A universal label-free fluorescent aptasensor based on Ru complex and quantum dots for adenosine, dopamine and 17β-estradiol detection

Fabrication of an innovative electrochemical sensor based on graphene-coated silver nanoparticles decorated over graphitic carbon nitride for efficient determination of estradiol

Monitoring small amount of endocrine disrupting chemical, estradiol (E2) residue in environmental and biological samples is extremely important because of its possible connections to breast and prostate malignancies and gastrointestinal disorders. The newly synthesized graphene-coated silver nanoparticles (GN@Ag) decorated on graphitic carbon nitride (g-C3N4)-based hybrid nanomaterial (GN@Ag/g-C3N4) was used to modify glassy carbon electrode (GCE) for electroanalytical measurement of E2. The GN@Ag/g-C3N4 nanocomposite prepared through ultrasonic-assisted reflux methodology was characterized using various physicochemical methods. The scanning electron microscopy and transmission electron microscopy have shown that GN@Ag nanoparticles were decorated and randomly dispersed over g-C3N4 sheets. The exceptional electrochemical response towards the oxidation of E2 was observed through cyclic voltammetry due to the quick electron transfer ability and superior conductivity of GN@Ag/g-C3N4/GCE. The detection limit was found to be 0.002 μM with wide linear range of E2 concentration (0.005-8.0 μM) along with remarkable stability of the fabricated electrode for 21 days showing 91% retention in initial current. The kinetic parameters such as catalytic rate constant and diffusion coefficient for E2 were estimated to be 1.1 × 105 M-1 s-1 and 1.9 × 10-4 cm2 s-1, respectively, by employing chronoamperometry. The proposed sensor also demonstrated its practical applicability for E2 determination in environmental and biological samples with a recovery range of 95-104%. Furthermore, the developed sensing platform is much better compared to reported methods in terms of simplicity, accuracy, detection limit, linearity range, and usefulness in real sample for E2 sensing.

A review of biomolecules conjugated lanthanide up-conversion nanoparticles-based fluorescence probes in food safety and quality monitoring applications

Upconversion nanoparticles (UCNPs) are known to possess unique characteristics, which allow them to overcome a number of issues that plague traditional fluorescence probes. UCNPs have been employed in a variety of applications, but it is arguably in the realm of optical sensors where they have shown the most promise. Biomolecule conjugated UCNPs-based fluorescence probes have been developed to detect and quantify a wide range of analytes, from metal ions to biomolecules, with great specificity and sensitivity. In this review, we have given much emphasis on the recent trends and progress in the preparation strategies of bioconjugated UCNPs and their potential application as fluorescence sensors in the trace level detection of food industry-based toxicants and adulterants. The paper discusses the preparation and functionalisation strategies of commonly used biomolecules over the surface of UCNPs. The use of different sensing strategies namely heterogenous and homogenous assays, underlying fluorescence mechanisms in the detection process of food adulterants are summarized in detail. This review might set a precedent for future multidisciplinary research including the development of novel biomolecules conjugated UCNPs for potential applications in food science and technology.

17β-estradiol biosensors based on different bioreceptors and their applications

17β-Estradiol (E2) is a critical sex steroid hormone, which has significant effects on the endocrine systems of both humans and animals. E2 is also believed to play neurotrophic and neuroprotective roles in the brain. Biosensors present a powerful tool to detect E2 because of their small, efficient, and flexible design. Furthermore, Biosensors can quickly and accurately obtain detection results with only a small sampling amount, which greatly meets the detection of the environment, food safety, medicine safety, and human body. This review focuses on previous studies of biosensors for detecting E2 and divides them into non-biometric sensors, enzyme biosensors, antibody biosensors, and aptamer biosensors according to different bioreceptors. The advantages, disadvantages, and design points of various bioreceptors for E2 detection are analyzed and summarized. Additionally, applications of different bioreceptors of E2 detection are presented and highlight the field of environmental monitoring, food and medicine safety, and disease detection in recent years. Finally, the development of E2 detection by biosensor is prospected.

Chitosan stabilized copper iodide nanoparticles enabled nano-bio-engineered platform for efficient electrochemical biosensing of dopamine

Neurodegenerative disorders are one of the significant challenges to the aging society, as per the United Nations, where 1 in 6 people globally over 65 years of age are expected to suffer by 2050. The exact pathophysiological root of these disorders is although not known adequately, but reduced dopamine (most significant neurotransmitters) levels have been reported in people affected by Parkinson's disease. Sensitive detection and effective monitoring of dopamine can help to diagnose these neurodegenerative disorders at a very early stage, which will help to properly treat these disorders and slow down their progression. Therefore, it is crucial to detect physiological and clinically acceptable amounts of dopamine with high sensitivity and selectivity in basic pathophysiology research, medication, and illness diagnosis. Here in this present investigation, nano-bio-engineered stable chitosan stabilized copper iodide nanoparticles (CS@CuI NPs) were synthesized to engineer the active biosensing platform for developing dopamine biosensors. Initially, the as-synthesized nano-bio-engineered CS@CuI NPs were subjected to its drop-casting onto an Indium tin oxide (ITO) conducting glass substrate. This substrate platform was then utilized to immobilize tyrosinase (Tyr) enzyme by drop-casting to fabricate Tyr/CS@CuI NPs/ITO bioelectrode for the ultrasensitive determination of dopamine. Several techniques were used to characterize the structural, optical, and morphological properties of the synthesized CS@CuI NPs and Tyr/CS@CuI NPs/ITO bioelectrode. Further, the as-prepared bioelectrode was evaluated for its suitability and electrocatalytic behaviour towards dopamine by cyclic voltammetry. A perusal of the electroanalytic results of the fabricated biosensor revealed that under the optimized experimental conditions, Tyr/CS@CuI NPs/ITO bioelectrode exhibits a very high electrochemical sensitivity of 11.64 μA μM-1 cm-2 towards dopamine with the low limit of detection and quantification of 0.02 and 0.386 μM, respectively. In addition, the fabricated bioelectrode was stable up to 46 days with only 4.82 % current loss, reusable till 20 scans, and it also performed effectively while real sample analysis. Therefore, the nano-bio-engineered biosensor platform being reported can determine deficient dopamine levels in a very selective and sensitive manner, which can help adequately manage neurodegenerative disorders, further slowing down the disease progression.

