Aptamer decorated PDA@magnetic silica microparticles for bacteria purification.

One significant constraint in the advancement of biosensors is the signal-to-noise ratio, which is adversely affected by the presence of interfering factors such as blood in the sample matrix. In the present investigation, a specific aptamer binding was chosen for its affinity, while exhibiting no binding affinity towards non-target bacterial cells. This selective binding property was leveraged to facilitate the production of magnetic microparticles decorated with aptamers. A novel assay was developed to effectively isolate S. pneumoniae from PBS or directly from blood samples using an aptamer with an affinity constant of 72.8 nM. The capture experiments demonstrated efficiencies up to 87% and 66% are achievable for isolating spiked S. pneumoniae in 1 mL PBS and blood samples, respectively.

Fluorescent and electrochemical detection of nuclease activity associated with Streptococcus pneumoniae using specific oligonucleotide probes.

Streptococcus pneumoniae (S. pneumoniae) represents a significant pathogenic threat, often responsible for community-acquired pneumonia with potentially life-threatening consequences if left untreated. This underscores the pressing clinical need for rapid and accurate detection of this harmful bacteria. In this study, we report the screening and discovery of a novel biomarker for S. pneumoniae detection. We used S. pneumoniae nucleases as biomarker and we have identified a specific oligonucleotide that works as substrate. This biomarker relies on a specific nuclease activity found on the bacterial membrane, forming the basis for the development of both fluorescence and electrochemical biosensors. We observed an exceptionally high sensitivity in the performance of the electrochemical biosensor, detecting as low as 102 CFU mL-1, whereas the fluorescence sensor demonstrated comparatively lower efficiency, with a detection limit of 106 CFU mL-1. Moreover, the specificity studies have demonstrated the biosensors' remarkable capacity to identify S. pneumoniae from other pathogenic bacteria. Significantly, both biosensors have demonstrated the ability to identify S. pneumoniae cultured from clinical samples, providing compelling evidence of the potential clinical utility of this innovative detection system.

Real-Time Biosensing Bacteria and Virus with Quartz Crystal Microbalance: Recent Advances, Opportunities, and Challenges.

Continuous monitoring of pathogens finds applications in environmental, medical, and food industry settings. Quartz crystal microbalance (QCM) is one of the promising methods for real-time detection of bacteria and viruses. QCM is a technology that utilizes piezoelectric principles to measure mass and is commonly used in detecting the mass of chemicals adhering to a surface. Due to its high sensitivity and rapid detection times, QCM biosensors have attracted considerable attention as a potential method for detecting infections early and tracking the course of diseases, making it a promising tool for global public health professionals in the fight against infectious diseases. This review first provides an overview of the QCM biosensing method, including its principle of operation, various recognition elements used in biosensor creation, and its limitations and then summarizes notable examples of QCM biosensors for pathogens, focusing on microfluidic magnetic separation techniques as a promising tool in the pretreatment of samples. The review explores the use of QCM sensors in detecting pathogens in various samples, such as food, wastewater, and biological samples. The review also discusses the use of magnetic nanoparticles for sample preparation in QCM biosensors and their integration into microfluidic devices for automated detection of pathogens and highlights the importance of accurate and sensitive detection methods for early diagnosis of infections and the need for point-of-care approaches to simplify and reduce the cost of operation.

Detection of viruses by probe-gated silica nanoparticles directly from swab samples.

Viral infection has been one of the major health issues for human life. The real-time reverse transcription polymerase chain reaction (RT-PCR)-based detection has primarily been used for virus detection as a highly reliable procedure. However, it is a relatively long and multi-stage process. In addition, required skilled personnel and complex instrumentation presents difficulties in large scale monitoring efforts. Therefore, we report here a direct and fast detection method for CoV-2 genome as applied in the nose-throat swab samples without any further processing. The detection principle is based on fluorescein-loaded mesoporous silica nanoparticles capped by specific gene sequences probes immobilized on the surface of the nanoparticles. Upon hybridization with the target viral genome, the fluorescein molecules were released from the mesopores. Testing with synthetic oligonucleotides, the NSP12 gene-based detection resulted in a strong signal. Target detection time could be optimized to 15 min and the limit of detection was 1.4 RFU with 84% sensitivity with clinical samples (n = 43).

Surface plasmon resonance aptasensor for soluble ICAM-1 protein in blood samples.

