Baleen-Mimicking Virtual Filters for Rapid Detection of Pathogenic Bacteria in Water Using Magnetic Nanoparticle Chains and a Halbach Ring

A Colorimetric Biosensor Integrating Rotifer-Mimicking Magnetic Separation with RAA/CRISPR-Cas12a for Rapid and Sensitive Detection of Salmonella

Efficient detection of foodborne bacteria is crucial for ensuring food safety, yet current methods often fall short in balancing speed, accuracy, sensitivity, and cost. This study presents an integrated biosensing platform for the rapid and sensitive detection of Salmonella in large-volume food samples. The platform incorporates a Rotifer-Mimicking Magnetic Separator (RMMS) that enhances the sample pretreatment by effectively mixing and isolating the bacteria from the sample. Coupled with this, the colorimetric biosensor utilizes a streamlined one-pot system that combines Recombinase Aided Amplification (RAA), betaine, and CRISPR-Cas12a to enable efficient pathogen detection. Initially, phenylboronic acid-modified magnetic beads (PBA-MBs) capture Salmonella, forming bacteria-PBA-MB complexes, which are then isolated using the RMMS. Target DNA amplicons activate ribonucleoprotein complexes, and Au@PtNPs-MBs with linker single DNAs are cleaved to release Au@PtNPs. The Au@PtNPs catalyze the H2O2-3,3',5,5'-tetramethylbenzidine, producing a visible blue color that indicates Salmonella concentration. This biosensor successfully detects Salmonella in 40 mL spiked milk samples within 75 min, achieving a detection limit of 89 CFU/mL. This work offers a simple, sensitive, low-cost detection method with potential applications in on-site testing, significantly enhancing food safety monitoring.

Microfluidic rapid isolation and electrochemical detection of S. pneumonia via aptamer-decorated surfaces

BACKGROUND

S. pneumoniae is widely recognized as a leading cause of respiratory infections worldwide, often resulting in high mortality rates. However, the advent of microfluidic technologies has brought significant advancements, including the simplified, sensitive, cost-effective, and rapid approach to pneumococcal bacteremia detection. In this study, a microfluidic magnetic platform is presented for rapid isolation, and an electrode array is utilized for the electrochemical detection of S. pneumoniae. Aptamer-decorated surfaces were employed for both isolation and detection. For isolation, silica magnetic microparticles were synthesized and decorated with aptamer.

RESULTS

Isolation performance was assessed for phosphate-buffered saline (PBS) and blood samples for different concentrations of S. pneumoniae. Electrical impedance spectroscopy (EIS) with fabricated gold interdigitated electrodes (IDEs) decorated with aptamer was implemented for the detection of S. pneumoniae at different bacteria concentrations. The microfluidic platform performed bacteria isolation at comparable isolation efficiency with batch systems but at a much faster rate (isolation took about a minute, and the aptamer-decorated electrode array exhibited a limit of detection (LOD) at 962 CFU/mL and linear range between 104 and 107 CFU/mL.

SIGNIFICANCE

Our method represents a significant advancement compared to previous reports. Our microfluidic platform can efficiently isolate 60 μL of the bacteria sample within about one minute. The entire process takes about two minutes including the detection step. Furthermore, our method achieves a notable improvement in the detection limit for S. pneumoniae compared to conventional ELISA and magnetic microfluidics ELISA.

Magnetic nanobead chain-assisted real-time impedance monitoring using PCB interdigitated electrode for Salmonella detection

Pathogen testing is effective to prevent food poisoning. Here, an electrochemical biosensor was explored for Salmonella detection by combining magnetic grid based bacterial separation with enzymatic catalysis based signal amplification on a PCB interdigitated electrode in a microfluidic chip. First, immune magnetic nanobeads, target bacteria, and immune polystyrene microspheres decorated with glucose oxidase were sufficiently mixed to form nanobead-bacteria-microsphere sandwich conjugates. Then, these conjugates were injected into the chip to form conjugate chains right over the electrode under an iron grid enhanced magnetic field. After non-conductive glucose was injected and catalyzed by glucose oxidase on the conjugate chains, conductive glucose acid and non-conductive hydrogen peroxide were continuously produced and rapidly diffused from the conjugate chains to the electrode. Finally, the impedance change was real-timely monitored and used to determine the bacterial amount. This sensor enabled detection of 50 CFU/mL Salmonella typhimurium in 1 h.

Prospects of coupled iron-based nanostructures in preclinical antibacterial therapy

Bacterial infections can threaten human health. Drug-resistant bacteria have become a challenge because of the excessive use of drugs. We summarize the current metallic antibacterial materials, especially Fe-based materials, for efficiently killing bacteria. The possible antibacterial mechanisms of metallic antibacterial agents are classified into interactions with bacterial proteins, iron metabolism, catalytic activity, and combinations of magnetic, photodynamic, and photothermal effects. This review will inspire the development of novel Fe-based antibacterial agents for clinical settings.