Fluorescent-Based Neurotransmitter Sensors: Present and Future Perspectives

Neurotransmitters (NTs) are endogenous low-molecular-weight chemical compounds that transmit synaptic signals in the central nervous system. These NTs play a crucial role in facilitating signal communication, motor control, and processes related to memory and learning. Abnormalities in the levels of NTs lead to chronic mental health disorders and heart diseases. Therefore, detecting imbalances in the levels of NTs is important for diagnosing early stages of diseases associated with NTs. Sensing technologies detect NTs rapidly, specifically, and selectively, overcoming the limitations of conventional diagnostic methods. In this review, we focus on the fluorescence-based biosensors that use nanomaterials such as metal clusters, carbon dots, and quantum dots. Additionally, we review biomaterial-based, including aptamer- and enzyme-based, and genetically encoded biosensors. Furthermore, we elaborate on the fluorescence mechanisms, including fluorescence resonance energy transfer, photon-induced electron transfer, intramolecular charge transfer, and excited-state intramolecular proton transfer, in the context of their applications for the detection of NTs. We also discuss the significance of NTs in human physiological functions, address the current challenges in designing fluorescence-based biosensors for the detection of NTs, and explore their future development.

Sensitive detection of 17β-estradiol at a picomolar level using an aptamer-assisted liquid crystal-based optical sensor

A liquid crystal (LC)-based aptasensor was developed that can detect 17β-estradiol (E2) at the picomolar level. This aptasensor is based on competitive reactions of the aptamer that interacts with cetyl trimethyl ammonium bromide (CTAB) and E2 at the aqueous/LC interface. The long alkyl chain of CTAB anchored the 4-cyano-4'-pentylbiphenyl (5CB) to a homeotropic state and controls the local anchoring depending on the extent of electrostatic interaction with the aptamer. Upon addition of the aptamer solution to the CTAB-saturated LC layer, LCs change from dark to bright optical response. This is due to the perturbed orientation of 5CB at the aqueous/LC interface as a result of electrostatic attraction of the cationic group of CTAB and the phosphate group of the aptamer. The conformational change of the aptamer due to specific binding with E2 weakens the electrostatic attraction between CTAB and aptamer. When specific binding becomes relatively dominant, CTAB induces the orientation of LCs to the homeotropic state, resulting in a dark optical image observed. We also analyzed the change in the optical response of LCs according to the interfacial events and compared the grayscale values of the optical image for each concentration of E2 to determine the detection limit. Accordingly, the detection limit of the E2 sensor was found to be 3.1 pM (0.8 pg/ml) in Tris-buffered saline (TBS), and 6.8 pM (1.9 pg/ml) in human urine. The LC-based optical aptasensor was thus shown to be highly sensitive and selective with no requirement for complex analysis equipment.

A "turn-on" fluorescence resonance energy transfer aptasensor based on carbon dots and gold nanoparticles for 17β-estradiol detection in sea salt

17β-estradiol is abused in the food industry. Excess 17β-estradiol can disturb the endocrine system or cause many diseases including obesity, diabetes, cardiac-cerebral vascular disease, and cancers in the human body. A "turn-on" fluorescence resonance energy transfer (FRET) aptasensor based on carbon dots (CDs) and gold nanoparticles (AuNPs) was developed for the detection of 17β-estradiol. A thiol-modified oligonucleotide was conjugated to AuNPs and amino modified oligonucleotide was linked to CDs. The 17β-estradiol aptamer was hybridized with the two oligonucleotides, shortening the distance between CDs and AuNPs. With 360 nm UV light excitation, FRET occurred between CDs and AuNPs. The system was "turn-off". When 17β-estradiol was detected, the aptamer specifically bound to 17β-estradiol, and the FRET system was destroyed, leading to the "turn-on" phenomenon. The fluorescence intensity recovery was detected in the concentration range of 400 pM to 5.5 μM. The limit of detection (LOD) was 245 pM. The FRET aptasensor demonstrated good selectivity for 17β-estradiol detection. Reasonable spiked recoveries were obtained in sea salt samples. It showed the potential for estrogen detection in food safety and environmental applications.

From Enzymatic Dopamine Biosensors to OECT Biosensors of Dopamine

Neurotransmitters are an important category of substances used inside the nervous system, whose detection with biosensors has been seriously addressed in the last decades. Dopamine, a neurotransmitter from the catecholamine family, was recently discovered to have implications for cardiac arrest or muscle contractions. In addition to having many other neuro-psychiatric implications, dopamine can be detected in blood, urine, and sweat. This review highlights the importance of biosensors as influential tools for dopamine recognition. The first part of this article is related to an introduction to biosensors for neurotransmitters, with a focus on dopamine. The regular methods in their detection are expensive and require high expertise personnel. A major direction of evolution of these biosensors has expanded with the integration of active biological materials suitable for molecular recognition near electronic devices. Secondly, for dopamine in particular, the miniaturized biosensors offer excellent sensitivity and specificity and offer cheaper detection than conventional spectrometry, while their linear detection ranges from the last years fall exactly on the clinical intervals. Thirdly, the applications of novel nanomaterials and biomaterials to these biosensors are discussed. Older generations, metabolism-based or enzymatic biosensors, could not detect concentrations below the micro-molar range. But new generations of biosensors combine aptamer receptors and organic electrochemical transistors, OECTs, as transducers. They have pushed the detection limit to the pico-molar and even femto-molar ranges, which fully correspond to the usual ranges of clinical detection of human dopamine in body humors that cover 0.1 ÷ 10 nM. In addition, if ten years ago the use of natural dopamine receptors on cell membranes seemed impossible for biosensors, the actual technology allows co-integrate transistors and vesicles with natural receptors of dopamine, like G protein-coupled receptors. The technology is still complicated, but the uni-molecular detection selectivity is promising.

