Aptamer-based label-free impedimetric biosensor for detection of progesterone

Recent advancements in aptamers as promising nanotool for therapeutic and diagnostic applications

Aptamers are single-strand oligonucleotide molecules having certain structural interactions which allow them to bind to specific targets. Modified nucleotides are added during or after a selection procedure like Systematic Evolution of Ligands by Exponential Enrichment i.e., SELEX to enhance the characteristics and functionality of aptamers. Aptamers are extensible molecular tools with several uses such as in drug administration, biosensing, bioimaging, drug therapies and diagnostics. The ability to detect is improved by using aptamer-based sensors in conjunction with biological molecules among other sensing techniques. Chemical modification, and strong resistance to denaturation, aptamers are appropriate biological recognizing agents for developing sensitive and repeatable aptasensors. This review discusses the most current developments in the aptamers, SELEX method, applications of aptamers as innovative diagnostic, therapeutic & theragnostic tool along with major limitations & prospective directions in the future.

Tailored microenvironment of functional DNA enables highly robust blood estradiol tests

Monitoring estradiol (E2) levels in the blood is crucial for obtaining reliable hormone levels necessary for assessing overall reproductive and cardiovascular health. While existing techniques like mass spectrometry and chemiluminescence immunoassays offer high sensitivity and selectivity, they are often complex, costly, and suffer from issues, such as cross-reactivity and limited biostability. Herein, we present a DNA-based method for E2 detection in blood, which mitigates the matrix effect using engineered DNA microenvironments. We demonstrate that incorporating heparin significantly enhances the binding between aptamers and E2 using fluorescence and electrochemical assays. Additionally, the presence of non-charged polymer on electrode surface reduces the apparent dissociation constant by over 70-fold, enabling us to design assays that overcome the dynamic range limitations of surface binding assays. Our method proves reliable for monitoring E2 levels in clinical samples, including those from women undergoing hormone replacement therapy, assisted reproductive technology, and throughout the menstrual cycle. Overall, our work presents a promising approach for E2 testing in blood and underscores the critical role of the DNA local environment in target recognition within biological settings.

SELEX-derived DNA aptamer utilized for sensitive electrochemical biosensing of Toxoplasma gondii surface antigen 1

Toxoplasma gondii (T. gondii) is a global parasitic pathogen with significant health implications. Effective diagnosis is crucial, especially for vulnerable populations like immunocompromised individuals and pregnant women. Here, we developed a novel electrochemical aptasensor for detecting Surface Antigen 1 (SAG1), a key biomarker for acute T. gondii infections. New high-affinity aptamers (SOK3, SOK14, and SOK18) specific to SAG1 were identified using SELEX method. The aptamers were then immobilized onto screen-printed carbon electrodes (SPE) modified with graphene quantum dots (GQDs). Physicochemical characterization confirmed successful aptasensor fabrication. SOK14 was identified as optimal for SAG1 detection due to its lower dissociation constant and distinct current response upon protein binding. Square wave voltammetry (SWV) showed a linear response from 0.01 to 100 nM SAG1 (n = 3), correlating with [Fe(CN)6]3-/4- oxidation peak current changes and achieving a low detection limit of 11.5 pM with relative standard deviations ranging from 3.3 to 4.9 %. Selectivity studies against other nonspecific biomarkers for other pathogens validated the aptasensor's specificity. Application of the aptasensor in spiked serum samples indicated its efficiency in complex biological samples. This platform enables rapid, on-site detection of T. gondii with high sensitivity, selectivity, and reliability in serum samples, supporting early diagnosis and timely treatment to prevent complications.

A Novel Aptamer-Based Fluorescent Biosensor for Imaging SIRT2 in Live Cells and Screening Its Modulators

Sirtuin 2 (SIRT2) is involved in the pathological processes of many diseases and is especially regarded as a potential therapeutic target for diabetes and neurodegenerative diseases. Imaging SIRT2 protein in live cells has important value for rapidly detecting SIRT2 and high-throughput screening SIRT2 modulators. As far as we know, there has been no method for imaging SIRT2 in live cells up to now. Here, we present a novel aptamer (Apt)-based "turn-on" fluorescent biosensor for imaging SIRT2 in live cells. To develop the recognition element of the biosensor, our work first discovered 12 aptamers (Apt) with high affinity to SIRT2 (Kd = 123.3-154.5 nM) using the magnetic beads-based systemic evolution of ligands by exponential enrichment (MB-SELEX) and selected Apt 45 (Kd = 123.3 nM) to fabricate the "turn-on" fluorescent biosensor, FAM-Apt 45/Black Hole Quencher1 (BHQ1)-cDNA/Au nanospheres, which had excellent specificity and low cytotoxicity. The experiment results demonstrated that the biosensor could image SIRT2 in three different cell lines, including Schwann, H9c2, and HUVECs cells. Further, we established a platform for screening SIRT2 modulators with the biosensor and discovered three SIRT2 modulators (astragaloside II, chlorogenic acid, and tanshinone IIA) that could increase SIRT2 levels in Schwann cells damaged by high glucose and lipid. This work provides an aptamer-based fluorescent biosensor for high-throughput screening of protein modulators at the cellular level, which could be a universal approach to screening aimed protein modulators by replacing the corresponding aptamer.