Intercellular Adhesion Molecule-1 (ICAM-1) is considered to be a cancer biomarker in the assessment of metastatic potential in patients and an early indicator of atherosclerosis. A labelless biosensor based on the surface plasmon resonance (SPR) signal from the specific affinity interaction of an aptamer and a soluble ICAM-1 protein was developed for blood samples. The developed aptasensor provided real-time information on the concentration of the ICAM-1 protein in blood when integrated to a purification step based on a magnetic pull-down separation. The SPR aptasensor was highly specific with a limit of detection of 1.4/0.2 ng ml-1, which was achieved through aptamer-functionalized silica-coated magnetic nanoparticles.

Surface microbiota and associated staphylococci of houseflies (Musca domestica) collected from different environmental sources.

Houseflies (Musca domestica) are important mechanical vectors for the transmission of pathogenic microorganisms. In this study, 129 houseflies (69 males and 60 females) were collected from 10 different environmental sources and a laboratory population was used. The surface microbiota of houseflies was identified by Next-Generation Sequencing. Staphylococci from the surfaces of houseflies were selectively isolated and their virulence genes, antibiotic susceptibilities, biofilm formation, and clonal relatedness were determined. Metagenomic analysis results demonstrated that Staphylococcus, Bacillus, and Enterococcus were mostly present on the surface of houseflies at the genus level. Additionally, the isolated 32 staphylococcal strains were identified as Staphylococcus sciuri (n = 11), S. saprophyticus (n = 9), S. arlettae (n = 6), S. xylosus (n = 4), S. epidermidis (n = 1) and S. gallinarum (n = 1). tetK, tetM, tetL, ermC, msrAB, and aad6 genes were found to carry by some of the staphylococcal strains. The strains were mostly resistant to oxacillin, penicillin, and erythromycin and three strains were multi-drug resistant. There was a statistical difference between housefly collection places and antibiotic resistance of isolated staphylococci to penicillin G, gentamicin, and erythromycin (p < 0.05). Biofilm test showed that 17 strains were strong biofilm formers, and it plays important role in the transmission of these bacteria on the surface of houseflies. Staphylococcal strains showed extracellular proteolytic and lipolytic activity in 31 and 12 strains, respectively. Closely related species were found in PFGE analysis from different environmental sources. By this study, surface microbiota and carriage of pathogenic staphylococci on the surfaces of houseflies and their virulence properties were elucidated.

Antibiotic administration in targeted nanoparticles protects the faecal microbiota of mice.

Antibiotic therapy comes with disturbances on human microbiota, resulting in changes of bacterial communities and thus leading to well-established health problems. In this study, we demonstrated that targeted teicoplanin administration maintains the faecal microbiota composition undisturbed in a mouse model while reaching therapeutic improvements for S. aureus infection.

Label-free lateral flow assay for Listeria monocytogenes by aptamer-gated release of signal molecules.

Lateral flow assay (LFA) type of biosensors have been popular due to cost-effectiveness and easy-interpretation for instant results, most common examples of applications being pregnancy tests, food safety or medical diagnostics. There are several examples of reports with high sensitivity, including pre-concentration of the sample by magnetic pull-down. However, sensitivity and direct detection designs with aptamers has been a limiting factor for developing aptamers-based LFA assays. In this study, we report a lateral flow design based on aptamer-gated silica nanoparticles to develop high sensitivity and direct bacterial assay by shifting aptamers-target interaction to conjugation pad. Aptamer-gated silica nanoparticles-based biosensors were reported for their high sensitivity, specificity and label-free detection for small molecules and whole cells. This label-free strategy for LFA can determine L. monocytogenes in minced chicken matrix at less than 5 min with a limit of detection (LOD) of 53 cells in one mL samples.

Aptamers: molecular tools for medical diagnosis.

Aptamers have been increasingly applied in biomedical field as a class of biorecognition elements that possess many advantages such as high specificity and binding affinity, easy synthesis, easy modification, small size, non-toxicity and good stability. Many diseases like cancer exhibit cellular aberrations at morphological and molecular levels. Medical diagnosis based on molecular features can be highly specific and extremely sensitive when proper recognition molecule and an efficient signal transduction system are employed. However, bioanalysis of human diseases at the molecular level is an extremely challenging field because effective probes to identify and recognize biomarkers of diseases are not readily available. Traditional bio-recognition molecule, antibody has been exploited to develop excellent diagnosis assays in many formats, but antibodies are insufficient to match the requirements of fast and portable biosensors for point-of-care applications, which are at high demand in pathogenic bacteria detection as well as other diseases like cancer. Aptamers are short single-stranded oligonucleotides, which can be selected from random combinatorial library by SELEX in vitro. This relatively new biorecognition agent has superior intrinsic characteristics for biosensor development. In this review, we first present major aptamer selection technologies and the main formats of biosensors, which were frequently employed in aptasensor development. Then, the current state of aptamers as applied to medical diagnosis was discussed for specifically cancer and pathogen diagnosis. Finally, an overview of aptamer-nanomaterials conjugates was presented in many applications such as diagnosis, bioimaging, and theranostics.

