A new aptamer/polyadenylated DNA interdigitated gold electrode piezoelectric sensor for rapid detection of Pseudomonas aeruginosa

Primer Exchange Reaction (PER)-Based Construction of Scaffold for Low-Speed Centrifugation-Based Isolation and Quantitative Analysis of P. aeruginosa and its application in analyzing uterine secretions with intrauterine adhesion

Efficient isolation and sensitive quantification of Pseudomonas aeruginosa (P. aeruginosa) are crucial for identifying intrauterine infections and preventing the occurrence of intrauterine adhesion (IUA). However, traditional approaches, such as culture-based approach, are time-consuming. Herein, we constructed a detection scaffold by using primer exchange reaction (PER) that integrated the low-speed centrifugation-based isolation and sensitive quantification of target pathogenic bacteria. The established approach possesses several advantages, including (i) the approach is capable of simultaneous isolation and sensitive quantification of target bacteria; (ii) low-speed centrifugation or even manual equipment could be used to isolate target bacteria; and (iii) a low limit of detection was obtained as 54 cfu/mL. Based on this, the approach is a promising approach in analyzing P. aeruginosa from uterine secretions with IUA.

Emerging Biomimetic Sensor Technologies for the Detection of Pathogenic Bacteria: A Commercial Viability Study

Ensuring a rapid and accurate identification of harmful bacteria is crucial in various fields including environmental monitoring, food safety, and clinical diagnostics. Conventional detection methods often suffer from limitations such as long analysis time, complexity, and the need for qualified personnel. Therefore, a lot of research effort is devoted to developing technologies with the potential to revolutionize the detection of pathogenic bacteria by offering rapid, sensitive, and user-friendly platforms for point-of-care analysis. In this light, biosensors have gained significant commercial attention in recent years due to their simplicity, portability, and rapid analysis capabilities. The purpose of this review is to identify a trend by analyzing which biosensor technologies have become commercially successful in the field of bacteria detection. Moreover, we highlight the characteristics that a biosensor must possess to finally arrive in the market and therefore in the hands of the end-user, and we present critical examples of the market applications of various technologies. The aim is to investigate the reason why certain technologies have achieved commercial success and extrapolate these trends to the future economic viability of a new subfield in the world of biosensing: the development of biomimetic sensor platforms. Therefore, an overview of recent advances in the field of biomimetic bacteria detection will be presented, after which the challenges that need to be addressed in the coming years to improve market penetration will be critically evaluated. We will zoom into the current shortcomings of biomimetic sensors based on imprinting technology and aptamers and try to come up with a recommendation for further development based on the trends observed from previous commercial success stories in biosensing.

Ultrasensitive Detection of Tumor Suppressor Gene Methylation by Piezoelectric Sensing Based on Enrichment of Transcription Activator-Like Effectors

The detection of DNA methylation at cytosine/guanine dinucleotide (CpG) islands in promoter regions of tumor suppressor genes has great potential for early cancer screening, diagnosis, and prognosis monitoring. Nevertheless, achieving accurate, sensitive, cost-effective, and quantitative detection of target methylated DNA remains challenging. Herein, we propose a novel piezoelectric sensor (series piezoelectric quartz crystal (SPQC)) based on transcription activator-like effectors (TALEs) for detecting DNA methylation of Ras association domain family 1 isoform A (RASSF1A) tumor suppressor genes (R-5mC). The sensor employs TALEs-Ni magnetic beads to specifically recognize and separate the R-5mC, thereby improving the detection selectivity. The TALEs-Ni magnetic beads-R-5mC complex is sheared by a nucleic acid enzyme (DNAzyme) to release the single-stranded DNA (ST). ST initiates a catalyzed hairpin assembly (CHA) reaction on the surface of the electrode, which in turn triggers the hybridization chain reaction (HCR) and silver staining for enhanced detection sensitivity. The strategy exhibits a linear response in the detection of R-5mC in the range of 1 fM to 1 nM with a detection limit of 0.79 fM. R-5mC as low as 0.01% can be detected, even in the presence of large numbers of unmethylated DNA. The detection of R-5mC in circulating cell-free DNA (cfDNA) derived from clinical plasma specimens of lung cancer patients yielded satisfactory results.

