Estradiol

Accordingly, the storage stability of the proposed QD nano-bioprobe was investigated. When the QD nano-bioprobe was stored in a refrigerator at 4 ^oC and measured at 3 day intervals, the decrease in the average maximum signal response in the absence of the analyte was<10% for the 17β-estradiol aptamer after 45 days of storage. Meanwhile, even when the average signal response for the 17β-estradiol specific aptamer slightly decreased, the QD nano-biosensor specific response was unaffected because all measurements were normalized with respect to the blank signal at the beginning of the daily analysis, and the signal shifts in the blank and sample measurements were generally the same. Thus, the developed QD-based aptasensor had sufficient stability. The stability and robustness of the QD nano-bioprobe was highly advantageous compared with other assays reported for 17β-estradiol, which also indicated the reliability of the proposed aptasensor for 17β-estradiol measurements.

The four metalloporphyrin–estradiol conjugates bound to the antibody 7A3 with a 2/1 stoichiometry, showing that, despite the bulky porphyrin, the estradiol anchor was still well accommodated by the antibody. The dissociation constants for the 4 metalloporphyrin–estradiol–7A3 complexes remained quite good, when compared to the affinity of the antibody for estradiol (KD ≈ 10^-9M), with respective KD values of 4× 10^-7M and 2 × 10^-6M for the Fe- and Mn(TMPyP)–estradiol–7A3 complexes and 2 × 10^-6 M and 9 × 10^-6M for the Fe– and Mn(TpSPP)–estradiol–7A3 complexes. The nature of the porphyrin (cationic or anionic), as well as that of the metal inserted had thus little influence on the association of the cofactor with the antibody.

However, metabolomics studies on osteoporosis models mainly focus on the effect of estrogen deficiency on the metabolome, and the effects of estradiol intervention is little researched. In addition, current biofluid (blood, urine etc.)metabolomics studies could merely provide downstream consequences caused by estradiol exposure, while lack of site and cell-specific effects evaluation. Evaluation of site- and cell-specific effects is particularly important for understanding the interaction mechanism between stimulus and targets. Using well-designed in vitro assays would provide complementary evidence for the in vivo studies, and give an insight into the specific interaction mechanism between estradiol and osteoporosis-related cells.

Recently, aptamer-based electrochemical biosensors and aptamer-based optical biosensors have been developed for simple estradiol detection. However, because 17b-estradiol is almost insoluble in water, watermiscible organic solvents are required in these methods to dissolve estradiol, and the distribution ratio of each component needs to be carefully optimized to ensure that estradiol is completely dissolved. Thus, these assays usually require multi-step complicated procedures. These limitations compromise the advantages of detection simplicity fromaptamers, and hinder the extensive application of such detection approaches.