Split aptamer-based sandwich-type ratiometric biosensor for dual-modal photoelectrochemical and electrochemical detection of 17β-estradiol

Background As one of the most potent environmental estrogens, 17 beta-estradiol (E2), which can be enriched into organisms through the food chain and cause harmful biological effects in humans, has been frequently detected in the water environment of the world. High performance liquid chromatography (HPLC) and gas chromatograohy-mass spectrometry (GC/MS) have been widely used for quantification of E2. Despite excellent accuracy, tedious pretreatment and expensive instruments result in their limited application. It is clear that there is an urgent need to establish simple, sensitive and accurate methods for the determination of E2.Results A split aptamer-based sandwich-type ratiometric biosensor based on split aptamer was developed by coupling photoelectrochemical and electrochemical assays for E2 detection. For analysis, the two fragments of split aptamer recognized E2 by forming sandwich structure, which triggered hybridization chain reaction (HCR) to produce double-stranded DNA (dsDNA) with CdTe quantum dots (QDs) labeled hairpin DNA. The resultant dsDNA can further absorb methylene blue (MB) to sensitize CdTe QDs for an enlarged photocurrent (I-PEC) and output a redox current of I-MB, and both of them acted as response signals for detection; [Fe(CN)(6)](3-/4-) probe produced redox current of I-[Fe(CN)6](3-/4-) as reference signal. Using I-MB/I-[Fe(CN)6](3-/4-) and I-PEC/I-[Fe(CN)6](3-/4-) as yardsticks, the developed split aptamer-based sandwich-type ratiometric biosensor provides two linear ranges of 0.1-5000 pg mL(-1) for I-MB/I-[Fe(CN)6](3-/4-) and 0.1-10000 pg mL(-1) for I-PEC/I-[Fe(CN)6](3-/4-) with detection limits of 0.06 pg mL(-1) and 0.02 pg mL(-1), respectively.Significance These results of the biosensor are benefiting from the coupling of photoelectrochemical (PEC) and electrochemical (EC) assays as well as the unique cooperative recognition mechanism of split aptamer. This method not only enabled the biosensor to be successfully applied to the determination of E2 in lake water, but also broadens the prospects for the realization of sensitive and accurate detection of E2.

Automated summary

The study developed a split aptamer-based sandwich-type ratiometric biosensor for the detection of 17 beta-estradiol (E2) using photoelectrochemical and electrochemical assays. The biosensor utilized split aptamer fragments to recognize E2 and trigger a hybridization chain reaction, resulting in the production of double-stranded DNA labeled with CdTe quantum dots. This DNA complex was able to sensitize CdTe quantum dots and generate response signals for E2 detection. The developed biosensor demonstrated high sensitivity and accuracy with two linear ranges and low detection limits.