Ag2 S Biocompatible Ensembles as Dual OCT Contrast Agents and NIR Ocular Imaging Probes.

Ag2 S nanoparticles (NPs) emerge as a unique system that simultaneously features in vivo near-infrared (NIR) imaging, remote heating, and low toxicity thermal sensing. In this work, their capabilities are extended into the fields of optical coherence tomography (OCT), as contrast agents, and NIR probes in both ex vivo and in vivo experiments in eyeballs. The new dual property for ocular imaging is obtained by the preparation of Ag2 S NPs ensembles with a biocompatible amphiphilic block copolymer. Rather than a classical ligand exchange, where surface traps may arise due to incomplete replacement of surface sites, the use of this polymer provides a protective extra layer that preserves the photoluminescence properties of the NPs, and the procedure allows for the controlled preparation of submicrometric scattering centers. The resulting NPs ensembles show extraordinary colloidal stability with time and biocompatibility, enhancing the contrast in OCT with simultaneous NIR imaging in the second biological window.

Optical detection of atherosclerosis at molecular level by optical coherence tomography: An in vitro study.

There is an urgent need for contrast agents to detect the first inflammation stage of atherosclerosis by cardiovascular optical coherence tomography (CV-OCT), the imaging technique with the highest spatial resolution and sensitivity of those used during coronary interventions. Gold nanoshells (GNSs) provide the strongest signal by CV-OCT. GNSs are functionalized with the cLABL peptide that binds specifically to the ICAM-1 molecule upregulated in the first stage of atherosclerosis. Dark field microscopy and CV-OCT are used to evaluate the specific adhesion of these functionalized GNSs to activated endothelial cells. This adhesion is investigated under static and dynamic conditions, for shear stresses comparable to those of physiological conditions. An increase in the scattering signal given by the functionalized GNSs attached to activated cells is observed compared to non-activated cells. Thus, cLABL-functionalized GNSs behave as excellent contrast agents for CV-OCT and promise a novel strategy for clinical molecular imaging of atherosclerosis.

Enhancing optical forces on fluorescent up-converting nanoparticles by surface charge tailoring.

3D remote control of multifunctional fluorescent up-converting nanoparticles (UCNPs) using optical forces is being required for a great variety of applications including single-particle spectroscopy, single-particle intracellular sensing, controlled and selective light-activated drug delivery and light control at the nanoscale. Most of these potential applications find a serious limitation in the reduced value of optical forces (tens of fN) acting on these nanoparticles, due to their reduced dimensions (typically around 10 nm). In this work, this limitation is faced and it is demonstrated that the magnitude of optical forces acting on UCNPs can be enhanced by more than one order of magnitude by a controlled modification of the particle/medium interface. In particular, substitution of cationic species at the surface by other species with higher mobility could lead to UCNPs trapping with constants comparable to those of spherical metallic nanoparticles.

Non-invasive paper-based sensors containing rare-earth-doped nanoparticles for the detection of D-glucose.

Today, diabetes mellitus is one of the most common diseases that affects the population on a worldwide scale. Patients suffering from this disease are required to control their blood-glucose levels several times a day through invasive methods such as piercing their fingers. Our NaGdF4: 5% Er3+, 3% Nd3+ nanoparticles demonstrate a remarkable ability to detect D-glucose levels by analysing alterations in their red-to-green ratio, since this sensitivity arises from the interaction between the nanoparticles and the OH groups present in the D-glucose molecules, resulting in discernible changes in the emission of the green and red bands. These luminescent sensors were implemented and tested on paper substrates, offering a portable, low-cost and enzyme-free solution for D-glucose detection in aqueous solutions with a limit of detection of 22 mg/dL. With this, our study contributes to the development of non-invasive D-glucose sensors, holding promising implications for managing diabetes and improving overall patient well-being with possible future applications in D-glucose sensing through tear fluid.

The role of temperature in the photoluminescence quantum yield (PLQY) of Ag2S-based nanocrystals.