Current Advances in Aptasensors for Pesticide Detection

The increasing use of pesticides necessitates the development of innovative analytical methods to regulate environmental impacts and ensure food safety. Aptamer-based sensors hold great promise for pesticide detection owing to their superior selectivity, stability, repeatability, and regenerative capabilities. Integrated with nanomaterials, aptasensors have demonstrated enhanced sensitivity for detecting a broad range of pesticides. This study first introduces the aptamer binding mechanism and presents the fundamental concept and justification for selecting aptamer over other biorecognition molecules. It then provides a comprehensive review of recent advancements and applications of various types of aptasensors for targeted pesticide detection, including electrochemical, fluorescent, colorimetric, electrochemiluminescent, and surface-enhanced Raman scattering (SERS) aptasensors. Additionally, it offers a comparative analysis of different aptasensors by evaluating their strengths and limitations. Finally, this review discusses strategies, such as advanced Systemic Evolution of Ligands by Exponential Enrichment (SELEX) technique, self-assembled monolayers (SAMs), and the use of antifouling agents to improve the aptamer's selectivity, signal-to-noise ratio, and mitigate nonspecific adsorption challenges. These developments are essential for creating highly sensitive and selective aptasensors, facilitating their practical use in environmental monitoring and food safety.

Molecular Shape-Preserving Au Electrode for Progesterone Detection

Quantifying progesterone levels in the body is an important indicator of early pregnancy and health. Molecular shape-preserving electrodes have garnered attention in electrochemical biosensors because they can detect targets without the need for expensive enzymes or antibodies. However, some of the currently used methods typically have low electrode durability. Here, progesterone, for which antibodies are typically expensive, was used to develop a molecular shape-preserving electrode using Au to enhance its long-term stability. The physical properties of the electrodes were characterized using scanning electron microscopy (SEM), the electrochemical surface area (ECSA), and cyclic voltammetry (CV). The specific structure of the electrode demonstrated an electrochemical double layer comparable to that of a smooth Au electrode, confirming its high durability. The detection performance was assessed using CV, square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS). The current response to progesterone increased in a concentration-dependent manner, but decreased from the saturated state owing to electrodeposition on the surface. Additionally, electrochemical impedance measurements showed high selectivity compared with hormones with similar structures. The fabricated molecular shape-preserving electrode exhibits an excellent durability, stability, and detection performance, confirming its suitability for long-term use. These findings pave the way to new possibilities for electrode fabrication.

Toward At-Home and Wearable Monitoring of Female Hormones: Emerging Nanotechnologies and Clinical Prospects

Steroid hormones, especially progesterone (P4), estradiol (E2), and testosterone (T), are key bioactive regulators in various female physiological processes, including growth and development, ovulation, and the reproductive cycle, as well as metabolism and mental health. As lipophilic molecules produced in sex glands, these steroid female hormones can be transported through blood vessels into various body fluids such as saliva, sweat, and urine. However, the ultralow concentration of steroid hormones down to picomolar (pM) level necessitates great demands for ultrasensitive but low-cost analytic tools to implement accurate, point-of-care or even continuous monitoring in a user-friendly fashion. This review focuses on the latest advances in materials and nanotechnologies to allow the rapid detection of female hormones at the pM level or below and the potentials in at-home and wearable hormone monitoring. We specifically summarize the optical and electrochemical strategies in this category, particularly those affording low cost and portable signal readout for at-home use. Furthermore, emerging flexible/wearable innovations are highlighted, which allow the continuous hormone cycle tracking in a noninvasive manner. The potential of these techniques is discussed to address the need for real-time acquisition of the hormone fluctuation, facilitating health monitoring at home. Lastly, we provide a comprehensive introduction to the prospects of female hormone monitoring in clinical diagnosis and treatment, from the perspective of gynecology and reproductive medicine clinicians.

Aptamer-based biosensors for the detection of neonicotinoid insecticides in environmental samples: A systematic review

Neonicotinoids, sometimes abbreviated as neonics, represent a class of neuro-active insecticides with chemical similarities to nicotine. Neonicotinoids are the most widely adopted group of insecticides globally since their discovery in the late 1980s. Their physiochemical properties surpass those of previously established insecticides, contributing to their popularity in various sectors such as agriculture and wood treatment. The environmental impact of neonicotinoids, often overlooked, underscores the urgency to develop tools for their detection and understanding of their behavior. Conventional methods for pesticide detection have limitations. Chromatographic techniques are sensitive but expensive, generate waste, and require complex sample preparation. Bioassays lack specificity and accuracy, making them suitable as preliminary tests in conjunction with instrumental methods. Aptamer-based biosensor is recognized as an advantageous tool for neonicotinoids detection due to its rapid response, user-friendly nature, cost-effectiveness, and suitability for on-site detection. This comprehensive review represents the inaugural in-depth analysis of advancements in aptamer-based biosensors targeting neonicotinoids such as imidacloprid, thiamethoxam, clothianidin, acetamiprid, thiacloprid, nitenpyram, and dinotefuran. Additionally, the review offers valuable insights into the critical challenges requiring prompt attention for the successful transition from research to practical field applications.

DeltaGzip: Computing Biopolymer-Ligand Binding Affinity via Kolmogorov Complexity and Lossless Compression

The design of biosequences for biosensing and therapeutics is a challenging multistep search and optimization task. In principle, computational modeling may speed up the design process by virtual screening of sequences based on their binding affinities to target molecules. However, in practice, existing machine-learned models trained to predict binding affinities lack the flexibility with respect to reaction conditions, and molecular dynamics simulations that can incorporate reaction conditions suffer from high computational costs. Here, we describe a computational approach called DeltaGzip that evaluates the free energy of binding in biopolymer-ligand complexes from ultrashort equilibrium molecular dynamics simulations. The entropy of binding is evaluated using the Kolmogorov complexity definition of entropy and approximated using a lossless compression algorithm, Gzip. We benchmark the method on a well-studied data set of protein-ligand complexes comparing the predictions of DeltaGzip to the free energies of binding obtained using Jarzynski equality and experimental measurements.

