Deep-tissue, high-contrast imaging at the in vivo level represents a critical diagnostic step both at the preclinical and clinical level. In our group, we push the limits of optical imaging approaches employing fluorescence nanoparticles operating in the so-called biological windows. These are spectral ranges located in the infrared region (750-1800 nm), in which tissues are partially transparent to the electromagnetic radiation.

We have been pioneers in the development of cost-effective, highly versatile experimental set-ups for in vivo infrared fluorescence imaging. We also develop suitable contrast agents composed of infrared-emitting semiconductor nanocrystals and rare earth-doped nanoparticles.
The imaging techniques we employ at nanoBIG include hyperspectral in vivo imaging, in vivo lifetime imaging, and subtissue fluorescence-assisted thermal videorecording (see figure).
Aside from purely imaging purposes, we employ the nanomaterials we develop for theranostics (combined therapy and diagnostics).

Monitoring of the thermal state of biological systems can afford information about processes occurring down to the single-cell level. On the other hand, in the context of thermal therapies (i.e., magnetic hyperthermia and photothermal therapy), real-time temperature monitoring allows on-the-fly adjustments of the therapeutic parameters.
To that end, in the toolbox of methods for non-invasive thermometry, semiconductor nanocrystals have emerged as efficient multifunctional fluorescent nano-thermometers capable of simultaneously generating intracellular imaging, as well as acting as optical thermal indicators. For example, they have been used for dynamical thermal monitoring of single cells in the proximity of heat sources or during externally induced thermogenesis processes.

Compared to other methods, semiconductor nanocrystals-based thermometry offer superior performance such as sub-micrometric resolutions, high contrast, good biocompatibility, excellent temperature resolution (of about 0.2 °C) and possibility of selective targeting via surface functionalization.

Optical tweezers are scientific instruments that use a highly focused laser beam to create an attractive or repulsive force - typically in the order of picoNewtons, and dependent upon the refractive index mismatch - to physically "grab" and move dielectric objects at the micro- and nanoscale.

Optical tweezers have been particularly useful for the study of a variety of biological systems in recent years, as they can be used to immobilize and manipulate small objects (e.g., a nanoparticle) into the system of interest (e.g., a cell).
Single-beam optical tweezers were initially introduced by Ashkin et al.: Therein, a single laser beam is focused through a high numerical aperture objective lens to generate a three-dimensional optical trap by exerting a radiation force on small objects.
Since then, optical tweezers have become calibrated tools to immobilize, orient, and transport sub-micrometric particles. The nanometer positioning ability along with sub-picoNewton force resolution have turned this approach into a valuable tool in biology. However, direct trapping and manipulation of smaller particles still represents a challenge, as they are substantially harder to trap.

Optical coherence tomography (OCT) is based on low-coherence interferometry, typically employing near-infrared light, which enables deep-tissue imaging with typical resolutions of ~10-20 µm and reaching penetration depths as large as 3 mm in nontransparent media.
In our lab, we host an intracoronary OCT (IC-OCT) system used in clinical practice at the Interventional Cardiology Unit of the Hospital Universitario La Princesa of Madrid (Dragonfly OPTIS Imaging Catheter St Jude Medical) as well as an open OCT system (Telesto Thorlabs OCT system).

We can harness the light scattering properties of plasmonic gold-based nanoparticles and PbS quantum dots to obtain positive OCT contrast (see image). In the case of near-infrared emitting PbS quantum dots, the simultaneous use of the OCT setup and an infrared camera enables OCT and two-dimensional luminescence imaging of arteries (see image). The use of highly absorbingplasmonic nanomaterials (e.g., CuS nanoparticles) allows instead to generate dark contrast in OCT images, which is envisaged to be of utility in the precise localization of atheromata.

Confocal fluorescence imaging has demonstrated to be a powerful technique for the characterization and understanding of a great variety of micro- and nano-photonic devices.
NanoBIG has worked extensively on the application of confocal fluorescence imaging for the acquisition of fluorescence images of ultrafast laser-inscribed photonic devices in laser gain media.

These images have been pivotal to understand the role played by the different micro-structural modifications induced by ultra-intense laser pulses (stress, damage, disorder) in the performance of diffeent structures ranging from waveguides to photonic crystals.