A new cognate aptamer pair-based sandwich-type electrochemical biosensor for sensitive detection of Staphylococcus aureus

Rotary fluorescence array microfluidic chip for rapid detection of multiple pathogens in foods using dual-discs assisted recycling for signal amplification

BACKGROUND

The ability to rapidly and on-site detect multiple pathogens in food is crucial for food safety monitoring. The microfluidic chip integrated with aptamer (Apt) probes stands as a powerful tool for this venture. However, the utility of these chips has been constrained by the need for cumbersome fluid control devices, such as syringe pumps and bulky optical detectors, so the development of highly integrated integrated chips has become one of the priorities of biosensor development in recent years.

RESULT

In this work, a novel rotary fluorescence array microfluidic chip has been engineered for the simultaneous and rapid detection of three pathogens. The chip has three different detection regions and a double-layer structure composed of PDMS and glass. The Apts and its complementary DNA strands were immobilized on the gold nanoparticle layer in the detection region for pathogen identification, the fluorescence (FL) from the double-stranded staining solution added after the reaction was used for signal amplification. Different arrays of gold discs can be employed to identify various bacteria. This method enables the detection of Staphylococcus aureus (S.A), Salmonella typhimurium (S.T), and Vibrio parahemolyticus (V.P) in food samples within 30 min at a sensitivity of 7-39 CFU/mL.

SIGNIFICANCE

The microfluidic chip has good specificity and sensitivity while avoiding cross interference, and the ratio form of quantification avoids background light interference. Different arrays can be used to identify different bacteria, which is of great significance for the rapid detection of a variety of foodborne pathogens in the field.

A highly selective electrochemical aptasensor for Pb2+ based on molecular imprinting technology and tetrahedral DNA nanostructure

A novel electrochemical biosensor for the detection of lead ions (Pb2+) with improved specificity and sensitivity was developed. The sensor design incorporated molecular imprinting technology, where chitosan was polymerized on the electrode surface to form a lead-specific cavity structure, thereby enhancing selectivity in complex sample matrices. Meanwhile, the tetrahedral DNA nanostructure was employed as the recognition probe to mitigate the entanglement issues commonly associated with single-stranded DNA, thus improving the sensitivity of the detection. The developed sensor exhibited a linear dynamic range from 0.050 to 2.000 μg/mL, with a limit of detection (LOD) of 0.0034 μg/mL. The aptasensor's efficacy was verified through the analysis of aquatic samples, demonstrating a high degree of reliability comparable to that of inductively coupled plasma mass spectrometry (ICP-MS).

Novel High-Throughput Electrochemical Detection of Staphylococcus Aureus, Bacillus Cereus, or Micrococcus Luteus Using AuNPs@Ti3C2Tz Functionalized with Sandwich Peptides

Affinity-based electrochemical biosensors hold promise for detecting pathogenic bacteria in environmental applications. This study focuses on detecting gram-positive bacteria, which can cause fatal infections and are a major global mortality factor. An electrochemical biosensor platform using high-throughput 16-channel gold disk electrodes (16-GDEs) inspired by bio-microelectromechanical systems (BioMEMS) is developed, it incorporates a nanocomposite (AuNPs@Ti3C2Tz) with sandwich peptide structures to enhance electroconductivity and biological antifouling. Using AuNPs@Ti3C2Tz-coated 16-GDEs, sensitive biosensors for gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, or Micrococcus luteus) are constructed and validated in fresh-water samples by spiking with bacteria, which showed linear correlations between normalized peak current and logarithmic concentrations of the target bacteria (adjusted R-square ≥ 0.93). A single high-throughput platform containing biosensors for S. aureus, M. luteus, or B. cereus is also developed, exhibiting specific responses without any cross-reactivity in real samples. This platform enabled sensitive simultaneous detection of multiple analytes in environmental samples (500 CFU mL⁻¹) and can be applied to detect any target analyte with a suitable peptide pair. The strategy is to implement a quantitative real-time polymerase chain reaction (RT-qPCR) adaptive sensing device to successfully detect gram-positive bacteria. The nanocomposite-enabled electrochemical biosensor platform on 16-GDEs offers a valuable tool for environmental and clinical diagnostics.

Whole-cell aptamer-based techniques for rapid bacterial detection: Alternatives to traditional methods

Controlling the spread of bacterial infectious diseases is a major public health issue, particularly in view of the pandemic of bacterial resistance to antibiotics. In this context, the detection and identification of pathogenic bacteria is a prerequisite for the implementation of control measures. Current reference methods are mainly based on culture methods, which generate a delay in obtaining a result and requires equipment. Consequently, focusing on the detection of the whole bacterium represents a very attractive alternative, since no culture is required. Several techniques have already been deployed to identify whole-cell bacteria. In recent decades, growing interest in nucleic acid aptamers has emerged as a viable alternative to antibodies as recognition elements, offering preferable stability, cost-efficiency, good specificity and affinity. This review explores current alternative methods for the detection of whole-cell bacteria, with particular emphasis on aptamer-based assays. These assays have shown promising results in various transduction mechanisms, including optical, electrochemical, and mechanical approaches, enhancing their versatility in different diagnostic platforms. The integration of aptamers in these detection methods offers rapid, sensitive, versatile and portable solutions for pathogen identification, positioning them as valuable tools in the fight against bacterial infections.

Multi-functional electrochemiluminescence biosensor for efficient capture, elimination, and sensitive monitoring of Staphylococcus aureus

In this study, we developed a novel strategy for effective bacteria capture, elimination, and detection. The aptamer of Staphylococcus aureus (S. aureus) was immobilized on Fe3O4 NPs and partly hybridized with the T strand, which exhibited good bacterial capture efficiency. Even though high concentration of S. aureus (7.7 × 106 CFU/mL) was introduced, almost all the bacteria were combined on Fe3O4 in 60 min. Meanwhile, efficient amplification strategies include strand-displacement reaction, DNA walker, and essential oil-synthesized Au:Ag NPs were developed for the sensitive measurement of the released T strand during the capture of S. aureus. The green-synthesized Au:Ag NPs can effectively kill S. aureus while also significantly improving the ECL signal (16.7-fold). Owing to the outstanding features of Au:Ag NPs, this novel biosensor displayed a wide linear range and a low detection limit for S. aureus measurement. As a result, this multifunctional technique shows great potential for practical applications in the fields of food safety and the environment.

A novel ratiometric electrochemical aptasensor based on graphene quantum dots/Cu-MOF nanocomposite for the on-site determination of Staphylococcus aureus

The sensitive detection of Staphylococcus aureus (S. aureus) holds great practical importance for ensuring public health and food safety. In this study, a sensitivity and stability ratiometric electrochemical aptasensor using graphene quantum dots/[Cu2.5 (benzotriazole-5-COO)1.5 (benzotriazole-5-COOH)0.5 (μ-Cl)0.5 (μ3-OH)-(H2O)]·3 H2O nanocomposite (GQDs/Cu-MOF) was constructed for S. aureus detection. The GQDs enhanced the sensitivity of the electrochemical aptasensor due to their excellent conductivity and provided stability through their abundant carboxyl groups. The Cu-MOF, possessing electrical activity, not only enhanced the performance of the electrochemical aptasensor but also served as a signal label. The single-stranded DNA1 (S1) was immobilized on the surface of a GQDs/Cu-MOF/screen-printed carbon electrode (S1/GQDs/Cu-MOF/SPCE) as the sensing interface. Subsequently, the S1/GQDs/Cu-MOF/SPCE was hybridized with the probe DNA-ferrocene (S2-Fc), resulting in the generation of electrochemical signals from Cu-MOF (ICu-MOF) and S2-ferrocene (IS2-FC) within the system. However, the electron transfer performance of DNA at the sensing interface was compromised, leading to a reduction in the ICu-MOF. When S. aureus was present in the system, S2-Fc reacted with it and detached from the sensing surface, resulting in a gradual decrease in IS2-FC and an increase in ICu-MOF. Then a ratiometric electrochemical aptasensor was established for S. aureus detection with remarkable sensitivity (0.97 CFU·mL-1), excellent stability, and a broad linear range. Furthermore, the aptasensor was successfully applied to detect S. aureus in tap water, milk, Lonicera japonica, urine, and Zhangjiang River. Additionally, this aptasensor design can be adapted for the detection of other foodborne pathogens, which indicates that the design scheme of the aptasensor has good universality.

