Detection Of 17β-estradiol Research Articles

Highly Responsive Cryogel Based Sensing Platform by Encapsulating Programmed DNA for Colorimetric Detection of 17β-estradiol

Responsive hydrogels show obvious superiorities when being employed at detection owing to their polymeric networks and optical properties. Albeit important, the slow response of traditional hydrogels against targets limits their further applications, and enhancing the responsiveness of hydrogel is therefore imperative. Herein, a cryogel with hierarchical structures was designed through adjusting the hydrogel structure by the freezing process to improve the responsive properties, and fabricated for rapid analysis of 17β-estradiol (E2). The cryogel encapsulating the DNA hairpins rapidly adsorbed the complementary DNA isolated from the aptamer in the presence of E2 and activated an efficient hybridization chain reaction (HCR). After integration with a smartphone system, a portable colorimetric sensing platform was created for sensitive detection of E2 with a low detection limit of 0.5 nM. Our work provides a promising way for highly responsive hydrogel-based biosensor design, and broadens their applications in rapid and portable target detection.

Molecularly Imprinted Polymers Electrochemical Sensing: The Effect of Inhomogeneous Binding Sites on the Measurements. A Comparison between Imprinted Polyaniline versus nanoMIP-Doped Polyaniline Electrodes for the EIS Detection of 17β-Estradiol.

Molecularly imprinted polymers (MIPs) are synthetic receptors made by template-assisted synthesis. MIPs might be ideal receptors for sensing devices, given the possibility to custom-design selectivity and affinity toward a targeted analyte and their robustness and ability to withstand harsh conditions. However, the synthesis of MIP is an inherently random process that produces a statistical distribution of binding sites, characterized by a variety of affinities. This is verified both for bulk MIP materials and for MIP's thin layers. In the present work, we aimed at assessing the effects of inhomogeneous versus homogeneous imprinted binding sites on electrochemical sensing measurements, and the possible implications on the sensor's performance. In the example of an Electrochemical Impedance Spectroscopy (EIS) sensor for the 17β-estradiol (E2) hormone, the scenario of inhomogeneous binding sites was studied by modifying electrodes with an E2-MIP polyaniline (PANI) thin layer, called the "Imprinted PANI layer". In contrast, the condition of discrete and uniform binding sites was epitomized by electrodes modified with a thin PANI layer purposedly doped with E2-MIP nanoparticles (nanoMIPs), which were referred to as "nanoMIP-doped PANI". The behaviors of the two EIS sensors were compared. Interestingly, the sensitivity of the nanoMIP-doped PANI was almost twice with respect to that of the imprinted PANI layer, strongly suggesting that the homogeneity of the binding sites has a fundamental role in the sensor's development. The nanoMIP-doped PANI sensor, which showed a response for E2 in the range 36.7 pM-36.7 nM and had a limit of detection of 2.86 pg/mL, was used to determine E2 in wastewater.

Glow-type luminol chemiluminescence based on a supramolecular enhancer of cyclodextrin

BackgroundChemiluminescence (CL) bioassay is one of the most advanced and used detection method in clinical diagnosis and biomedical research because of the advantages of low background, easy operation, and wide-field imaging without a light source or microscope. The luminol/hydrogen peroxide/horseradish peroxidase (luminol/H2O2/HRP) system is the most popular CL system, but its application in high-throughput imaging detection is challenged due to its low luminescence efficiency and flash-type emission which is difficult in ensuring the reproducibility and consistency of detection results. ResultsWe reported a glow-type CL system of luminol@CD/H2O2/HRP by using a supramolecular enhancer of cyclodextrin (CD). This luminol@CD/H2O2/HRP system exhibited a luminescence lifetime of 41 min for sensitive and accurate imaging analysis. The long-lasting CL emission was attributed to the formation of a 1:1 host–guest complex between luminol and CD, which could stabilize the emitter and effectively reduce nonradiative relaxation. The formation of luminol@CD complex was determined through NMR experiments and theoretical analysis. Under optimum conditions, the luminol@CD/H2O2/HRP system showed higher sensitivity and much better precision than classical luminol/H2O2/HRP system for imaging detection of HRP. Especially, this glow-type luminol@CD/H2O2/HRP system realized CL imaging of microwell arrays on microfluidic chips. In addition, the luminol@CD/H2O2/HRP system was successfully applied for point-of-care detection of 17β-estradiol based on a competitive mechanism of host–guest recognition. SignificanceAn efficient CL system is crucial for obtaining reproducible and consistent results for accurate detection. Our luminol@CD/H2O2/HRP system emitted strong and persistent luminescence, resulting in reliability and efficiency at both CL macroscopic and microscopic imaging detection. We expected the luminol@CD/H2O2/HRP CL system to be applied in various detection fields.

