title: A novel, label-free immunosensor for the detection of alpha-fetoprotein using functionalised gold nanoparticles.
abstract: OBJECTIVE
  Novel immunoassay methods based on electrochemical sensors have been developed, but most of these immunosensors are unsuitable for clinical detection because their preparation requires complicated chemical procedures and because their detection sensitivity is restricted. In order to develop a highly sensitive, label-free amperometric sensor for immunoassays, we synthesised novel, functionalized gold nanoparticles (SV-GNP) by covalently capping the surface of gold nanoparticles (GNP) with 1,1'-bis-(2-mercapto)-4,4'-bipyridinium dibromide, a kind of sulfhyrdryl viologen (SV).
  
  
  METHODS
  We fabricated an immunosensor in a multi-step fashion, by first coating the SV-GNP onto a glassy carbon electrode surface; the resulting electrode core could then adsorb a suitable antibody in a second step to afford the desired immunosensor. alpha-fetoprotein (AFP) was used as a model analyte in this work.
  
  
  RESULTS
  The anti-AFP/SV-GNP-modified electrode was sensitive to AFP with a linear relationship between 1.25 and 200 ng/mL and a correlation coefficient of 0.9983; the detection limit at a signal to noise ratio of 3 was 0.23 ng/mL under optimal conditions. In addition, the proposed immunosensor exhibited good sensitivity, selectivity, stability and long-term maintenance of bioactivity.
  
  
  CONCLUSIONS
  The described immunosensor preparation and immunoassay methods offer promise for label-free, simple, and cost-effective analysis of biological samples.
authors.affiliation: Chongqing Key Laboratory of Analytical Chemistry, College of Chemistry and Chemical Engineering, Southwest University, Chongqing, PR China.
authors.forename: Wenbin
authors.initials: W
authors.lastname: Liang
authors.forename: Weijing
authors.initials: W
authors.lastname: Yi
authors.forename: Shuhui
authors.initials: S
authors.lastname: Li
authors.forename: Ruo
authors.initials: R
authors.lastname: Yuan
authors.forename: An
authors.initials: A
authors.lastname: Chen
authors.forename: Sha
authors.initials: S
authors.lastname: Chen
authors.forename: Guiming
authors.initials: G
authors.lastname: Xiang
authors.forename: Chuanmin
authors.initials: C
authors.lastname: Hu
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation / Q000379:methods; D002244:Carbon / Q000737:chemistry; D004563:Electrochemistry / Q000379:methods; D004566:Electrodes; D006046:Gold / Q000737:chemistry*; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation / Q000379:methods; D053768:Metal Nanoparticles / Q000737:chemistry*; D015394:Molecular Structure; D012680:Sensitivity and Specificity; D013499:Surface Properties; D000509:alpha-Fetoproteins / Q000032:analysis*
chemical_list: D000509:alpha-Fetoproteins; D002244:Carbon; D006046:Gold