Highly sensitive colorimetric detection of 17β-estradiol using split DNA aptamers immobilized on unmodified gold nanoparticles

Abstract

Gold nanoparticle (AuNP) based colorimetric aptasensor have been developed for many analytes recently largely because of the ease of detection, high sensitivity, and potential for high-throughput analysis. Most of the target aptamers for detection have short sequences. However, the approach shows poor performance in terms of detection sensitivity for most of the long-sequence aptamers. To address this problem, for the first time, we split the 76 mer aptamer of 17β-estradiol into two short pieces to improve the AuNP based colorimetric sensitivity. Our results showed that the split P1 + P2 still retained the original 76 mer aptamer's affinity and specificity but increased the detection limit by 10-fold, demonstrating that as low as 0.1 ng/mL 17β-estradiol could be detected. The increased sensitivity may be caused by lower aptamer adsorption concentration and a lower affinity to the AuNPs of a short single-strand DNA (ssDNA) sequence. Our study provided a new way to use long-sequence aptamers to develop a highly sensitive AuNP-based colorimetric aptasensor.

Figure 1. Schematic illustration of a gold nanoparticle based colorimetric aptasensor to detect 17β-estradiol using split aptamers.

Figure 2. Secondary structure of the 17β-estradiol aptamer illustrated in the report of Kim et al..

The red arrow indicates the splitting site, where P1 and P2 are shown.

Figure 3. Comparison of the minimum aptamer concentrations of the 76 mer aptamer and split P1 + P2 to stabilize AuNPs with 125 mM NaCl.

Figure 4. Photographs of the AuNP solutions adsorbing the 76 mer aptamer and split P1 + P2 under different concentrations of 17β-estradiol.

Figure 5. Sensitivity for detecting 17β-estradiol with the original 76 mer aptamer or split P1 + P2 adsorbed onto AuNPs.

(A) Absorption spectra of the AuNP solutions with 76 mer aptamer adsorption under different 17β-estradiol concentrations. (B) Typical calibration curve for 17β-estradiol with the 76 mer aptamer adsorbed AuNPs. (C) Absorption spectra of the AuNP solutions with P1 + P2 adsorption under different 17β-estradiol concentrations. (D) Typical calibration curve for 17β-estradiol with P1 + P2 adsorbed AuNPs.

Figure 6. Control experiments to verify that the split P1 and P2 can retain partial affinity to 17β-estradiol.

Figure 7. Selectivity evaluation of the P1 + P2 or original 76 mer aptamer based AuNP colorimetric assay.