Aptamer and DNAzyme Based Colorimetric Biosensors for Pathogen Detection

The detection of pathogens is critical for preventing and controlling health hazards across clinical, environmental, and food safety sectors. Functional nucleic acids (FNAs), such as aptamers and DNAzymes, have emerged as versatile molecular tools for pathogen detection due to their high specificity and affinity. This review focuses on the in vitro selection of FNAs for pathogens, with emphasis on the selection of aptamers for specific biomarkers and intact pathogens, including bacteria and viruses. Additionally, the selection of DNAzymes for bacterial detection is discussed. The integration of these FNAs into colorimetric biosensors has enabled the development of simple, cost-effective diagnostic platforms. Both non-catalytic and catalytic colorimetric biosensors are explored, including those based on gold nanoparticles, polydiacetylenes, protein enzymes, G-quadruplexes, and nanozymes. These biosensors offer visible detection through color changes, making them ideal for point-of-care diagnostics. The review concludes by highlighting current challenges and future perspectives for advancing FNA-based colorimetric biosensing technologies for pathogen detection.

Glycosylation-Targeting Aptamer for the Feasible Construction of a Dual Aptamer-Based Plasmonic Immunosandwich Assay in Cancer Diagnostics

Fibroblast activation protein (FAP) is an important antigen in the tumor microenvironment, which plays a crucial role in promoting extracellular matrix remodeling and tumor cell metastasis. A circulating form of soluble FAP has also been identified in the serum, becoming a biomarker for pan-cancer diagnosis and prognosis. However, the current peptide substrate-based enzymatic activity detection or antibody-dependent detection methods have been hindered by insufficient selectivity and complex operations, so it is valuable to develop effective nucleic acid aptamers as FAP affinity ligands. In order to deeply explore the biomimetic recognition technology, this study proposed an elaborate aptamer screening strategy for targeting the protein characteristic structure. Taking the glycosylation of the FAP protein as a target, four FAP-specific aptamers with high performance were successfully generated. Further, using the champion aptamer as a recognition tool and combining it with ultrasensitive detection technology-surface enhanced Raman scattering (SERS), a novel dual aptamer-based sandwich sensor was constructed for the rapid determination of FAP. Due to the dual-specific recognition of the orthogonal aptamer pair, the sandwich method obviously improved the selectivity to FAP protein, with a maximum cross-reactivity of less than 8% and a quantitation limit of 100 pg/mL. It was conveniently applied in high-sensitive and high-selective detection of serum FAP in cancer patient samples. Therefore, the research of this study not only opens new access for the selection of antiglycan aptamers but also boosts the application of the FAP aptamer as a recognition tool in cancer diagnostics.

In situ noninvasive monitoring of cell secretions based on MOFs/AAO hybrid membrane induced asymmetric ion transport

Nanofluidic hybrid membranes display distinct ionic current rectification (ICR) properties and provide high surface area for immobilizing probes on the outer surface, exhibiting great potential in detection of biomolecules. Herein, we fabricated MOFs/AAO hybrid membrane with aptamers functionalized on the outer surface for in situ detection of living cells released secretions. TNF-α (a small molecular protein secreted by macrophages) was used as a model. After TNF-α was specifically captured by aptamers on the membrane surface, the asymmetry of surface charge on the hybrid membrane was amplified, the ICR was increased from 3.89 to 18.85. According to the ICR change, TNF-α was sensitively measured with a detection limit of ∼0.49 pM, which was significantly lower than other reported methods. When the hybrid membrane was clamped in the middle of self-made device, PET membrane incubated macrophages was rolled up and inserted into the chamber to mimic cellular microenvironment. Macrophages released TNF-α could be real time monitored with ionic current, macrophages and normal cells could be effectively distinguished according to the released TNF-α level. Thus, we proposed a nanofluidic platform for accurately measuring cell secretions in an engineered cellular microenvironment with a direct manner, without the need for labels or amplification steps.

Swift and precise detection of unlabeled pathogens using a nanogap electrode impedimetric sensor facilitated by electrokinetics

For the protection of human health and environment, there is a growing demand for high-performance, user-friendly biosensors for the prompt detection of pathogenic bacteria in samples containing various substances. We present a nanogap electrode-based purely electrical impedimetric sensor that utilizes the dielectrophoresis (DEP) mechanism. Our nanogap sensor can directly and sensitively detect pathogens present at concentrations as low as 1-10 cells/assay in buffers and drinking milk without the need for separation, purification, or specific ligand binding. This is achieved by minimizing the electrical double-layer effect and electrode polarization in nanogap impedance sensors, reducing signal loss. In addition, even at low DEP voltages, nanogap sensors can quickly establish strong DEP forces between the nanogap electrodes to control the spatial concentration of pathogens around the electrodes. This activates and stabilizes inter-electrode signal transmission along the nanogap-aligned pathogens, increasing sensitivity and reducing errors during repeated measurements. The DEP-enabled nanogap impedance sensor developed in this study is valuable for a variety of pathogen detection and monitoring systems including point-of-care testing (POCT) as it can detect pathogens in diverse samples containing multiple substances quickly and with high sensitivity, is compatible with complex solutions such as food and beverages, and provides highly reproducible results without the need for separate binding and separation processes.

Recent Developments in Aptamer-Based Sensors for Diagnostics

Chronic and non-communicable diseases (NCDs) account for a large proportion of global disorders and mortality, posing significant burdens on healthcare systems. Early diagnosis and timely interference are critical for effective management and disease prevention. However, the traditional methods of diagnosis still suffer from high costs, time delays in processing, and infrastructure requirements that are usually unaffordable in resource-constrained settings. Aptamer-based biosensors have emerged as promising alternatives to offer enhanced specificity, stability, and cost-effectiveness for disease biomarker detection. The SELEX (Systematic Evolution of Ligands by Exponential Enrichment) methodology allows developing aptamers with high-affinity binding capabilities to a variety of targets, for instance proteins, cells, or even small molecules, hence rendering them suitable for NCD diagnosis. Aptasensors-recent developments in the electrochemical and optical dominion-offer much enhanced sensitivity, selectivity, and stability of detection across a diverse range of diseases from lung cancer and leukemia to diabetes and chronic respiratory disorders. This study provides a comprehensive review of progress in aptamer-based sensors, focusing on their role in point-of-care diagnostics and adaptability in a real-world environment with future directions in overcoming current limitations.