Advances in Bioreceptor Layer Engineering in Nanomaterial-based Sensing of Pseudomonas Aeruginosa and its Metabolites

Pseudomonas aeruginosa is a pathogen that infects wounds and burns and causes severe infections in immunocompromised humans. The high virulence, the rise of antibiotic-resistant strains, and the easy transmissibility of P. aeruginosa necessitate its fast detection and control. The gold standard for detecting P. aeruginosa, the plate culture method, though reliable, takes several days to complete. Therefore, developing accurate, rapid, and easy-to-use diagnostic tools for P. aeruginosa is highly desirable. Nanomaterial-based biosensors are at the forefront of detecting P. aeruginosa and its secondary metabolites. This review summarises the biorecognition elements, biomarkers, immobilisation strategies, and current state-of-the-art biosensors for P. aeruginosa. The review highlights the underlying principles of bioreceptor layer engineering and the design of optical, electrochemical, mass-based, and thermal biosensors based on nanomaterials. The advantages and disadvantages of these biosensors and their future point-of-care applications are also discussed. This review outlines significant advancements in biosensors and sensors for detecting P. aeruginosa and its metabolites. Research efforts have identified biorecognition elements specific and selective towards P. aeruginosa. The stability, ease of preparation, cost-effectiveness, and integration of these biorecognition elements onto transducers are pivotal for their application in biosensors and sensors. At the same time, when developing sensors for clinically significant analytes such as P. aeruginosa, virulence factors need to be addressed, such as the sensor's sensitivity, reliability, and response time in samples obtained from patients. The point-of-care applicability of the developed sensor may be an added advantage since it enables onsite determination. In this context, optical methods developed for P. aeruginosa offer promising potential.

Diagnosis and Therapeutic Strategies Based on Nucleic Acid Aptamers Selected against Pseudomonas aeruginosa: The Challenge of Cystic Fibrosis

Antimicrobial resistance (AMR) is a rapidly spreading global health problem, and approximately five million deaths associated with AMR pathogens were identified prior to the COVID-19 pandemic. Pseudomonas aeruginosa has developed increasing AMR, and in patients with cystic fibrosis (CF) colonized by this bacterium, rare phenotypes have emerged that complicate the diagnosis and treatment of the hosts, in addition to multiple associated "epidemic strains" with high morbidities and mortalities. The conjugation of aptamers with fluorochromes or nanostructures has allowed the design of new identification strategies for Pseudomonas aeruginosa with detection limits of up to 1 cell ⋅ mL-1 , and the synergy of aptamers with antibiotics, antimicrobial peptides and nanostructures has exhibited promising therapeutic qualities. Some selected aptamers against this bacterium have shown intrinsic antimicrobial activity. However, these aptamers have been poorly evaluated in clinical isolates and have shown decreased interactions for CF isolates, demonstrating, in these cases, uncommon phenotypes resulting from the selective qualities of this disease as well as the great adaptive capacity of the pathogen. Therefore, finding an aptamer or set of aptamers that have the ability to recognize strange phenotypes of this bacillus is crucial in the battle against AMR.

Bacteriophage-based biosensors for detection of pathogenic microbes in wastewater

Wastewater is discarded from several sources, including industry, livestock, fertilizer application, and municipal waste. If the disposed of wastewater has not been treated and processed before discharge to the environment, pathogenic microorganisms and toxic chemicals are accumulated in the disposal area and transported into the surface waters. The presence of harmful microbes is responsible for thousands of human deaths related to water-born contamination every year. To be able to take the necessary step and quick action against the possible presence of harmful microorganisms and substances, there is a need to improve the effective speed of identification and treatment of these problems. Biosensors are such devices that can give quantitative information within a short period of time. There have been several biosensors developed to measure certain parameters and microorganisms. The discovered biosensors can be utilized for the detection of axenic and mixed microbial strains from the wastewaters. Biosensors can further be developed for specific conditions and environments with an in-depth understanding of microbial organization and interaction within that community. In this regard, bacteriophage-based biosensors have become a possibility to identify specific live bacteria in an infected environment. This paper has investigated the current scenario of microbial community analysis and biosensor development in identifying the presence of pathogenic microorganisms.