Highly emissive Ag2S nanocrystals (NCs) passivated with a gradated shell incorporating Se and Zn were synthesized in air, and the temperature dependence of their photoluminescence quantum yield (PLQY) was quantified in both organic and aqueous media at ∼1200 nm. The relevance of this parameter, measured at physiological temperatures, is highlighted for applications that rely on the near infrared (NIR) photoluminescence of NCs, such as deep NIR imaging or luminescence nanothermometry. Hyperspectral NIR imaging shows that Ag2S-based NCs with a PLQY in organic media of about 10% are inefficient for imaging at 40 °C through 20 mm thick tissue with low laser irradiation power densities. In contrast, water-transferred Ag2S-based NCs with an initial PLQY of 2% in water exhibit improved robustness against temperature changes, enabling improved imaging performance.

3D Optical Coherence Thermometry Using Polymeric Nanogels.

In nanothermometry, the use of nanoparticles as thermal probes enables remote and minimally invasive sensing. In the biomedical context, nanothermometry has emerged as a powerful tool where traditional approaches, like infrared thermal sensing and contact thermometers, fall short. Despite the strides of this technology in preclinical settings, nanothermometry is not mature enough to be translated to the bedside. This is due to two major hurdles: the inability to perform 3D thermal imaging and the requirement for tools that are readily available in the clinics. This work simultaneously overcomes both limitations by proposing the technology of optical coherence thermometry (OCTh). This is achieved by combining thermoresponsive polymeric nanogels and optical coherence tomography (OCT)-a 3D imaging technology routinely used in clinical practice. The volume phase transition of the thermoresponsive nanogels causes marked changes in their refractive index, making them temperature-sensitive OCT contrast agents. The ability of OCTh to provide 3D thermal images is demonstrated in tissue phantoms subjected to photothermal processes, and its reliability is corroborated by comparing experimental results with numerical simulations. The results included in this work set credible foundations for the implementation of nanothermometry in the form of OCTh in clinical practice.

Eosin Y-Functionalized Upconverting Nanoparticles: Nanophotosensitizers and Deep Tissue Bioimaging Agents for Simultaneous Therapeutic and Diagnostic Applications.

Functionalized upconverting nanoparticles (UCNPs) are promising theragnostic nanomaterials for simultaneous therapeutic and diagnostic purposes. We present two types of non-toxic eosin Y (EY) nanoconjugates derived from UCNPs as novel nanophotosensitizers (nano-PS) and deep-tissue bioimaging agents employing light at 800 nm. This excitation wavelength ensures minimum cell damage, since the absorption of water is negligible, and increases tissue penetration, enhancing the specificity of the photodynamic treatment (PDT). These UCNPs are uniquely qualified to fulfil three important roles: as nanocarriers, as energy-transfer materials, and as contrast agents. First, the UCNPs enable the transport of EY across the cell membrane of living HeLa cells that would not be possible otherwise. This cellular internalization facilitates the use of such EY-functionalized UCNPs as nano-PS and allows the generation of reactive oxygen species (ROS) under 800 nm light inside the cell. This becomes possible due to the upconversion and energy transfer processes within the UCNPs, circumventing the excitation of EY by green light, which is incompatible with deep tissue applications. Moreover, the functionalized UCNPs present deep tissue NIR-II fluorescence under 808 nm excitation, thus demonstrating their potential as bioimaging agents in the NIR-II biological window.

Bismuth Selenide Nanostructured Clusters as Optical Coherence Tomography Contrast Agents: Beyond Gold-Based Particles.

Optical coherence tomography (OCT) is an imaging technique currently used in clinical practice to obtain optical biopsies of different biological tissues in a minimally invasive way. Among the contrast agents proposed to increase the efficacy of this imaging method, gold nanoshells (GNSs) are the best performing ones. However, their preparation is generally time-consuming, and they are intrinsically costly to produce. Herein, we propose a more affordable alternative to these contrast agents: Bi2Se3 nanostructured clusters with a desert rose-like morphology prepared via a microwave-assisted method. The structures are prepared in a matter of minutes, feature strong near-infrared extinction properties, and are biocompatible. They also boast a photon-to-heat conversion efficiency of close to 50%, making them good candidates as photothermal therapy agents. In vitro studies evidence the prowess of Bi2Se3 clusters as OCT contrast agents and prove that their performance is comparable to that of GNSs.

Nanoparticles for In Vivo Lifetime Multiplexed Imaging.

Lifetime multiplexed imaging refers to the simultaneous labeling of different structures with fluorescent probes that present identical photoluminescence spectra and distinct fluorescence lifetimes. This technique allows extracting quantitative information from multichannel in vivo fluorescence imaging. In vivo lifetime multiplexed imaging requires fluorophores with excitation and emission bands in the near-infrared (NIR) and tunable fluorescence lifetimes, plus an imaging system capable of time-resolved image acquisition and analysis.