A novel polydiacetylene-functionalized fibrinogen paper-based biosensor for on-spot and rapid detection of Staphylococcus aureus

Staphylococcus aureus contamination continues to be a harmful foodborne pathogen threatening of human health, and there is a growing need for rapid detection technologies. This study proposed a novel paper biosensor based on a polydiacetylene (PDA) polymer functionalized fibrinogen (Fg) for the detection of S. aureus in food sources. The fluorophore was developed based on the high binding ability of fibrinogen-binding proteins on the surface of S. aureus. This binding caused twisting in the PDA backbone, leading to changes in chromatic and fluorescent. The detection limit of this method was 50.1 CFU/mL for S. aureus-contaminated foodstuffs and 65.0 CFU/mL for the pure S. aureus culture, and the novelty came from its rapidity and selectivity for S. aureus compared to other foodborne bacteria. In summary, the present work provides a rapid detection method for S. aureus detection, which will help in addressing food safety-related issues.

Highly Sensitive One-Pot Isothermal Assay Combining Rolling Circle Amplification and CRISPR/Cas12a for Aflatoxin B1 Detection

Occurrences of mycotoxins in cereals are widespread throughout the world. However, the lack of efficient and ultrasensitive tests has largely impeded the identification of these substances in actual samples. Herein, a novel one-pot isothermal assay that integrates rolling-circle amplification (RCA) and CRISPR/Cas12a to detect aflatoxin B1 (AFB1) is reported. Upon addition of AFB1 to the magnetic bead functionalized with a duplex of the AFB1 aptamer and its complementary DNA (cDNA), the specific recognition of AFB1 by the aptamer causes the release of cDNA to activate the RCA reaction. Subsequently, the RCA amplicon initiates both trans-cleavage and cis-cleavage activities of the endonuclease Cas12a. The synergistic coupling of RCA and CRISPR/Cas12a enables exponential amplification of cDNA, which further promotes CRISPR/Cas12a to nonspecifically cleave the single-stranded DNA reporters with enhanced detection signals. Remarkably, the CRISPR/Cas12a-assisted one-pot isothermal assay can not only achieve ultrasensitive quantitative detection through fluorescence detection, but also achieve visual detection through a lateral flow strip, which improves accessibility to mycotoxin detection in resource-limited regions. The limit of detection was 0.016 and 0.408 ng/mL, respectively. The proposed assay successfully applies in real samples with satisfactory recoveries from 90 to 114%. This study presents a powerful and versatile method for reliable and ultrasensitive detection of mycotoxins in various applications.

Advances in nucleic acid aptamer-based detection of respiratory virus and bacteria: a mini review

Respiratory pathogens infecting the human respiratory system are characterized by their diversity, high infectivity, rapid transmission, and acute onset. Traditional detection methods are time-consuming, have low sensitivity, and lack specificity, failing to meet the needs of rapid clinical diagnosis. Nucleic acid aptamers, as an emerging and innovative detection technology, offer novel solutions with high specificity, affinity, and broad target applicability, making them particularly promising for respiratory pathogen detection. This review highlights the progress in the research and application of nucleic acid aptamers for detecting respiratory pathogens, discussing their selection, application, potential in clinical diagnosis, and future development. Notably, these aptamers can significantly enhance the sensitivity and specificity of detection when combined with detection techniques such as fluorescence, colorimetry and electrochemistry. This review offers new insights into how aptamers can address the limitations of traditional diagnostic methods and advance clinical diagnostics. It also highlights key challenges and future research directions for the clinical application of nucleic acid aptamers.

Bioreceptor modified electrochemical biosensors for the detection of life threating pathogenic bacteria: a review

The lack of reliable and efficient techniques for early monitoring to stop long-term effects on human health is an increasing problem as the pathogenesis effect of infectious bacteria is growing continuously. Therefore, developing an effective early detection technique coupled with efficient and continuous monitoring of pathogenic bacteria is increasingly becoming a global public health prime target. Electrochemical biosensors are among the strategies that can be utilized for accomplishing that goal with promising potential. In recent years, identifying target biological analytes by interacting with bioreceptors modified electrodes is among the most commonly used detection techniques in electrochemical biosensing strategies. The commonly employed bioreceptors are nucleic acid molecules (DNA or RNA), proteins, antibodies, enzymes, organisms, tissues, and biomimetic components such as molecularly imprinted polymers. Despite the advancement in electrochemical biosensing, developing a reliable and effective biosensor for detecting pathogenic bacteria is still in the infancy stage with so much room for growth. A major milestone in addressing some of the issues and improving the detection pathway is the investigation of specific bacterial detection techniques. The present study covers the fundamental concepts of electrochemical biosensors, human PB illnesses, and the latest electrochemical biosensors based on bioreceptor elements that are designed to detect specific pathogenic bacteria. This study aims to assist researchers with the most up-to-date research work in the field of bio-electrochemical pathogenic bacteria detection and monitoring.

Advances in DNA-based electrochemical biosensors for the detection of foodborne pathogenic bacteria

The detection of foodborne pathogenic bacteria is critical in preventing foodborne diseases. DNA-based electrochemical biosensors, with the merits of high sensitivity and short detection time, provide an effective detecting method for foodborne pathogens, attracting significant interest for the past few years. This review mainly describes the important research progress of DNA-based electrochemical biosensors for the detection of foodborne pathogenic bacteria through four perspectives: representative foodborne pathogens detection using electrochemical approaches, DNA immobilization strategies of aptamers, DNA-based signal amplification strategies used in electrochemical DNA sensors, and functional DNA used in electrochemical DNA sensors. Finally, perspectives and challenges are presented in this field. This review will contribute to DNA-based electrochemical biosensor in enhancing the nucleic acid signal amplification.

N vacancy and self-enhancement induced high anodic electrochemiluminescence of 3D g-C3N4 for sensitive staphylococcus aureus analysis

Here, 3D g-C3N4 with dense N vacancy in its 3D porous interconnected open-framework was synthesized, and the co-reactive 3-(dibutylamino)propylamine (DBAPA) was further covalently coupled onto the surface, resulting in a strong self-enhanced anodic electrochemiluminescence (ECL). Through introduction of high-density N vacancy, for the obtained 3D g-C3N4-NV, the band gap was broadened and the electrical conductivity was enhanced, realizing an obvious ECL improvement. Moreover, after the covalent binding of co-reactive DBAPA, the obtained 3D g-C3N4-NV-DBAPA exhibited a more intensive self-enhanced ECL signal due to the higher co-reaction efficiency originated from shorter electron transfer distance and lower energy loss. Based on the high initial signal of the proposed 3D g-C3N4-NV-DBAPA, a sensitive ECL biosensor with signal "on-off" was fabricated in assistance with multiple horizontal ordered hybridization chain reaction (HO-HCR). Through orderly fixing the reacted DNA chains on the Y-shape DNA structure on the electrode could effectively decrease diffusion process and improve the reaction efficiency of HCR process, resulting in the formation of numerous long horizontal double-strand DNA that could immobilize abundant ferrocene-doxorubicin (Fc-Dox) with ECL quenching effect. Meanwhile, compared to the traditional vertical HCR, the HO-HCR could make the quench reagent closer to the ECL emitter on the electrode surface and obtain a more effective quenching effect to enhance the sensing sensitivity. As a result, the proposed ECL biosensor archived the sensitive measurement of staphylococcus aureus with a detection limit of 10.3 aM.