Cell-SELEX for aptamer discovery and its utilization in constructing electrochemical biosensor for rapid and highly sensitive detection of Legionella pneumophila serogroup 1

This study introduces an innovative electrochemical aptasensor designed for the highly sensitive and rapid detection of Legionella pneumophila serogroup 1 (L. pneumophila SG1), a particularly virulent strain associated with Legionellosis. Employing a rigorous selection process utilizing cell-based systematic evolution of ligands by exponential enrichment (cell-SELEX), we identified new high-affinity aptamers specifically tailored for L. pneumophila SG1. The selection process encompassed ten rounds of cell-SELEX cycles with live L. pneumophila, including multiple counter-selection steps against the closely related Legionella sub-species. The dissociation constant (Kd) of the highest affinity sequence to L. pneumophila SG1 was measured at 14.2 nM, representing a ten-fold increase in affinity in comparison with the previously reported aptamers. For the development of electrochemical aptasensor, a gold electrode was modified with the selected aptamer through the formation of self-assembled monolayers (SAMs). The newly developed aptasensor exhibited exceptional sensitivity, and specificity in detecting and differentiating various Legionella sp., with a detection limit of 5 colony forming units (CFU)/mL and an insignificant/negligible cross-reactivity with closely related sub-species. Furthermore, the aptasensor effectively detected L. pneumophila SG1 in spiked water samples, demonstrating an appreciable recovery percentage. This study shows the potential of our aptamer-based electrochemical biosensor as a promising approach for detecting L. pneumophila SG1 in diverse environments.

A nitrogen-doped hollow carbon nanospheres-based aptasensor for non-invasive salivary detection of progesterone

Developing an easy-to-use and non-invasive sensor for monitoring progesterone (P4) as a multi-functional hormone is highly demanded for point-of-care testing. In this study, an ultrasensitive electrochemical aptasensor is fabricated for monitoring P4 in human biofluids. The sensing interface was designed based on the porous nitrogen-doped hollow carbon spheres (N-HCSs). The N-HCSs covalently immobilized high-dense aptamer (Apt) sequences as the bioreceptor of P4. The electron transfer of the redox probe was hindered by incubating P4 on the aptasensor surface and forming the P4-Apt complexes. Meanwhile, the signaling was decreased under two wide linear dynamic ranges (LDRs) from 10 fM to 5.6 μM with a limit of detection (LOD) value of 3.33 fM. The aptasensor presented satisfactory selectivity in the presence of different off-target species with successful feasibility for P4 detection in some human urine and saliva samples. The aptasensor with high sensitivity, as an advantage for on-site and sensitive measurement of P4, can be considered a non-invasive tool for routine analysis of real-world clinical samples method.

Integrating aptasensor with an explosive mass-tag signal amplification strategy for ultrasensitive and multiplexed analysis using a miniature mass spectrometer

Mass probes attached with aptamers and mass tags offer excellent specificity and sensitivity for multiplexed detection, wherein the dissociation of mass tags from the mass probes is as important as their labeling. Herein, aggregation-induced emission luminogen (AIEgen)-tagged mass probes (AIEMPs) were established to analyze estrogens, which integrated aptasensor with an explosive mass-tag signal amplification strategy via a simple ultrasound-assisted emulsification of nanoliposomes. The AIEMPs were assembled by the hybridization of aptamer-modified Fe3O4 nanoparticles (Fe NPs@Apt) and nanoliposomes loaded with massive AIEgen mass tags and partially complementary DNA strands (AIE NLs@cDNA). The aptamer was preferentially and specifically bound to estrogen, resulting in the detachment of AIE NLs from AIEMPs. Subsequently, the AIEMPs were deposited with electrospray solvents for explosive release of mass tags. Using nanoelectrospray ionization mass spectrometry (nanoESI-MS), the AIEMP-based aptasensor achieved ultrasensitive analysis of estrogens with limits of detection of 0.168-0.543 pg/mL and accuracies in the range of 87.9-114.0%. Compared to direct nanoESI-MS detection, the AIEMP-based aptasensor provides a signal amplification of four orders of magnitude. Furthermore, the utilization of different AIEMPs enables multiplexed detection of three estrogens with a miniature mass spectrometer, showing promising potential for on-site detection. This work expands the diversity of mass-tagging strategy and provides a versatile mass probe-based aptasensor platform for routine MS detection of trace analytes.

A homogeneous label-free electrochemical aptasensor based on an omega-like DNA nanostructure for progesterone detection

A novel homogeneous label-free electrochemical aptamer sensor for the detection of progesterone was prepared by combining a well-designed omega (Ω)-like DNA (Ω-DNA) nanostructure, with an isothermal cycling amplification strategy based on the highly efficient exonuclease III (Exo III). The omega-like (Ω) DNA is composed of two oligonucleotide strands: DNA1 and DNA2. The Pro aptamer triggers a chain displacement reaction of Ω-DNA nanostructures, forms a new double-stranded DNA structure (aptamer precursor-DNA2), and releases DNA1. Then, Exo III selectively cleaves the DNA duplex and releases the Pro aptamer to participate in a new displacement reaction. Meanwhile, the released DNA1 strands gain access to the strongly bound hemin, forming a hemin/G-quadruplex (DNAzyme). In the presence of hydrogen peroxide (H2O2), differential pulse voltammetry (DPV) was used to detect the current signal from the oxidation of o-phenylenediamine (OPD) to aminoazobenzene (DAP) catalyzed by DNAzyme. However, the amount of released DNA1 from the Ω-DNA nanostructures is reduced in the presence of the target Pro, and the DPV signal declines because of the small amount of DNAzyme formed. The developed electrochemical aptasensor has a wide dynamic linear relationship in the range of 1 pg mL-1 to 10 ng mL-1 under optimal conditions. Its detection limit is down to 0.3 pg mL-1, providing a potential platform for a sensitive Pro assay among electrochemical assays.