Aptamer-based NanoBioSensors for seafood safety

Chemical and biological contaminants are of primary concern in ensuring seafood safety. Rapid detection of such contaminants is needed to keep us safe from being affected. For over three decades, immunoassay (IA) technology has been used for the detection of contaminants in seafood products. However, limitations inherent to antibody generation against small molecular targets that cannot elicit an immune response, along with the instability of antibodies under ambient conditions greatly limit their wider application for developing robust detection and monitoring tools, particularly for non-biomedical applications. As an alternative, aptamer-based biosensors (aptasensors) have emerged as a powerful yet robust analytical tool for the detection of a wide range of analytes. Due to the high specificity of aptamers in recognising targets ranging from small molecules to large proteins and even whole cells, these have been suggested to be viable molecular recognition elements (MREs) in the development of new diagnostic and biosensing tools for detecting a wide range of contaminants including heavy metals, antibiotics, pesticides, pathogens and biotoxins. In this review, we discuss the recent progress made in the field of aptasensors for detection of contaminants in seafood products with a view of effectively managing their potential human health hazards. A critical outlook is also provided to facilitate translation of aptasensors from academic laboratories to the mainstream seafood industry and consumer applications.

A Synergistic Dual-Channel Sensor for Ultrasensitive Detection of Pseudomonas aeruginosa by DNA Nanostructure and G-Quadruplex

Pseudomonas aeruginosa is one of the foodborne pathogenic bacteria that greatly threatens human health. An ultrasensitive technology for P. aeruginosa detection is urgently demanded. Herein, based on the mechanism of aptamer-specific recognition, an electrochemical-colorimetric dual-mode ultrasensitive sensing strategy for P. aeruginosa is proposed. The vertices of DNA tetrahedral nanoprobes (DTNPs), that immobilized on the gold electrode were modified with P. aeruginosa aptamers. Furthermore, the G-quadruplex, which was conjugated with a P. aeruginosa aptamer, was synthesized via rolling circle amplification (RCA). Once P. aeruginosa is captured, a hemin/G-quadruplex, which possesses peroxidase-mimicking activity, will separate from the P. aeruginosa aptamer. Then, the exfoliated hemin/G-quadruplexes are collected for oxidation of the 3,3',5',5'-tetramethylbenzidine for colorimetric sensing. In the electrochemical mode, the hemin/G-quadruplex that is still bound to the aptamer catalyzes polyaniline (PANI) deposition and leads to a measurable electrochemical signal. The colorimetric and electrochemical channels demonstrated a good forward and reverse linear response for P. aeruginosa within the range of 1-10⁸ CFU mL^-1, respectively. Overall, compared with a traditional single-mode sensor for P. aeruginosa, the proposed dual-mode sensor featuring self-calibration not only avoids false positive results but also improves accuracy and sensitivity. Furthermore, the consistency of the electrochemical/colorimetric assay was verified in practical meat samples and showed great potential for applications in bioanalysis.

Aptamer-based biosensors for Pseudomonas aeruginosa detection

Pseudomonas aeruginosa possesses innate antibiotic resistance mechanisms, and carbapenem-resistant Pseudomonas aeruginosa has been considered the number one priority in the 2017 WHO list of antimicrobial-resistant crucial hazards. Early detection of Pseudomonas aeruginosa can circumvent treatment challenges. Various techniques have been developed for the detection of P. aeruginosa detection. Biosensors have recently attracted unprecedented attention in the field of point-of-care diagnostics due to their easy operation, rapid, low cost, high sensitivity, and selectivity. Biosensors can convert the specific interaction between bioreceptors (antibodies, aptamers) and pathogens into optical, electrical, and other signal outputs. Aptamers are novel and promising alternatives to antibodies as biorecognition elements mainly synthesized by systematic evolution of ligands by exponential enrichment and have predictable secondary structures. They have comparable affinity and specificity for binding to their target to antibody recognition. Since 2015, there have been about 2000 journal articles published in the field of aptamer biosensors, of which 30 articles were on the detection of P. aeruginosa. Here, we have focused on outlining the recent progress in the field of aptamer-based biosensors for P. aeruginosa detection based on optical, electrochemical, and piezoelectric signal transduction methods.