Development and characterization of a portable electrochemical aptasensor for IsdA protein and Staphylococcus aureus detection

Staphylococcus aureus (S. aureus) is recognized as one of the most common causes of gastroenteritis worldwide. This pathogen is a major foodborne pathogen that can cause many different types of various infections, from minor skin infections to lethal blood infectious diseases. Iron-regulated surface determinant protein A (IsdA) is an important protein on the S. aureus surface. It is responsible for iron scavenging via interaction with hemoglobin, haptoglobin, and hemoglobin-haptoglobin complexes. This study develops a portable aptasensor for IsdA and S. aureus detection using aptamer-modified gold nanoparticles (AuNPs) integrated into screen-printed carbon electrodes (SPCEs). The electrode system was made of three parts, including a carbon counter electrode, an AuNPs/carbon working electrode, and a silver reference electrode. The aptamer by Au-S bonding was conjugated on the electrode surface to create the aptasensor platform. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized to investigate the binding interactions between the aptasensor and the IsdA protein. CV studies showed a linear correlation between varying S. aureus concentrations within the range of 101 to 106 CFU/mL, resulting in a limit of detection (LOD) of 0.2 CFU/mL. The results demonstrated strong reproducibility, selectivity, and sensitivity of the aptasensor for enhanced detection of IsdA, along with about 93% performance stability after 30 days. The capability of the aptasensor to directly detect S. aureus via the IsdA surface protein binding was further investigated in a food matrix. Overall, the aptasensor device showed the potential for rapid detection of S. aureus, serving as a robust approach to developing real-time aptasensors to identify an extensive range of targets of foodborne pathogens and beyond.

Flexible microfluidic co-recognition coupled with magnetic enrichment and silent SERS sensing for simultaneous analysis of bacteria in food

Food safety represents a critical global public health issue, with safety challenges posed by foodborne pathogens garnering extensive attention. Therefore, we introduce a co-recognition, enrichment and sensing (CES) all-in-one strategy for analysis of bacteria with low background and high specificity. This method employs antimicrobial peptide (AMP) functionalized magnetic nanoparticles (MNPs) to enrich bacteria and uses aptamer@Au@PBA (KxMFe(CN)6 (M = Pb and Ni)) NPs as silent SERS tags. When both S. aureus and E. coli O157:H7 are present, the silent SERS probes could specifically label the target bacteria, forming a sandwich-like structure. This binding induces silent Raman shifts (2139 cm-1 and 2197 cm-1), enabling quantification of two bacteria. Coupling with the modular flexible microfluidics and magnetic control slider device, this platform facilitates rapid switching between magnetic loading and elution. The CES SERS method demonstrated linear relationships for both S. aureus and E. coli O157:H7 at 50-1600 cfu mL-1, with detection limits of 14 and 18 cfu mL-1, respectively. The method achieved recovery rates of 85.6-112% and relative standard deviations of 1.5-8.6%. Validation using the ELISA method revealed relative errors between -7.5 and 4.3%. The CES approach has potential applications in food safety, environmental monitoring, and biomedical diagnosis.

A novel fluorescent aptasensor for sensitive and selective detection of environmental toxins fumonisin B1 based on enzyme-assisted dual recycling amplification and 2D δ-FeOOH-NH2 nanosheets

Fumonisin (FB) is a pervasive hazardous substance in the environment, presenting significant threats to human health and ecological systems. Thus, the selective and sensitive detection of fumonisin B1 (FB1) is crucial due to its high toxicity and wide distribution in corn, oats, and related products. In this work, we developed a novel and versatile fluorescent aptasensor by combining enzyme-assisted dual recycling amplification with 2D δ-FeOOH-NH2 nanosheets for the determination of FB1. The established CRISPR/Cas12a system was activated by using activator DNA (aDNA), which was released via a T7 exonuclease-assisted recycling reaction. Additionally, the activated Cas12a protein was utilized for non-specifically cleavage of the FAM-labeled single-stranded DNA (ssDNA-FAM) anchored on δ-FeOOH-NH2 nanosheets. The pre-quenched fluorescence signal was restored due to the desorption of the cleaved ssDNA-FAM. Due to the utilization of this T7 exonuclease-Cas12a-δ-FeOOH-NH2 aptasensor for signal amplification, the detection range of FB1 was expanded from 1 pg/mL to 100 ng/mL, with a limit of detection (LOD) as low as 0.45 pg/mL. This study not only provides novel insights into the development of fluorescence biosensors based on 2D nanomaterials combined with CRISPR/Cas12a, but also exhibits remarkable applicability in detecting other significant targets.

Ultra-sensitive and rapid detection of Salmonella enterica and Staphylococcus aureus to single-cell level by aptamer-functionalized carbon nanotube field-effect transistor biosensors

Foodborne diseases caused by Salmonella enterica (S. enterica) and Staphylococcus aureus (S. aureus) significantly impact public health, underscoring the imperative for highly sensitive, rapid, and accurate detection technologies to ensure food safety and prevent human diseases. Nanomaterials hold great promise in the development of high-sensitivity transistor biosensors. In this work, field-effect transistor (FET) comprising high-purity carbon nanotubes (CNTs) were fabricated and modified with corresponding nucleic acid aptamers for the high-affinity and selective capture of S. enterica and S. aureus. The aptamer-functionalized CNT-FET biosensor demonstrated ultra-sensitive and rapid detection of these foodborne pathogens. Experimental results indicated that the biosensor could detect S. enterica at a limit of detection (LOD) as low as 1 CFU in PBS buffer, and S. aureus at an LOD of 1.2 CFUs, achieving single-cell level detection accuracy with exceptional specificity. The biosensor exhibited a rapid response time, completing single detections within 200 s. Even in the presence of interference from six complex food matrices, the biosensor maintained its ultra-sensitive (3.1 CFUs) and rapid response (within 200 s) characteristics for both pathogens. The developed aptamer-functionalized CNT-FET biosensor demonstrates a capability for low-cost, ultra-sensitive, label-free, and rapid detection of low-abundance S. enterica and S. aureus in both buffer solutions and complex environments. This innovation holds significant potential for applying this detection technology to on-site rapid testing scenarios, offering a promising solution to the pressing need for efficient and reliable pathogen monitoring in various settings.

Recent Advances in Aptamer-Based Biosensors for Bacterial Detection

The rapid and sensitive detection of pathogenic bacteria is becoming increasingly important for the timely prevention of contamination and the treatment of infections. Biosensors based on nucleic acid aptamers, integrated with optical, electrochemical, and mass-sensitive analytical techniques, have garnered intense interest because of their versatility, cost-efficiency, and ability to exhibit high affinity and specificity in binding bacterial biomarkers, toxins, and whole cells. This review highlights the development of aptamers, their structural characterization, and the chemical modifications enabling optimized recognition properties and enhanced stability in complex biological matrices. Furthermore, recent examples of aptasensors for the detection of bacterial cells, biomarkers, and toxins are discussed. Finally, we explore the barriers to and discuss perspectives on the application of aptamer-based bacterial detection.

