**5.3 Theragnostics and diagnostics**

The field of theragnostics has been rapidly amplified in the last years, thanks to nanotechnology. As it has been commented above, nanomaterials can provide useful action following a great variety of stimuli, be they internal (enzymes, redox potential, pH, and temperature) or external (light, heat, magnetic fields, and ultrasounds-US). In Ref. [119], an interesting review of US-responsive theragnostic nanomaterials under the following categories can be found: microbubbles, micelles, liposomes (conventional and echogenic), niosomes, nanoemulsions, polymeric nanoparticles, chitosan nanocapsules, dendrimers, hydrogels, nanogels, gold nanoparticles, titania nanostructures, carbon nanostructures, mesoporous silica nanoparticles, and fuel-free nano/ micro-motors. Theragnostic nanomaterials in service can produce an imaging signal and/or a therapeutic effect, which frequently involves cell death. It is much interesting to combine the ability for theragnostics of the nanocarriers designed with the

clinical imaging ultrasound technique. High-intensity-focused ultrasound appears as a promising and minimally invasive therapeutic modality against various solid tumors. Although it has received considerable attention in the biomedical field, both the accuracy and efficacy of this technique are currently unsatisfactory. A nanometer-sized organic/inorganic hybrid enhancement agent for photoacoustic imaging-guided highintensity-focused ultrasound therapy was designed and fabricated by concurrently encapsulating both Cu2-xS nanodots and perfluorooctyl bromide into a PLGA nanocapsule. These nanocapsules assumed a unique core/satellite/shell sandwich structure and combined the merits of small and uniform particle size, favorable biosafety, and multifunctional theragnostic ability into one system [120]. A biocompatible theragnostic platform consisting of luminescent upconversion nanocapsules encapsulated with cellulose acetate, a biocompatible polymer, was developed. This theragnostic platform is able to simultaneously perform diagnosis and drug delivery. On the one hand, the luminescence properties of the nanocapsules were observed to remain stable even after encapsulation. On the other, the chemotherapeutic drug doxorubicin was successfully loaded onto the nanocapsules [121]. Also, a new theragnostic nanoplatforms based on nanocapsules and PLGA, which were chemically modified so that they could incorporate several imaging moieties was produced. The nanocapsules can be endowed with a magnetic resonance imaging reporter, two fluorescence imaging probes (blue/NIR), and a positron emission tomography (PET) reporter. *In vitro* toxicity was not observed in any of the two different types of human endothelial cells with concentrations up to 100 μg mL−1. Versatile *in vitro*/*in vivo* multimodal imaging ability was observed, as well as excellent biosafety and over 1% wt protein loading. In the same way, nanocapsules fabricated from biodegradable and photoluminescent polyester with PLGA were reported. Superparamagnetic iron oxide nanoparticles (SPIONs) were incorporated into the polymeric shell so as to transform the system into a magnetic resonance/photoluminescence dual-modal imaging theragnostic platform [122, 123]. Polydopamine is a polymer with adhesive properties; nanoparticles were prepared from it where cisplatin prodrug has been loaded via supramolecular interaction between β-cyclodextrin and adamantyl groups [124]. The nanoparticles exhibited photoacoustic imaging capacity for *in vivo* monitoring of the drug in the tumor site, and the chemo-photothermal therapy of the system showed a powerful anticancer activity against osteosarcoma cells *in vitro*. This is an innovative strategy for the preparation of multifunctional nanotheragnostics for combined anticancer therapy [125]. Polymeric Pluronic-F127-chitosan nanocapsules were obtained and explored as theragnostic agents. IR780 iodide, a near-infrared fluorescent dye that can be applied as a photosensitizer in photodynamic and photothermal therapies, was loaded for single-wavelength NIR laser imagingassisted dual-modal phototherapy. Besides, the nanocapsules were functionalized with folic acid so as to activate their targeting capacity against folate receptor-expressing ovarian cancer cells [126]. The same compound was encapsulated in PEG-PLA nanocapsules and demonstrated potential as a multifunctional theragnostic agent for breast cancer treatment, with increased cellular uptake and photodynamic activity, and more reliable tracking in cell-image studies [127]. Magnetic lipid nanocapsules that show higher structural stability and better theragnostic properties than traditional lipidbased nanocarriers were reported as therapeutic nanocarriers displaying drug-delivery capacity. These nanocapsules are 16 times more efficient than free drugs and their diagnostic imaging capability was also demonstrated [128]. Increasing attention is being payed to multilayer nanocarriers loaded with optically activated payloads, since they are expected to provide new mechanisms of energy transfer in health-oriented applications, at the same time as they look promising for energy storage and environmental

*Lipid and Polymeric Nanocapsules DOI: http://dx.doi.org/10.5772/intechopen.103906*

protection. The combination of a careful selection of optical components for efficient Förster resonance energy transfer and surface engineering of the nanocarriers allowed to synthesize and characterize novel theragnostic nanosystems for deep-seated tumors diagnosis and therapy [129]. Recently, a review has been published where the most interesting advances in nanocarriers applications, including polymeric nanocapsules as tools for Alzheimer's diagnosis and treatment, are compiled [130].
