Effect of different-sized gold nanoflowers on the detection performance of immunochromatographic assay for human chorionic gonadotropin detection

Traditional colloidal gold based immunochromatographic assays (ICAs) that use 20–40 nm gold nanospheres (AuNSs) as signal reporters have low sensitivity given the insufficient brightness of AuNSs. Gold nanoflowers (AuNFs) possess high optical brightness and strong target binding affinity because of their multibranched structures and large specific surface areas. Thus, ICAs with AuNF reporters have better sensitivity than ICAs with conventional AuNSs reporters. In addition, large AuNFs exhibit higher optical absorbance than small AuNFs. To elucidate the effect of AuNF size on the sensitivity of sandwich ICA, AuNFs with five different sizes of 33, 47, 79, 152, and 195 nm were synthesized and used as reporters in ICA strips for pregnancy diagnosis based on the detection of human chorionic gonadotropin (HCG). Medium-sized AuNFs with diameters of 47–79 nm showed the highest sensitivity of 9 mIU/mL. When used to test actual HCG-spiked urine samples, the 47 nm AuNF-based ICA showed two independent linear correlations in low (9 mIU/mL ~ 288 mIU/mL) and high (288 mIU/mL ~ 2304 mIU/mL) HCG concentrations for HCG quantitative detection. The intra- and interassay recovery rates for HCG spiked urine samples ranged from 81.19% to 114.44% with the coefficient of variation (CV) from 3.29% to 8.08%. These results collectively indicate that the AuNF-based ICA has high accuracy. In addition, the proposed AuNF-based ICA method exhibited excellent selectivity for HCG determination. In summary, medium-sized AuNFs can serve as optimal ICA labels in the high-sensitivity detection of disease-related protein biomarkers.