Cystamine

The CKAAKN was provided from Baiaotai Biotechnology Inc. (Guangzhou, China). Trypsin was purchased from Gibco BRL, USA. Fetal bovine serum (FBS) was purchased from Sijiqing Biologic, China. The PKH67 fluorescent cell linker, 1-Ethyl-3 (3-dimethylaminopropyl) carbodiimide (EDC), N-hydroxysuccinimide (NHS), ultra-small superparamagnetic iron oxide (USPIO), 3-(4,5-dimethylthiazol-2-yl)-2,5 –diphe nyltetrazolium bromide (MTT), Coumarin 6, and cystamine were purchased from Sigma–Aldrich (St. Louis, MO, USA). Sodium hyaluronic acid (HA molecular weight: ~48,000 Da) was purchased from Freda Biochem Co., Ltd. (Shandong, China). Vitamin E succinate (VES) was purchased from Aladdin Bio-Chem Technology Co., Ltd. (Shanghai, China). All other solvents were of analytical or chromatographic grade.

4-aminothiophenol (4-ATP or pATP), cysteamine (CYS), cystamine, L-cysteine, mercaptopropionic acid (MPA), mercaptoundecanoic acid (MUA), 4-mercaptobenzoic acid (4-MB), hexanethiol (HT), imidazole, 2,6-dimethoxyphenol (DMP), NHS (N-hydroxysuccinimide), EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride), Na₂HPO₄, NaH₂PO₄H₂O, and sodium chloride (NaCl) were obtained from Sigma-Aldrich. Sodium fluoride (NaF) and sodium azide (NaN₃) were obtained from Merck-Suprapur. All chemicals were used as received without further purification.

The aptamer sequences against S. typhimurium were obtained from literature [3 (link)]. Two sequences with high affinities to S. typhimurium were APT33, 5′-TATGG-CGGCG-TCACC-CGACG-GGGAC-TTGAC-ATTAT-GACAG-3′, and APT45, 5′-GAGGA-AAGTC-TATAG-CAGAG-GAGAT-GTGTG-AACCG-AGTAA-3′ were selected from random ssDNA sequence pools. In both AFM and SPR experiments, the aptamer sequence was modified by twenty thymine bases as the spacer and the amine group as the linker at 5′ end. The modified sequence was purchased from Integrated DNA Technologies (Coralville, IA, USA). In AFM experiment, the aptamer was attached by its amine group to the linker molecule and in turn to the gold coated tip. The polymer linker thiol-(polyethylene glycol)-acid (HS-PEG-COOH, M.W. 2000) was purchased from Creative PEGWorks (Winston Salem, NC, USA). The cystamine, carboxymethylated-dextran (CD), N-hydroxysuccinimide (NHS), and ethanolamine were all purchased from Sigma-Aldrich (St. Louis, MO, USA). The 1-(3-dimethylaminopropyl)-3-ethylcarbodimide hydrochloride (EDC) was purchased from Flucka Chemicals (Sigma-Aldrich, St. Louis, MO, USA). Phosphate buffer saline (PBS, pH 7.2) was purchased from Pierce (Thermo Scientific, Waltham, MA, USA). Triplet deionized water was provided by a Barnstead Nanopure Diamond Laboratory Water System (Barnstead Thermolyne, Dubuque, IA, USA).