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 V₂CT_x MXene. The resulting metal-organic framework nanosheets benefited from the advantages of V₂CT_x 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 V₂CT_x MXene nanosheets. The sensor's detection limit was ultralow at 0.81 fg mL^-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.

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 0.05-0.8 nM, with the limit of detection at 13.1 pM. 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.

Sensing High 17β-Estradiol Concentrations Using a Planar Microwave Sensor Integrated with a Microfluidic Channel

The global issue of pollution caused by endocrine-disrupting chemicals (EDCs) has been gaining increasing attention. Among the EDCs of environmental concern, 17β-estradiol (E2) can produce the strongest estrogenic effects when it enters the organism exogenously through various routes and has the potential to cause harm, including malfunctions of the endocrine system and development of growth and reproductive disorders in humans and animals. Additionally, in humans, supraphysiological levels of E2 have been associated with a range of E2-dependent disorders and cancers. To ensure environmental safety and prevent potential risks of E2 to human and animal health, it is crucial to develop rapid, sensitive, low cost and simple approaches for detecting E2 contamination in the environment. A planar microwave sensor for E2 sensing is presented based on the integration of a microstrip transmission line (TL) loaded with a Peano fractal geometry with a narrow slot complementary split-ring resonator (PF-NSCSRR) and a microfluidic channel. The proposed technique offers a wide linear range for detecting E2, ranging from 0.001 to 10 mM, and can achieve high sensitivity with small sample volumes and simple operation methods. The proposed microwave sensor was validated through simulations and empirical measurements within a frequency range of 0.5-3.5 GHz. The E2 solution was delivered to the sensitive area of the sensor device via a microfluidic polydimethylsiloxane (PDMS) channel with an area of 2.7 mm² and sample value of 1.37 µL and measured by a proposed sensor. The injection of E2 into the channel resulted in changes in the transmission coefficient (S₂₁) and resonance frequency (F_r), which can be used as an indicator of E₂ levels in solution. The maximum quality factor of 114.89 and the maximum sensitivity based on S₂₁ and F_r at a concentration of 0.01 mM were 1746.98 dB/mM and 40 GHz/mM, respectively. Upon comparing the proposed sensor with the original Peano fractal geometry with complementary split-ring (PF-CSRR) sensors without a narrow slot, several parameters were evaluated, including sensitivity, quality factor, operating frequency, active area, and sample volume. The results showed that the proposed sensor exhibited an increased sensitivity of 6.08% and had a 40.72% higher quality factor, while the operating frequency, active area, and sample volume showed decreases of 1.71%, 25%, and 28.27%, respectively. The materials under tests (MUTs) were analyzed and categorized into groups using principal component analysis (PCA) with a K-mean clustering algorithm. The proposed E2 sensor has a compact size and simple structure that can be easily fabricated with low-cost materials. With the small sample volume requirement, fast measurement with a wide dynamic range, and a simple protocol, this proposed sensor can also be applied to measure high E2 levels in environmental, human, and animal samples.

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).

A tag-free fluorescent aptasensor for tobramycin detection using a hybridization of three aptamer strands and SYBR Green I dye

In this study, a sensitive fluorescent method is designed to detect tobramycin (TOB) drug applying a hybrid structure of three aptamer strands and SYBR Green I (SGI) fluorescent dye as the bioreceptor segment and signal indicator, respectively. The preferential binding of the aptamers to TOB resulted in the collapse of the hybridized aptamer skeleton to the single strands. So, the intercalation of SGI molecules reduced that quenched the fluorescence response. The aptasensing assay provided the superior target specificity with a detection limit (LOD) of 0.153 pM and a wide linear dynamic range over 0.5 pM-300 μM. The aptasensor could successfully quantify TOB in human serum samples. The tag-free sensor with the remarkable advantages of simplicity, easy-to-use, cost-effectiveness, and high sensitivity is superior to be applicable for clinical samples.

Determination of adenosine by CRISPR-Cas12a system based on duplexed aptamer and molecular beacon reporter linked to gold nanoparticles

Adenosine as a potential tumor marker is of great value for clinical disease diagnosis. Since the CRISPR-cas12a system is only capable of recognizing nucleic acid targets we expanded the CRISPR-cas12a system to determine small molecules by designing a duplexed aptamer (DA) converting g-RNA recognition of adenosine to recognition of aptamer complementary DNA strands (ACD). To further improve the sensitivity of determination, we designed a molecule beacon (MB)/gold nanoparticle (AuNP)-based reporter, which has higher sensitivity than traditional ssDNA reporter. In addition, the AuNP-based reporter enables more efficient and fast determination. The determination of adenosine under 488-nm excitation can be realized within 7 min, which is more than 4 times faster than traditional ssDNA reporter. The linear determination range of the assay to adenosine was 0.5-100 μM with the determination limit of 15.67 nM. The  assay was applied to recovery determination of adenosine in serum samples with satisfactory results. The recoveries were between 91 and 106% and the RSD values of different concertation were below  4.8%. This sensitive, highly selective, and stable sensing system is expected to play a role in the clinical determination of adenosine and other biomolecules.