Molecular Imaging of Infarcted Heart by Biofunctionalized Gold Nanoshells.

The unique combination of physical and optical properties of silica (core)/gold (shell) nanoparticles (gold nanoshells) makes them especially suitable for biomedicine. Gold nanoshells are used from high-resolution in vivo imaging to in vivo photothermal tumor treatment. Furthermore, their large scattering cross-section in the second biological window (1000-1700 nm) makes them also especially adequate for molecular optical coherence tomography (OCT). In this work, it is demonstrated that, after suitable functionalization, gold nanoshells in combination with clinical OCT systems are capable of imaging damage in the myocardium following an infarct. Since both inflammation and apoptosis are two of the main mechanisms underlying myocardial damage after ischemia, such damage imaging is achieved by endowing gold nanoshells with selective affinity for the inflammatory marker intercellular adhesion molecule 1 (ICAM-1), and the apoptotic marker phosphatidylserine. The results here presented constitute a first step toward a fast, safe, and accurate diagnosis of damaged tissue within infarcted hearts at the molecular level by means of the highly sensitive OCT interferometric technique.

Perspectives for Ag2S NIR-II nanoparticles in biomedicine: from imaging to multifunctionality.

Research on near-infrared (NIR) bioimaging has progressed very quickly in the past few years, as fluorescence imaging is reaching a credible implementation as a preclinical technique. The applications of NIR bioimaging in theranostics have contributed to its increasing impact. This has brought about the development of novel technologies and, simultaneously, of new contrast agents capable of acting as efficient NIR optical probes. Among these probes, Ag2S nanoparticles (NPs) have attracted increasing attention due to their temperature-sensitive NIR-II emission, which can be exploited for deep-tissue imaging and thermometry, and their heat delivery capabilities. This multifunctionality makes Ag2S NPs ideal candidates for theranostics. This review presents a critical analysis of the synthesis routes, properties and optical features of Ag2S NPs. We also discuss the latest and most remarkable achievements enabled by these NPs in preclinical imaging and theranostics, together with a critical assessment of their potential to face forthcoming challenges in biomedicine.

Lifetime-Encoded Infrared-Emitting Nanoparticles for in Vivo Multiplexed Imaging.

Advanced diagnostic procedures are required to satisfy the continuously increasing demands of modern biomedicine while also addressing the need for cost reduction in public health systems. The development of infrared luminescence-based techniques for in vivo imaging as reliable alternatives to traditional imaging enables applications with simpler and more cost-effective apparatus. To further improve the information provided by in vivo luminescence images, the design and fabrication of enhanced infrared-luminescent contrast agents is required. In this work, we demonstrate how simple dopant engineering can lead to infrared-emitting rare-earth-doped nanoparticles with tunable (0.1-1.5 ms) and medium-independent luminescence lifetimes. The combination of these tunable nanostructures with time-gated infrared imaging and time domain analysis is employed to obtain multiplexed in vivo images that are used for complex biodistribution studies.

Core-shell rare-earth-doped nanostructures in biomedicine.

The current status of the use of core-shell rare-earth-doped nanoparticles in biomedical applications is reviewed in detail. The different core-shell rare-earth-doped nanoparticles developed so far are described and the most relevant examples of their application in imaging, sensing, and therapy are summarized. In addition, the advantages and disadvantages they present are discussed. Finally, a critical opinion of their potential application in real life biomedicine is given.

Rare-earth-doped fluoride nanoparticles with engineered long luminescence lifetime for time-gated in vivo optical imaging in the second biological window.

Biomedicine is continuously demanding new luminescent materials to be used as optical probes for the acquisition of high resolution, high contrast and high penetration in vivo images. These materials, in combination with advanced techniques, could constitute the first step towards new diagnosis and therapy tools. In this work, we report on the synthesis of long lifetime rare-earth-doped fluoride nanoparticles by adopting different strategies: core/shell and dopant engineering. The here developed nanoparticles show intense infrared emission in the second biological window with a long luminescence lifetime close to 1 millisecond. These two properties make the here presented nanoparticles excellent candidates for time-gated infrared optical bioimaging. Indeed, their potential application as optical imaging contrast agents for autofluorescence-free in vivo small animal imaging has been demonstrated, allowing high contrast real-time tracking of gastrointestinal absorption of nanoparticles and transcranial imaging of intracerebrally injected nanoparticles in the murine brain.

