Effect Of The Tip Length Of Multi-branched AuNFs On The Detection Performance Of Immunochromatographic Assays

The present paper has studied the effect of the tip length of gold nanoparticles?Au NP? on the detection performance of immunochromatographic assay?ICA?. Three types of Au NPs with average diameters of 30–40 nm, including conventional gold nanospheres?Au NSs, no tip?, short-tip gold nanoflowers?Au NFs, tip length, 7–8 nm?,and long-tip Au NFs?the tip length 13–15 nm?, were synthesized according to reduction methods and seeding mediated growth method, respectively. Three types of Au NPs were used as labeled probes in competitive inmmunochromatographic assays for detection of Ochratoxin A?OTA?. The T/C ratio method was suggested as the model of the quantitative strip. The effects of the tip length of Au NPs on the detection performance of ICA including the binding kinetics, the consumption of Au NP probes for each strip, the cut-off limit of the qualitative strips by the naked eye, the half maximal inhibitory concentration?IC50?, detection limit?LOD?, and the interpretation time for quantitative analysis, were systematically evaluated.The optimal parameters for preparation of three kinds of strips were as follows:1.2 mg/m L of BSA-OTA conjugates and 0.4 mg/m L of donkey anti-mouse antibodies were used to dispense onto the NC membrane as test and control lines, respectively.The labeled amounts of anti-OTA ascitic fluids on three kinds of Au NP solutions?50pmol/L? were 4.5 ?g/m L. The dispensation rate of three kinds of Au NP-m Abs probes on the conjugation pad were 4 ?L/cm, 2 ?L/cm and 0.8 ?L/cm to ensure the same optical density?OD? on the test line of three kinds of strips for OTA negative sample.Under the optimal conditions, the interpretation times and the T/C ratios of Au NS-,short-tip Au NF-, and long-tip Au NF-based strips for OTA quantitative analysis were17 min, 15 min, 12 min, and 0.67 ± 0.03, 0.95 ± 0.01, 1.29 ± 0.02, indicating that long-tip Au NFs as labeled probes in ICA showed a higher immunological kinetic efficiency and a higher affinity to OTA-BSA conjugate on the test line. The cut-off limits of three kinds of trips for naked eye were 5 ng/m L?3 ng/m L, and 2 ng/m L,respectively. The standard curves of three kinds of strips for OTA quantitativedetection were described by a logistic four-parameter equation. The regression equation of Au NS-based strip is y = 145.6914/[1 +?x/2.9255?-1.0554]-1.8735?R² =0.9903?, where y is the competitive inhibition rate?1-B/B0? × 100% and x is the OTA concentrations from 0 ng/m L to 5 ng/m L. The regression equation of short-tip Au NF-based strip is y = 259.0171/[1+?x/5.4329?-0.7548]-1.1688?R²=0.9937?, and the equation of long-tip Au NF-based strip is y =226.9642/[1+?x/1.9879?-^1.0601]+0.0713?R² =0.9960?. The IC50 and LOD values of three kinds of strips were 1.68 ng/m L, 0.84 ng/m L, 0.61 ng/m L and 0.29 ng/m L, 0.1 ng/m L, 0.07ng/m L, respectively. The values of cut-off limit, IC50 and LOD of the long-tip Au NF-based strip were 2.5, 2.75, and 4.14 times lower than those of the conventional Au NS-based strip.In summary, long-tip Au NFs exhibit significant application potential as an alternative to traditional Au NSs for labeled probes in the ICA platform.