A sensitive aptasensor based on molybdenum carbide nanotubes and label-free aptamer for detection of bisphenol A

Bisphenol A contamination in Hilsa shad and assessment of potential health hazard: A pioneering investigation in the national river Ganga, India

The anadromous Hilsa, often known as the "Queen of Fishes" (Tenualosa ilisha), is the most valuable fishery in the Ganga-Hooghly delta estuary. Although BPA exposure has been shown to be harmful to aquatic organisms, no research has looked at the effects of BPA on the commercially valuable Hilsa shad of river Ganga. To close this information vacuum, we examined BPA levels in Hilsa fish from the Ganga estuary. Liver, muscle, kidney, and gonads were all positive for BPA among the Hilsa fish of all ages. Liver BPA levels were highest in adult males (272.16 ± 0.38 ng/g-dw), and lowest in juveniles (5.46 ± 0.06 ng/g-dw). BPA concentrations in the Hilsa shad muscle were highest in reproductively mature females (196.23 ± 0.41 ng/g-dw). The study also discovered a correlation between fish development and BPA exposure, with higher levels of BPA being identified in adult Hilsa species. This is the first study to look at the impact of BPA pollution on aquatic ecosystems and fisheries, and it showed that Hilsa shad is contaminated with BPA and poses health hazards to human beings. The results, which demonstrate BPA contamination, are useful for protecting Hilsa in the river Ganga.

Recent Advances of Seed-Mediated Growth of Metal Nanoparticles: from Growth to Applications

Unprecedented advances in metal nanoparticle synthesis have paved the way for broad applications in sensing, imaging, catalysis, diagnosis, and therapy by tuning the optical properties, enhancing catalytic performance, and improving chemical and biological properties of metal nanoparticles. The central guiding concept for regulating the size and morphology of metal nanoparticles is identified as the precise manipulation of nucleation and subsequent growth, often known as seed-mediated growth methods. However, since the growth process is sensitive not only to the metal seeds but also to capping agents, metal precursors, growth solution, growth/incubation time, reductants, and other influencing factors, the precise control of metal nanoparticle morphology is multifactorial. Further, multiple reaction parameters are entangled with each other, so it is necessary to clarify the mechanism by which each factor precisely regulates the morphology of metal nanoparticles. In this review, to exploit the generality and extendibility of metal nanoparticle synthesis, the mechanisms of growth influencing factors in seed-mediated growth methods are systematically summarized. Second, a variety of critical properties and applications enabled by grown metal nanoparticles are focused upon. Finally, the current progress and offer insights on the challenges, opportunities, and future directions for the growth and applications of grown metal nanoparticles are reviewed.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

Selective and ratiometric fluorescence sensing of bisphenol A in canned food based on portable fluorescent test strips

In this study, a conversion method and molecular imprinting technology were used to design molecularly imprinted polymers (MIP)-based ratiometric fluorescence test papers. The ZnO quantum dots (ZnO QDs) acted as the background quantum dots and ZIF-8 raw material. Carbon dots (CDs) were used as the identification signals. The imprinting layer achieved a selective function. Therefore, a ZnO@ZIF-8/CDs@MIPs sensor was designed for the detection of Bisphenol A (BPA). The sensor exhibited a fast response time for BPA detection. In addition, the sensor demonstrated that effective detection of BPA can still be achieved in complex environments. The detection limit of this sensor was 0.778 nM with a linear range of 0-60 nM. The corresponding test solutions exhibited clear changes from blue to yellow. The selectivity experiments results demonstrated that ZnO@ZIF-8/CDs@MIPs only exhibit excellent selective recognition effect for BPA. ZnO@ZIF-8/CDs@MIPs-2 was used for the detection of BPA in canned food and compared with the results of HPLC detection of BPA. The two spiked recovery ranges were 96.58-102.04% and 97.43-103.82%, respectively. In addition, the prepared ZnO@ZIF-8/CDs@MIPs-2 test paper visually recognized BPA under ultraviolet light. This study provides guidelines for the design and application of fluorescent test papers for quick detection in practical applications.

