Siliconized low retention microcentrifuge tubes

NaCl, NaOH, HCl, KNO₃, sodium citrate, ethylene glycol (EG), Whatman grade 1 chromatography paper (180 μm thick, 20 cm × 20 cm sheets, linear flow rate of water = 0.43 cm/min) and siliconized low-retention microcentrifuge tubes were purchased from Fisher Scientific (Pittsburgh, PA). HAuCl₄, NaSH, CF₃COOAg, phosphate-buffered saline (PBS, pH=7.4, P3813), bovine serum albumin (BSA) and polyvinylpyrrolidone (PVP, MW~55,000 g/mol) were purchased from Sigma Aldrich (St Louis, MO). Boric acid was purchased from EM Science (Gibbstown, NJ).
Conductive carbon paste (Cl-2042) was purchased from Engineered Conductive Materials (Delaware, OH). Streptavidin-coated, 1.0 μm-diameter magnetic beads (MμBs, Dynabeads, MyOne Streptavidin T1, 10 mg/mL) were obtained from Invitrogen (Grand Island, NY). Citrate-capped sAgNPs (nominal 20-nm diameter) were purchased from nanoComposix (San Diego, CA). Monoclonal immunoglobulin G anti-NT-proBNP 13G12 (Ab) was obtained from HyTest (Turku, Finland) and bioinylated, polyclonal anti-mouse immunoglobulin G secondary antibody (SAb) was obtained from Abcam (Cambridge, UK). All solutions were made using deionized (DI) water (>18.0 MΩ-cm, Milli-Q Gradient System, Millipore, Burlington, MA). The buffers were 1x PBS.

Lyophilized peptide stocks (10 mg, LifeTein) were mixed with ice cold HFIP and transferred to sterile silicone coated tubes (Fisherbrand™ Siliconized Low-Retention Microcentrifuge Tubes) at 0.5 mg per tube, and dried via speed vac (2 hrs) and further dried to completion under N₂ stream (2 hr). Immediately prior to assay, dried peptide stocks were thawed and dissolved into filtered HPLC-grade dimethyl sulfoxide, and allowed to solubilize for at least 30 min rocking at room temperature.

DLS was performed on a compact goniometer system (ALV CGS-3, ALV, Langen Germany) equipped with a multi-tau digital correlator (ALV 7004, Langen, Germany) and a laser light source of wavelength λ = 632.8 nm (He-Ne, JDS Uniphase Corp, USA). All measurements were done at T = 298 ± 0.5 K. The solvents and buffers used to make the DNA and protein solutions were first sterilized, filtered through 0.2 µm Whatman Anotop syringe filters (Whatman, USA). The samples were prepared in siliconized microcentrifuge tubes (Fisherbrand™ Siliconized Low-Retention Microcentrifuge Tubes) to prevent sample from binding to the walls of the tube. The hydrodynamic radii, R_H (nm), of the samples were obtained using relaxation times, τ (ms), measured at a fixed scattering angle of θ = 90° and the Stokes - Einstein relation. Peptides were prepared as described above for gel shift assay. Salmon Sperm DNA (sDNA) was purchased from Invitrogen (Carlsbad, Ca).