Gold-silver synergism has been well documented in many scientific works dealing with luminescent nanostructures that are exploitable in biomedical and environmental application. Frequently, the ratio of Au : Ag in synthetic mixtures was varied to influence the extent of Au-Ag synergism of the resulting luminescent gold-silver nanoclusters (GSNCs). However, in our approach, a new step, maturing under differing conditions using the same Au : Ag ratio (5 : 1), has been investigated systematically for the very first time. As referent systems, monometallic gold nanoclusters (AuNCs) and protein treated by the conditions of synthesis and maturing were prepared and investigated. The selected types of maturing conditions led to distinct changes in fluorescence characteristics and, consequently, Au-Ag synergism extent (evaluated as the ratio of fluorescence quantum yields of GSNCs versus AuNCs). The best synergism was obtained for GSNCs matured at 37°C for 2.5 h. The stability of luminescent signal of these GSNCs was tested in the presence of an excess (to 20 mM) of Cu(II) and/or Fe(III) ions (crucial cofactors in living systems). The same metallic ion concentration caused different extents of GSNC luminescence quenching, for which a plausible reasoning is suggested.

• Klíčová slova
• bimetallic nanocluster, fluorescent nanocomposite, gold–silver nanocluster, luminescent nanocomposite, protein template, synergistic effect,
• Publikační typ
• časopisecké články MeSH

Nanocomposites serving as dual (bimodal) probes have great potential in the field of bio-imaging. Here, we developed a simple one-pot synthesis for the reproducible generation of new luminescent and magnetically active bimetallic nanocomposites. The developed one-pot synthesis was performed in a sequential manner and obeys the principles of green chemistry. Briefly, bovine serum albumin (BSA) was exploited to uptake Au (III) and Fe (II)/Fe (III) ions simultaneously. Then, Au (III) ions were transformed to luminescent Au nanoclusters embedded in BSA (AuNCs-BSA) and majority of Fe ions were bio-embedded into superparamagnetic iron oxide nanoparticles (SPIONs) by the alkalization of the reaction medium. The resulting nanocomposites, AuNCs-BSA-SPIONs, represent a bimodal nanoprobe. Scanning transmission electron microscopy (STEM) imaging visualized nanostructures with sizes in units of nanometres that were arranged into aggregates. Mössbauer spectroscopy gave direct evidence regarding SPION presence. The potential applicability of these bimodal nanoprobes was verified by the measurement of their luminescent features as well as magnetic resonance (MR) imaging and relaxometry. It appears that these magneto-luminescent nanocomposites were able to compete with commercial MRI contrast agents as MR displays the beneficial property of bright luminescence of around 656 nm (fluorescence quantum yield of 6.2 ± 0.2%). The biocompatibility of the AuNCs-BSA-SPIONs nanocomposite has been tested and its long-term stability validated.

• Klíčová slova
• MRI assessment, SPION, bovine serum albumin, gold nanocluster, imaging, luminescence material, nanocomposite material,
• Publikační typ
• časopisecké články MeSH

Bovine serum albumin-embedded Au nanoclusters (BSA-AuNCs) are thoroughly probed by continuous wave electron paramagnetic resonance (CW-EPR), light-induced EPR (LEPR), and sequences of microscopic investigations performed via high-resolution transmission electron microscopy (HR-TEM), scanning transmission electron microscopy (STEM), and energy dispersive X-ray analysis (EDS). To the best of our knowledge, this is the first report analyzing the BSA-AuNCs by CW-EPR/LEPR technique. Besides the presence of Au(0) and Au(I) oxidation states in BSA-AuNCs, the authors observe a significant amount of Au(II), which may result from a disproportionation event occurring within NCs: 2Au(I) → Au(II) + Au(0). Based on the LEPR experiments, and by comparing the behavior of BSA versus BSA-AuNCs under UV light irradiation (at 325 nm) during light off-on-off cycles, any energy and/or charge transfer event occurring between BSA and AuNCs during photoexcitation can be excluded. According to CW-EPR results, the Au nano assemblies within BSA-AuNCs are estimated to contain 6-8 Au units per fluorescent cluster. Direct observation of BSA-AuNCs by STEM and HR-TEM techniques confirms the presence of such diameters of gold nanoclusters in BSA-AuNCs. Moreover, in situ formation and migration of Au nanostructures are observed and evidenced after application of either a focused electron beam from HR-TEM, or an X-ray from EDS experiments.

• Klíčová slova
• fluorescent nanoprobe, gold nanostructures, noble metal nanocrystal, protein nanocomposite,
• Publikační typ
• časopisecké články MeSH

Chlorosomes are the main light-harvesting complexes of green photosynthetic bacteria that are adapted to a phototrophic life at low-light conditions. They contain a large number of bacteriochlorophyll c, d, or e molecules organized in self-assembling aggregates. Tight packing of the pigments results in strong excitonic interactions between the monomers, which leads to a redshift of the absorption spectra and excitation delocalization. Due to the large amount of disorder present in chlorosomes, the extent of delocalization is limited and further decreases in time after excitation. In this work we address the question whether the excitonic interactions between the bacteriochlorophyll c molecules are strong enough to maintain some extent of delocalization even after exciton relaxation. That would manifest itself by collective spontaneous emission, so-called superradiance. We show that despite a very low fluorescence quantum yield and short excited state lifetime, both caused by the aggregation, chlorosomes indeed exhibit superradiance. The emission occurs from states delocalized over at least two molecules. In other words, the dipole strength of the emissive states is larger than for a bacteriochlorophyll c monomer. This represents an important functional mechanism increasing the probability of excitation energy transfer that is vital at low-light conditions. Similar behaviour was observed also in one type of artificial aggregates, and this may be beneficial for their potential use in artificial photosynthesis.

• MeSH
• Bacteria metabolismus   MeSH
• bakteriální proteiny metabolismus   MeSH
• bakteriochlorofyly metabolismus   MeSH
• biologické pigmenty metabolismus   MeSH
• fotosyntéza * MeSH
• přenos energie MeSH
• proteinové agregáty * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bacteriochlorophyll c MeSH Prohlížeč
• bakteriální proteiny MeSH
• bakteriochlorofyly MeSH
• biologické pigmenty MeSH
• proteinové agregáty * MeSH