An Overview of Aptamer-Based Sensor Platforms for the Detection of Bisphenol-A

Endocrine disruptive compounds are natural or anthropogenic environmental micropollutants that alter the function of the endocrine system ultimately damaging the metabolism. Bisphenol A (BPA) is the most common of these pollutants and it is often used in epoxy coatings and polycarbonates as a plasticizer. Therefore, monitoring BPA levels in different environments is very important and challenging. In recent years, an increasing number of BPA detection methods have been proposed. This article presents a critical review of aptamer-based electrochemical, fluorescence-based, colorimetric, and several other BPA detection platforms published in the last decade. Furthermore, a statistical evaluation has been made using principle component analysis showing analytical performance parameters do not create very different clusters. Comparisons to other BPA detection methods are also presented so that the reader has an overall literature overview.

Green Synthesis of ZnO/BC Nanohybrid for Fast and Sensitive Detection of Bisphenol A in Water

A nanohybrid of zinc oxide and biochar (ZnO/BC) with high conductivity was green synthesized using a simple hydrothermal method, and utilized for the sensitive detection of bisphenol A (BPA) by coating the nanohybrid film on an electrode of glassy carbon. The ZnO/BC presented greatly improved electrocatalytic performance and electron transfer ability compared to the zinc oxide and biochar. The ZnO/BC film-coated electrode could detect the BPA in aqueous solution within 3 min while neglected interference from higher concentrations of regularly existing ions and similar concentrations of estradiol (E2), phenol, dichlorophenol (DCP), and ethinylestradiol (EE2). Under optimal conditions, the linear range of BPA detection was 5 × 10−7~1 × 10−4 mol/L, with a detection limit of 1 × 10−7 mol/L, and the detection sensitivity was 92 mA/M. In addition, the ZnO/BC electrode could detect BPA in a real water sample with good signal recovery. This electrode, with the advantages of an easy preparation, low cost, and fast response time, could be potentially applicable for environmental monitoring.

Aptamer-Based Biosensors for the Analytical Determination of Bisphenol A in Foodstuffs

Bisphenol A (BPA) is a synthetic compound utilized to manufacture plastics for Food Contact Materials (FCMs) or resins for the inside of food containers. Since it was recognized as an Endocrine-Disrupting Chemical (EDC), its implications in pathologies, such as cancer, obesity, diabetes, immune system alterations, and developmental and mental disorders, have been widely documented. Diet is considered the main source of exposure for humans to BPA. Consequently, continuous monitoring of the levels of BPA in foods is necessary to assess the risk associated with its consumption in one’s diet. So far, many reviews have been published on biosensors and aptamer-based biosensors, but none of them focus on their applications in their analyses of bisphenols in food matrices. With this review, the authors aim to fill this gap and to take a snapshot of the current state-of-the-art research on aptasensors designed to detect BPA in food matrices. Given that a new TDI value has recently been proposed by the EFSA (0.04 ng/kg), the search for new sensitive tools for the quantitative analysis of BPA is more topical and urgent than ever. From this perspective, aptasensors prove to be a good alternative to traditional analytical techniques for determining BPA levels in food.

A fluorescent aptasensor based on berberine for ultrasensitive detection of bisphenol A in tap water

The residues of bisphenol A (BPA) in food packaging and water systems have a potential impact on human health; therefore, its analysis and detection have drawn scientists' attention. In this work, based on the change in fluorescence intensity resulting from the conformational switch of a berberine/BPA-aptamer system in the presence and absence of BPA, an ultra-sensitive fluorescence aptasensing system is proposed, in which BPA-aptamer is employed as the identification unit and berberine as the fluorescent probe. Various factors affecting the detection of BPA, including the concentration of the fluorescent probe, BPA-aptamer, BPA, pH, system stability time and other experimental conditions, were investigated in detail. Under the optimal experimental conditions, the fluorescence intensity of the sensing system of berberine/BPA-aptamer exhibited a good linear correlation with the BPA concentration in the range of 0-1300 μM with a LOD of 32 nM. The proposed fluorescent sensing system also exhibited excellent recoveries of 92.4-102.3% in tap water samples and showed good application prospects for the analysis and detection of BPA.