Aptamers: A prospective tool for infectious diseases diagnosis

It is well known that people's health is seriously threatened by various pathogens (such as Mycobacterium tuberculosis, Treponema pallidum, Novel coronavirus, HIV, Mucor, etc.), which leads to heavy socioeconomic burdens. Therefore, early and accurate pathogen diagnosis is essential for timely and effective therapies. Up to now, diagnosing human contagious diseases at molecule and nano levels is remarkably difficult owing to insufficient valid probes when it comes to determining the biological markers of pathogens. Aptamers are a set of high‐specificity and high‐sensitivity plastic oligonucleotides screened in vitro via the selective expansion of ligands by exponential enrichment (SELEX). With the advent of aptamer‐based technologies, their merits have aroused mounting academic interest. In recent years, as new detection and treatment tools, nucleic acid aptamers have been extensively utilized in the field of biomedicine, such as pathogen detection, new drug development, clinical diagnosis, nanotechnology, etc. However, the traditional SELEX method is cumbersome and has a long screening cycle, and it takes several months to screen out aptamers with high specificity. With the persistent development of SELEX‐based aptamer screening technologies, the application scenarios of aptamers have become more and more extensive. The present research briefly reviews the research progress of nucleic acid aptamers in the field of biomedicine, especially in the diagnosis of contagious diseases.

Multiple amplification-based fluorometric aptasensor for highly sensitive detection of Staphylococcus aureus

Rapid and accurate detection and identification of Staphylococcus aureus (S. aureus) are of great significance for food safety, environmental monitoring, early clinical diagnosis, and prevention of the spread of drug-resistant bacteria. Herein, we design a fluorometric aptasensor for ultra-sensitive, specific, and rapid detection of S. aureus. The apasensor combines the enrichment and separation of magnetic nanoparticles (MNPs), the biotin-streptavidin conjugation system, and a single S. aureus can release four signaling probes for signal amplification. Aptamer acts as a specific biorecognition element of S. aureus. Four FAM-labeled partially complementary sequences (FAM-pcDNAs) were used as signaling probes. The aptamers were sequential hybridized with the four FAM-pcDNAs to form aptamer&pcDNAs, which were then bound to MNPs via the biotin-streptavidin. When the aptamer specifically recognizes and binds to S. aureus, the FAM-pcDNAs signaling probes are replaced and released into the supernatant. The concentration of S. aureus can be quantified by measuring the fluorescence intensity (λexc/em = 492/520 nm) of the replaced signaling probe FAM-pcDNAs. The results show that the proposed fluorometric aptasensor displays good specificity, ultra-high sensitivity (1.23 cfu/mL), wide linear range (1 ~ 10⁸ cfu/mL), and fast detection speed (~ 1.5 h). The recovery test verifies further that the proposed fluorometric aptasensor can detect S. aureus in spiked blood samples. Since aptamers are easy to customize, we believe that fluorometric aptasensors based on multiple amplification have broad prospects in the construction of practical high-performance biosensors for bacterial detection. KEY POINTS: • Multiple amplification-based fluorometric aptasensor for S. aureus is developed • The aptasensor displays high specificity with a LOD of 1.23 CFU/mL • The aptasensor can directly detect S. aureus in spiked blood samples.

Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application

Foodborne pathogens contamination is one of the main sources of food safety problems. Although the existing detection methods have been developed for a long time, the complexity of food samples is still the main factor affecting the detection time and sensitivity, and the rapid separation and enrichment of pathogens is still an objective to be studied. Magnetic separation strategy based on magnetic nanoparticles (MNPs) is considered to be an effective tool for rapid separation and enrichment of foodborne pathogens in food. Therefore, this study comprehensively reviews the development of MNPs in the separation of foodborne pathogens over the past decade. First, various biorecognition reagents for identification of foodborne pathogens and their modifications on the surface of MNPs are introduced. Then, the factors affecting the separation of foodborne pathogens, including the size of MNPs, modification methods, separation strategies and separation forms are discussed. Finally, the application of MNPs in integrated detection methods is reviewed. Moreover, current challenges and prospects of MNPs for the analysis of foodborne pathogens are discussed. Further research should focus on the design of multifunctional MNPs, the processing of large-scale samples, the simultaneous analysis of multiple targets, and the development of all-in-one small analytical device with separation and detection.

