Ultra-small water-dispersible fluorescent chitosan nanoparticles: synthesis, characterization and specific targeting Padmavathy Tallury a , Sounitra Kar a and Swadeshmukul Santra a,b,c * Suwussa Bamrungsap, d Yu-Fen Huang, d and Weihong Tan d ES1 Materials Chitosan polymer (low molecular wight), Triton X-100, N-hydroxysuccinimide (NHS), 1-ethyl-3-(3-dimethylaminopropyl carbodiimide hydrochloride) (EDC) were purchased from Sigma-Aldrich Chemical Co., USA; Fluorescein isothiocyanate (FITC), anhydrous ethanol were purchased from Fisher Scientific. Dialysis cellulose membrane (MWCO, 6-8 kD) was purchased from Spectrum Laboratories (Rancho Dominguez, CA). Deoxyribonucleotides and 5’-carboxyl modifiers were purchased from Glen Research (Sterling, VA). All solvents and reagents were obtained from Fisher Scientific and were used without further purification. CCRF-CEM cells (CCL-119 T-cell, human acute lymphoblastic leukemia) and Ramos cells (CRL-1596, B-cell, human Burkitt’s lymphoma) were obtained from American Type Culture Association, USA. All of the cells were grown in RPMI-1640 containing 10% fetal bovine serum (FBS) and 100 IU/mL penicillin-Streptomycin at 37 °C in a humid atmosphere with 5% CO 2 . G25 Sephadex size- exclusion column (NAP TM -5) was procured from Amersham Pharmacia Biotech, USA. Instrumentation Degree of deacetylation of chitosan was determined by elemental analysis at the Atlantic Microlabs, Norcross, GA. JEOL JEM 1011 100kV transmission electron microscope (TEM) was used to characterize particle size. TEM sample was prepared by placing a drop of the chitosan nanoparticles on a carbon coated copper grid (400 mesh size) followed by air drying. Particle size distribution and zeta potential in deionized water was measured by using the Malvern Zeta Sizer (model: NanoZS) Dynamic Light Scattering (DLS) instrument. The concentration of activated aptamer and the amount of FITC in FITC-Chitosan conjugate polymer was determined Supplementary Material (ESI) for Chemical Communications This journal is © The Royal Society of Chemistry 2009