Nanomaterial based aptasensors for clinical and environmental diagnostic applications

Nanomaterials have been exploited extensively to fabricate various biosensors for clinical diagnostics and food & environmental monitoring. These materials in conjugation with highly specific aptamers (next-gen antibody mimics) have enhanced the selectivity, sensitivity and rapidness of the developed aptasensors for numerous targets ranging from small molecules such as heavy metal ions to complex matrices containing large entities like cells. In this review, we highlight the recent advancements in nanomaterial based aptasensors from the past five years also including the basics of conventionally used detection methodologies that paved the way for futuristic sensing techniques. The aptasensors have been categorised based upon these detection techniques and their modifications viz., colorimetric, fluorometric, Raman spectroscopy, electro-chemiluminescence, voltammetric, impedimetric and mechanical force-based sensing of a multitude of targets are discussed in detail. The bio-interaction of these numerous nanomaterials with the aptameric component and that of the complete aptasensor with the target have been studied in great depth. This review thus acts as a compendium for nanomaterial based aptasensors and their applications in the field of clinical and environmental diagnosis.

Simple and rapid detection of bisphenol A using a gold nanoparticle-based colorimetric aptasensor

A colorimetric aptasensor was developed for the simple and rapid detection of bisphenol A (BPA). The aptasensor was designed to consist of colloidal gold nanoparticles (AuNPs) and a BPA-specific 24-bp aptamer. The AuNP-aptamer conjugates underwent an electrolyte-induced aggregation in the presence of sub-ppb levels of BPA. The surface plasmon resonance shift of AuNPs facilitated a color change from red to blue upon aggregation, which was visually observed by the naked eye. The corresponding visual limit of detection of BPA was as low as 1 pg/mL (0.004 nM). The aptasensor also achieved a selective detection of BPA over a variety of BPA analogs. The applicability of the aptasensor was verified via a successful detection of BPA in a single grain of rice. This result indicates that the colorimetric aptasensor can be used in a screening procedure for food and environmental monitoring, with reliable performance to sub-ppb levels of BPA detection.

Exploration of Catalytic Nucleic Acids on Porphyrin Metalation and Peroxidase Activity by in Vitro Selection of Aptamers for N-Methyl Mesoporphyrin IX

To develop a novel light-up probe and DNAzyme, we selected aptamers for N-methyl mesoporphyrin IX (NMM), a common fluorogenic analogue of coenzyme hemin, by a modified affinity chromatography-based systematic evolution of ligands by exponential enrichment (SELEX). Two truncated aptamers Nm1 and Nm2 with low micromolar dissociation constants (0.75 and 13.27 μM) were obtained after 11 rounds of selection and the final minimized 39-mer aptamer Nm2.1 showed 24-fold fluorescence enhancement for NMM at saturated concentration. Study of the interactions between aptamers and other porphyrin compounds by circular dichroism (CD) and absorption spectroscopy showed that Nm1 mainly assembled as a stem-loop structure, which exhibited a catalytic activity for the metal insertion reaction of mesoporphyrin IX with 3.3-fold rate enhancement. In contrast, the G-rich Nm2 and Nm2.1 were likely to form G-quadruplexes in the presence of alkali metal cations (K⁺ and Na⁺), which displayed excellent peroxidase activity exhibiting 19-fold higher catalytic efficiency than hemin alone. The selected aptamers could therefore be used as novel light-up fluorescent probes and DNAzymes by pairing with porphyrin compounds that have potential to construct sensors for various applications.

Upconversion fluorescent aptasensor for bisphenol A and 17β-estradiol based on a nanohybrid composed of black phosphorus and gold, and making use of signal amplification via DNA tetrahedrons

This study describes an upconversion fluorescent aptasensor based on black phosphorus nanohybrids and self-assembled DNA tetrahedrons dual-amplification strategy for rapid detection of the environmental estrogens bisphenol A (BPA) and 17β-estradiol (E2). Tetrahedron complementary DNAs (T-cDNAs) were self-assembled in an oriented fashion on a 2D nanohybrid composed of black phosphorus (BP) and gold to give a materials of architecture BP-Au@T-cDNAs. In parallel, core-shell upconversion nanoparticles were modified with aptamers (UCNPs@apts) and used as capture probes. On complementary pairing, the BP-Au@T-cDNA quench the fluorescence of UCNPs@apts (measured at an excitation wavelength 808 nm and at main emission peaks at 545 nm and 805 nm.) Compared with single-stranded probes based on black phosphorus and gold, the dual-amplification strategy increases quenching efficiency by nearly 25%-30% and reduces capture time to 10 min. This is due to the higher optical absorption of 2D nanohybrid and the reduction of steric hindrance by T-cDNAs. Exposure to BPA or E2 cause the release of UCNPs@apts from the BP-Au@T-cDNAs due to stronger binding between aptamer and analyte. Hence, fluorescence recovers at 545 nm for BPA and 805 nm for E2. Based on these findings, a dually amplified aptamer assay was constructed that covers the 0.01 to 100 ng mL^-1 BPA concentration range, and the 0.1 to 100 ng mL^-1 E2 concentration range. The detection limits are 7.8 pg mL^-1 and 92 pg mL^-1, respectively. This method was applied to the simultaneous determination of BPA and E2 in spiked samples of water, food, serum and urine. Graphical abstract Schematic presentation of novel quenching probes designed by tetrahedron complementary DNAs oriented self-assembled on the surface of black phosphorus/gold nanohybrids. Combined with aptamer-modified upconversion nanoparticles, a dual-amplification self-assembled fluorescence nanoprobe was constructed for simultaneous detection of BPA and E2.