Exogenous dopamine improves resistance to Botryosphaeria dothidea by increasing autophagy activity in pear

Pear ring rot, a fungal disease caused by Botryosphaeria dothidea (B. dothidea), is one of the most damaging diseases in pear production, affecting fruit yield and causing economic losses. It is not clear whether dopamine, one of the catecholamines, has any role in pear ring rot resistance. In this study, we found that dopamine treatment of B. dothidea resulted in a significant upregulation of PbrTYDC expression compared to H₂O treatment (control) and reduced the levels of Hydrogen Peroxide (H₂O₂) and Superoxide Anion (O₂^-), increased Peroxidase (POD), Catalase (CAT), Superoxide Dismutase (SOD) and Phenylalanine Ammonia-Lyase (PAL) activities, and induced a significant upregulation of related gene expression. Dopamine treatment promoted the oxidationreduction capacity of the AsA-GSH cycle to scavenge Reactive Oxygen Species (ROS), increased the expression of autophagy-related genes and the accumulation of autophagic structures, and enhanced autophagic activity. Silencing PbrTYDC and PbrATG8 in pear increased H₂O₂ and·O₂^-, decreased POD, CAT and SOD activities and reduced resistance to B. dothidea, which was restored by dopamine treatment. In conclusion, exogenous dopamine enhances resistance to B. dothidea by increasing the antioxidant capacity and autophagic activity of pears, and this study provides new insights for subsequent studies on B. dothidea as well as autophagy.

3D printed neural tissues with in situ optical dopamine sensors

Engineered neural tissues serve as models for studying neurological conditions and drug screening. Besides observing the cellular physiological properties, in situ monitoring of neurochemical concentrations with cellular spatial resolution in such neural tissues can provide additional valuable insights in models of disease and drug efficacy. In this work, we demonstrate the first three-dimensional (3D) tissue cultures with embedded optical dopamine (DA) sensors. We developed an alginate/Pluronic F127 based bio-ink for human dopaminergic brain tissue printing with tetrapodal-shaped-ZnO microparticles (t-ZnO) additive as the DA sensor. DA quenches the autofluorescence of t-ZnO in physiological environments, and the reduction of the fluorescence intensity serves as an indicator of the DA concentration. The neurons that were 3D printed with the t-ZnO showed good viability, and extensive 3D neural networks were formed within one week after printing. The t-ZnO could sense DA in the 3D printed neural network with a detection limit of 0.137 μM. The results are a first step toward integrating tissue engineering with intensiometric biosensing for advanced artificial tissue/organ monitoring.

A Review on Bio- and Chemosensors for the Detection of Biogenic Amines in Food Safety Applications: The Status in 2022

This article provides an overview on the broad topic of biogenic amines (BAs) that are a persistent concern in the context of food quality and safety. They emerge mainly from the decomposition of amino acids in protein-rich food due to enzymes excreted by pathogenic bacteria that infect food under inappropriate storage conditions. While there are food authority regulations on the maximum allowed amounts of, e.g., histamine in fish, sensitive individuals can still suffer from medical conditions triggered by biogenic amines, and mass outbreaks of scombroid poisoning are reported regularly. We review first the classical techniques used for selective BA detection and quantification in analytical laboratories and focus then on sensor-based solutions aiming at on-site BA detection throughout the food chain. There are receptor-free chemosensors for BA detection and a vastly growing range of bio- and biomimetic sensors that employ receptors to enable selective molecular recognition. Regarding the receptors, we address enzymes, antibodies, molecularly imprinted polymers (MIPs), and aptamers as the most recent class of BA receptors. Furthermore, we address the underlying transducer technologies, including optical, electrochemical, mass-sensitive, and thermal-based sensing principles. The review concludes with an assessment on the persistent limitations of BA sensors, a technological forecast, and thoughts on short-term solutions.

Ultrasensitive Automatic Detection of Small Molecules by Membrane Imaging of Single Molecule Assays

Determination of trace amounts of targets or even a single molecule target has always been a challenge in the detection field. Digital measurement methods established for single molecule counting of proteins, such as single molecule arrays (Simoa) or dropcast single molecule assays (dSimoa), are not suitable for detecting small molecule, because of the limited category of small molecule antibodies and the weak signal that can be captured. To address this issue, we have developed a strategy for single molecule detection of small molecules, called small molecule detection with single molecule assays (smSimoa). In this strategy, an aptamer is used as a recognition element, and an addressable DNA Nanoflower (DNF) attached on the magnetic beads surface, which exhibit fluorescence imaging, is employed as the output signal. Accompanied by digital imaging and automated counting analysis, E2 at the attomolar level can be measured. The smSimoa breaks the barrier of small molecule detection concentration and provides a basis for high throughput detection of multiple substances with fluorescence encoded magnetic beads.

New Trends in Fluorescent Nanomaterials-Based Bio/Chemical Sensors for Neurohormones Detection-A Review

The study of neurotransmitters and stress hormones allows the determination of indicators of the current stress load in the body. These species also create a proper strategy of stress protection. Nowadays, stress is a general factor that affects the population, and it may cause a wide range of serious disorders. Abnormalities in the level of neurohormones, caused by chronic psychological stress, can occur in, for instance, corporate employees, health care workers, shift workers, policemen, or firefighters. Here we present a new nanomaterials-based sensors technology development for the determination of neurohormones. We focus on fluorescent sensors/biosensors that utilize nanomaterials, such as quantum dots or carbon nanomaterials. Nanomaterials, owing to their diversity in size and shape, have been attracting increasing attention in sensing or bioimaging. They possess unique properties, such as fluorescent, electronic, or photoluminescent features. In this Review, we summarize new trends in adopting nanomaterials for applications in fluorescent sensors for neurohormone monitoring.