Progesterone and β-hCG Determination Using an Electrochemical Combo-Strip for Pregnancy Monitoring

The development of analytical devices that can allow an easy, rapid and cost-effective measurement of multiple markers, such as progesterone and β-hCG, could have a role in decreasing the burden associated with pregnancy-related complications, such as ectopic pregnancies. Indeed, ectopic pregnancies are a significant contributor to maternal morbidity and mortality in both high-income and low-income countries. In this work, an effective and highly performing electrochemical strip for a combo determination of progesterone and β-hCG was developed. Two immunosensing approaches were optimized for the determination of these two hormones on the same strip. The immunosensors were realized using cost-effective disposable electrode arrays and reagent-saving procedures. Each working electrode of the array was modified with both the IgG anti-β-hCG and anti-progesterone, respectively. By adding the specific reagents, progesterone or β-hCG can then be determined. Fast quantitative detection was achieved, with the analysis duration being around 1 h. Sensitivity and selectivity were assessed with a limit of detection of 1.5 × 10-2 ng/mL and 2.45 IU/L for progesterone and β-hCG, respectively. The proposed electrochemical combo-strip offers great promise for rapid, simple, cost-effective, and on-site analysis of these hormones and, thus, for the development of a point-of-care diagnostic tool for early detection of pregnancy-related complications.

Signal "On-Amplified-Off" Strategy Based on Hafnium Dioxide Nanomaterials as Electrochemiluminescence Emitters for Progesterone Detection

When consumed, excess progesterone (P4)─found in food and the environment─can lead to severe illnesses in humans. Therefore, quantitative analysis of P4 is critical for identifying its hazardous levels. In this study, a novel signal "on-amplified-off" P4 detection mode was proposed, which was based on the utilization of hafnium oxide (HfO2) as a unique electrochemiluminescence (ECL) emitter, produced by calcining UiO-66(Hf). This is the first time that HfO2 has been used as an ECL emitter. HfO2 displayed excellent conductivity and a high specific surface area, allowing it to connect with numerous aptamers and produce a "signal-on" effect. Ni-doped ZnO (Ni-ZnO) acted as a coreaction accelerator, enhancing the ECL strength of HfO2 by generating more tripropylamine radicals. cDNA was labeled with Ni-ZnO, and Ni-ZnO was linked to the aptamer via base complementary pairing, affording "signal-amplified". The presence of the target molecule P4 instigated a specific binding process with the aptamer, triggering the shedding of cDNA-Ni-ZnO and resulting in "signal-off". This novel "on-amplified-off" strategy effectively improved the sensitivity and specificity of P4 analysis, introducing a practical method for detecting biomolecules beyond the scope of this study, which holds immense potential for future applications.

Single vs sandwich aptamers: Towards the detection of human epidermal growth factor receptor 2 using composites of phthalocyanine and nanoparticles

The superiority of the sandwich over a single aptamer based aptasensor assay for the detection of the human epidermal growth factor receptor 2 (HER2) is demonstrated for the first time. Cobalt tris-3,5 dimethoxy-phenoxy pyridine (5) oxy (2)- carboxylic acid phthalocyanine (CoMPhPyCPc) and sulphur/nitrogen doped graphene quantum dots (SNGQDs) and cerium oxide nanoparticles (CeO₂NPs) nanocomposite (SNGQDs@CeO₂NPs) were used for electrode modification of glassy carbon electrode (GCE) both individually and combined to form the substrates: GCE/SNGQDs@CeO₂NPs, GCE/CoMPhPyCPc and GCE/SNGQDs@CeO₂NPs/CoMPhPyCPc. The designed substrates were used as immobilization platforms for the amino functionalized HB5 aptamer for the development of both single and sandwich aptasensor assays. A novel bioconjugate, made of the HB5 aptamer and nanocomposite (HB5-SNGQDs@CeO₂NPs) was fabricated, and characterized using ultra-violet/visible, Fourier transform infrared, and Raman spectroscopies as well as scanning electron microscopy. HB5-SNGQDs@CeO₂NPs was applied as a secondary aptamer in the design of novel sandwich assays towards the electrochemical detection of HER2. The performance of the designed aptasensors were evaluated using electrochemical impedance spectroscopy. The sandwich assay gave low limit of detection of 0.00088 pg/mL, high sensitivity of 773925 Ω pg^-1mL, showed stability, and good precision in real samples towards HER2 detection.

A ratiometric self-powered aptasensor for simultaneous detection of cortisol and progesterone based on spatially resolved tri-channel photofuel cell

In this work, a self-powered sensor was proposed for simultaneous detection of two typical steroid hormones, namely cortisol (COR) and progesterone (P4). A tri-channel photofuel cell (PFC) consisting of three spatially resolved SnS₂@SnO₂ photoanodes and one Pt cathode was designed to generate the electricity to drive the sensing process under the control of a multiplex switch. Among three photoanodes, one served as the control, while the other two were modified with COR-binding or P4-binding aptamer to respond specifically to the COR or P4 target. The ratios of the inhibited PFC output from aptamer-immobilized photoanodes to the reference signal from the control photoanode were utilized for simultaneous detection of COR and P4. The results showed that the developed self-powered sensor exhibited broad concentration ranges toward targets, with COR concentration ranging from 1 nM to 1000 nM and P4 concentration ranging from 1 nM to 500 nM. The detection limits for COR and P4 were calculated to be 0.88 nM and 0.52 nM, respectively. Moreover, the proposed sensing platform demonstrated high selectivity, good reproducibility, and high stability. Finally, the sensor was successfully applied to the simultaneous determination of COR and P4 in a human female serum sample.

