Nanoparticles possess unique optical and physic-chemical properties that may potentiate applications in biomedicine, in particular in diagnostics, therapy and imaging. Advances on biomolecular diagnostics strategies have greatly focused on single molecule detection and characterization of DNA, RNA or proteins through improved nanoparticle-based platforms. Nanoparticles improve analytical capability when compared to traditional techniques with high resolution and medium-high throughput. Also, particular interest has been directed at SNP detection, gene expression profiles and biomarker characterization through colorimetric, spectrometric or electrochemical strategies.
Molecular imaging has also benefited from the introduction of nanoparticles in standard techniques towards non-invasive imaging procedures that can be used to highlight regions of interest, allowing the characterization of biological processes at the cellular and/or molecular level. Several imaging modalities are associated with low sensitivity, an issue that can be tackled by the use of probes, e.g. contrast agents for X-ray and magnetic resonance imaging, radiolabelled molecules for nuclear medicine. Furthermore, nanoparticles can be used as vehicles that deliver specifically these contrast agents, leading to overcome the limitations of conventional modalities.
This chapter will discuss the use of nanoparticles in biomolecular recognition and imaging applications, focusing those already being translated into clinical settings. Current knowledge will be addressed as well as its evolution towards the future of nanoparticle-based biomedical applications.

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Over the past few years, modern medicinal chemistry has evolved towards providing us new and alternative chemotherapeutic compounds with high cytotoxicity towards tumor cells, alongside with reduced side effects in cancer patients. Organometallic compounds and their unique physic-chemical properties typically used in homogenous catalysis are now being translated as potential candidates for medical purposes. Their structural diversity, ligand exchange, redox and catalytic properties make them promising drug candidates for cancer therapy. Over the last decade this area has witnessed a steady growth and a few organometallic compounds have in fact already entered clinical trials, emphasizing its increasing importance and clinical relevance. Here we intend to stress out the different applications of organometallic compounds in medicine with emphasis on cancer therapy, as well as address setbacks regarding formulation issues, systemic toxicity and off-target effects. Advantages over classical coordination metal complexes, their nanovectorisation and specific molecular targets are also discussed.

The design of small interfering RNA (siRNA) delivery materials showing efficacy in vivo is at the forefront of nanotherapeutics research. Polyurea (PURE-type) dendrimers are ‘smart’ biocompatible 3D polymers that unveil a dynamic and elegant back-folding mechanism involving hydrogen bonding between primary amines at the surface and tertiary amines and ureas at the core. Similarly, to a biological proton pump, they are able to automatically and reversibly transform their conformation in response to pH stimulus. Here, we show that PURE-G4 is a useful gene silencing platform showing no cellular toxicity. As a proof of concept we investigated the PURE-G4-siRNA dendriplex, which was shown to be an attractive platform with high transfection efficacy. The simplicity associated with the complexation of siRNA with polyurea dendrimers makes them a powerful tool for efficient cytosolic siRNA delivery.

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The design and preparation of highly efficient drug delivery platforms using green methodologies is at the forefront of nanotherapeutics research. POxylated polyurea dendrimers are efficiently synthesized using a supercritical-assisted polymerization in carbon dioxide. These fluorescent, pH-responsive and water-soluble core-shell smart nanocarriers show low toxicity in terms of cell viability and absence of glutathione depletion, two of the major side effect limitations of current vectors. The materials are also found to act as good transfection agents, through a mechanism involving an endosomal pathway, being able to reduce 100-fold the IC50 of paclitaxel.

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