Development of an MSPQC Nucleic Acid Sensor Based on CRISPR/Cas9 for the Detection of Mycobacterium tuberculosis

Accurate and rapid detection of nucleic acid plays a vital role in the clinical treatment of tuberculosis caused by Mycobacterium tuberculosis (M.TB). However, false-negative and false-positive results caused by base mismatches could affect the detection accuracy. Inspired by the unique property of CRISPR/Cas9, we proposed a new MSPQC M.TB sensor based on the CRISPR/Cas9 system, which can distinguish single-base mismatches in 10 bases from the protospacer adjacent motif (PAM) region. In the proposed sensor, single-stranded DNA on Au interdigital electrodes was used as a capture probe for the target and an initiator for hybridization chain reaction (HCR). HCR was used to generate long double-stranded DNA (dsDNA), which could span the Au interdigital electrodes. CRISPR/Cas9 was used as recognition components to recognize capture/target dsDNA. When the target existed, the capture probe hybridized with the target to form dsDNA, which could be recognized and cut by CRISPR/Cas9. Thus, the DNA connection between electrodes was cut off and resulted in the MSPQC response. When no target existed, the capture probe remained single-stranded and could not be recognized and cut by CRISPR/Cas9. Therefore, DNA connection between electrodes was reserved. Moreover, silver staining technology was utilized to improve the sensitivity of detection. M.TB was detected by the proposed sensor using specific sequence fragments of 16S rRNA of M.TB as the target. The detection time was down to 2.3 h. The limit of detection (LOD) was 30 CFU/mL.

Mycobacterium tuberculosis piezoelectric sensor based on AuNPs-mediated enzyme assisted signal amplification

Rapid diagnosis of tuberculosis disease (TB) still remained a pressing need for TB control efforts all over the world. However, the existing detection approaches cannot satisfy demand of rapid detection of clinical Mycobacterium tuberculosis (M. tuberculosis) because of the long detection time and high cost. Herein, we proposed a new M. tuberculosis piezoelectric sensor based on AuNPs-mediated enzyme assisted signal amplification. A hairpin-shaped DNA duplex with a protrusion of the 3' end was designed. In the presence of specific 16 S rDNA fragment of M. tuberculosis, the hairpin probe was opened, which triggered the selective cleavage of hairpin probe by Exonuclease III (Exo III), resulting in the release of uncut DNA probe and target DNA. The released target DNA hybridized with another hairpin-shaped DNA duplex, and a new digestion cycle was started, thus generating large amounts of uncut DNA probes. The uncut DNA was pulled to the electrode surface by the hybridization with capture probe modified on the electrode. Subsequently detection probe labeled AuNPs was hybridized with uncut DNA and entered between the two electrodes. The AuNPs linked to hybridized detection probe were grown in the HAuCl₄ and Nicotinamide adenine dinucleotide (NADH) solution and offered the conductive connection between the gaps of electrode. The changes were monitored by the piezoelectric sensor. The piezoelectric biosensor could achieve a detection of M. tuberculosis (10²-10⁸ CFU mL^-1) within 3 h, the detection limit (LOD) was 30 CFU mL^-1. The methodology could be transformed into different microbial targets, which is suitable for further development of small portable equipment and multifunctional detection.

Upconversion nanoparticles-based FRET system for sensitive detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a pathogenic bacterium that seriously endangers food safety. Herein, a rapid, sensitive and specific aptasensor based on upconversion fluorescence resonance energy transfer (FRET) was developed for S. aureus detection in food. Aptamer-functionalized gold nanoparticles (AuNPs-aptamers) were bonded to cDNA-modified upconversion nanoparticles (UCNPs-cDNA) by complementary pairing, resulting in fluorescence quenching. After adding S. aureus into the system, the aptamers preferentially combined with S. aureus, dissociated UCNPs-cDNA from AuNPs-aptamers, and the fluorescence was recovered. Under optimized conditions, there was a significant linear correlation between fluorescence intensity and S. aureus concentration over the range 47-4.7 × 10⁷ CFU/mL (R² = 0.9904) with a detection limit of 10.7 CFU/mL. Furthermore, the precision and accuracy of the developed biosensor were validated using standard plate count method, yielding no significant differences. The proposed method has potential application for rapid and sensitive quantification of S. aureus in food.

