Silver nanoparticles in size of 8.0 nm was prepared by the trisodium citrate and used to label goat anti-human fibrinogen. In the pH 5.8 Na 2 HPO 4 -NaH 2 O 4 buffer solution (PBS) and in the presence of polyethylene glycol (PEG) and KCl, the immune reaction between silver-labeled goat anti-human fibrinogen and fibrinogen took place and led the resonance scattering intensity at 465 nm (I 465 ) to decreasing. The I 465 decreased intensity was linear to the fibrinogen concentration in the range from 0.067 to 1.67 μg/mL, with a detection limit of 0.024 μg/mL. This method was applied to determination of fibrinogen in human plasma, with satisfactory results. silver-nanoparticle, fibrinogen, goat anti-human immune fibrinogen serum, resonance scattering spectral assay Fibrinogen(Fg) was synthesized by liver and megalocaryocyte, and it is a serum glucoprotein which participating in last hemagglutination process, and is also the highest content of coagulation albumen in the plasma [1] . According to the reported [2] , Fg gene defect can led Fg decreased or disappeared, and led Fg function abnormality, and also showing hemorrhagia in clinic. Recently, epidemiological researches indicated that it has close relation with cardiovascular diseases, thrombus disease, diabetesmellitus, malignancy disease, Fg increased is associated with the one risk of coronary heart disease. Its detmination was used as a diagnostic index of congealed blood disease [3][4][5] . Recently, three types of assays have been reported for measuring Fg, including immunoassay [6,7] , functional assay [3,[8][9][10][11][12] and physical-chemical analysis. Among this methods, immunoassay such as hemorrhagic, immunonephelometric, enzyme-linked immunosorbent [13] , radioimmannoassay, rocket immunoelectrophoresis, radical immunodiffusion, has good selectivity, high sensitivity, with detection limit of about 0.25 mg/L. It is not only simple but also playing an important role in diagnosis of some Fg abnormal disease. Functional assays include weight assay [8] , spectrometric assay [9,10] , dynamic Fg assay [3] , and von Clauss [11] , with low sensitivity. Physical-chemical methods include salting-out, heating-precipitation and eletrophoresis. Biuret was commonly used as the colored reagent of salting-out assay, with a linear range of 0-10 g/L Fg and detection limit of 0.5 mg/L. These methods are rapid and simple, but they have poor selectivity and much influence factors. In addition to, a PT calculation assay was reported for determination of 0.490 to 2.45 g/L Fg. It is economic, simple and rapid [14] . When Fg is normal, this method has good correlation with von Clauss, but when Fg decreased, the results were higher than normal values [15] .Silver colloidal was as a chromatic reagent, in order to improve the sensitivity for immune reaction [16] . At present, there has been reported for determining protein, with silver colloidal enhanced function [17,18] , but its quantitative analysis is few and there is no report about assay of protein using silver-la...
