A　facile　and　simple　electrochemical　immunoassay　for　ultrasensitive　determination　of　streptomycin　residues　(STR)　in　food　was　designed　by　using　nanogold-assembled　mesoporous　silica　(GMSNs)　as　bionanolabels　on　a　three-dimensional　redox-active　organosilica-functionalized　sensing　interface.　To　construct　such　a　sensing　interface,　we　initially　synthesized　organosilica　colloids　by　using　wet　chemical　method,　and　then　utilized　the　prepared　colloidal　organosilica　nanocomposites　for　the　immobilization　of　monoclonal　anti-STR　antibodies　on　a　glassy　carbon　electrode　based　on　a　sol-gel　method.　The　bionanolabels　were　prepared　based　on　coimmobilization　of　horseradish　peroxidase　(HRP)　and　STR-bovine　serum　albumin　conjugates　(STR-BSA)　on　the　GMSNs.　With　a　competitive-type　immunoassay　format,　the　assay　toward　STR　analyte　was　carried　out　in　pH　5.5　acetate　acid　buffer　(ABS)　by　using　redox-active　organosilica　nanocomposites　as　electron　mediators,　biofunctionalized　GMSNs　as　traces,　and　hydrogen　peroxide　(H2O2)　as　enzyme　substrate.　Under　optimal　conditions,　the　reduction　current　of　the　electrochemical　immunosensor　decreased　with　the　increase　in　STR　level　in　the　sample,　and　displayed　a　wide　dynamic　range　of　0.05-50　ng　mL-1　with　a　low　detection　limit　(LOD)　of　5　pg　mL-1　at　3sB.　Intra-　and　interassay　coefficients　of　variation　were　less　than　8.7　and　9.3%　for　STR　detection,　respectively.　In　addition,　the　methodology　was　validated　with　STR　spiked　samples　including　honey,　milk,　kidney,　and　muscle,　receiving　a　good　correspondence　with　the　results　obtained　from　high-performance　liquid　chromatography　(HPLC).　©　2011　American　Chemical　Society.