Non-enzymatic detection of 17β-estradiol in real samples using PANI@CeO2 nanocomposite

Herein, we developed a non-enzymatic biosensing platform using polyaniline (PANI) polymer matrix grafted with CeO2. The one-pot synthesized nanocomposite has been used for the detection of 17β-estradiol (E2). The homogeneous distribution of CeO2 onto the PANI matrix leads to an increase in surface area, conductivity, and effectiveness of the synthesized nanocomposite PANI@CeO2. The PANI@CeO2 nanocomposite was characterized using structural and morphological techniques. Further, the electrode fabrication was performed electrophoretically by depositing the PANI@CeO2 nanocomposite onto the ITO electrode. The PANI@CeO2/ITO showed enhanced electrochemical behavior as compared to PANI/ITO. Detection of E2 was carried out using the differential pulse voltametric technique (DPV). Linearity has been observed through the detection range of 1 µM–100 µM with LOD = 2.15 µM. The developed biosensor has been found to be stable and selective towards E2. It has been successfully utilized for the detection of E2 in real samples like tap water and human urine samples. Thus, this research encourages its use for more applications in clinical diagnosis and biomedical sciences.

Biofuel cell-based self-powered immunosensor for detection of 17β-estradiol by integrating the target-induced biofuel release and biogate immunoassay.

A novel biofuel cell (BFC)-based self-powered electrochemical immunosensing platform was developed by integrating the target-induced biofuel release and biogate immunoassay for ultrasensitive 17β-estradiol (E2) detection. The carbon nanocages/gold nanoparticle composite was employed in the BFCs device as the electrode material, through which bilirubin oxidase and glucose oxidase were wired to form the biocathode and bioanode, respectively. Positively charged mesoporous silica nanoparticles (PMSN) were encapsulated with glucose molecules as biofuel and subsequently coated by the negatively charged AuNPs-labelled anti-E2 antibody (AuNPs-Ab) serving as a biogate. The biogate could be opened efficiently and the trapped glucose released once the target E2 was recognized and captured by AuNPs-Ab due to the decreased adhesion between the antigen-antibody complex and PMSN. Then, glucose oxidase oxidized the glucose to produce a large number of electrons, resulting in significantly increased open-circuit voltage (EOCV). Promisingly, the proposed BFC-based self-powered immunosensor demonstrated exceptional sensitivity for the detection of E2 in the concentration range from 1.0pgmL-1 to 10.0ngmL -1, with a detection limit of 0.32pgmL-1 (S/N = 3). Furthermore, the prepared BFC-based self-powered homogeneous immunosensor showed significant potential for implementation as a viable prototype for a mobile and an on-site bioassay system in food and environmental safety applications.

Laser-Induced Electrochemical Biosensor Modified with Graphene-Based Ink for Label-Free Detection of Alpha-Fetoprotein and 17β-Estradiol.

In this research, a novel electrochemical biosensor is proposed based on inducing graphene formation on polyimide substrate via laser engraving. Graphene polyaniline (G-PANI) conductive ink was synthesized by planetary mixing and applied to the working zone of the developed sensor to effectively enhance the electrical signals. The laser-induced graphene (LIG) sensor was used to detect alpha-fetoprotein (AFP) and 17β-Estradiol (E2) in the phosphate buffer saline (PBS) buffer and human serum. The electrochemical performance of the biosensor in determining these biomarkers was investigated by differential pulse voltammetry (DPV) and chronoamperometry (CA). In a buffer environment, alpha-fetoprotein (AFP) and 17β-Estradiol detection range were 4-400 ng/mL and 20-400 pg/mL respectively. The experimental results showed a limit of detection (LOD) of 1.15 ng/mL and 0.96 pg/mL for AFP and estrogen, respectively, with an excellent linear range (R2 = 0.98 and 0.99). In addition, the designed sensor was able to detect these two types of biomarkers in human serum successfully. The proposed sensor exhibited excellent reproducibility, repeatability, and good stability (relative standard deviation, RSD = 0.96%, 1.12%, 2.92%, respectively). The electrochemical biosensor proposed herein is easy to prepare and can be successfully used for low-cost, rapid detection of AFP and E2. This approach provides a promising platform for clinical detection and is advantageous to healthcare applications.

