by high doses of this stimulant. Thus, in this study, CAF was loaded into magnetic gelatin/alginate (Gel/Alg/MNP) hydrogels at 18.5 mg/ghydrogel. The in vitro release of CAF was evaluated in the absence and presence of an external magnetic field (EMF) and Ca2+. In all cases, the presence of Ca2+ (0.002 M) retarded the release of CAF due to favorable interactions between them. Remarkably, the release of CAF from Gel/Alg/MNP in PBS/CaCl2 (0.002 M) at 37 °C under an EMF was more sustained due to synergic effects. In PBS/CaCl2 (0.002 M) and at 37 °C, the amounts of CAF released after 45 min from Gel/Alg and Gel/Alg/MNP/EMF were 8.3 ± 0.2 mg/ghydrogel and 6.1 ± 0.8 mg/ghydrogel, respectively. The concentration of CAF released from Gel/Alg and Gel/Alg/MNP hydrogels amounted to ~0.35 mM, thereby promoting an increase in cell viability for 48 h. Gel/Alg and Gel/Alg/MNP hydrogels can be applied as reservoirs to release CAF at suitable concentrations, thus forestalling possible side effects and improving the viability of SH-SY5Y cells.
ABSTRACT
Nanoporous gold (NPG) structures were prepared on the surface of a gold microelectrode (Au-µE) by an anodization-reduction method. Cyclic voltammetry and field emission scanning electron microscopy were used to study the electrochemical properties and the morphology of the nanostructured film. Voltammetry showed an improved sensitivity for dopamine (DA) oxidation at this microelectrode when compared to a bare gold microelectrode, with a peak near 0.2 V (vs. Ag/AgCl) at a scan rate of 0.1 V s-1. This is due to the increased surface area and roughness. Square wave voltammetry shows a response that is linear in the 0.1-10 µmol L-1 DA concentration range, with a 30 nmol L-1 detection limit and a sensitivity of 1.18 mA (µmol L-1)-1 cm-2. The sensor is not interfered by ascorbic acid. The reproducibility, repeatability, long-term stability and real sample analysis (spiked urine) were assessed, and acceptable performance was achieved. The "proof-of-concept" detection of dopamine release was demonstrated by using scanning electrochemical microscopy (SECM) with the aim of future applications for single cell analysis. Graphical abstract A reproducible electrochemical approach was proposed to fabricate an NPG-microelectrode for DA detection, with enhanced sensitivity and selectivity. Besides, a proof-of-concept detection of DA release was also demonstrated by using SECM.