Rapid and ultra-sensitive lateral flow assay for pathogens based on multivalent aptamer and magnetic nanozyme

Ultra-sensitive LFA methods for pathogen detection commonly depended on tedious and time-consuming nucleic acid amplification. Here, a high affinity multivalent aptamer (multi-Apt) for S. aureus was obtained through exquisite engineering design. The scaffold and conformation of the multi-Apt were found to be key factors in the detection signal of aptsensors. After optimization, the binding affinity of the multi-Apt to S. aureus was improved by more than 8-fold from 135.9 nM to 16.77 nM. By the joint use of the multi-Apt and a multifunctional nanozyme Fe3O4@MOF@PtPd, a fast and ultra-sensitive LFA for S. aureus was developed (termed MA-MN LFA). In this method, a Fe3O4@MOF@PtPd nanozyme was modified with vancomycin and could efficiently capture and separate S. aureus. Moreover, the multi-Apt worked together with the nanozyme to bind with S. aureus to form a ternary complex at the same time, which simply the fabrication of LFA strip. The developed MA-MN LFA could detect S. aureus as low as 2 CFU/mL within 30 min and a wide linear range of 10-1 × 108 CFU/mL was obtained. The detection is easily operated, fast (can be completed within 30 min) and versatile for Gram-positive pathogens, thus has great potential as a powerful tool in pathogen detection.

Electrochemical biosensors for pathogenic microorganisms detection based on recognition elements

The worldwide spread of pathogenic microorganisms poses a significant risk to human health. Electrochemical biosensors have emerged as dependable analytical tools for the point-of-care detection of pathogens and can effectively compensate for the limitations of conventional techniques. Real-time analysis, high throughput, portability, and rapidity make them pioneering tools for on-site detection of pathogens. Herein, this work comprehensively reviews the recent advances in electrochemical biosensors for pathogen detection, focusing on those based on the classification of recognition elements, and summarizes their principles, current challenges, and prospects. This review was conducted by a systematic search of PubMed and Web of Science databases to obtain relevant literature and construct a basic framework. A total of 171 publications were included after online screening and data extraction to obtain information of the research advances in electrochemical biosensors for pathogen detection. According to the findings, the research of electrochemical biosensors in pathogen detection has been increasing yearly in the past 3 years, which has a broad development prospect, but most of the biosensors have performance or economic limitations and are still in the primary stage. Therefore, significant research and funding are required to fuel the rapid development of electrochemical biosensors. The overview comprehensively evaluates the recent advances in different types of electrochemical biosensors utilized in pathogen detection, with a view to providing insights into future research directions in biosensors.

A 2D carbon nitride-based electrochemical aptasensor with reverse amplification for highly sensitive detection of okadaic acid in shellfish

Okadaic acid (OA) is one of the main virulence factors of diarrheal shellfish toxins (DSP). It is of great significance to detect OA with an accurate, specific and cost-effective technique in the fields of seafood safety and water quality control. In this work, an electrochemical aptasensor with reverse amplification was developed for the sensitive detection of OA. A two-dimensional graphite-phase nanomaterial (carbon nitride) modified with an anti-OA aptamer and thionine (Th) was immobilized onto the surface of the electrochemical electrode as the sensitive element to capture target OA molecules. ssDNA-modified carbon nitride was used as the reverse amplification element by hybridizing with non-OA linked aptamers. The preparation of the electrochemical aptasensor was well characterized by Scanning Electron Microscopy (SEM), zeta potential detection, UV-Vis absorption, Brunner-Emmet-Teller (BET) measurements, and electrochemical measurements. The quantitative assessment of OA was achieved by differential pulse voltammetry (DPV). Experimental results indicated that this aptasensor showed a concentration-dependent response to OA with a good detection performance including in terms of selectivity, repeatability, reproducibility, and stability. It exhibited 100-fold selectivity between OA and other toxins including dinophysistoxins (DTX), pectenotoxins (PTX), and yessotoxins (YTX). In addition, it showed a much wider quantification range, which is 10-13 M-10-10 M (0.080-80.50 pg mL-1). The detection limit was as low as 10-13 M (0.080 pg mL-1). The aptasensor also successfully achieved significant practicality on real shellfish samples contaminated by OA. All these results demonstrated that the reverse amplification strategy for marine toxin detection may provide a label-free and rapid detection approach for portable applications in the fields of environmental monitoring and food security.

Nanomaterial-based methods for sepsis management

Sepsis is a serious disease caused by an impaired host immune response to infection, resulting in organ dysfunction, tissue damage and is responsible for high in-hospital mortality (approximately 20%). Recently, WHO documented sepsis as a global health priority. Nevertheless, there is still no effective and specific therapy for clinically detecting sepsis. Nanomaterial-based approaches have appeared as promising tools for identifying bacterial infections. In this review, recent biosensors are introduced and summarized as nanomaterial-based platforms for sepsis management and severe complications. Biosensors can be used as tools for the diagnosis and treatment of sepsis and as nanocarriers for drug delivery. In general, diagnostic methods for sepsis-associated bacteria, biosensors developed for this purpose are presented in detail, and their strengths and weaknesses are discussed. In other words, readers of this article will gain a comprehensive understanding of biosensors and their applications in sepsis management.

Recent advances in electrochemical aptasensors and genosensors for the detection of pathogens

In recent years, pathogenic microorganisms have caused significant mortality rates and antibiotic resistance and triggered exorbitant healthcare costs. These pathogens often have high transmission rates within human populations. Rapid diagnosis is crucial in controlling and reducing the spread of pathogenic infections. The diagnostic methods currently used against individuals infected with these pathogens include relying on outward symptoms, immunological-based and, some biomolecular ones, which mainly have limitations such as diagnostic errors, time-consuming processes, and high-cost platforms. Electrochemical aptasensors and genosensors have emerged as promising diagnostic tools for rapid, accurate, and cost-effective pathogen detection. These bio-electrochemical platforms have been optimized for diagnostic purposes by incorporating advanced materials (mainly nanomaterials), biomolecular technologies, and innovative designs. This review classifies electrochemical aptasensors and genosensors developed between 2021 and 2023 based on their use of different nanomaterials, such as gold-based, carbon-based, and others that employed other innovative assemblies without the use of nanomaterials. Inspecting the diagnostic features of various sensing platforms against pathogenic analytes can identify research gaps and open new avenues for exploration.

Group selective aptamers: Broad-spectrum recognition of target groups in Cronobacter species and implementation of electrochemical biosensors as receptors

Aptamers are a versatile class of receptors with a high affinity and selectivity for specific targets. Although their ability to recognize individual targets has been extensively studied, some scenarios require the development of receptors capable of identifying all target groups. This study investigated the use of aptamers to achieve the broad-spectrum recognition of groups instead of individual targets. Aptamers were screened for selectively distinct groups of Cronobacter species associated with foodborne diseases. Seven Cronobacter spp. were divided into Group A (C. sakazakii, C. malonaticus, C. turicensis, and C. muytjensii) and Group B (C. dublinensis, C. condimenti, and C. universalis). Aptamers with exclusive selectivity for each group were identified, allowing binding to the species within their designated group while excluding those from the other group. The screened aptamers demonstrated reliable affinity and specificity with dissociation constants ranging from 1.3 to 399.7 nM for Group A and 4.0-24.5 nM for Group B. These aptamers have also been successfully employed as receptors in an electrochemical biosensor platform, enabling the selective detection of each group based on the corresponding aptamer (limit of detection was 7.8 and 3.2 CFU for Group A and Group B, respectively). The electrochemical sensor effectively detected the extent of infection in each group in powdered infant formula samples. This study highlights the successful screening and application of group-selective aptamers as sensing receptors, emphasizing their potential for diverse applications in different fields such as food safety, environmental monitoring, and clinical diagnostics, where the selective biosensing of target groups is crucial.