Enzymatic biofuel cells-based self-powered electrochemical biosensor for detection of 17β-estradiol based on dual-enzyme cascade amplification and bioconjugate

Self-powered electrochemical biosensors (SPEB) based on enzymatic biofuel cells (EBFC) have garnered significant attention due to their distinctive characteristic of not necessitating the source of external power supply. This study developed a novel EBFC-based SPEB by incorporating dual-enzyme cascade amplification and bioconjugate for extremely precise detection of 17β-estradiol (E2). The carbon nanocages/gold nanoparticles composite was employed as substrate to immobilize bilirubin oxidase (BOD) and complementary ssDNA (csDNA) to form bioconjugate. The carbon nanotubes/gold nanoparticles composite was used in the EBFC device as the electrode material, through which glucose oxidase (GOD) and E2 aptamer were wired to form the bioanode and biocathode, respectively. The biocathode further linked with bioconjugate via a hybridization reaction between E2 aptamer and csDNA. The bioconjugate integrates the recognition and signal probes for homogeneous electrochemical assay of targets, which released from biocathode once the target E2 was recognized and hindered the transfer of electrons produced by GOD on bioanode. Thus, the open-circuit voltage (EOCV) of the EBFC-based SPEB dramatically decreased, exhibiting exceptional sensitivity for the detection of E2 over a concentration range from 10 pg mL−1 to 20 ng mL−1, with a detection limit of 3.3 pg mL−1 (S/N = 3). Furthermore, the prepared EBFC-based SPEB showed significant potential for implementation as a viable prototype for a mobile and an on-site bioassay system in food and environmental safety applications.

Engineering of dual recognition functional aptamer-molecularly imprinted polymeric solid-phase microextraction for detecting of 17β-estradiol in meat samples

In this study, an enhanced selective recognition strategy was employed to construct a novel solid-phase microextraction fiber coating for the detection of 17β-estradiol, characterized by the combination of aptamer biorecognition and molecularly imprinted polymer recognition. Benefiting from the combination of molecularly imprinted and aptamer, aptamer-molecularly imprinted (Apt-MIP) fiber coating had synergistic recognition effect. The effects of pH, ion concentration, extraction time, desorption time and desorption solvent on the adsorption capacity of Apt-MIP were investigated. The adsorption of 17β-estradiol on Apt-MIP followed pseudo-second order kinetic model, and the Freundlich isotherm. The process was exothermic and thermodynamically spontaneous. Compared with polymers that only rely on imprinted recognition, non-imprinted recognition or aptamer affinity, Apt-MIP had the best recognition performance, which was 1.30–2.20 times that of these three materials. Furthermore, the adsorption capacity of Apt-MIP for 17β-estradiol was 885.36–1487.52 times than that of polyacrylate and polydimethylsiloxane/divinylbenzone commercial fiber coatings. Apt-MIP fiber coating had good stability and could be reused for more than 15 times. Apt-MIP solid-phase microextraction coupled with high-performance liquid chromatography was successfully applied to the determination of 17β-estradiol in pork, chicken, fish and shrimp samples, with satisfactory recoveries of 79.61 %–105.70 % and low limits of detection (0.03 μg/kg). This work provides new perspectives and strategies for sample pretreatment techniques based on molecular imprinting technology and improves analytical performance.

A liposome encapsulated methylene blue-mediated electrochemical and UV–visible dual mode split-type immunoassay for the detection of 17β-estradiol

Herein, we fabricated an electrochemical (EC) and UV–visible absorption (UV–vis) dual mode split-type immunoassay for the detection of 17β-estradiol (E2), which was mediated by liposome encapsulated methylene blue (MB@lip). MB molecule acted as the probe in the EC and UV–vis absorption dual mode detections, and its release was controlled by liposome. The competitive immune recognition was conducted between the E2 in the sample and E2 conjugated bovine serum protein (E2-BSA) adsorbed on the 96-wells plate in combining with E2 antibody labeled with MB@lip (E2-Ab/MB@lip). MB molecule could be released from the resulting immune composite of E2-BSA/E2-Ab/MB@lip in the presence of Triton X-100, and quantified by UV–vis and EC methods. The three-dimensional cross-linked reduced graphene oxide/Ti3C2 (3D-rGO/Ti3C2) aerogel was prepared through hydrothermal method, then complexed with the electroactive anthraquinone (AQ) and used as the electrode modified material. The AQ/3D-rGO/Ti3C2 composite had high surface area and provided abundant adsorption sites for MB, and the displacement/competitive behavior between AQ and MB could dexterously achieve the ratiometric EC detection of E2. In addition, the inherent blue color of MB allowed it to be analyzed by UV–vis absorption method. The proposed dual mode detection method exhibited broad linear ranges of 0.1 pg mL−1 to 50 ng mL−1 (by UV–vis) and 0.03 pg mL−1 to 50 ng mL−1 (by EC) for E2 detection, and the detection limits were 0.023 pg mL−1 (S/N = 3) and 8.0 fg mL−1 (S/N = 3), respectively. Moreover, the proposed immunoassay exhibited good practicability and was applied to monitor E2 in milk and serum successfully.