NanoKeepers: stimuli responsive nanocapsules for programmed specific targeting and drug delivery.

Bacterial resistance is a high priority clinical issue worldwide. Thus, an effective system that rapidly provides specific treatment for bacterial infections using controlled dose release remains an unmet clinical need. Herein, we report on the NanoKeepers approach for the specific targeting of S. aureus with controlled release of antibiotics based on nuclease activity.

Pathogen detection by core-shell type aptamer-magnetic preconcentration coupled to real-time PCR.

The presence of pathogenic bacteria is a major health risk factor in food samples and the commercial food supply chain is susceptible to bacterial contamination. Thus, rapid and sensitive identification methods are in demand for the food industry. Quantitative polymerase chain reaction (PCR) is one of the reliable specific methods with reasonably fast assay times. However, many constituents in food samples interfere with PCR, resulting in false results and thus hindering the usability of the method. Therefore, we aimed to develop an aptamer-based magnetic separation system as a sample preparation method for subsequent identification and quantification of the contaminant bacteria by real-time PCR. To achieve this goal, magnetic beads were prepared via suspension polymerization and grafted with glycidylmethacrylate (GMA) brushes that were modified into high quantities of amino groups. The magnetic beads were decorated with two different aptamer sequences binding specifically to Escherichia coli or Salmonella typhimurium. The results showed that even 1.0% milk inhibited PCR, but our magnetic affinity system capture of bacteria from 100% milk samples allowed accurate determination of bacterial contamination at less than 2.0 h with limit of detection around 100 CFU/mL for both bacteria in spiked-milk samples.

Portable bioactive paper-based sensor for quantification of pesticides.

A paper-based biosensor was developed for the detection of the degradation products of organophosphorus pesticides. The biosensor quantifies acetylcholine esterase inhibitors in a fast, disposable, cheap, and accurate format. We specifically focused on the use of sugar or protein stabilizer to achieve a biosensor with long shelf-life. The new biosensor detected malathion with a detection limit of 2.5 ppm in 5 min incubation time. The operational stability was confirmed by testing 60 days storage at 4°C when glucose was used as stabilizer.

Nanoparticle embedded enzymes for improved lateral flow sensors.

In this study, combining the nanoparticle embedded sensors with lateral flow assays, a novel strategy for ensuring the quality of signalling in lateral flow assays (LFAs) was developed. A LFA for reactive oxygen species (ROS) is reported that is based on horse radish peroxidase (HRP) which is co-entrapped with Texas Red dextran inside porous polyacrylamide nanoparticles. In this system, enzymes are protected in the porous matrix of polyacrylamide which freely allows the diffusion of the analyte. The sensor is rapid and sensitive for quantification of hydrogen peroxide concentrations. A test solution of hydrogen peroxides was quantified with this novel LFA-ROS sensor to obtain a linear range between 1 and 25 µM. Nanoparticle embedding of enzymes is proposed here as a general strategy for developing enzyme-based lateral flow assays, eliminating adverse effects associated with biological samples.

Antimicrobial aptamers for detection and inhibition of microbial pathogen growth.

Discovery of alternative sources of antimicrobial agents are essential in the ongoing battle against microbial pathogens. Legislative and scientific challenges considerably hinder the discovery and use of new antimicrobial drugs, and new approaches are in urgent demand. On the other hand, rapid, specific and sensitive detection of airborne pathogens is becoming increasingly critical for public health. In this respect affinity oligonucleotides, aptamers, provide unique opportunities for the development of nanotechnological solutions for such medical applications. In recent years, aptamers specifically recognizing microbial cells and viruses showed great potential in a range of analytical and therapeutic applications. This article describes the significant advances in the development of aptamers targeting specific pathogens. Therapeutic application of aptamers as neutralizing agents demonstrates great potential as a future source of antimicrobial agent.