Aptamer-Based Smart Targeting and Spatial Trigger-Response Drug-Delivery Systems for Anticancer Therapy

In recent years, the field of drug delivery has witnessed remarkable progress, driven by the quest for more effective and precise therapeutic interventions. Among the myriad strategies employed, the integration of aptamers as targeting moieties and stimuli-responsive systems has emerged as a promising avenue, particularly in the context of anticancer therapy. This review explores cutting-edge advancements in targeted drug-delivery systems, focusing on the integration of aptamers and stimuli-responsive platforms for enhanced spatial anticancer therapy. In the aptamer-based drug-delivery systems, we delve into the versatile applications of aptamers, examining their conjugation with gold, silica, and carbon materials. The synergistic interplay between aptamers and these materials is discussed, emphasizing their potential in achieving precise and targeted drug delivery. Additionally, we explore stimuli-responsive drug-delivery systems with an emphasis on spatial anticancer therapy. Tumor microenvironment-responsive nanoparticles are elucidated, and their capacity to exploit the dynamic conditions within cancerous tissues for controlled drug release is detailed. External stimuli-responsive strategies, including ultrasound-mediated, photo-responsive, and magnetic-guided drug-delivery systems, are examined for their role in achieving synergistic anticancer effects. This review integrates diverse approaches in the quest for precision medicine, showcasing the potential of aptamers and stimuli-responsive systems to revolutionize drug-delivery strategies for enhanced anticancer therapy.

Sensitive dual-mode sensing platform for Amyloid β detection: Combining dual Z-scheme heterojunction enhanced photoelectrochemistry analysis and dual-wavelength ratiometric electrochemiluminescence strategy

As a tumor biomarker, the accumulation of amyloid β oligomers (Aβo) in the brain has been suggested as a key feature in the pathogenesis and progression of Alzheimer's disease (AD). In this work, we designed a novel photoelectrochemical (PEC) and electrochemiluminescence resonance energy transfer (ECL-RET) dual-mode biosensor to achieve ultra-sensitive detection of Aβo. Specifically, the electrode surface modified Carbon Dots (C Dots) and the electrodeposited polyaniline (PANI) film formed a Z-scheme heterojunction reversing the photocurrent signal, and then the Aβo specific recognition peptide was attached to the surface via amide bonding between the amino group of PANI and carbonyl group of peptide. After that, in the presence of CdTe labeled specific recognition aptamer for Aβ (CdTe-Apt), Aβo was captured to construct a sandwich-type biosensor and exhibited a significantly enhanced cathodic photocurrent response because the formed dual Z-scheme heterojunction promoted charge separation efficiency. Interestingly, the proposed biosensor also caused a ratiometric change in the ECL intensity at 555 nm and 640 nm. Therefore, the developed biosensor achieved dual-mode detection of Aβo, where the PEC detection range of Aβo was from 10 fM to 0.1 μM (with a detection limit of 4.27 fM) and the ECL method provided a linear detection range of 10 fM to 10 nM (with a detection limit of 6.41 fM). The stability and reliability of the experimental results indicate that this has been a promising biosensing pattern and could be extended to the analysis of other biomarkers.

Integrating Ligands into Nucleic Acid Systems

Signal transduction from non-nucleic acid ligands (small molecules and proteins) to structural changes of nucleic acids plays a crucial role in both biomedical analysis and cellular regulations. However, how to bridge between these two types of molecules without compromising the expandable complexity and programmability of the nucleic acid nanomachines is a critical challenge. Compared with the previously most widely applied transduction strategies, we review the latest advances of a kinetically controlled approach for ligand-oligonucleotide transduction in this Concept article. This new design works through an intrinsic conformational alteration of the nucleic acid aptamer upon the ligand binding as a governing factor for nucleic acid strand displacement reactions. The functionalities and applications of this transduction system as a ligand converter on biosensing and DNA computation are described and discussed. Furthermore, we propose some potential scenarios for utilization of this ligand transduction design to regulate gene expression through synthetic RNA switches in the cellular contexts. Finally, future perspectives regarding this ligand-oligonucleotide transduction platform are also discussed.

Vancomycin-modified nitrogen and chloride doped carbon dots and their application as a Staphylococcus aureus probe

In this research, N, Cl-doped carbon dots (N, Cl-CDs) were prepared in choline chloride-glycerol deep eutectic solvent (DES) by microwave method. N, Cl-CDs surface was modified with vancomycin for detection of Staphylococcus aureus (S. aureus) bacteria in the range of 10²-10⁷ colony-forming unit per milliliter (CFU/mL). The detection limit was 10¹ CFU/mL. Morphology and structure of N, Cl-CDs were characterized by transmission electron microscopy (TEM), X-ray photon spectroscopy (XPS), photoluminescence spectroscopy, FT-IR spectroscopy, energy dispersive X-ray spectroscopy (EDXS) and zeta potential. The prepared N, Cl-CDs had excellent dispersion in water, particle size range of 2-3 nm, and quantum yield of 38.75%. Speed, wide linear range and more convenient were advantages of new probe with respect to other methods.

Biomineralization-inspired artificial clickase for portable click SERS immunoassay of Salmonella enterica serovar Paratyphi B in foods

Inspired by a biomineralization behavior, we prepared a nanoflower-like artificial clickase (namely LCN clickase) for portable and sensitive click SERS immunoassay of foodborne bacterial pathogen. Encouraged by its high click catalytic activity to trigger Cu(I)-catalyzed azide-alkyne cycloaddition reaction, LCN clickase was successfully used for establishing a novel click SERS immunoassay by combining the clickase-mediated SERS signal variation at Raman-silent region. The developed method not only effectively eliminated the interferences between Raman reporter and biological species, but also reduced the complex sample matrix interference. Compared with traditional CuAAC-based immunoassays, the established method avoided the superfluous dissolution process of nanocatalysts and eliminated the requirement of reducing agent during detection, thereby shortening detection time and improving detection reliability. Impressively, the proposed method showed high selectivity and sensitivity for detection of Salmonella enterica serovar Paratyphi B with a low LOD of 20 CFU/mL, exhibiting a great potential in detection of foodborne bacterial pathogen in food samples.

Staphylococcus aureus - Review on potential targets for sensors development

Staphylococcus aureus (S. aureus) is accountable for a wide variety of clinical disease with a high rate of morbidity and mortality around the globe. It has a leading place into the ESKAPE group that includes six pathogens and exhibit multidrug resistance and are the major cause of healthcare associated infections: Enterococcus faecium, S. aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. A critical overview regarding the development of sensors for both S. aureus and his, more dangerous alter ego, Methicillin-resistant S. aureus (MRSA) was presented focusing on the bacteria targets starting with the detection of the whole cell, up to specific wall components, toxins or other virulence factors. The literature data was systematically assessed having in sight the design of the sensing platforms, the analytical performances, and possible courses of action to be implemented in real practice as point-of-care (POC) devices. Moreover, a distinct section was dedicated to commercially available devices and out of the box approaches, namely the use of bacteriophages as an alternative to antimicrobial therapy and as sensors modifiers. The reviewed sensors and devices were discussed in terms of their suitability for different biosensing applications, in early screening of contamination regarding food analysis, environmental monitoring and in clinical diagnosis.

