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S C HW E R P U N K T 16 ticles in numerous studies, they are not yet suitable for use in biological systems, for instance, those in the hu- man body. »Everyone knows about the health risks posed by UV radiation«, states Schacher. »Administering medi- cines that require intense UV radiation to be released into the body is not an option.« The chemists therefore aim for shifting the wavelength required to stimula- te these light-sensitive nanoparticles to, from biological point of view, safe range, i.e. visible and near infrared wa- velength range. When working within this »biological window«, exposure to light within this wavelength range allows deep penetration of up to ten millimeters into the tissue which was already proven to be well-tolerated. Energy converters set off a chain reaction Photosensitive molecules within this wavelength range, which can achieve similar effects, have not been availab- le by now. Schacher and his team thus opted for an alternative approach. In cooperation with Prof. Benjamin Diet- zek’s research group, they want to inte- grate so-called energy converters into the nanoparticles. These are either mo- lecules or small crystallites which are able to absorb harmless infrared light and convert it into high-energy UV radiation at a specific location. This could then activate the photoacids and thus induce the release of the active Contact Prof. Dr Felix Schacher Institute for Organic Chemistry and Makromolecular Chemistry Lessingstr. 8, D-07743 Jena, Germany Phone: +49 36 41 9-48250 Email: felix.schacher@uni-jena.de www.jenano.de Further information Light-Responsive Terpolymers Based on Po- lymerizable Photoacids, Polymer Chemistry (2017), DOI: 10.1039/c7py00571g substance from the particle. »As this happens locally, within the particle, the UV light cannot harm the orga- nism«, highlights Felix Schacher. Lego model blueprint for nanoparticles The chemist uses a 20-centimetre mo- del made of coloured Lego bricks to show what the blueprint for light-con- trolled nanoparticles might look like (see photograph on p. 17). The par- ticles are made up of several layers which combine the different functions. They contain a core made of lantha- nide-doped nanoparticles (NaYF4:Y- b,Tm) and have a diameter of appro- ximately 20 nanometers. This core acts as an energy converter. It absorbs the irradiated visible or infrared light and converts it into short-wavelength and high energy ultraviolet radiation. The core is surrounded by the active, light-sensitive layer (red). This is whe- re the potential active substance is located (green). When the photoacids are »switched on« by the UV light, this layer swells and the active substance is released from the particle. In order to make the whole ensemble suitable for use as a transport system for me- dication, the nanoparticles must be surrounded by another layer (yellow). This layer is made of polyethylene gly- col, or PEG, and protects the particles from the accumulation of proteins in the blood which can extend their cir- culation time.  The team led by Prof. Dr Felix Schacher is not just inventive in the eld of photoche- mistry. They are also using a Lego model to show the structure of the nanoparticles with a »light switch«. The green bricks represent the photoacids which are embed- ded in a polymer matrix having a different solubility depending on the pH value (red bricks).