Recent Advances and a Roadmap to Aptamer-Based Sensors for Bloodstream Infections

The present review is intended to describe bloodstream infections (BSIs), the major pathogens responsible for BSIs, conventional tests and their limitations, commercially available methods used, and the aptamer and nanomaterials-based approaches developed so far for the detection of BSIs. The advantages associated with aptamers and the aptamer-based sensors, the comparison between the aptamers and the antibodies, and the various types of aptasensors developed so far for the detection of bloodstream infections have been described in detail in the present review. Also, the future outlook and roadmap toward aptamer-based sensors and the challenges associated with the aptamer development have also been concluded in this review.

Aptamers and Aptamer-Coupled Biosensors to Detect Water-Borne Pathogens

Aptamers can serve as efficient bioreceptors for the development of biosensing detection platforms. Aptamers are short DNA or RNA oligonucleotides that fold into specific structures, which enable them to selectively bind to target analytes. The method used to identify aptamers is Systematic Evolution of Ligands through Exponential Enrichment (SELEX). Target properties can have an impact on aptamer efficiencies. Therefore, characteristics of water-borne microbial targets must be carefully considered during SELEX for optimal aptamer development. Several aptamers have been described for key water-borne pathogens. Here, we provide an exhaustive overview of these aptamers and discuss important microbial aspects to consider when developing such aptamers.

A fluorescent sensing strategy for ultrasensitive detection of oxytetracycline in milk based on aptamer-magnetic bead conjugate, complementary strand of aptamer and PicoGreen

Misuse of antibiotics in animal husbandry and presence of their residues in animal foods is a serious crisis worldwide and thus, monitoring the level of them in food samples is vital for human health. Herein, a fluorescent aptasensor was developed for highly sensitive quantification of oxytetracycline (OTC) in food samples. This method is based on OTC aptamer conjugated to magnetic beads, functioned as recognition element, complementary strand of OTC aptamer, and PicoGreen (PG) as a sensitive double-stranded DNA (dsDNA) fluorescent dye. Formation of OTC aptamer-magnetic bead conjugate provides the opportunity of sample condensation and separation technology. Additionally, the presence of complementary strand leads to significant fluorescence signal alteration of aptasensor in the presence or absence of target and a noteworthy improvement of the aptasensor sensitivity. In the absence of target, complementary strand could bind to aptamer and form dsDNA on the surface of magnetic bead. As a consequence, adding PG to the sample leads to observation of high fluorescence signal from sample. In contrast, once OTC is added to the sample, it binds to OTC aptamer-magnetic bead complex and prevents hybridization of OTC aptamer and its complementary strand. Hence, after addition of PG to the sample, a weak fluorescence intensity is measured. Under optimized conditions, the linear ranges for OTC detection were 0.2-2 nM and 2-800 nM. The detection limit was calculated to be as low as 0.15 nM for the fabricated aptasensor. Besides the great sensitivity, proposed method demonstrated superior specificity towards OTC once it was used against several antibiotics. More significantly, the recovery rates of OTC in milk ranged from 96.46% to 101.5%, implying the great feasibility of designed sensor as well as its potential to be employed for analysis of OTC in real samples.

Aptamer-based approaches for the detection of waterborne pathogens

Waterborne ailments pose a serious threat to public health and are a huge economic burden. Lack of hygiene in drinking and recreational water is the chief source of microbial pathogens in developing countries. Poor water quality and sanitation account for more than 3.4 million deaths a year worldwide. This has urged authorities and researchers to explore different avenues of pathogen detection. There is a growing demand for rapid and reliable sensor technologies, in particular those that can detect in situ and perform in harsh conditions. Some of the major waterborne pathogens include Vibrio cholerae, Leptospira interrogans, Campylobacter jejuni, Shigella spp., enterotoxigenic Escherichia coli, Clostridium difficile, Cryptosporidium parvum, Entamoeba histolytica, and Hepatitis A virus. While conventional methods of pathogen detection like serodiagnosis and microbiological methods have been superseded by nucleic acid amplification methods, there is still potential for improvement. This review provides an insight into aptamers and their utility in the form of aptasensors. It discusses how aptamer-based approaches have emerged as a novel strategy and its advantages over more resource-intensive and complex biochemical approaches.

