Dynamic light scattering and fluorescence dual-signal sensing of cancer antigen-125 via recognition of the polymerase chain reaction product with gold nanoparticle probe

Cancer antigen 125 (CA - 125) is an important biomarker for the diagnosis of ovarian cancer. In this paper, oligonucleotide 5′-GACAGGCCCGAAGGAATAGATAATACGACTCACTATAGGGAGACAAGAATAAACGCTCAA-3′ (oligo 1) contains an aptamer of CA - 125, and was designed partly complementary to oligonucleotide 5′-CTCTCTCTCCACCTTCTTCTTTGAGCGTTTATTCTTGTCT-3′ (oligo 2). Oligo 1 · oligo 2 was extended with the Klenow fragment (exo−) polymerase for further polymerase chain reaction (PCR) processes in the presence of two primers: deoxyribose nucleoside triphosphate and Taq polymerase. Single-stranded DNA was produced at two sides of the PCR product by introducing a C18 spacer into the two primers, which could hybridize with AuNPs-DNA probes, investigated by dynamic light scattering and fluorescence. The addition of CA - 125 can interrupt the hybridization between oligo 1 and oligo 2, causing the average diameter of AuNPs-DNA probes to decrease with the increase of CA-125 within the range of 5 fg mL−1 – 50 ng mL−1. The linear regression equation of this relationship was D = 430.48–49.60 log10C, with a detection limit of 1.1 fg mL−1. Fluorescein molecules were modified at the end of the forward primer. The fluorescence intensity of the PCR product can be measured simultaneously, with the fluorescence intensity increasing linearly with the logarithm of CA-125 concentration within a linear range from 10 fg mL−1 to 50 ng mL−1, with a detection limit of 1.5 fg mL−1.