Molecularly imprinted ratiometric fluorescence sensor for visual detection of 17β-estradiol in milk: A generalized strategy toward imprinted ratiometric fluorescence construction.

17β-Estradiol (E2) is the typical endocrine disruptor of steroidal estrogens and is widely used in animal husbandry and dairy processing. In the environment, even lower concentrations of E2 can cause endocrine dysfunction in organisms. Herein, we have developed a novel molecularly imprinted ratiometric fluorescent sensor based on SiO2-coated CdTe quantum dots (CdTe@SiO2) and 7-hydroxycoumarin with a post-imprint mixing strategy. The sensor selectively detected E2 in aqueous environments due to its two fluorescent signals with a self-correction function. The sensor has been successfully used for spiking a wide range of real water and milk samples. The results showed that the sensor exhibited good linearity over the concentration range 0.011-50 μg/L, obtaining satisfactory recoveries of 92.4-110.6% with precisions (RSD) < 2.5%. Moreover, this sensor obtained an ultra-low detection limit of 3.3ng/L and a higher imprinting factor of 13.66. By using estriol (E3), as a supporting model, it was confirmed that a simple and economical ratiometric fluorescent construction strategy was provided for other hydrophobic substances.

Non-Faradaic aptasensor based on NH2-GO/PPy for the detection of 17β-estradiol

Non-Faradaic aptasensor based on NH2-GO/PPy for the detection of 17β-estradiol

Design and Validation of a Short Novel Estradiol Aptamer and Exploration of Its Application in Sensor Technology.

The specific and sensitive detection of 17β-estradiol (E2) is critical for diagnosing and treating numerous diseases, and aptamers have emerged as promising recognition probes for developing detection platforms. However, traditional long-sequence E2 aptamers have demonstrated limited clinical performance due to redundant structures that can affect their stability and recognition ability. There is thus an urgent need to further optimize the structure of the aptamer to build an effective detection platform for E2. In this work, we have designed a novel short aptamer that retains the key binding structure of traditional aptamers to E2 while eliminating the redundant structures. The proposed aptamer was evaluated for its binding properties using microscale thermophoresis, a gold nanoparticle-based colorimetric method, and electrochemical assays. Our results demonstrate that the proposed aptamer has excellent specific recognition ability for E2 and a high affinity with a dissociation constant of 92 nM. Moreover, the aptamer shows great potential as a recognition probe for constructing a highly specific and sensitive clinical estradiol detection platform. The aptamer-based electrochemical sensor enabled the detection of E2 with a linear range between 5 pg mL-1 and 10 ng mL-1 (R2 = 0.973), and the detection capability of a definite low concentration level was 5 pg mL-1 (S/N = 3). Overall, this novel aptamer holds great promise as a valuable tool for future studies on the role of E2 in various physiological and pathological processes and for developing sensitive and specific diagnostic assays for E2 detection in clinical applications.

Prepared Three-Dimensional Flowerlike MoS2/Ag@rGO Nanocomposite as a Self-Cleaning SERS Substrate for the Trace Detection of 17β-Estradiol in Environmental Water

Prepared Three-Dimensional Flowerlike MoS₂/Ag@rGO Nanocomposite as a Self-Cleaning SERS Substrate for the Trace Detection of 17β-Estradiol in Environmental Water

Fluorescence nanoprobes bearing low temperature-derived biochar nanoparticles as efficient quenchers for the detection of single-stranded DNA and 17β-estradiol and their analytical potential.