Quantitative screening for endocrine-disrupting bisphenol A in consumer and household products using NanoAptamer assay

The NanoAptamer assay is a bisphenol A (BPA) quantification method that uses magnetic beads, quantum dot nanoparticles, and a BPA-specific aptamer. In this study, screening of various consumer and household products for BPA was demonstrated utilizing the NanoAptamer assay. First, the experimental conditions suitable for BPA detection using the NanoAptamer assay were examined in terms of incubation time, temperature, and buffer composition. The range of BPA quantification via the NanoAptamer assay was determined to be 0.005-1000 ng/mL of BPA. The selectivity was confirmed by detecting BPA in an analog mixture containing bisphenol S and bisphenol F. Finally, a leaching experiment using 20 consumer and household products classified into 4 categories was performed to demonstrate the capability of the NanoAptamer assay for BPA detection. The experiment was validated by high-performance liquid chromatography analysis (correlation coefficient, r = 0.99).

Critical Review: DNA Aptasensors, Are They Ready for Monitoring Organic Pollutants in Natural and Treated Water Sources?

There is a growing need to monitor anthropogenic organic contaminants detected in water sources. DNA aptamers are synthetic single-stranded oligonucleotides, selected to bind to target contaminants with favorable selectivity and sensitivity. These aptamers can be functionalized and are used with a variety of sensing platforms to develop sensors, or aptasensors. In this critical review, we (1) identify the state-of-the-art in DNA aptamer selection, (2) evaluate target and aptamer properties that make for sensitive and selective binding and sensing, (3) determine strengths and weaknesses of alternative sensing platforms, and (4) assess the potential for aptasensors to quantify environmentally relevant concentrations of organic contaminants in water. Among a suite of target and aptamer properties, binding affinity is either directly (e.g., organic carbon partition coefficient) or inversely (e.g., polar surface area) correlated to properties that indicate greater target hydrophobicity results in the strongest binding aptamers, and binding affinity is correlated to aptasensor limits of detection. Electrochemical-based aptasensors show the greatest sensitivity, which is similar to ELISA-based methods. Only a handful of aptasensors can detect organic pollutants at environmentally relevant concentrations, and interference from structurally similar analogs commonly present in natural waters is a yet-to-be overcome challenge. These findings lead to recommendations to improve aptasensor performance.

DNA-fueled target recycling-induced two-leg DNA walker for amplified electrochemical detection of nucleic acid

Taking advantage of the homogeneous and heterogeneous electrochemical biosensors, a simple, sensitive, and selective electrochemical biosensor is constructed by combining entropy-driven amplification (EDA) with DNA walker. This electrochemical biosensor realizes the biorecognition and EDA operation in homogeneous solution, which is beneficial to improve the recognition and amplification efficiency. A two-leg DNA walker generated by EDA can walk on the surface of gold electrode for cleaving the immobilized substrate DNA and releasing the electroactive labels, giving rise to a significant decrease of the electrochemical signal. The immobilization of the electroactive labels ensures the reproducibility and reliability of the biosensor. The present cascade amplification assay can be applied to detect target DNA with a detection limit of 0.29 fM, and base mutations can be easily distinguished. Moreover, the proposed electrochemical biosensor shows a satisfactory performance for the detection of target DNA in human serum. Thus, the novel electrochemical biosensor holds promising potential for a future application in disease diagnosis.