Current Progress in Aptasensor for Ultra-Low Level Monitoring of Parkinson's Disease Biomarkers

In today's world, Parkinson's disease (PD) has been introduced as a long-term degenerative disorder of the central nervous system which mainly affects approximately more than ten million people worldwide. The vast majority of diagnostic methods for PD have operated based on conventional sensing platforms, while the traditional laboratory tests are not efficient for diagnosis of PD in the early stage due to symptoms of this common neurodegenerative syndrome starting slowly. The advent of the aptasensor has revolutionized the early-stage diagnosis of PD by measuring related biomarkers due to the myriad advantages of originating from aptamers which can be able to sensitive and selective capture various types of related biomarkers. The progress of numerous sensing platforms and methodologies in terms of biosensors based on aptamer application for PD diagnosis has revealed promising results. In this review, we present the latest developments in myriad types of aptasensors for the determination of related PD biomarkers. Working strategies, advantages and limitations of these sensing approaches are also mentioned, followed by prospects and challenges.

NIR persistent luminescence nanoparticles based turn-on aptasensor for autofluorescence-free determination of 17β-estradiol in milk

Consistent exposure to 17β-estradiol through drinking water and food can cause health problems. Although many simple and sensitive fluorescence sensors of 17β-estradiol have been reported, most of them are based on fluorescence quenching test mode working in visible light range, which are inferior in anti-interference ability and quantitative range. Here, we developed a near-infrared (NIR) phosphorescence aptasensor for the detection of 17β-estradiol that has no background fluorescence. The aptasensor was based on Foster resonance energy transfer (FRET) between aptamer conjugated NIR persistent luminescence nanoparticles (PLNPs-Apt) and MoS₂ nanosheets. The 17β-estradiol was quantified by the recovery of PLNPs' phosphorescence. This assay can detect 17β-estradiol in 0.5 mL samples with the LOD of 0.29 ng mL^-1 and in concentrations of more than three orders of magnitude (from 0.5 ng mL^-1 to 1.2 μg mL^-1). This aptasensor exhibited selectivity for 17β-estradiol and was applicable in complex milk samples.

Fast dopamine detection based on evanescent wave detection platform

A compact evanescent wave detection platform (EWDP) is developed for the detection of fluorescence gold nanoclusters. The EWDP employs a simple optical system and a Si-based photodetector SOP-1000 assembly to improve the optical efficiency and detection sensitivity. A microfluidic sample cell is also used to decrease the amount of analyte to 200 μL (The volume of sample cell is really about 30 μL). On this basis, we design a strategy for detecting dopamine (DA) based on the photoinduced electron transfer (PET) quenching mechanism. By introduction of tyrosinase (TYR) during the detection, the testing time is shortened to 1 min. The fluorescence emission signal decreased dramatically and the quenching ratio (F₀-F)/F₀ is linearly related to the concentration of DA in the range of 0.03-60 μM with a detection limit of 0.03 μM. Additionally, this detection platform has potential applications for DA fast detection in the microsamples.

A magnetic relaxation switch sensor for determination of 17β-estradiol in milk and eggs based on aptamer-functionalized Fe3 O4 @Au nanoparticles

BACKGROUND

A simple and rapid detection method for 17β-estradiol (E₂ ) in complex food matrix is greatly desirable. A magnetic relaxation switch (MRS) sensor for detecting E₂ based on the aptamer-functionalized gold-coated iron oxide (Fe₃ O₄ @Au) nanocomposite was designed in this study. Fe₃ O₄ @Au nanoparticles (NPs) played as a 'switch' between dispersed and aggregated states, while aptamer served as the recognition unit.

RESULTS

According to the sensing effect of monocomponent relaxation time (T_2W ) for E₂ , the volume ratio of aptamers to Fe₃ O₄ @Au, the sodium chloride (NaCl) concentration, the concentration of Fe₃ O₄ @Au@Apt, and reaction time were optimized to be 4:1, 0.03 mol L^-1 , 4 μmol L^-1 and 15 min, respectively. For the analysis of food sample, the E₂ was quantified over a concentration range of 1 to 100 nmol L^-1 with a detection limit of 7.6 nmol L^-1 for milk samples, while a linearity range of 20 to 100 nmol L^-1 and a detection limit of 8.57 nmol L^-1 for egg samples.

CONCLUSION

These results exhibited that the MRS sensor could be a promising platform for the rapid detecting of E₂ in food sample. © 2021 Society of Chemical Industry.

Exogenous dopamine and overexpression of the dopamine synthase gene MdTYDC alleviated apple replant disease

Apple replant disease (ARD) is a soil-borne disease that leads to economic losses due to reduced plant growth and diminished fruit yields. Dopamine is involved in interactions between plants and pathogens. However, it remains unclear whether dopamine can directly stimulate defense responses to ARD. In this study, an exogenous dopamine treatment and dopamine synthetase MdTYDC (tyrosine decarboxylase) transgenic plants were used to verify the role of dopamine in treating ARD. First, 2-year-old apple trees (Malus domestica cv. Fuji), grafted onto rootstock M26, were grown in replant soils. The addition of dopamine (100 μM) to the soil promoted seedling growth and changed the accumulation of mineral elements in plants in replant soils. Such supplementation improved the activity of invertase, urease, proteinase and phosphatase under replant conditions. Sequencing analysis of 16S rDNA and internal transcribed spacer (ITS) rDNA revealed that dopamine had a slight influence on bacterial diversity but had an obvious effect on the fungal diversity in replant soils. The application of dopamine to replant soil changed the composition of bacterial and fungal communities. Second, overexpression of MdTYDC in apple plants alleviated the effects of ARD. MdTYDC transgenic lines exhibited mitigated ARD through inhibited degradation of photosynthetic pigment, maintaining the stability of photosystems I and II and improving the antioxidant system. Furthermore, overexpression of MdTYDC improved arbuscular mycorrhizal fungi colonization by improving the accumulation of soluble sugars under replant conditions. Together, these results demonstrated that dopamine enhances the tolerance of apples to ARD.