Bagasse-derived biochar nanoparticles obtained under a low pyrolysis condition (400 °C) were first revealed to be capable of highly efficiently quenching the fluorescence of 6-carboxyfluorescein, with a significantly improved quenching rate constant over that of other quenchers and high-temperature prepared ones, and were designated as bagasse-derived quencher nanoparticles (BQNPs). The BQNPs are suitable for the construction of fluorescence nanoprobes, taking advantage of their various beneficial properties, including low cost, environmental friendliness, high dispersibility, and rich functional groups that allow their easy and versatile molecular modification. They were demonstrated to be capable of stably binding single-stranded oligonucleotides through both adsorption and covalent interactions and were utilized for the construction of both BQNPs/DNA and BQNPs/aptamer probes. The BQNPs/DNA probe had strong resistance against degradation by deoxyribonuclease I and showed high precision and selectivity for the detection of single-stranded DNA, with a limit of detection of 1.04 nM. Moreover, the BQNPs/aptamer probe demonstrated the rapid and sensitive detection of 17β-estradiol (E2) with a limit of detection of 0.4 ng mL-1 with no cross-reactivity with the analogues, and it was also applied for real environmental sample detection and demonstrated reasonable signal recoveries. Benefiting from their strong quenching ability, low cost, and great dispersibility, the BQNPs show great potential for the development of cost-effective and sensitive fluorescence sensors.

A self-powered electrochemical aptasensor for the detection of 17β-estradiol based on carbon nanocages/gold nanoparticles and DNA bioconjugate mediated biofuel cells.

17β-Estradiol (E2) is an important endogenous estrogen, which disturbs the endocrine system and poses a threat to human health because of its accumulation in the human body. Herein, a biofuel cell (BFC)-based self-powered electrochemical aptasensor was developed for E2 detection. Porous carbon nanocage/gold nanoparticle composite modified indium tin oxide (CNC/AuNP/ITO) and glucose oxidase modified CNC/AuNP/ITO were used as the biocathode and bioanode of BFCs, respectively. [Fe(CN)6]3- was selected as an electroactive probe, which was entrapped in the pores of positively charged magnetic Fe3O4 nanoparticles (PMNPs) and then capped with a negatively charged E2 aptamer to form a DNA bioconjugate. The presence of the target E2 triggered the entrapped [Fe(CN)6]3- probe release due to the removal of the aptamer via specific recognition, which resulted in the transfer of electrons produced by glucose oxidation at the bioanode to the biocathode and produced a high open-circuit voltage (EOCV). Consequently, a "signal-on" homogeneous self-powered aptasensor for E2 assay was realized. Promisingly, the BFC-based self-powered aptasensor has particularly high sensitivity for E2 detection in the concentration range of 0.5 pg mL-1 to 15 ng mL-1 with a detection limit of 0.16 pg mL-1 (S/N = 3). Therefore, the proposed BFC-based self-powered electrochemical aptasensor has great promise to be applied as a successful prototype of a portable and on-site bioassay in the field of environment monitoring and food safety.

A novel fluorescent sensor based on aptamer recognition and DNA walker amplification strategy and its determination of 17β-estradiol

17β-Estradiol (E2) is a common environmental endocrine and excessive estrogen will disturb the endocrine balance of human body and lead to diseases because of its accumulation in human body. The main aim of this study is to determine the trace amount of E2 in various foods. Based on aptamer specific recognition, DNA walker molecular machine and Exonuclease III-assisted dual cycle signal amplification technology, a fluorescent aptamer sensor was constructed and applied to the detection of 17β-estradiol. Atomic force microscopy (AFM) and polyacrylamide gel electrophoresis (PAGE) were used to verify the feasibility of DNA walker participating in the reaction. Under the optimal conditions, 17β-estradiol concentration showed a good linear relationship with fluorescence in the range of 5.0 × 10−10–1.8 × 10−8 M, and the detection limit was 5.6 × 10−11 M. The fluorescent aptamer sensor established in this study has good selectivity, simple operation and good specificity, and the results of its application in the determination of milk samples are satisfactory. Research findings revealed that the E2 concentration in water and milk is less than the safe limits, indicating the foods in the market are safe and can be consumed. Though the foods are safe in present content, the health risk still exists because of continuous intake of trace E2.

