RESUMO

Lanthanide (LnIII)-doped sodium gadolinium tetrafluoride (NaGdF4) nanoparticles have been excelled as attractive upconversion systems for anti-counterfeiting or energy conversion for instance, with a special interest in the visible upconversion of EuIII and TbIII. The core@shell architecture has enabled the bright upconversion of EuIII and TbIII in this matrix by interfacial energy transfer sensibilized by the TmIII/YbIII pair. Another approach to enable EuIII and TbIII upconversion could be the interparticle energy transfer (IPET) between LnIII-doped sensitizer and acceptor nanoparticles. Yet, the low molar absorptivity of the LnIII through 4f ↔ 4f electronic transitions and the large distance between the nanoparticles are shortcomings that should decrease the energy transfer efficiency. On the other hand, it is feasible to predict that the association of organic ligands displaying large molar absorptivity on the acceptor nanoparticle surface could help to overcome the absorption limitation. Inspired by this exciting possibility, herein, we present the EuIII/TbIII upconversion intermediated by IPET between the donor TmIII, YbIII-doped NaGdF4 nanoparticle and the acceptor LnIII-doped NaGdF4 (Ln = Eu and/or Tb) nanoparticles functionalized with a series organic ligands on the surface (tta- = thenoyltrifluoroacetonate, acac- = acetylacetonate, or 3,5-bbza- = 3,5-dibromebenzoate). Either in solid state or in suspension, upon excitation at 980 nm, visible EuIII/TbIII upconversion could be observed. This emission comes from the absorption of the TmIII, YbIII pair in the donor nanoparticle, followed by IPET from the TmIII excited levels to the ligand singlet/triplet states on the acceptor nanoparticle surface, ligand-to-EuIII/TbIII energy transfer, and upconversion emission. Spectroscopic evidences from the analysis of the donor level lifetimes indicate the contribution of non-radiative energy transfer for the IPET mechanism; the radiative mechanism also contributes for the IPET. Moreover, the design herein introduced enables the development of luminescence temperature probes with relative thermal sensitivity as high as 1.67% K-1 at 373 K. Therefore, this new upconversion pathway opens an avenue of possibilities in an uncharted territory to tune the visible upconversion of LnIII ions.

RESUMO

In this work, we synthesized a polydimethylsiloxane membrane containing two emitter groups chemically attached to the membrane structure. For this, we attached the anthracene group and the [Eu(bzac)3] complex as blue and red emitters, respectively, in the matrix via hydrosilylation reactions. The synthesized membrane can be used as a bifunctional temperature and oxygen ratiometric optical probe by analyzing the effects that temperature changes and oxygen levels produce on the ratio of anthracene and europium(III) emission components. As a temperature probe, the system is operational in the 203-323 K range, with an observed maximum relative sensitivity of 2.06% K-1 at 290 K and temperature uncertainties below 0.1 K over all the operational range. As an oxygen probe, we evaluated the ratiometric response at 25, 30, 35, and 40 °C. These results show an interesting approach to obtaining bifunctional ratiometric optical probes and also suggest the presence of an anthracene → europium(III) energy transfer, even though there is no chemical bonding between species.

Assuntos

RESUMO

Acute myocardial infarction (AMI) is nowadays the leading death cause worldwide. For that reason, the early diagnosis of AMI is of central importance to reduce the risk of death. In this sense, aptamer-based sensors for surface-enhanced Raman spectroscopy (SERS aptasensors) emerged as an interesting alternative for future high-performance diagnostic tools. SERS aptasensors combine the fast, precise, and sensitive nature of SERS measurements with the selectivity of aptamers for specific biological targets. Herein, we report an efficient SERS aptasensor for the detection of cardiac troponin I (cTnI), a gold-standard biomarker for AMI. Our SERS platform comprises a magnetite core with an intermediate silica shell, and a flower-shaped silver layer (Fe3O4@SiO2@Ag) to confer excellent plasmonic properties and ease of collection by magnetism. The branched silver structure combined with magnetic aggregation offers a high near-field amplification to superior SERS performance. Additionally, a tailored DNA aptamer with high specificity for cTnI was anchored to the silver surface to produce the aptasensor with increased sensing capability towards cTnI. With our SERS aptasensor, a cTnI concentration as low as 10 ng ml-1 (10-11 mol l-1) could be detected. This value is ten times lower than the upper threshold of the typical concentration range of cTnI of AMI patients. Hence, our SERS aptasensor holds great promise to be explored in AMI diagnosis.

Assuntos

RESUMO

This work reports an alternative aproach to obtain the Judd-Ofelt intensity parameters of Sm(III) complexes with the general formula: [Sm(tta)(3)(L)(n)], with L = H(2)O, triphenylphosphine oxide (tppo), 2,2'-bipyridine (bipy) and 1,10-phenantroline (phen); n = 2 for H(2)O and tppo and n = 1 for phen and bipy, using the absorption spectra of rare earth complexes where the powders are dispersed in KBr pellets. This approach can be applied to other complexes of rare earth ions that have spin allowed transitions and it is validated by comparing the emission spectra of the complexes with those dispersed in KBr pellets.

Assuntos