Ultrasensitive Detection of 17β-Estradiol (E2) Based on Multistep Isothermal Amplification

17β-Estradiol (E2) can cause an adverse effect on the human endocrine system even at the nanomolar level. Measurements of very low levels of E2 remain a critical challenge due to insufficient sensitivity. In this study, a multistep isothermal amplification fluorescence strategy was constructed, which could realize the exponential amplification of target E2. Specifically, strand displacement reaction (SDA), rolling circle amplification (RCA), and multiprimed rolling circle amplification (MRCA) were combined in a series to quantify trace complementary strand of E2 (cDNA). The E2 aptamer and cDNA were hybridized and modified on the magnetic beads. E2 could bind to its aptamer and cause the release of the cDNA. Then, cDNA would combine with the template DNA, initiating the SDA-RCA-MRCA. The molecular beacons, possessing low background signal, whose fluorescence was quenched in the state of chain folding, could be specifically recognized by the long single-stranded DNA (L-ssDNA) generated by the multistep isothermal amplification triggered by cDNA, and then the fluorescence of the molecular beacons could be restored. Therefore, the E2 could be quantitatively detected by the recovery fluorescence intensity. The fluorescence value showed a good linear relationship with the concentration of E2 in the range of 0.001836-183.6 nM, and the limit of detection (LOD) was as low as 63.09 fM. In addition, the recovery rates of this method spiked in milk and water were 80.8-107.0%, respectively. This method has the advantage of multistep isothermal amplification to obtain abundant fluorescence signals, which may provide a new possibility for highly sensitive detection of other small-molecule targets.

Fullerene carbon dot catalytic amplification-aptamer assay platform for ultratrace As+3 utilizing SERS/RRS/Abs trifunctional Au nanoprobes

Under microwave conditions, Au-doped carbon dots (CD_Au) were prepared using fullerene as a precursor, and characterized in details. It is found that CD_Au can strongly catalyze the reaction of HAuCl₄-fructose to generate gold nanoparticles (AuNPs). The new nanocatalytic reaction was studied by surface-enhanced Raman scattering (SERS), resonance Rayleigh scattering (RRS) and absorption (Abs) spectrometry. Based on the specific aptamer (Apt_As)-As⁺³ reaction mediated the CD_Au-HAuCl₄-fructose nanoreaction, and the products of AuNPs as SERS/RRS/Abs trifunctional indicator nanoprobes, a new trimode Apt assay strategy was developed for detection of ultratrace As⁺³. A 0.07-0.70, 0.10-0.60 and 0.20-0.70 μg L^-1 were determined by SERS, RRS and Abs, with detection limits (DL) of 0.04, 0.06, 0.10 μg L^-1 respectively. The aptamer-regulation CD_Au catalytic amplification platform can be also used to assay 1.7-13.3 nmol L^-1 Pb²⁺ and 2.0-12 μmol L^-1 Hg²⁺, with DL of 0.80 nmol L^-1 and 0.90 μmol L^-1 respectively.

Selective dopamine detection by SPR sensor signal amplification using gold nanoparticles

In this study, selective and sensitive detection of neurotransmitter dopamine from both aqueous solution and biological samples was performed by surface plasmon resonance sensor based on molecular imprinting technique.

Controlling dopamine binding by the new aptamer for a FRET-based biosensor

Dopamine is one of the most important neurotransmitters. A high-quality DNA aptamer for dopamine was reported in 2018. However, fundamental understanding of its binding and folding is lacking, which is critical for related biosensor design. Herein, we performed careful assays using a label-free technique called isothermal titration calorimetry (ITC) to study its secondary structure. We divided this aptamer into four regions and individually examined each of them. We confirmed two stems, but the third stem is believed to be part of a loop. The aptamer was then truncated. The original aptamer had a Kd of 2.2 ± 0.3 μM at 25 °C. Shortening the structure by one or two base pairs increased the Kd to 6.9 and 44.4 μM, respectively. Dopamine binding was promoted by both increasing the Mg2+ concentration and decreasing the temperature. At 5 °C, a Kd of 0.4 μM was achieved. Based on this understanding, we designed two fluorescence resonance energy transfer (FRET) quenching biosensors that differ only by a base pair. The shorter sensor had 3-fold higher sensitivity and a detection limit of 0.9 μM. In 1% fetal bovine serum, the sensor retained a similar limit of detection of 1.14 μM. A two-fluorophore ratiometric FRET sensor was also demonstrated with a low detection limit of 0.12 μM. This work indicated the feasibility of designing folding-based sensors for dopamine, and this design can be extended to other sensing modalities such as electrochemistry and colorimetry.

Electrogenerated chemiluminescence of Ru(bpy)32+ at MoS2 nanosheets modified electrode and its application in the sensitive detection of dopamine

Electrogenerated chemiluminescence (ECL) of Ru(bpy)₃²⁺ was studied at a MoS₂ nanosheets modified glassy carbon electrode (MoS₂NS/GCE) in neutral condition. Electrochemical results revealed that MoS₂ nanosheets could significantly catalyze the electrochemical oxidation of Ru(bpy)₃²⁺, as a result, strong anodic ECL was obtained. Several impact factors, such as the modified amount of MoS₂ nanosheets suspension, the pH value, and the concentration of Ru(bpy)₃²⁺, were investigated to obtain the optimal experimental condition. Dopamine exhibited apparent inhibiting effect on ECL intensity of Ru(bpy)₃²⁺-MoS₂ nanosheets through energy transfer process, and could be sensitively detected in the range of 1.0 × 10^-9 to 1.0 × 10^-4 mol L^-1. The linear equation between the decrease of ECL intensity and the logthium of dopamine concentration was determined as ΔI = 9965.02 + 1077.03lgC (C in mol L^-1), with the detection of 8.5 × 10^-10 mol L^-1 (3σ). The modified electrode exhibited satisfactory sensitivity, selectivity, and stability, which can be used to detect dopamine in real samples.