Competitive ECL immunosensor for ultrasensitive 17β-estradiol detection based on synergistic promotion strategy using CdSe–ZnSe nanocomposites

A novel competitive ECL immunosensor for detection of 17β-Estradiol (E2) has been fabricated successfully. CdSe–ZnSe nanocomposites (CdSe–ZnSe NCs) with high catalytic properties, large surface area and good conductivity were used synergistically as the ECL nanocarriers of Pt nanoparticles (PtNPs). The ECL intensity of CdSe–ZnSe NCs increased and stabilized with luminol-PtNPs (luminol-PtNPs@CdSe–ZnSe NCs) because of electron transfer. To achieve the successful assembling of competitive ultrasensitive ECL immunosensor with high sensitivity and synergistic effect, Ag@TiO2 core-shell was introduced as label. Ag@TiO2 acted as a signal amplifier and also exhibited the high catalytic activity towards H2O2. This firmly anchored the E2 Antigen with covalent bond and converted the longer wavelength radiations to shorter wavelength. Under optimized conditions, our proposed strategy quantify the selective and reliable analysis of E2 with detection limit of 2.51 fg/mL (S/N = 3) within the linear range of 0.0001–30 ng/mL. The assembled synergistic strategy-based ECL immunosensor manifested the promising sensitivity, selectability along with high level of repeatability. Thus, the fabricated ECL immunosensor has potential valuable application for E2 detection along with many other environmental pollutants.

Defective porphyrin-based metal-organic framework nanosheets derived from V2CTx MXene as a robust bioplatform for impedimetric aptasensing 17β-estradiol

An electrochemical aptasensor was prepared for the efficient, sensitive, and selective detection of 17β-estradiol. The sensor was based on a defective two-dimensional porphyrin-based metal-organic framework derived from V2CTx MXene. The resulting metal-organic framework nanosheets benefited from the advantages of V2CTx MXene nanosheets and porphyrin-based metal-organic framework, two-dimensional porphyrin-based metal-organic framework nanosheets demonstrated amplified electrochemical response and enhanced aptamer-immobilization ability compared with V2CTx MXene nanosheets. The sensor's detection limit was ultralow at 0.81fgmL-1 (2.97 fM), and the 17β-estradiol concentration range was wide, thereby outperforming most reported aptasensors. The high selectivity, superior stability and reproducibility, and excellent regeneration performance of the constructed aptasensor indicated its remarkable potential application for 17β-estradiol determination in diverse real samples. This aptasensing strategy can be used to analyze other targets by replacing the corresponding aptamer.

Ratiometric upconversion-luminescence in-situ sampling aptasensing platform integrated with smartphone-based device for visual detection of 17β-estradiol

Rapid initial screening of health markers and food hazards are crucial indicators for ensuring human well-being. Hence, an upconversion-luminescence based aptasensing platform for the in-situ sampling of hazards has been proposed with portable equipment for point-of-care testing (POCT). The aptasensing platform consists of a polymethylmethacrylate needle and a paper-based microfluidic strip patterned with a sacrificial valve, paraffin barriers, and three independent detection zones. The detection zones were assembled with a luminescence resonance energy transfer system constructed by the core/shell/shell structure of upconversion nanoparticles (UCNPs) as the donor, SYBR Green Ⅰ as the acceptor with an aptamer bridge. The biosensing platform has been extended for 17β-estradiol to validate its feasibility in a dual-mode signal readout system based on smartphone imaging and spectrometer. Under the optimal conditions, good linear relationships were achieved based on images (0.05–200 ng/mL) and ratiometric spectra (0.02–200 ng/mL), respectively. Thus, the biosensing platform with portable equipment might provide an economic and viable route for POCT.

Highly sensitive colorimetric aptasensor for 17β-estradiol detection in milk based on the repetitive-loop aptamer.

Trace of 17β-estradiol (E2) contamination in food has been a concern for its negative impacts on human health, leading to the need for an E2-monitoring system. This work reported a new simple, sensitive, and colorimetric E2 detection based on the designed repetitive-loop aptamer and gold nanoparticles (AuNPs). The designed aptamers (L2-L5) exhibited a higher binding capability to E2 than the original truncated aptamer (L1). Although L3-L5 aptamers exhibited the highest binding capability, only L3-aptasensor demonstrated the sensitive detection of E2 in a range of 0.05-0.8nM, with the limit of detection at 13.1pM. The developed L3-aptasensor was 7.7-folds more sensitive for E2 detection than the L1-aptasensor. It selectively detected E2, but not the other tested chemicals with similar structures: progesterone, genistein, diethylstilbestrol, bisphenol A, and chloramphenicol. The L3-aptasensor efficiently detected E2 spiked in milk samples within the precision acceptance criterion of recovery rates (100.1%-113.0%) and the relative standard deviations (5.24%-11.06%). These results demonstrated the development of a new aptasensor based on the designed repetitive-loop aptamer that could enhance E2-detection sensitivity and be potentially used for detecting E2 in milk samples with high accuracy and reliability.