Electrochemical biosensors for monitoring of selected pregnancy hormones during the first trimester: A systematic review

The hormones human chorionic gonadotropin, progesterone, estrogen and four of its metabolites (estradiol, estrone, estriol, estetrol), as well as relaxin play an essential role in the development of the fetus during the first trimester. Imbalances in these hormones during the first trimester have been directly linked to miscarriages. However, frequent monitoring of the hormones is limited by the current conventional centralized analytical tools that do not allow a rapid response time. Electrochemical sensing is considered an ideal tool to detect hormones owing to its advantages such as quick response, user-friendliness, low economic costs, and possibility of use in point-of-care settings. Electrochemical detection of pregnancy hormones is an emerging field that has been demonstrated primarily at research level. Thus, it is timely with a comprehensive overview of the characteristics of the reported detection techniques. This is the first extensive review focusing on the advances related to electrochemical detection of hormones linked to the first trimester of pregnancy. Additionally, this review offers insights into the main challenges that must be addressed imminently to ensure progress from research to clinical applications.

Development of an Impedimetric Aptasensor for Detection of Progesterone in Undiluted Biological Fluids

A cost-effective, deployable, and quantitative progesterone biosensor is desirable for regular progesterone sensing in biological and environmental samples to safeguard public health. Aptasensors have been shown to be affordable as compared to antibody-based sensors, but so far, none of the progesterone aptamers could detect it in undiluted and unprocessed biological samples. Thus, to select an aptamer suitable for biosensing in unprocessed biological samples, a modified magnetic bead-based approach with counter-selection in milk and serum was performed. G-quadruplex forming progesterone aptamers were preferentially screened through in silico, gold nanoparticle-based adsorption-desorption assay and circular dichroism spectroscopy. GQ5 aptamer showed extended stability and a high progesterone binding affinity (K D 5.29 ± 2.9 nM) as compared to any other reported progesterone aptamers (P4G11 and P4G13). Under optimized conditions, GQ5 aptamer was coated on the gold electrode to develop an impedimetric aptasensor (limit of detection: 0.53, 0.91, and 1.9 ng/mL in spiked buffer, undiluted milk, and serum, respectively, with the dynamic range of detection from 0.1 to 50 ng/mL in buffer and 0.1 to 30 ng/mL in both milk and serum). The aptasensor exhibited a very high level of κ value (>0.9) with ELISA to detect progesterone in milk and serum. The aptasensor could be regenerated three times and can be stored for up to 10 days at 4 °C. Therefore, GQ5 may be used to develop a portable impedimetric aptasensor for clinical and on-site progesterone sensing in various biological and environmental samples.

Clinically Applicable Homogeneous Assay for Serological Diagnosis of Alpha-Fetoprotein by Impact Electrochemistry

Tumor protein quantification with high specificity, sensitivity, and efficiency is of great significance to enable early diagnosis and effective treatment. The existing methods for protein analysis usually suffer from high cost, time-consuming operation, and insufficient sensitivity, making them not clinically friendly. In this work, a label-free homogeneous sensor based on the nano-impact electroanalytic (NIE) technique was proposed for the detection of tumor protein marker alpha-fetoprotein (AFP). The detection principle is based on the recovery of current of single PtNP catalyzed hydrazine oxidation due to the release of the pre-adsorbed passivating aptamers on PtNPs from the competition of the stronger binding between the specific interaction of the AFP aptamer and AFP. The intrinsic one-by-one analytical ability of NIE allows highly sensitive detection, which can be further improved by reducing the reaction/incubation volume. Meanwhile, the current sensor avoids a laborious labeling procedure as well as the separation and washing steps due to the in situ characteristic of NIE. Accordingly, the current sensor enables efficient, highly sensitive, and specific AFP analysis. More importantly, the reliable detection of AFP in diluted real sera from hepatocellular carcinoma (HCC) patients is successfully achieved, indicating that the impact electrochemistry-based sensing platform has great potential to be applied in point-of-care devices for HCC liquid biopsy.

Graphene-based nanocomposites and nanohybrids for the abatement of agro-industrial pollutants in aqueous environments

Incessant release of a large spectrum of agro-industrial pollutants into environmental matrices remains a serious concern due to their potential health risks to humans and aquatic animals. Existing remediation techniques are unable to remove these pollutants, necessitating the development of novel treatment approaches. Due to its unique structure, physicochemical properties, and broad application potential, graphene has attracted a lot of attention as a new type of two-dimensional nanostructure. Given its chemical stability, large surface area, electron mobility, superior thermal conductivity, and two-dimensional structure, tremendous research has been conducted on graphene and its derived composites for environmental remediation and pollution mitigation. Various methods for graphene functionalization have facilitated the development of different graphene derivatives such as graphene oxide (GO), functional reduced graphene oxide (frGO), and reduced graphene oxide (rGO) with novel attributes for multiple applications. This review provides a comprehensive read on the recent progress of multifunctional graphene-based nanocomposites and nanohybrids as a promising way of removing emerging contaminants from aqueous environments. First, a succinct overview of the fundamental structure, fabrication techniques, and features of graphene-based composites is presented. Following that, graphene and GO functionalization, i.e., covalent bonding, non-covalent, and elemental doping, are discussed. Finally, the environmental potentials of a plethora of graphene-based hybrid nanocomposites for the abatement of organic and inorganic contaminants are thoroughly covered.

Association between community psychological label and user portrait model based on multimodal neural network

By analyzing traditional deep learning multimode retrieval methods, an optimized multimode retrieval model based on convolutional neural network is established. This article proposes an innovative semi-supervised social network user portrait analysis model (UPAM) based on user portrait model, which integrates users’ social information and some known user attribute information (such as educational background and residence) into a unified topic model framework. Finally, a semi-supervised user portrait analysis method based on user social information and partial known user attribute information is proposed. According to the correlation of user attributes, the cross-validation method is used to train model prediction task and improve the prediction effect. In the first-level model, using a different model to extract the features in the user query, the basis of the second hierarchy model, Stacking is used to further integrate characteristics, finally realizing the attribute population forecast, and experimental verification showing the proposed model’s effectiveness in various attributes of a population.