Practical Application of Aptamer-Based Biosensors in Detection of Low Molecular Weight Pollutants in Water Sources

Water pollution has become one of the leading causes of human health problems. Low molecular weight pollutants, even at trace concentrations in water sources, have aroused global attention due to their toxicity after long-time exposure. There is an increased demand for appropriate methods to detect these pollutants in aquatic systems. Aptamers, single-stranded DNA or RNA, have high affinity and specificity to each of their target molecule, similar to antigen-antibody interaction. Aptamers can be selected using a method called Systematic Evolution of Ligands by EXponential enrichment (SELEX). Recent years we have witnessed great progress in developing aptamer selection and aptamer-based sensors for low molecular weight pollutants in water sources, such as tap water, seawater, lake water, river water, as well as wastewater and its effluents. This review provides an overview of aptamer-based methods as a novel approach for detecting low molecular weight pollutants in water sources.

Extraction and detection of bisphenol A in human serum and urine by aptamer-functionalized magnetic nanoparticles

A new type of magnetic nanoparticles (MNPs), as the absorbents of bisphenol A (BPA), was prepared by functionalization of Fe₃O₄@SiO₂ with BPA-specific aptamer in this work. ssDNA aptamer was immobilized on the Fe₃O₄@SiO₂ surface through biotin-avidin interactions, playing a role of the specific probe for BPA. The resultant materials (Apt-MNPs) exhibited outstanding magnetic responsibility and can be separated efficiently by the magnetic field. Experimental results also showed that Apt-MNPs had large adsorption capacity and high competitive selectivity for the targeted compound BPA. Furthermore, Apt-MNPs were adopted as the specific absorbents to extract and enrich BPA from human serum and urine samples. Therefore, an efficient detection method of BPA was developed in combination with high-performance liquid chromatography (HPLC). The linearity of the method was over a range of 5-10,000 ng mL^-1 with a correlation coefficient of 0.99997, and the limit of detections (LODs) for serum and urine were 2.0 and 1.0 ng mL^-1, respectively. The recoveries of BPA in the spiked human serum and urine samples were 90.8 ± 7.3% (RSD) and 92.3 ± 1.5%, respectively. Our results demonstrated that Apt-MNPs were high-performance adsorbents for extracting and enriching BPA, resulting in fast and efficient detection of BPA in serum and urine samples. Graphical abstract Aptamer-MNPs were effective for BPA separation from serum and urine.

Recent Progress in Biosensors for Environmental Monitoring: A Review

The environmental monitoring has been one of the priorities at the European and global scale due to the close relationship between the environmental pollution and the human health/socioeconomic development. In this field, the biosensors have been widely employed as cost-effective, fast, in situ, and real-time analytical techniques. The need of portable, rapid, and smart biosensing devices explains the recent development of biosensors with new transduction materials, obtained from nanotechnology, and for multiplexed pollutant detection, involving multidisciplinary experts. This review article provides an update on recent progress in biosensors for the monitoring of air, water, and soil pollutants in real conditions such as pesticides, potentially toxic elements, and small organic molecules including toxins and endocrine disrupting chemicals.

Smart DNA Machine for Carcinoembryonic Antigen Detection by Exonuclease III-Assisted Target Recycling and DNA Walker Cascade Amplification

A synthetic DNA machine performs quasi-mechanical movements in response to external intervention, suggesting the promise of constructing sensitive and specific biosensors. Herein, a smart DNA walker biosensor for label-free detection of carcinoembryonic antigen (CEA) is developed for the first time by a novel cascade amplification strategy of exonuclease (Exo) III-assisted target recycling amplification (ERA) and DNA walker. ERA as the first stage of amplification generates the walker DNA, while the autonomous traveling of the walker DNA on the substrate-modified silica microspheres as the second stage of amplification produces an ultrasensitive fluorescent signal with the help of N-methylmesoporphyrin IX (NMM). The DNA machine as a biosensor could be applied for transducing and quantifying signals from isothermal molecular amplifications, avoiding the complicated reporter elements and thermal cycling. The present biosensor achieves a detection limit of 1.2 pg·mL^-1 within a linear range of 10 pg·mL^-1 to 100 ng·mL^-1 for CEA, along with a favorable specificity. The practical applicability of the biosensor is demonstrated by the detection of CEA in human serum with satisfactory results; thus, it shows great potential in clinical diagnosis.