Materials

4′-Hydroxyazobenzene-2-carboxylic acid (HABA), biotin, N-(2-aminoethyl)maleimide trifluoroacetate salt (amino-maleimide), acetic acid, sodium acetate, phosphorous acid, magnesium chloride, Tween 20, Tween 80, bovine serum albumin (BSA), dimethyl sulfoxide (DMSO), dextran (Dex; MW 15–25 kg mol⁻¹—M_n 16 kg/mol; lyophilized before use), 4-nitrophenyl chloroformate (PNC; sublimated before use), LiCl (dried at 110 °C before use), tyramine (TA), anhydrous pyridine, anhydrous N,N-dimethylformamide (DMF), N,N-Diisopropylethylamine (DIPEA), piperidine, amino acids, acetic anhydride, triisopropylsilane, trifluoroacetic acid (TFA), sodium hydroxide (NaOH), N-Boc-1,4-butanediamine (NH₂-Boc), sodium bicarbonate (NaHCO₃), biotin-atto565, biotin-4-fluorescein (biotin-FITC), 6-aminofluorescein, horseradish peroxidase (HRP, type VI), biotin-HRP, hydrogen peroxide (H₂O₂; with inhibitor), fetal bovine serum (FBS), calcein AM, ethidium homodimer-1 (EthD-1), Thiazolyl Blue Tetrazolium Blue (MTT), and all other solvents, unless otherwise stated, were purchased from Sigma-Aldrich. The bone-shaped master was purchased from LEGO. Polydimethylsiloxane (PDMS; Sylgard 184) was purchased from Dow Corning. Phosphate-buffered saline (PBS) was purchased from Lonza. Recombinant human BMP7 (354-BP-010), 3,3′,5,5′-tetramethylbenzidine (TMB), and H₂SO₄ were purchased from R&D Systems. Fmoc-Rink 4-methylbenzhydrylamine (MBHA) resin (50 mg scale, substitution 0.52 mmol g⁻¹) and N,N,N′,N′-Tetramethyl-O-(1H-benzotriazol-1-yl)uronium hexafluorophosphate (HBTU) were purchased from MultiSynTech. Chloroform and 1-methyl-2-pyrrolidinone (NMP) were purchased from WR Chemicals. V_HH antibody against BMP7 (Q32c-lab, clone G7) and polyclonal rabbit antibody against V_HH (K1216) were purchased from QVQ. Biotinylated IL-1β antibody (508301, clone JK1B2, RRID:AB_315512) was purchased from Biolegend. Biotinylated IgG (Biotin-SP AffiniPure Donkey Anti-Rabbit IgG; 711-065-152) was purchased from Jackson Immunoresearch. HRP-conjugated secondary goat antibody against rabbit (P0448) was purchased from Dako. Biotinylated gold nanoparticles (20 nm) were purchased from Cytodiagnostics. The biotinylated peptide with amino acid sequence KGLPLGNSH was purchased from Pepscan. Succinimidyl 6-(biotinamido)hexanoate (biotin-LC-NHS) was purchased from ApexBio. Neutravidin, N-hydroxysuccinimide-desthiobiotin (EZ-Link NHS-desthiobiotin), 4′,6-diamidino-2-phenylindole (DAPI), and 3,3′-diaminobenzidine (DAB) staining kit were purchased from ThermoFisher Scientific. Pre-activated sensors for amine coupling (G-type easy2spot) were purchased from Ssens BV. Dulbecco’s Modified Eagle’s Medium (DMEM), Penicillin and Streptomycin, and trypsin-EDTA were purchased from Gibco. Reporter Lysis Buffer (E397A), luciferase assay reagent (E1483), and QuantiFluor dsDNA System were purchased from Promega. C2C12-BRE-Luc cells were kindly provided by prof. Daniel B. Rifkin.