## 2 Experimental Section  
The following chemicals were purchased from Aldrich, Rehovot, Israel, and were used without further purification: zinc chloride (ZnCl\({}_{2}\), 98%), benzoyl peroxide (BP, 98%), Tetrahydrofuran (THF), dimethylformamide (DMF), divinylbenzene (DVB, 80%), sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP, \(M_{w}\) = 360,000 g/mol), ethanol (HPLC), 2-methoxy ethanol (HPLC), dibutyl phthalate (DBP) and methylene chloride (HPLC). Styrene (S, 99%) was passed through activated alumina (ICN) to remove inhibitors before use. Water was purified by passing deionized water through an Elgastat Spectrum reverse osmosis system (Elga Ltd., High Wycombe, UK). Uniform micrometer-sized PDVB microspheres of 5.4 \(\pm\) 0.1 \(\upmu\)m were prepared by a single-step swelling process at room temperature of polystyrene (PS) template microspheres with DBP (swelling solvent) containing DVB and BP, followed by polymerization at elevated temperature and dissolving the PS template part, as described previously [16; 17; 18]. Briefly, PS template microspheres of 2.3 \(\pm\) 0.1 \(\upmu\)m were swollen up to 8.1 \(\pm\) 0.2 \(\upmu\)m by the following procedure: 1.5 mL DBP containing 10 mg BP and 1.5 mL DVB were added to a 20 mL vial containing 10 mL SDS aqueous solution (0.75% \(w\)/\(v\)). Emulsion droplets of the swelling solvent were then formed by sonication (Sonics and Materials, model VCX-750, Ti-horn 20 kHz) of the mixture for 1 min. An aqueous dispersion (3.5 mL) of the PS template microspheres (7% _w/v_) was then added to the stirred DBP emulsion. After the swelling of the PS particles was complete and the mixture did not contain any small droplets of the emulsified swelling solvent, as verified by optical microscopy, the monomer within the swollen particles was polymerized by raising the temperature of the shaken vial containing the swollen particles to 73 \(\,\)C for 24 h. The composite PS/PDVB microspheres produced were then washed from undesired reagents by extensive centrifugation cycles with water and ethanol. Uniform porous crosslinked micrometer-sized PDVB particles of 5.4 \(\pm\) 0.1 \(\,\)m were then prepared by dissolving the PS template part of the PS/PDVB composite microspheres with methylene chloride, acetone and DMF. Briefly, PS/PDVB composite particles were dispersed in 50 mL methylene chloride:acetone (1:2), and then shaken at room temperature for _ca._ 15 min. The dispersed microspheres were then centrifuged, and the supernatant containing the dissolved PS template polymer was discarded. This procedure was repeated four times with methylene chloride:acetone (1:2), DMF, ethanol, and water. The obtained crosslinked PDVB microspheres were then dried by lyophilization. ZnCl\({}_{2}\)-PDVB composite microspheres were prepared by evacuating 100 mg of the PDVB porous template microspheres for 30 min, using a diaphragm vacuum pump in a 50 mL double neck round bottom flask closed with a septum. Then 0.1 mL of ZnCl\({}_{2}\) solution in THF (20% _w/v_) was injected into the round-bottom flask. The PDVB microspheres containing the ZnCl\({}_{2}\) were then mixed and dried by vacuum evaporation. \"Cauliflower-like\" ZnO microparticles were prepared by calculating the ZnCl\({}_{2}\)-PDVB microspheres in an air atmosphere at 600 \(\,\)C (wire wound tube furnace TF-25-250/H, Carbolite, Hope, UK). Optical and fluorescence microscopy images were obtained using an Olympus optical/fluorescent microscope (model AX70, filter WU: excitation 330-385 nm, emission \(>\)420 nm). Surface morphology was characterized with a scanning electron microscope (SEM, model Inspect S, FEI, Eindhoven, The Netherland). The samples were coated with gold in vacuum prior to scanning with SEM. The samples for the TEM analysis were prepared by milling a small amount of the \"cauliflower-like\" ZnO microparticles, dissolving them in ethanol and dispersing a small drop of the sonnicated solution on a TEM copper grid.