Truncated affinity-improved aptamers for 17β-estradiol determination by AuNPs-based colorimetric aptasensor

17β-estradiol (E2) residues could enrich in organisms via food chain and lead to harmful biological effects for human body. To ascertain the binding domain of original E2 aptamer (E00) with long-sequence (76-mer), we developed novel truncated aptamers from E00, through rationally designed truncation by intercepting a single ring or a combination of rings (containing hairpin loop, interior loop or multiloop) at different sites and retaining appropriate double helix regions. Through comparison, 15-mer E09 presented improved affinity and higher specificity, indicating the hairpin loop near to 3' end of E00 served on the binding domain to E2. E09 was used for gold nanoparticles (AuNPs)-based colorimetric determination of E2, achieved the detection limit of 0.02 μg/mL. The truncated aptamer (only 15-mer) first proposed in this study has great application potential in E2 determination, and this work provides proof-of-concept study for truncation of other long-sequence aptamers.

A fluorescent amplification strategy for high-sensitive detection of 17 β-estradiol based on EXPAR and HCR

Environmental endocrine disruptors in the environment and food, especially 17 β-estradiol (E2), are important factors affecting the growth and development of organisms. In this research, we constructed a fluorescence strategy for two-step amplification that combined two currently popular methods, exponential amplification reaction (EXPAR) and hybridization chain reaction (HCR). E2 competed with the complementary DNA (cDNA) to bind the aptamer modified on the magnetic beads. The free complementary strand in the supernatant was used as a trigger sequence to activate EXPAR, producing a large amount of short single-stranded DNA (ssDNA). The amplified ssDNA can trigger the second HCR amplification, producing many long double-stranded DNA (dsDNA) analogues. According to the principle of fluorescence resonance energy transfer, the carboxyfluorescein (FAM) signals in H1 and H2 hairpins were quenched by black hole quencher (BHQ-1). After the addition of E2 and initiation of amplification, the initially quenched fluorescent signal would be restored. This strategy with a detection limit of 0.37 pg mL^-1 (S/N = 3) showed a good linear relationship in the range of 0.4-800 pg mL^-1. In addition, the recovery rates of the method for milk and water samples were 98.55%-116.95% and 92.32%-107.00%, respectively. This is the first report of the combined detection of EXPAR and HCR, providing a reference for rapid and highly sensitive detection using multiple isothermal amplification methods.

Luminescence-Sensing Tb-MOF Nanozyme for the Detection and Degradation of Estrogen Endocrine Disruptors

Using flexible structures and components of metal-organic framework (MOF) materials, we designed and developed an artificial nanozyme with dual functions of a catalyst and luminescent sensor specifically for the determination and degradation of hormone 17β-estradiol (E2) and its derivatives (E1, E3, and EE2), a class of disruptors with strong effect on the human endocrine system. This nanozyme composed of the luminescent Tb³⁺ ion, catalytic coenzyme factor hemin, and light-harvesting ligand can be used to both degrade E2 like natural horseradish peroxidase (HRP) and sense E2 as low as 50 pM by its luminescence. The nanozyme catalyzes the decomposition of E2 and its derivatives through a mechanism of active hydroxyl radicals and oxidative high-valent iron-oxo intermediates. The prepared nanozyme is pluripotent, stable, and cheap and can replace the widely used combination of natural enzyme and chromogenic substrate. The present strategy of constructing artificial enzymes directly from functional units provides a new way for the design and development of smart, multifunctional artificial enzymes.

Recent Advances in Electrochemical and Optical Sensing of Dopamine

Nowadays, several neurological disorders and neurocrine tumours are associated with dopamine (DA) concentrations in various biological fluids. Highly accurate and ultrasensitive detection of DA levels in different biological samples in real-time can change and improve the quality of a patient's life in addition to reducing the treatment cost. Therefore, the design and development of diagnostic tool for in vivo and in vitro monitoring of DA is of considerable clinical and pharmacological importance. In recent decades, a large number of techniques have been established for DA detection, including chromatography coupled to mass spectrometry, spectroscopic approaches, and electrochemical (EC) methods. These methods are effective, but most of them still have some drawbacks such as consuming time, effort, and money. Added to that, sometimes they need complex procedures to obtain good sensitivity and suffer from low selectivity due to interference from other biological species such as uric acid (UA) and ascorbic acid (AA). Advanced materials can offer remarkable opportunities to overcome drawbacks in conventional DA sensors. This review aims to explain challenges related to DA detection using different techniques, and to summarize and highlight recent advancements in materials used and approaches applied for several sensor surface modification for the monitoring of DA. Also, it focuses on the analytical features of the EC and optical-based sensing techniques available.

