Ptfe syringe filters

Gel permeation chromatography (GPC) was carried out on a GPC system with UV-Vis detector SPD-6AV (Shimadzu, Duisburg, Germany) in hexafluoroisopropanol (HFIP; containing 4% ammonium trifluoroacetate) at room temperature using a PFG column (100 Å, 1000 Å; PSS, Mainz, Germany). The flow rate was set to 1 mL/min. The endpoint of the measurements was determined with an internal standard (toluene). Alternatively, GPC measurements were performed on a Polymer Standard Service (PSS, Mainz, Germany) System (MDS, RI detector) running under Win GPC software and using a 50 mm PFG precolumn and three 300 mm PFG columns (Mixed Bed PSS PFG linear M, 7 μm PSS, Mainz, Germany) for measurements in HFIP (containing 5 mmol/L ammonium trifluoroacetate). Columns were kept at 40 °C and the flow rate was set to 1 mL/min. Prior each measurement, samples were filtered through 0.2 μm PTFE syringe filters (Roth, Karlsruhe, Germany). Calibration of both GPC-Systems was performed using poly(methyl methacrylate) standards (PSS, Mainz, Germany) with molar masses from 0.8 kg/mol to 1600 kg/mol.

Peptide solutions were freshly prepared by solubilizing the peptide in water or phosphate buffered saline solution pH 7.4 (PBS). The solutions were centrifuged (13,000 g, 10 min) and the supernatants filtrated with 0.22 µm PTFE syringe filters (Carl Roth, Germany). The peptide concentrations were determined by UV/vis spectroscopy using the absorbances at 280, 320 and 350 nm. PEGMUA solutions were 1 mM in water. PEGMUA und L1-N-Lys were mixed in a molar ratio 3:1 and GNPs were added under stirring (500 rpm). After thorough shaking of the container, the mixtures were stirred (400 rpm) for 16 h at room temperature. In the case of GNP40s, 50,000 ligands were added per GNP, in the case of GNP30s, 100,000 ligands were added per GNP. After functionalisation the GNPs were concentrated and purified by repeated centrifugation (1,000–5,000 g, 10–15 min) and replacement of the supernatants with water. The final samples had 12 nM (~3.8 g/l) in PBS in the case of GNP40s, while GNP30s had 13 nM (~2.4 g/l) in artificial cerebrospinal fluid. A detailed description of the synthesis and characterisation of these functionalised GNPs can be found in ref.^{20 (link)}.