The internal structure of hollow AgAu nanorods created by partial galvanic replacement was manipulated reversibly, and its effect on optical properties was mapped with nanometer resolution. Using the electron beam in a scanning transmission electron microscope to create solvated electrons and reactive radicals in an encapsulated solution-filled cavity in the nanorods, Ag ions were reduced nearby the electron beam, reshaping the core of the nanoparticles without affecting the external shape. The changes in plasmon-induced near-field properties were then mapped with electron energy-loss spectroscopy without disturbing the internal structure, and the results are supported by finite-difference time-domain calculations. This reversible shape and near-field control in a hollow nanoparticle actuated by an external stimulus introduces possibilities for applications in reprogrammable sensors, responsive materials, and optical memory units. Moreover, the liquid-filled nanorod cavity offers new opportunities for in situ microscopy of chemical reactions.
Hollow AgAu nanostructures have a myriad of potential applications related to their strong and tunable localized surface plasmon resonances. Here, we describe how the hydrolysis of the Au precursor, AuCl 4 − , produces AuCl 4−x (OH) x − , where x is both time and pH-dependent, and how this can be used to control the morphology of hollow nanoshells in the co-reduction-assisted galvanic replacement of Ag by Au. Controlling the degree of hydrolysis is the key to obtain smooth shells: too small values of x (low hydrolysis) yield inhomogeneously replaced rough shells whereas too large values of x lead to the dominance of Au nucleation over galvanic replacement. Kinetic studies reveal two time constants for the galvanic replacement varying with temperature and composition; a short (<10 min) half-life component associated with the initial void creation and a long (>100 min) half-life component associated with the continuous reduction and replacement of Ag. By optimizing the reaction's pH and Au speciation, we obtained smooth alloy shells with fine control of composition, size, and shape over a broad range, thereby tuning the optical properties. This framework for understanding and controlling reaction kinetics and nanoshell morphology is applicable to other metallic systems and precursors, providing new ways to rationally design nanostructure syntheses.
Key Messages• Myocardial infarction induces apoptosis in the amygdala.• Probiotics reverse the increase in caspase activities in the amygdala after MI, and their beneficial outcome is abolished by vagotomy.• This finding underscores vagus nerve involvement in the beneficial effect of probiotics in an animal model of post-MI depression.• Probiotics were administered daily, 14 days before myocardial ischemia and until euthanasia. Vagotomy was induced in designed groups before 40 min of myocardial ischemia. After 3 days of reperfusion activity of the caspase-3 or -8 in the amygdala was determined. AbstractBackground Myocardial infarction (MI) is associated with apoptosis in the amygdala and, ultimately, with clinical signs of depression. Different treatments have proven to be beneficial in preventing depression, including combination of the probiotics Lactobacillus helveticus and Bifidobacterium longum for prophylaxis. We have speculated previously that the benefit of these probiotics is due to their anti-inflammatory properties, and evidence suggests that an intact vagus nerve is important for this effect to occur. This study was designed to ascertain vagus nerve involvement in the beneficial influence of probiotics on caspase activities in our post-MI animal model of depression.Methods Probiotics and/or vehicle were administered daily to male adult rats, 14 days before MI and until euthanasia. Vagotomy was performed in subgroups of rats 40 min before MI. They were sacrificed after 3 days of reperfusion, and MI size was assessed along with caspase-3 and -8 activities in the amygdala. Key Results Probiotics had no effect on infarct size but vagotomy increased it. Caspase-3 and caspase-8 activities in the amygdala were higher in MI than in sham-operated rats, and this outcome was reversed by probiotics. The beneficial influence of probiotics was abolished by vagotomy. Conclusions & Inferences Our data indicate that the effect of probiotics on caspase activities in the amygdala after MI depends on an intact vagus nerve.
A co-reduction assisted method for the synthesis of Ag–Au hollow nanoparticles with enhanced control over plasmon wavelength and scattering intensity.
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