Ultrasensitive detection of Staphylococcus aureus using a non-fluorescent cDNA-grafted dark BBQ®-650 chromophore integrated hydrophilic upconversion nanoparticles/aptamer system

A highly structured fluorometric bioassay has been proposed for screening Staphylococcus aureus (S. aureus). The study exploits (i) the spectral attributes of the hexagonal NaYF₄:Yb,Er upconversion nanoparticle (UCNP)-coated 3-aminopropyl)triethoxysilane; (ii) the intrinsic non-fluorescent quenching features of the highly stable dark blackberry (BBQ®-650) receptor; (iii) the aptamer (Apt-) biorecognition and binding affinity, and (iv) the complementary DNA hybridizer-linkage efficacy. The principle relied on the excited state energy transfer between the donor Apt-labeled NH₂-UCNPs at the 3' end, and cDNA-grafted BBQ®-650 at the 5' end, as the effective receptors. The donor moieties in proximity (< 10.0 nm) trigger hybridization with the cDNA-grafted dark BBQ®-650, as the receptors of energy from the ²F_5/2 level of Yb³⁺ ions to initiate the Förster resonance energy transfer pathway. This was confirmed by the decline in the excited-state lifetimes from 223.52 μs (τ₁) to 179.26 μs (τ₂). The existence of the target S. aureus in the bioassay attracts the Apt- resulting in the detachment of the acceptor, and disintegration of the complex configuration via conformation reversal. The re-activated fluorescence monitored at λex/em = 980/652 nm, as a function of the logarithmic concentration of S. aureus (42 to 4.2 × 10⁸ CFU mL^-1), yielded an ultra-low detection response of 2.0 CFU mL^-1. The bioassay screening of S. aureus in real samples revealed satisfactory recoveries (92.44-107.82%) and validation results (p > 0.05). Hence, the comprehensive Apt-labeled NH₂-UCNPs-cDNA-grafted dark BBQ®-650 bioassay offered fast and precise S. aureus screening in food and environmental settings.

An ultrasensitive electrochemical aptasensor using Tyramide-assisted enzyme multiplication for the detection of Staphylococcus aureus

In this study, we aimed to introduce a new electrochemical aptasensor based on the tyramide signal amplification (TSA) technology for a highly-sensitive detection of the pathogenic bacterium, Staphylococcus aureus, as a model of foodborne pathogens. In this aptasensor, the primary aptamer, SA37, was used to specifically capture bacterial cells; the secondary aptamer, SA81@HRP, was used as the catalytic probe; and a TSA-based signal enhancement system comprising of biotinyl-tyramide and streptavidin-HRP as electrocatalytic signal tags was adopted to fabricate the sensor and improve the detection sensitivity. S. aureus cells were selected as the pathogenic bacteria to verify the analytical performance of this TSA-based signal-enhancement electrochemical aptasensor platform. After the simultaneous binding of SA37-S. aureus-SA81@HRP formed on the gold electrode, thousands of @HRP molecules could be bound onto the biotynyl tyramide (TB) displayed on the bacterial cell surface through a catalytic reaction between HRP and H₂O₂, resulting in the generation of the highly amplified signals mediated by HRP reactions. This developed aptasensor could detect S. aureus bacterial cells at an ultra-low concentration, with a limit of detection (LOD) of 3 CFU/mL in buffer. Furthermore, this chronoamperometry aptasensor successfully detected target cells in both tap water and beef broth with LOD to be 8 CFU/mL, which are very high sensitivity and specificity. Overall, this electrochemical aptasensor using TSA-based signal-enhancement could be a very useful tool for the ultrasensitive detection of foodborne pathogens in food and water safety and environmental monitoring.

A Microfluidic Dual-Aptamer Sandwich Assay for Rapid and Cost-Effective Detection of Recombinant Proteins

While monitoring expression of recombinant proteins is essential for obtaining high-quality biopharmaceutical and biotechnological products, existing assays for recombinant protein detection are laborious, time-consuming and expensive. This paper presents a microfluidic approach to rapid and cost-effective detection of tag-fused recombinant proteins via a dual-aptamer sandwich assay. Our approach addresses limitations in current methods for both dual-aptamer assays and generation of aptamers for such assays by first using microfluidic technology to isolate the aptamers rapidly and then employing these aptamers to implement a microfluidic dual-aptamer assay for tag-fused recombinant protein detection. The use of microfluidic technology enables the fast generation of aptamers and rapid detection of recombinant proteins with minimized consumption of reagents. In addition, compared with antibodies, aptamers as low-cost affinity reagents with an ability of reversible denaturation further decreases the cost of recombinant protein detection. For demonstration, an aptamer pair is isolated rapidly toward His-tagged IgE within two days, and then used in the microfluidic dual-aptamer assay for detecting His-tagged IgE in cell culture media within 10 min and with a limit of detection of 7.1 nM.

Sandwich-Type Electrochemical Aptasensor for Highly Sensitive and Selective Detection of Pseudomonas Aeruginosa Bacteria Using a Dual Signal Amplification Strategy

An electrochemical aptasensor developed to realize the detection of Pseudomonas aeruginosa (P. aeruginosa) bacteria based on a signal amplification strategy. The carbon screen-printed electrode (CSPE) surface was modified by MIL-101(Cr)/Multi-walled carbon nanotubes (MWCNT), which significantly increased the effective surface area of the electrode, thus resulting in further F23 aptamer immobilization at the surface of the modified electrode. As a result, the P. aeruginosa can be efficiently captured onto the surface of the aptasensor. Moreover, aptamer immobilized on the two-dimensional graphitic carbon nitride complex with silver nanoparticles (AgNPs/c-g-C₃N₄/Apt) was used as an electrochemical signal label, connected to P. aeruginosa bacteria at the modified electrode. This strategy increased the aptamer surface density and the sensitivity for detecting P. aeruginosa. Also, the resultant material was thoroughly characterized using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis techniques. A highly sensitive voltammetric aptasensor for P. aeruginosa detection was obtained via this strategy at the limit of detection of 1 Colony-forming unit (CFU)/mL (σ = 3). Therefore, this proposed strategy with dual signal amplification can be a promising platform for simple, practical, reliable, and sensitive method for P. aeruginosa.

Biosensors for healthcare: current and future perspectives

Biosensors are utilized in several different fields, including medicine, food, and the environment; in this review, we examine recent developments in biosensors for healthcare. These involve three distinct types of biosensor: biosensors for in vitro diagnosis with blood, saliva, or urine samples; continuous monitoring biosensors (CMBs); and wearable biosensors. Biosensors for in vitro diagnosis have seen a significant expansion recently, with newly reported clustered regularly interspaced short palindromic repeats (CRISPR)/Cas methodologies and improvements to many established integrated biosensor devices, including lateral flow assays (LFAs) and microfluidic/electrochemical paper-based analytical devices (μPADs/ePADs). We conclude with a discussion of two novel groups of biosensors that have drawn great attention recently, continuous monitoring and wearable biosensors, as well as with perspectives on the commercialization and future of biosensors.

