Subtissue Plasmonic Heating Monitored with CaF₂:Nd³⁺,Y³⁺ Nanothermometers in the Second Biological Window

Measuring temperature in biological environments is an ambitious goal toward supporting medical treatment and diagnosis. Minimally invasive techniques based on optical probes require very specific properties that are difficult to combine within a single material. These include high chemical stability in aqueous environments, optical signal stability, low toxicity, high emission intensity, and, essential, working at wavelengths within the biological transparency windows so as to minimize invasiveness while maximizing penetration depth. We propose CaF₂:Nd³⁺,Y³⁺ as a candidate for thermometry based on an intraband ratiometric approach, fully working within the biological windows (excitation at 808 nm; emission around 1050 nm). We optimized the thermal probes through the addition of Y³⁺ as a dopant to improve both emission intensity and thermal sensitivity. To define the conditions under which the proposed technique can be applied, gold nanorods were used to optically generate subtissue hot areas, while the resulting temperature variation was monitored with the new nanothermometers

Light Management in Upconverting Nanoparticles: Ultrasmall Core/Shell Architectures to Tune the Emission Color

Ultrasmall NaGdF₄ nanoparticles with core/shell and core/shell/shell architectures have been synthesized following a microwave-based thermolysis procedure, allowing us to rapidly obtain homogeneous nanoparticles compared to conventional heating. To analyze the possibilities of the proposed structure in terms of tuning the emission color, core and shells have been doped with different lanthanide ion pairs (either Er³⁺/Yb³⁺ and/or Tm³⁺/Yb³⁺), keeping them therefore spatially separated inside the different layers of the nanoparticles. Here, we demonstrate that the position of the dopants inside the nanoparticles affects the intensity of the different emission bands of the luminescing Tm³⁺ and Er³⁺ ions and show how it has a relevant effect on the overall emission color of the luminescence obtained after 975 nm excitation

Temperature-Induced Energy Transfer in Dye-Conjugated Upconverting Nanoparticles: A New Candidate for Nanothermometry

Lanthanide-doped upconverting nanoparticles (UCNPs) are highly promising candidates for bioimaging and for cellular nanothermometry as a novel diagnostic tool. Aiming for the diagnosis of diseases at very early stages in order to optimize therapy and recovery of the patient, it must be taken into account that thermal singularities are often one of the first indicators of a disease. It is therefore our goal to develop a nanothermometer based on UCNPs that is suitable to detect the temperature at a subcellular level in the physiological range. Thus, upconverting NaGdF₄:Er³⁺,Yb³⁺ nanoparticles that convert near-infrared (NIR) into visible (VIS) light are synthesized by thermal decomposition. Appropriate surface modification with a thermoresponsive polymer pNIPAM (poly­(<i>N</i>-isopropylacrylamide)) guarantees dispersibility in aqueous media required for biomedical applications. In a further step, the combination of the obtained UCNPs with an organic dye (FluoProbe532A) provides potential donor-acceptor-pairs allowing for energy transfer processes, whereas the light emitted by the Er³⁺ ions (donors) is absorbed by the organic dye (acceptor). It has been demonstrated that the dye-conjugated UCNPs undergo a temperature-dependent energy transfer process inducing a temperature-dependent increase in the thermal sensitivity when compared to unlabeled UCNPs. This result indicates the great potential of the presented nanoprobes for applications in nanothermometry

Sensitive Detection of ssDNA Using an LRET-Based Upconverting Nanohybrid Material

Water-dispersible, optical hybrid nanoparticles are preferred materials for DNA biosensing due to their biocompatibility. Upconverting nanoparticles are highly desirable optical probes in sensors and bioimaging owing to their sharp emission intensity in the visible region. We herein report a highly sensitive ss-DNA detection based on an energy transfer system that uses a nanohybrid material synthesized by doping NaYF₄:Tm³⁺/Yb³⁺ upconverting nanoparticles (UCNPs) on silica coated polystyrene-<i>co</i>-acrylic acid (PSA) nanoparticles (PSA/SiO₂) as the donor, and gold nanoparticles (AuNPs) decorated with Ir­(III) complex as the acceptor. UCNPs tagged on PSA/SiO₂ and the cyclometalated Ir­(III)/AuNP conjugates were then linked through the ss-DNA sequence. Sequential addition of the target DNA to the probe molecular beacon complex resulted in the separation of the optical nanohybrid material and the quencher, leading to a measurable increase in the blue fluorescence emission intensity. Our results have shown a linear relationship between the fluorescence intensity and target DNA concentration down to the picomolar