Molecularly Imprinting–Aptamer Techniques and Their Applications in Molecular Recognition

Molecular imprinting–aptamer techniques exhibit the advantages of molecular imprinting and aptamer technology. Hybrids of molecularly imprinted polymer–aptamer (MIP–aptamer) prepared by this technique have higher stability, binding affinity and superior selectivity than conventional molecularly imprinted polymers or aptamers. In recent years, molecular imprinting–aptamer technologies have attracted considerable interest for the selective recognition of target molecules in complex sample matrices and have been used in molecular recognition such as antibiotics, proteins, viruses and pesticides. This review introduced the development of molecular imprinting–aptamer-combining technologies and summarized the mechanism of MIP–aptamer formation. Meanwhile, we discussed the challenges in preparing MIP–aptamer. Finally, we summarized the application of MIP–aptamer to the molecular recognition in disease diagnosis, environmental analysis, food safety and other fields.

An Allosteric Transcription Factor DNA-Binding Electrochemical Biosensor for Progesterone

We describe an electrochemical strategy to transduce allosteric transcription factor (aTF) binding affinity to sense steroid hormones. Our approach utilizes square wave voltammetry to monitor changes in current output as a progesterone (PRG)-specific aTF (SRTF1) unbinds from the cognate DNA sequence in the presence of PRG. The sensor detects PRG in artificial urine samples with sufficient sensitivity suitable for clinical applications. Our results highlight the capability of using aTFs as the biorecognition elements to develop electrochemical point-of-care biosensors for the detection of small-molecule biomarkers and analytes.

Backbone extension via peptidomimetics at N-terminal; self-assembled nanofibrous cluster and application to selective progesterone detection in an aqueous medium

Despite the adequacy of the endogenous steroid (progesterone) levels in biological functioning, elevated levels of progesterone hormone have several physiological effects that are amplified due to its direct and indirect uptake from the environment, food products, and medical therapy. So, it is much needed to evaluate the progesterone levels in environmental samples as well as for biological fluids. In this work, we focused on the development of the nano sensing probe for the selective detection of progesterone among the library of steroid hormones belonging to the class of female sex hormones. Herein, functionalization of dipeptide is carried out at N-terminal to produce N-functionalized dipeptide (SS3), and simultaneously, its self-assembly properties are explored. Furthermore, HR-TEM imaging was also performed to examine the morphology of the self-assembled architectures before and after the addition of the steroid hormone. To investigate the binding mechanism of the sensing probe, Fluorescence spectroscopy, Circular Dichroism (CD), MD-Simulation, and DFT studies were performed and studied in detail. Moreover, to check the potency of the real-time application of the developed nanoprobe, we have successfully determined the spiked concentration of progesterone levels in pharmaceutical and biological fluid samples with functional percentage recovery. Also, the stability and other competitive binding studies of the probe with the coexisting substances are performed to check the rationality of the sensing probe at physiological conditions.

A Significant Fluorescent Aptamer Sensor Based on Carbon Dots and Graphene Oxide for Highly Selective Detection of Progesterone

In this paper, a fluorescent aptamer sensor was constructed based on the carbon dots (CDs) and graphene oxide (GO). This sensor combines the excellent fluorescence performance of CDs with the high specificity of aptamer, which can detect progesterone (P₄) with high sensitivity and selectivity. In the absence of P₄, the CDs-aptamer system and GO form a fluorescence resonance energy transfer process (FRET), which quenches the fluorescence of the CDs. When P₄ is added, the aptamer specifically binds to it, resulting the fluorescence of the CDs is recovered. At optimal conditions, the fluorescence intensity recovered by the CDs has a linear relationship with the concentration of P₄ in the range of 0.1-120 nM and the detection limit is 3.3 × 10^-11 M. Besides, the sensor has satisfactory detection results of P₄ in milk, indicating that constructed method has enormous potential for application in food safety.

Comprehensive review of conventional and state-of-the-art detection methods of Cryptosporidium

Cryptosporidium is a critical waterborne protozoan pathogen found in water resources that have been a major cause of death and serious illnesses worldwide, costing millions of dollars annually for its detection and treatment. Over the past several decades, substantial efforts have been made towards developing techniques for the detection of Cryptosporidium. Early diagnostic techniques were established based on the existing tools in laboratories, such as microscopes. Advancements in fluorescence microscopy, immunological, and molecular techniques have led to the development of several kits for the detection of Cryptosporidium spp. However, these methods have several limitations, such as long processing times, large sample volumes, the requirement for bulky and expensive laboratory tools, and the high cost of reagents. There is an urgent need to improve these existing techniques and develop low-cost, portable and rapid detection tools for applications in the water quality industry. In this review, we compare recent advances in nanotechnology, biosensing and microfluidics that have facilitated the development of sophisticated tools for the detection of Cryptosporidium spp.Finally, we highlight the advantages and disadvantages, of these state-of-the-art detection methods compared to current analytical methodologies and discuss the need for future developments to improve such methods for detecting Cryptosporidium in the water supply chain to enable real-time and on-site monitoring in water resources and remote areas.

Portable on-chip colorimetric biosensing platform integrated with a smartphone for label/PCR-free detection of Cryptosporidium RNA

Cryptosporidium, a protozoan pathogen, is a leading threat to public health and the economy. Herein, we report the development of a portable, colorimetric biosensing platform for the sensitive, selective and label/PCR-free detection of Cryptosporidium RNA using oligonucleotides modified gold nanoparticles (AuNPs). A pair of specific thiolated oligonucleotides, complementary to adjacent sequences on Cryptosporidium RNA, were attached to AuNPs. The need for expensive laboratory-based equipment was eliminated by performing the colorimetric assay on a micro-fabricated chip in a 3D-printed holder assembly. A smartphone camera was used to capture an image of the color change for quantitative analysis. The detection was based on the aggregation of the gold nanoparticles due to the hybridization between the complementary Cryptosporidium RNA and the oligonucleotides immobilized on the AuNPs surface. In the complementary RNA's presence, a distinctive color change of the AuNPs (from red to blue) was observed by the naked eye. However, in the presence of non-complementary RNA, no color change was observed. The sensing platform showed wide linear responses between 5 and 100 µM with a low detection limit of 5 µM of Cryptosporidium RNA. Additionally, the sensor developed here can provide information about different Cryptosporidium species present in water resources. This cost-effective, easy-to-use, portable and smartphone integrated on-chip colorimetric biosensor has great potential to be used for real-time and portable POC pathogen monitoring and molecular diagnostics.