Aptasensor for the Detection of Moraxella catarrhalis Adhesin UspA2

Innovative point-of-care (PoC) diagnostic platforms are desirable to surpass the deficiencies of conventional laboratory diagnostic methods for bacterial infections and to tackle the growing antimicrobial resistance crisis. In this study, a workflow was implemented, comprising the identification of new aptamers with high affinity for the ubiquitous surface protein A2 (UspA2) of the bacterial pathogen Moraxella catarrhalis and the development of an electrochemical biosensor functionalized with the best-performing aptamer as a bioreceptor to detect UspA2. After cell-systematic evolution of ligands by exponential enrichment (cell-SELEX) was performed, next-generation sequencing was used to sequence the final aptamer pool. The most frequent aptamer sequences were further evaluated using bioinformatic tools. The two most promising aptamer candidates, Apt1 and Apt1_RC (Apt1 reverse complement), had K_d values of 214.4 and 3.4 nM, respectively. Finally, a simple and label-free electrochemical biosensor was functionalized with Apt1_RC. The aptasensor surface modifications were confirmed by impedance spectroscopy and cyclic voltammetry. The ability to detect UspA2 was evaluated by square wave voltammetry, exhibiting a linear detection range of 4.0 × 10⁴-7.0 × 10⁷ CFU mL^-1, a square correlation coefficient superior to 0.99 and a limit of detection of 4.0 × 10⁴ CFU mL^-1 at pH 5.0. The workflow described has the potential to be part of a sensitive PoC diagnostic platform to detect and quantify M. catarrhalis from biological samples.

Culture-Free Quantification of Bacteria Using Digital Fluorescence Imaging in a Tunable Magnetic Capturing Cartridge for Onsite Food Testing

Accurate, onsite detection of pathogenic bacteria from food matrices is required to rapidly respond to pathogen outbreaks. However, accurately detecting whole-cell bacteria in large sample volumes without an enrichment step remains a challenge. Therefore, bacterial samples must be concentrated, identified, and quantified. We developed a tunable magnetic capturing cartridge (TMCC) and combined it with a portable digital fluorescence reader for quick, onsite, quantitative detection of Staphylococcus aureus. The TMCC platform integrates an absorption pad impregnated with water-soluble polyvinyl alcohol (PVA) with an injection-molded polycarbonate (PC) plate that has a hard magnet on its back and an acrylonitrile-butadiene-styrene case. An S. aureus-specific antibody conjugated with magnetic nanoparticles was used to concentrate bacteria from a large-volume sample and capture bacteria within the TMCC. The retention time for capturing bacteria on the TMCC was adjusted by controlling the concentration and volume of the PVA solution. Concentrated bacterial samples bound to target-specific aptamer probes conjugated with quantum dots were loaded into the TMCC for a controlled time, followed by attachment of the bacteria to the PC plate and removal of unbound aptamer probes with wash buffer. The captured bacteria were quantified using a digital fluorescence reader equipped with an embedded program that automatically counts fluorescently tagged bacteria. The bacterial count made using the TMCC was comparable to a standard plate count (R² = 0.9898), with assay sensitivity and specificity of 94.3 and 100%, respectively.

One-step high-throughput detection of low-abundance biomarker BDNF using a biolayer interferometry-based 3D aptasensor

Although biosensors for signal monitoring have been extensively developed, their application in one-step high-throughput detection of low-abundance disease biomarkers remains challenging. This study presents a 3D aptasensor based on a biolayer interferometry (BLI) technique, followed by the sensitive and rapid detection of the specific biomarker brain-derived neurotrophic factor (BDNF) for early screening of glaucoma, an irreversible disease that causes blindness. The developed 3D aptasensor enabled one-step batch conversion of the low-abundance biomarker BDNF binding into optical interference signal, which was mainly attributed to the following factors: (1) A dimeric aptamer with extremely high targeting affinity was constructed as a biorecognition molecule, (2) highly sensitive 3D matrix sensors were integrated as signal transduction elements, and (3) the BLI Octet system with automated, high-throughput, and real-time online monitoring capabilities was used for reporting. The 3D aptasensor exhibited a broad detection window from 0.41 to 250 ng/mL BDNF, with a limit of detection of 0.2 ng/mL. Furthermore, detection of BDNF in glaucoma patient serum using the aptasensor showed good agreement with ELISA findings as well as the clinical diagnosis of the patient, demonstrating the feasibility of the system as a screening tool for glaucoma. This one-step high-throughput screening approach provides a valuable solution for the early diagnosis of glaucoma and may reduce the risk of blindness in visually impaired people.

Sandwich-Based Immunosensor for Dual-Mode Detection of Pathogenic F17-Positive Escherichia coli Strains

Bacterial diseases cause tremendous economic losses due to high morbidity and mortality in livestock animals. F17A protein, the major subunit of F17 fimbriae, is one of the most prevalent and crucial virulence factors among the pathogenic Escherichia coli (E. coli) isolated from diarrheic and septicemic animals of various species. Purification and detection of this protein is regarded as an interesting field of investigation due to its important role as a therapeutic target, such as vaccines, and as a diagnostic tool. In this context, polyclonal rabbit antibodies recognizing F17A protein (anti−F17A antibody) were developed and used for its detection. In fact, sandwich biosensor using anti−F17A/gold nanoparticles conjugates as capture probe and anti−F17A antibody labelled with horseradish peroxidase as signal amplification probe was developed for electrochemical and fluorescent detection of purified F17A protein and live F17–positive E. coli bacteria. Good specificity and sensitivity for detection of F17–positive E. coli strains were obtained. The dynamic range for the biosensor varies from 1 × 10² to 1 × 10⁹ CFU·mL⁻¹ (R² = 0.998) and the detection limit (LOD) and the IC₅₀ value were estimated to be 37 CFU·mL⁻¹ and 75 CFU·mL⁻¹, respectively.

Recent Advances in Aptasensors For Rapid and Sensitive Detection of Staphylococcus Aureus

The infection of Staphylococcus aureus (S.aureus) and the spread of drug-resistant bacteria pose a serious threat to global public health. Therefore, timely, rapid and accurate detection of S. aureus is of great significance for food safety, environmental monitoring, clinical diagnosis and treatment, and prevention of drug-resistant bacteria dissemination. Traditional S. aureus detection methods such as culture identification, ELISA, PCR, MALDI-TOF-MS and sequencing, etc., have good sensitivity and specificity, but they are complex to operate, requiring professionals and expensive and complex machines. Therefore, it is still challenging to develop a fast, simple, low-cost, specific and sensitive S. aureus detection method. Recent studies have demonstrated that fast, specific, low-cost, low sample volume, automated, and portable aptasensors have been widely used for S. aureus detection and have been proposed as the most attractive alternatives to their traditional detection methods. In this review, recent advances of aptasensors based on different transducer (optical and electrochemical) for S. aureus detection have been discussed in details. Furthermore, the applications of aptasensors in point-of-care testing (POCT) have also been discussed. More and more aptasensors are combined with nanomaterials as efficient transducers and amplifiers, which appears to be the development trend in aptasensors. Finally, some significant challenges for the development and application of aptasensors are outlined.

Aptamers against Pathogenic Bacteria: Selection Strategies and Apta-assay/Aptasensor Application for Food Safety

Pathogenic bacteria are primarily kinds of detrimental agents that cause mankind illness via contaminated food with traits of multiple types, universality, and low content. In view of the detection demands for rapidity, aptamer recognition factors emerged as a substitution for antibodies, which are short single strands of nucleic acid selected via in vitro. They display certain superiorities over antibodies, such as preferable stability, liable modification, and cost-efficiency. Taking advantage of the situation, numerous aptamers against pathogenic bacteria have been successfully selected and applied, yet there are still restrictions on commercial availability. In this review, the strategies/approaches to key sections in pathogen aptamers SELEX and post-SELEX are summarized and sorted out. Recently, optical, electrochemical, and piezoelectric aptamer-based assays or sensors dedicated to pathogen detection have been critically reviewed. Ultimately, the existing challenges and future trends in this field are proposed to further promote development prospects.