Microfluidic Chip for Multiplex Detection of Trace Chemical Contaminants Based on Magnetic Encoded Aptamer Probes and Multibranched DNA Nanostructures as Signal Tags

The development of multiplex assays to simultaneously monitor multiclass chemical contaminants that commonly coexist in foods, such as heavy metal ions, antibiotics, and estrogen residues, is gaining attention. Here, a microfluidic chip (MC)-based multianalysis method coupled with magnetic encoded aptamer probes was used for simultaneous detection of kanamycin, 17β-estradiol, and lead ion (Pb²⁺). Using this innovative strategy, the magnetic bead (MB)-based encoded probes labeled with aptamer hybrid chains were first used to selectively capture multiple targets, followed by generating single-stranded primers. The primers triggered a multibranched hybridization chain reaction (mHCR). Finally, three kinds of complementary strands (C-DNAs) with different lengths were hybridized with the arms of the mHCR products to form three types of multibranched DNA nanostructures. The decrement signals of C-DNAs were employed for qualification of targets. As the signal tags corresponded to different targets, the DNA nanostructures realized "one target for the decrease of massive C-DNAs" to improve sensitivity. The use of MB-based encoded probes could achieve magnetic separation to eliminate interference in the complex. The detection limits of this method were 1.76 × 10^-4 nM (kanamycin), 1.18 × 10^-4 nM (17β-estradiol), and 1.29 × 10^-4 nM (lead ion). Furthermore, the MC platform is reusable and can be used for more than 4000 samples. The assay combining the MC with MB-based encoded probes with multibranched DNA signal tags offers a universal, reusable, and high-throughput detection platform for screening multiclass chemical contaminants in food samples with complex matrices.

Recent advances in the detection of 17β-estradiol in food matrices: A review

Pollution of endocrine disrupting chemicals has become a global issue. As one of the hormonally active compounds, 17β-estradiol produces the strongest estrogenic effect when it enters the organism exogenously including food intakes, bringing potential harmfulness such as malfunction of the endocrine system. Therefore, in order to assure food safety and avoid potential risks of 17β-estradiol to humans, it is of great significance to develop rapid, sensitive and selective approaches for the detection of 17β-estradiol in food matrices. In this review, the harmfulness and main sources of 17β-estradiol are firstly introduced, followed by the description of the principles and applications of different approaches for 17β-estradiol detection including high performance liquid chromatography, electrochemistry, Raman spectroscopy, fluorescence and colorimetry. Particularly, applications in detecting 17β-estradiol in food matrices over the years of 2010-2018 are discussed. Finally, advantages and limitations of these detection methods are highlighted and perspectives on future developments in the detection methods for 17β-estradiol are also proposed. Although many detection approaches can achieve trace or ultratrace detection of 17β-estradiol, further studies should be focused on the development of in-situ and real-time methods to monitor and evaluate 17β-estradiol for food safety.

Multiplex detection of quality indicator molecule targets in urine using programmable hairpin probes based on a simple double-T type microchip electrophoresis platform and isothermal polymerase-catalyzed target recycling

Recently, it has been crucial to be able to detect and quantify small molecular targets simultaneously in biological samples. Herein, a simple and conventional double-T type microchip electrophoresis (MCE) based platform for the multiplex detection of quality indicator molecule targets in urine, using ampicillin (AMPI), adenosine triphosphate (ATP) and estradiol (E2) as models, was developed. Several programmable hairpin probes (PHPs) were designed for detecting different targets and triggering isothermal polymerase-catalyzed target recycling (IPCTR) for signal amplification. Based on the target-responsive aptamer structure of PHP (Domain I), target recognition can induce PHP conformational transition and produce extension duplex DNA (dsDNA), assisted by primers & Bst polymerase. Afterwards, the target can be displaced to react with another PHP and initiate the next cycle. After several rounds of reaction, the dsDNA can be produced in large amounts by IPCTR. Three targets can be simultaneously converted to dsDNA fragments with different lengths, which can be separated and detected using MCE. Thus, a simple double-T type MCE based platform was successfully built for the homogeneous detection of multiplex targets in one channel. Under optimal conditions, the assay exhibited high throughput (48 samples per hour at most, not including reaction time) and sensitivity to three targets in urine with a detection limit of 1 nM (ATP), 0.05 nM (AMPI) and 0.1 nM (E2) respectively. The multiplex assay was successfully employed for the above three targets in several urine samples and combined the advantages of the high specificity of programmable hairpin probes, the excellent signal amplification of IPCTR, and the high through-put of MCE which can be employed for screening in biochemical analysis.

In Vivo Use of a Multi-DNA Aptamer-Based Payload/Targeting System To Study Dopamine Dysregulation in the Central Nervous System

The delivery of therapeutics across the blood-brain barrier remains a considerable challenge in investigating central nervous system related processes. In this work, a liposome vehicle was surface-modified with an aptamer that binds to the transferrin receptor and was loaded with two different dopamine-binding aptamer payloads. This system was effectively used to promote the delivery of the aptamer cargo from the peripheral injection site into the brain. The effect of these delivered aptamers on behavior was investigated in vivo in a locomotor task. The first dopamine binding aptamer assessed was a DNA aptamer, the binding of which had been previously validated through the aptamer-based biosensor development reported by several independent research groups. The second aptamer investigated was the result of a novel in vitro selection experiment described herein. Our data suggest that systemic administration of the modified liposomes led to delivery of the dopamine aptamers into the brain. Fluorescence microscopy revealed differential distribution of fluorescence based on the presence or absence of the transferrin receptor aptamer on the surface of fluorescently modified liposomes. In a behavioral experiment using cocaine administration to induce elevated concentrations of neural dopamine, systemic pretreatment with the dopamine aptamer-loaded liposomes reduced cocaine-induced hyperlocomotion. Multiple controls including a transferrin-negative liposome control and transferrin-positive liposomes loaded with either a nonbinding, base-substituted dopamine aptamer or a random oligonucleotide were investigated. None of these controls altered cocaine-induced hyperlocomotion. Chronic systemic administration of the modified liposomes produced no deleterious neurobehavioral or neural degenerative effects. Importantly, this work is one example of an application for this versatile multiaptamer payload/targeting system. Its general application is limited only by the availability of aptamers for specific neural targets.