Editing Magnetic beads Preparation Methods (section)

== Synthesis of NTA-PEG3400-Si(OMe)3 NTA-PEG3400-VS ==

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2533260/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2533260/]

NHS-PEG3400-VS (0.85 g, 0.25 mol) and NTA (0.33 g, 1.25 mmol) were dissolved in 8.5 ml of DMSO. Triethylamine (TEA) (2.00 ml, 14.30 mmol) was added and the solution stirred at room temperature for 24 h before quenching with 2N HCl (28.3 mmol). The solution was then dialyzed for 24 h against 1 L of distilled water using a dialysis membrane (Spectra/Por, MWCO 1000) and the retentate lyophilized. The NTA-PEG3400-VS product was stored at −20 °C until use.

NTA-PEG3400-Si(OMe)3 Silanation of NTA-PEG3400-VS was performed by free radical addition of mercaptopropyltrimethoxysilane (MPTS) to the vinyl sulfone substituent as shown in Scheme 1.34,35 NTA-PEG3400-VS and an eight-fold excess of freshly distilled MPTS were added to toluene in a round bottom flask, followed by the addition of a 0.4-fold excess of 2,2′-azobisisobutyronitrile (AIBN) relative to NTA-PEG3400-VS. The mixture was stirred for 24 h at 60 °C under a N2 atmosphere before precipitation of the product with anhydrous Et2O. The precipitate was filtered, washed with excess Et2O, and dried under reduced pressure to give NTA-PEG3400-Si(OMe)3 as a white powder in 53% yield. 1H NMR (CDCl3): δ 3.9-3.15 (br, CH2CH2O), 2.45 (t, J=6.0 Hz, NHCH2), 1.68-1.14 (br, NHCH2(CH2)3CHCOOH), and 0.6 (CH2Si).

Surface preparation and characterization Silicon wafers or cover glasses were immersed into fresh piranha solution for 1 h and rinsed by bath sonication in deionized water. Piranha solution was prepared by mixing pure sulphuric acid and hydrogen peroxide (30% solution) in a 7:3 volume ratio. Piranha solutions are potentially explosive and highly corrosive! Handle with extreme caution! The clean substrates were dried under N2 gas and then immersed in toluene solutions of mPEG5000-Si(OMe)3 or NTA-PEG3400-Si(OMe)3 (10 mg PEG derivative/ml) for 16 h at 60 °C.35 The NTA-PEG3400-VS-modified surfaces were prepared as follows: piranha cleaned surfaces were immersed in 1% MPTS in toluene for 4 h and washed with toluene. The dried MPTS-modified surface was then incubated in NTA-PEG-VS (10 mg/ml) in 0.01M phosphate buffered saline (PBS) for 16 h at room temperature.36