Prospective Application of Aptamer-based Assays and Therapeutics in Bloodstream Infections

Sepsis is still a severe health problem worldwide with high morbidity and mortality. Blood bacterial culture remains the gold standard for the detection of pathogenic bacteria in bloodstream infections, but it is time-consuming, and both the sophisticated equipment and well-trained personnel are required. Immunoassays and genetic diagnosis are expensive and limited to specificity and sensitivity. Aptamers are single-stranded deoxyribonucleic acid (ssDNA) and ribonucleic acid (RNA) oligonucleotide or peptide sequence generated in vitro based on the binding affinity of aptamer-target by a process known as Systematic Evolution of Ligands by Exponential Enrichment (SELEX). By taking several advantages over monoclonal antibodies and other conventional small-molecule therapeutics, such as high specificity and affinity, negligible batch-to-batch variation, flexible modification and production, thermal stability, low immunogenicity and lack of toxicity, aptamers are presently becoming promising novel diagnostic and therapeutic agents. This review describes the prospective application of aptamerbased laboratory diagnostic assays and therapeutics for pathogenic bacteria and toxins in bloodstream infections.

Recent Advances in Aptamer-Based Biosensors for Detection of Pseudomonas aeruginosa

Increasing concerns about nosocomial infection, food and environmental safety have prompted the development of rapid, accurate, specific and ultrasensitive methods for the early detection of critical pathogens. Pseudomonas aeruginosa is one of the most common pathogens that cause infection. It is ubiquitous in nature, being found in water, soil, and food, and poses a great threat to public health. The conventional detection technologies are either time consuming or readily produce false positive/negative results, which makes them unsuitable for early diagnosis and spot detection of P. aeruginosa. To circumvent these drawbacks, many efforts have been made to develop biosensors using aptamers as bio-recognition elements. Various aptamer-based biosensors for clinical diagnostics, food, and environmental monitoring of P. aeruginosa have been developed in recent years. In this review, we focus on the latest advances in aptamer-based biosensors for detection of P. aeruginosa. Representative biosensors are outlined according to their sensing mechanisms, which include optical, electrochemical and other signal transduction methods. Possible future trends in aptamer biosensors for pathogen detection are also outlined.

Hollow carbon nanocapsules-based nitrogen-doped carbon nanofibers with rosary-like structure as a high surface substrate for impedimetric detection of Pseudomonas aeruginosa

The design of hollow mesoporous carbon-based materials has attracted tremendous attention, due to their sizeable intrinsic cavity to load specific chemical and unique physical/chemical properties in various applications. Herein, we have established an effective strategy for the preparation of novel hollow carbon nanocapsules-based nitrogen-doped carbon nanofibers (CNCNF) with rosary-like structure. By embedding ultrafine hollow carbon nanocapsules into electrospun polyacrylonitrile (PAN) skeleton, the as-designed composite CNFs were carbonized into hierarchical porous CNFs, consisted of interconnected nitrogen-doped hollow carbon nanocapsules. Due to its individual structural properties and unique chemical composition, the performance of CNCNF was evaluated in aptasensor application via the detection of Pseudomonas aeruginosa (PA). Under optimized conditions, the aptasensor based on CNCNF has a detection limit of 1 CFU⋅mL^-1 and a linear range from 10¹ CFU ⋅mL^-1 to 10⁷ CFU ⋅mL^-1 (n = 3). Moreover, the designed aptasensor possesses high sensivity, high selectivity, low detection limit, and high reproducibility. These studies showed that the CNCNF material offers a wide variety of enhanced electrochemical features as an electrode material for aptasensor application.

