Towards three dimensional functional polymer based nanosystems: Soft matter-semiconductor nanocrystal hybrids
Direct delivery of therapeutic compounds to cellular targets can enhance drug efficacy and safety, but such techniques require careful monitoring within the body. Semiconductor nanocrystals can have superior photonic properties, which make them very promising in sensing devices and in biological imaging. Integrating QDs in functional systems requires molecular engineering of the QDs surface which can be achieved by designer polymers (Figure 1). The MTP team, in collaboration with the MESA+ groups SMCT, MNF and Nanobiophysics, and with A*STAR Singapore, developed various nanosystems that encompass fluorescent QDs and hold the promise to light up the pathways of critical biological processes.
Fig.1: Quantum dots can be made water soluble by adding an amphiphilic polymer coating
Fluorescent markers, such as chemical dyes, are often attached to biomolecules to track their movements inside living cells. Quantum dots (QD) - semiconductor nanocrystals with extraordinary light-emitting capabilities such as bright fluorescence emissions and long lifetimes - promise to radically advance biological imaging by offering a brighter, longer-lived source of fluorescent light than any comparable dye. When combined with other fluorophores, QDs may provide sensing platforms with molecular sensitivity. Researchers in MTP developed a polymeric shell to solubilize QDs in water and to allow covalent attachment of QDs into functional nanosctructures by “click chemistry” . Clicking can also be used to prepare controlled composite spherical microparticles with well-defined nanoparticle loading (Figure 2).
Fig.2: “Click” chemistry was used with success to prepare polymer cross-linked microparticles with QD loading 
QDs exhibit bright fluorescence emissions and long lifetimes. Using the “molecular printboard” approach developed by David Reinhoudt and his coworkers, QDs with molecular receptors were immobilized at patterned substrates . The receptors provide binding sites for various analytes. Analyte detection via supramolecular host–guest binding and QD-based fluorescence resonance energy transfer (FRET) signal transduction mechanism were demonstrated in another “highlighted” study (Figure 3).
Fig.3: Fluorescence energy transfer allows sensitive detection of fluorophore labeled analytes by a surface immobilized QD platform 
 Jańczewski, D., Tomczak, N., Liu, S. , Han, M.-Y., Vancso, G.J.
Covalent assembly of functional inorganic nanoparticles by "click" chemistry in water (2010) Chemical Communications, 46 (19), pp. 3253-3255.
 Dorokhin, D., Hsu, S.-H., Tomczak, N., Blum, C., Subramaniam, V., Huskens, J , Reinhoudt, D.N , Velders, A.H., Vancso, G.J.
Visualizing resonance energy transfer in supramolecular surface patterns of β-CD-functionalized quantum dot hosts and organic dye guests by fluorescence lifetime imaging (2010) Small, 6 (24), pp. 2870-2876.