Self-monitored photothermal nanoparticles based on core-shell engineering.

The continuous development of nanotechnology has resulted in the actual possibility of the design and synthesis of nanostructured materials with pre-tailored functionabilities. Nanostructures capable of simultaneous heating and local thermal sensing are in strong demand as they would constitute a revolutionary solution to several challenging problems in bio-medicine, including the achievement of real time control during photothermal therapies. Several approaches have been demonstrated to achieve simultaneous heating and thermal sensing at the nanoscale. Some of them lack of sufficient thermal sensitivity and others require complicated synthesis procedures for heterostructure fabrication. In this study, we demonstrate how single core/shell dielectric nanoparticles with a highly Nd(3+) ion doped shell and an Yb(3+),Er(3+) codoped core are capable of simultaneous thermal sensing and heating under an 808 nm single beam excitation. The spatial separation between the heating shell and sensing core provides remarkable values of the heating efficiency and thermal sensitivity, enabling their application in single beam-controlled heating experiments in both aqueous and tissue environments.

In Vivo Deep Tissue Fluorescence and Magnetic Imaging Employing Hybrid Nanostructures.

Breakthroughs in nanotechnology have made it possible to integrate different nanoparticles in one single hybrid nanostructure (HNS), constituting multifunctional nanosized sensors, carriers, and probes with great potential in the life sciences. In addition, such nanostructures could also offer therapeutic capabilities to achieve a wider variety of multifunctionalities. In this work, the encapsulation of both magnetic and infrared emitting nanoparticles into a polymeric matrix leads to a magnetic-fluorescent HNS with multimodal magnetic-fluorescent imaging abilities. The magnetic-fluorescent HNS are capable of simultaneous magnetic resonance imaging and deep tissue infrared fluorescence imaging, overcoming the tissue penetration limits of classical visible-light based optical imaging as reported here in living mice. Additionally, their applicability for magnetic heating in potential hyperthermia treatments is assessed.

A highly sensitive luminescent lectin sensor based on an α-D-mannose substituted Tb3+ antenna complex.

Lectin-carbohydrate interactions are the basis of many biological processes and essentially they constitute the language through which intercellular communications are codified. Thus they represent powerful tools in the examination and interpretation of changes that occur on cell surfaces during both physiological and, more importantly, pathological events. The development of optical techniques that exploit the unique properties of luminescent lanthanoid metal complexes in the investigation of lectin-carbohydrate recognition can foster research in the field of ratiometric biosensing and disease detection. Here we report the synthesis of a Tb(3+)-DO3A complex (Tb⊂1) bearing an α-D-mannose residue and the related study of binding affinity with concanavalin A (Con A) labeled with rhodamine-B-isothiocyanate (RITC-Con A). Luminescence spectroscopy and dynamic studies show changes in emission spectra that can be ascribed to a luminescence resonance energy transfer (LRET) from Tb⊂1 (donor) to RITC-Con A (acceptor). The binding constant value between the two species was found to be one order of magnitude larger than those previously reported for similar types of recognition. To the best of our knowledge this is the first example of the use of a pre-organized luminescent lanthanoid complex in the study of carbohydrate-protein interactions by LRET.

Temperature sensing using fluorescent nanothermometers.

Acquiring the temperature of a single living cell is not a trivial task. In this paper, we devise a novel nanothermometer, capable of accurately determining the temperature of solutions as well as biological systems such as HeLa cancer cells. The nanothermometer is based on the temperature-sensitive fluorescence of NaYF(4):Er(3+),Yb(3+) nanoparticles, where the intensity ratio of the green fluorescence bands of the Er(3+) dopant ions ((2)H(11/2) --> (4)I(15/2) and (4)S(3/2) --> (4)I(15/2)) changes with temperature. The nanothermometers were first used to obtain thermal profiles created when heating a colloidal solution of NaYF(4):Er(3+),Yb(3+) nanoparticles in water using a pump-probe experiment. Following incubation of the nanoparticles with HeLa cervical cancer cells and their subsequent uptake, the fluorescent nanothermometers measured the internal temperature of the living cell from 25 degrees C to its thermally induced death at 45 degrees C.