Aptamer-Based Biosensors for Environmental Monitoring

Due to their relative synthetic and chemical simplicity compared to antibodies, aptamers afford enhanced stability and functionality for the detection of environmental contaminants and for use in environmental monitoring. Furthermore, nucleic acid aptamers can be selected for toxic targets which may prove difficult for antibody development. Of particular relevance, aptamers have been selected and used to develop biosensors for environmental contaminants such as heavy metals, small-molecule agricultural toxins, and water-borne bacterial pathogens. This review will focus on recent aptamer-based developments for the detection of diverse environmental contaminants. Within this domain, aptamers have been combined with other technologies to develop biosensors with various signal outputs. The goal of much of this work is to develop cost-effective, user-friendly detection methods that can complement or replace traditional environmental monitoring strategies. This review will highlight recent examples in this area. Additionally, with innovative developments such as wearable devices, sentinel materials, and lab-on-a-chip designs, there exists significant potential for the development of multifunctional aptamer-based biosensors for environmental monitoring. Examples of these technologies will also be highlighted. Finally, a critical perspective on the field, and thoughts on future research directions will be offered.

An ultrasensitive biosensor for fast detection of Salmonella using 3D magnetic grid separation and urease catalysis

Screening of pathogenic bacteria plays a crucial role in preventing foodborne disease outbreaks. In this study, an ultrasensitive biosensor was developed for fast detection of Salmonella using self-assembled magnetic nanoparticle (MNP) chains for continuous-flow separation of Salmonella from large-volume sample, urease coated gold nanoparticles (GNPs) for specific labelling of Salmonella and efficient amplification of signal, and linear scan voltammetry for sensitive detection of catalysate. First, MNP chains were formed and distributed in a 3D spiral channel using mutually repelling cylindrical magnets and ring iron gears to control anti-Salmonella monoclonal antibody coated MNPs. After bacterial sample was continuous-flow drawn into the channel, bacteria-MNP complexes (magnetic bacteria) were formed on the chains, resulting in specific separation of target bacteria from sample background. Then, anti-Salmonella polyclonal antibodies and urease coated GNPs were drawn to label the magnetic bacteria, resulting in the formation of enzymatic bacteria. After washing to remove residual GNPs, urea was drawn and catalyzed by urease on enzymatic bacteria, resulting in the produce of catalysate (ammonium carbonate). Finally, the catalysate was transferred into a microfluidic chip with a thin-film Ag/AgCl reference electrode array for linear scan voltammetric measurement, and the resistance of catalysate was obtained to determine the amount of target bacteria. This biosensor could quantitatively detect Salmonella from 1.0 × 10¹ to 1.0 × 10⁶ CFU/mL in 1 h with low detection limit of 10¹ CFU/mL. The mean recovery for Salmonella in spiked milk was about 104.3%.

The construction of Mycobacterium tuberculosis 16S rDNA MSPQC sensor based on Exonuclease III-assisted cyclic signal amplification

Tuberculosis caused by Mycobacterium tuberculosis (M. tuberculosis) remains one of the most serious infectious diseases all over the world. The key to reduce the spread and mortality rate of tuberculosis is to develop faster and more sensitive approaches for detection of M. tuberculosis. However, current detection methods can not meet the requirements of rapid clinical M. tuberculosis detection in terms of detection time. Herein, a new 16S rDNA multichannel series piezoelectric quartz crystal (MSPQC) sensor based on Exonuclease III (Exo III)-aided target recycling has been developed for rapid detection of M. tuberculosis. The specific 16S rDNA fragment of M. tuberculosis was used as biomarker, DNA capture probes complementary to the biomarker were designed and modified on the surface of AuNPs. The Exo III which could recognise hybrid duplexes and selectively digest DNA capture probe was used to assist digestion cycle by digesting DNA capture probe and releasing the intact target fragment. After all DNA probes loading on the surface of AuNPs were removed, the surface of AuNPs was exposed and conductive connection was formed between the nanogap network electrode by self-catalytic growth of exposed AuNPs in the glucose and HAuCl₄ solution. This resulted in sensitive response of M. tuberculosis sensor and M. tuberculosis was detected by recording this response. The limit of detection (LOD) of the method was 20 CFU/mL and the detection time was less than 3 h. It was expected to be widely used in detection methods of M. tuberculosis.