1 octadecanethiol

1,3,5-tris(4-carboxyphenyl)benzene [BTB] (98%), 1,3,5-tris(4’carboxy[1,1᾿-biphenyl]-4-yl)benzene [BBC] (95%), copper (II) acetate monohydrate, 16-mercaptohexadecanoic acid [MHDA] (90%), 11-mercapto-1-undecanol [MUD] (97%), 1-octadecanethiol [ODT] (98%), hydrochloric acid (ACS reagent, 37%), anhydrous propylene carbonate [PC], and anhydrous dimethyl sulfoxide [DMSO] are from Sigma Aldrich (St. Louis, MO). Absolute, anhydrous ethanol (200 proof, ACS/USP Grade) was obtained from Phamco-Aaper (Shelbyville, KY). These chemicals were used as received. Ferrocene (Fc, Sigma Aldrich) and tetrabutylammonium tetrafluoroborate (TBATFB, Sigma Aldrich) were dried at 120 °C under vacuum for 12 h prior to transferring to an Ar-filled glovebox (less than 1 ppm O₂/H₂O). Silicon wafers with a 5 nm Ti adhesion layer and a 100 nm Au layer were obtained from Platypus Technologies (New Orleans, LA). Ge (100) wafers were obtained from MTI Corporation (Richmond, CA).

Cholera toxin (CT) from Vibrio cholera, Triton X-100, 1-octadecanethiol (98%), and n-octadecyltrichlorosilane (OTS, 90+%) were from Sigma-Aldrich (St. Louis, MO). Trehalose was from Swanson Health Products (Fargo, ND).
1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-|6-[(7-nitro-2−1,3-benzoxadiazol-4-yl)amino]hexanoyl}-sn-glycero-3-phosphocholine (NBD-PC) were from Avanti Polar Lipids (Alabaster, AL). Monosialoganglioside GM1 (NH₄⁺ salt) and monosialoganglioside GM2 (NH₄⁺ salt) were from Matreya (Pleasant Gap, PA). Monosialoganglioside GM3 was from EMD Biosciences (La Jolla, CA). BK-7 glass substrates were from Corning (Painted Post, NY). Chromium and gold used for electron-beam evaporation were acquired as pellets of 99.99% purity from Kurt J. Lesker (Jefferson Hills, PA).

A total amount of 2 μmole of lipid mixture (Avanti Polar Lipids) was prepared by mixing DPPC (10 mM), cholesterol (10 mM), DSPE-PEG (2000) azide (3 mM), and DOPS (5 mM) in a clean 25 mL round-bottom flask. The solvent chloroform in the lipid mixture was removed by rotary evaporator. A uniformly thin lipid layer formed on the bottom of the flask, which was then further dried under vacuum overnight. HEPES buffer (20 mM, Sigma-Aldrich, wt 238.30 g) was added to the dried lipid layer (1 mL 10 mM HEPES buffer per 1 μmole lipid), and the mixture was sonicated for 5 min to form a clear liposome solution. For each 500 μL of liposome solution, 50 μL of Au NP pellet (2×10¹¹ particles/mL) was added. Subsequently, 40 μL of 1-Octadecanethiol (8.72 mM, Sigma-Aldrich, wt 286.56 g) dissolved in ethanol was added. The final volume was brought to 1 mL with HEPES buffer. The mixed solution was then shaken for 5 h, 18 h or 24 h, respectively. The NP were subsequently washed three times through centrifugation (720g, 10 min) and re-suspended in HEPES buffer.