Advances and Challenges in Small-Molecule DNA Aptamer Isolation, Characterization, and Sensor Development

Aptamers are short oligonucleotides isolated in vitro from randomized libraries that can bind to specific molecules with high affinity, and offer a number of advantages relative to antibodies as biorecognition elements in biosensors. However, it remains difficult and labor-intensive to develop aptamer-based sensors for small-molecule detection. Here, we review the challenges and advances in the isolation and characterization of small-molecule-binding DNA aptamers and their use in sensors. First, we discuss in vitro methodologies for the isolation of aptamers, and provide guidance on selecting the appropriate strategy for generating aptamers with optimal binding properties for a given application. We next examine techniques for characterizing aptamer-target binding and structure. Afterwards, we discuss various small-molecule sensing platforms based on original or engineered aptamers, and their detection applications. Finally, we conclude with a general workflow to develop aptamer-based small-molecule sensors for real-world applications.

Bioanalytical methodologies for clinical investigation of endocrine-disrupting chemicals: a comprehensive update

Endocrine-disrupting chemicals (EDCs) are xenobiotics that disrupt the endocrine system in humans at ecologically significant concentrations. Various substances are exposed to human health via routes including food, water, air and skin that result in disastrous maladies at low doses as well. Therefore EDCs need a meticulous strategy of analysis for dependable and consistent monitoring in humans. The management and risk assessment necessitate advancements in the detection methodologies of EDCs. Hyphenated MS-based chromatograph and other validated laboratory analysis methods are widely available and employed. Besides, in vitro bioassay techniques and biosensors are also used to conduct accurate toxicological tests. This article provides a revision of various bioanalytical detection methods and technologies for the clinical estimation of EDCs.

Aptasensors for Point-of-Care Detection of Small Molecules

Aptamers, a group of nucleic acids which can specifically bind to a target molecule, have drawn extensive interest over the past few decades. For analytics, aptamers represent a viable alternative to gold-standard antibodies due to their oligonucleic nature combined with advantageous properties, including higher stability in harsh environments and longer shelf-life. Indeed, over the last decade, aptamers have been used in numerous bioanalytical assays and in various point-of-care testing (POCT) platforms. The latter allows for rapid on-site testing and can be performed outside a laboratory by unskilled labor. Aptamer technology for POCT is not limited just to medical diagnostics; it can be used for a range of applications, including environmental monitoring and quality control. In this review, we critically examine the use of aptamers in POCT with an emphasis on their advantages and limitations. We also examine the recent success of aptasensor technology and how these findings pave the way for the analysis of small molecules in POCT and other health-related applications. Finally, the current major limitations of aptamers are discussed, and possible approaches for overcoming these challenges are presented.

Dual-recognition molecularly imprinted aptasensor based on gold nanoparticles decorated carboxylated carbon nanotubes for highly selective and sensitive determination of histamine in different matrices

In this study, an electrochemical aptamer based sensor (aptasensor) was proposed for specific recognition of histamine (HIS). The electrochemical aptasensor based on fabrication of glassy carbon electrode (GCE) with molecular imprinted polymer (MIP) and DNA aptamers on gold nanoparticles (AuNPs) and carboxylated carbon nanotubes (cCNTs) (MIP-apta/AuNPs/cCNTs/GCE). The aptasensor exhibits high selectivity towards HIS detection as it has two recognition elements which are MIP cavities and aptamer interaction. Upon exposure of MIP-apt/AuNPs/cCNTs/GCE to HIS, the current of redox probe was decreased that depends on the template (HIS) concentration. The effects of aptamer concentration, incubation time, pH and AuNPs electro-deposition time were optimized. Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques were used to analyze HIS in complicated matrices. Favorable performance of MIP-apt/AuNPs/cCNTs/GCE was achieved with linearity ranges of 0.46-35 nmol L^-1 and 0.35-35 nmol L^-1 with limits of detection (LODs, S/N = 3) of 0.15 nmol L^-1 and 0.11 nmol L^-1 using DPV and EIS, respectively. The fabricated aptasensor displayed high selectivity, desirable reproducibility and stability. The MIP-apt/AuNPs/cCNTs/GCE was used to detect HIS in human plasma and canned tuna samples with good recoveries % and RSDs %.

Impedimetric Aptamer-Based Biosensors: Applications

Impedimetric aptamer-based biosensors show high potential for handheld devices and point-of-care tests. In this review, we report on recent advances in aptamer-based impedimetric biosensors for applications in biotechnology. We detail on analytes relevant in medical and environmental biotechnology as well as food control, for which aptamer-based impedimetric biosensors were developed. The reviewed biosensors are examined for their performance, including sensitivity, selectivity, response time, and real sample validation. Additionally, the benefits and challenges of impedimetric aptasensors are summarized.

3D-Printed Flow Cells for Aptamer-Based Impedimetric Detection of E. coli Crooks Strain

Electrochemical spectroscopy enables rapid, sensitive, and label-free analyte detection without the need of extensive and laborious labeling procedures and sample preparation. In addition, with the emergence of commercially available screen-printed electrodes (SPEs), a valuable, disposable alternative to costly bulk electrodes for electrochemical (bio-)sensor applications was established in recent years. However, applications with bare SPEs are limited and many applications demand additional/supporting structures or flow cells. Here, high-resolution 3D printing technology presents an ideal tool for the rapid and flexible fabrication of tailor-made, experiment-specific systems. In this work, flow cells for SPE-based electrochemical (bio-)sensor applications were designed and 3D printed. The successful implementation was demonstrated in an aptamer-based impedimetric biosensor approach for the detection of Escherichia coli (E. coli) Crooks strain as a proof of concept. Moreover, further developments towards a 3D-printed microfluidic flow cell with an integrated micromixer also illustrate the great potential of high-resolution 3D printing technology to enable homogeneous mixing of reagents or sample solutions in (bio-)sensor applications.

A label-free electrochemical DNA biosensor for kanamycin detection based on diblock DNA with poly-cytosine as a high affinity anchor on graphene oxide

It is urgent to develop a more simple and sensitive method to detect antibiotic residues considering the harm of antibiotic residues in food to the human body. Herein we designed a label-free electrochemical DNA biosensor for the sensitive detection of kanamycin (KAN) based on diblock DNA with a 15-mer of poly-cytosine (poly-C). The diblock DNA can be immobilized on graphene oxide (GO) due to strong physical adsorption between the 15-mer of poly-C and GO. The aptamer of KAN acted as the other block for rapidly binding the target. It can specifically capture the target, which leads to the change of electrochemical signal. Consequently, the DNA biosensor exhibited high sensitivity and specificity towards KAN, the linear range was from 0.05 pM to 100 nM with a detection limit of 0.0476 pM. The developed DNA biosensor was constructed easily and showed promising applications for the detection of antibiotic residues for food safety.

Functional Molecular Interfaces for Impedance-Based Diagnostics

In seeking to develop and optimize reagentless electroanalytical assays, a consideration of the transducing interface features lies key to any subsequent sensitivity and selectivity. This review briefly summarizes some of the most commonly used receptive interfaces that have been employed within the development of impedimetric molecular sensors. We discuss the use of high surface area carbon, nanoparticles, and a range of bioreceptors that can subsequently be integrated. The review spans the most commonly utilized biorecognition elements, such as antibodies, antibody fragments, aptamers, and nucleic acids, and touches on some novel emerging alternatives such as nanofragments, molecularly imprinted polymers, and bacteriophages. Reference is made to the immobilization chemistries available along with a consideration of both optimal packing density and recognition probe orientation. We also discuss assay-relevant mechanistic details and applications in real sample analysis.

Mapping the binding region of aptamer targeting small molecule: Dabigatran etexilate, an anti-coagulant

Aptamers are single-stranded DNA or RNA, which have attracted considerable scientific interest due to their characteristic of specific and selective binding to target molecules. They are evolved from the in vitro process known as systematic evolution of ligands by exponential enrichment (SELEX). This paper reports a simple experimental approach to elucidate the binding region of small targets binding aptamers. A previously isolated 60-mer aptamer for the anti-coagulant dabigatran etexilate (DBG) was used for this investigation. Complimentary sequences labelled with a fluorophore and a quencher were used for testing the binding region by change in the fluorescence signal. The full-length aptamer was truncated to multiple shorter copies including a 38 nucleotides sequence that showed 47 fold high affinity compared to the original aptamer. Circular dichroism spectroscopy (CD) measurements indicate that the 38-mer is remarkably more sensitive than the parent aptamer. The truncated 38-mer sequence was used to construct a turn-on fluorescence sensor with the detection limit of 1 nM. The performance of the sensor was examined in blood serum samples and showed excellent recovery percentages exceeding 98%. The reported screening protocol could be applied to the growing small targets aptasensors that require efficient binding aptamer sequences coupled with optimum signal transduction methods.

Selection, characterization, and electrochemical biosensing application of DNA aptamers for sepiapterin

Sepiapterin reductase deficiency (SR) is a rare inborn disorder of neurotransmitter metabolism. The early diagnosis of SR disease should be achieved through the determination of the sepiapterin level in body fluids of suspected patients. Here, we report the selection, identification, and characterization of DNA aptamers against sepiapterin. The aptamer selection was achieved via the systematic evolution of ligand by the exponential enrichment technique. After ten rounds of selection, high-affinity aptamers were identified. The binding affinities of the selected aptamers were evaluated using fluorescence binding assays showing dissociation constants ranging from 37.3 to 79.0 nM. The highest affinity aptamer was then integrated into a competitive electrochemical biosensor. The biosensor achieved outstanding sensitivity with a detection limit of 0.8 pg/ml which was much lower than the reported chromatographic method for sepiapterin quantification. The aptasensor has also shown a high degree of selectivity against the closely-related compound. The aptasensor was then challenged by detecting the sepiapterin in spiked serum samples where a good recovery percentage was achieved.

Magnetic-Optical Core-Shell Nanostructures for Highly Selective Photoelectrochemical Aptasensing

Selectivity is a crucial parameter for photoelectrochemical (PEC) sensing in a practical setting. Despite the use of specific probes such as aptamers, antibodies, and enzymes, coexisting interferences can still result in inaccuracies in PEC sensing, especially for complex biosample matrixes. Here we report the design of an Fe₃O₄@SiO₂@TiO₂ magnetic-optical bifunctional beacon applied in a novel PEC sensor that can selectively capture progesterone in complex biosamples, be magnetically separated and cleaned, and be detected in pure phosphate buffer solution (PBS). The magnetic separation strategy efficiently removes the complex coexisting species from the modified electrode surface and drastically enhances the selectivity of the as-designed PEC sensor. The as-designed PEC sensor is cost-effective, easy to fabricate, highly selective and sensitive, and highly reliable, making it a promising platform for efficient aptasensing.