Silent Raman imaging of highly effective anti-bacterial activity synchronous with biofilm breakage using poly(4-cyanostyrene)@silver@polylysine nanocomposites

Biofilms are known to be a great challenge for their anti-bacterial activity as they obstruct drug action for deeper and more thorough bacteria-killing effects. Therefore, developing highly effective antibacterial agents to destroy biofilms and eradicate bacteria is of great significance. Herein, a new type of nanocomposites (denoted as poly(4-cyanostyrene)@silver@polylysine) is proposed, in which polylysine (PLL) could rapidly capture the biofilms and exhibit excellent antibacterial efficacy together with decorated silver (Ag) nanoparticles (NPs) through the charge effect and Ag⁺ release. Notably, nearly 100% antibacterial rates against Gram-positive bacterium (Staphylococcus aureus, S. aureus) and Gram-negative bacterium (Escherichia coli, E. coli) were achieved. More importantly, poly(4-cyanostyrene) with biological silent Raman imaging capacity is able to illustrate the relationship between antibacterial efficiency and biofilm breakage. In short, such novel nanocomposites can improve the bioavailability of each component and display tremendous potential in antibacterial applications.

Bacteria capture with magnetic nanoparticles modified with cationic carbosilane dendritic systems

Bacteria elimination from water sources is key to obtain drinkable water. Hence, the design of systems with ability to interact with bacteria and remove them from water is an attractive proposal. A diversity of polycationic macromolecules has shown bactericide properties, due to interactions with bacteria membranes. In this work, we have grafted cationic carbosilane (CBS) dendrons and dendrimers on the surface of iron oxide magnetic nanoparticles (MNP), leading to NP (ca. 10 nm) that interact with bacteria by covering bacteria membrane. Application of an external magnetic field removes MNP from solution sweeping bacteria attached to them. The interaction of the MNP with Gram-positive S. aureus bacteria is more sensible to the size of dendritic system covering the MNP, whereas interaction with Gram-negative E. coli bacteria is more sensible to the density of cationic groups. Over 500 ppm of NPM, MNP covered with dendrons captured over 90% of both type of bacteria, whereas MNP covered with dendrimers were only able to capture S. aureus bacteria (over 90%) but not E. coli bacteria. Modified MNP were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), Z potential and dynamic light scattering (DLS). Interaction with bacteria was analyzed by UV, TEM and scanning electron microscopy (SEM). Moreover, the possibility to recycle cationic dendronized MNP was explored.

A lab-on-a-tube biosensor for automatic detection of foodborne bacteria using rotated Halbach magnetic separation and Raspberry Pi imaging

A lab-on-a-tube biosensor was established to rapidly, sensitively and automatically detect foodborne bacteria through a rotatable Halbach magnet to form and rotate magnetic nanobead (MNB) chains for specific isolation of target bacteria, gold@platinum nanocatalysts (Au@PtNCs) to label target bacteria for efficient amplification of detection signal and Raspberry Pi App to collect and analyze the image of catalysate. First, the glass tube was successively preloaded with the mixture of MNBs, sample and Au@PtNCs, the washing buffer (skim milk) and the substrate (hydrogen peroxide-3,30,5,50-tetramethylbenzidine), and they were separated by air gaps. After the tube was placed on the biosensor, the MNB chains were stably formed and continuously rotated using the Halbach magnet and the mixture was moved back and forth using a programmable peristaltic pump, thus making the formation of MNB-bacteria-Au@PtNCs complexes. After the washing buffer was moved to wash the complexes, the substrate was then moved to resuspend the complexes, resulting in the catalytic reaction that changed the color of the substrate. Finally, the catalysate was moved to the designated area, the image of which was analyzed by the Raspberry Pi App to quantitatively determine the concentration of bacteria in the samples. This biosensor was able to detect Salmonella in spiked chicken samples in 1 h with lower detection limit of 8 CFU/50 μL and a recovery from 88.96% to 99.74%. This biosensor based on a single tube is very promising to automatically detect foodborne bacteria due to its low cost, high integration and simple operation.

Recent advances in magnetic nanoparticle-based microfluidic devices for the pretreatment of pathogenic bacteria

Rapid and sensitive detection of pathogenic bacteria in various samples, including food and drinking water, is important to prevent bacterial diseases. Most bacterial solutions contain only a small number of bacteria in complex matrices with impurities; hence, pretreatment is necessary to separate and concentrate target bacteria before sensing. Among various pretreatment methods, iron oxide magnetic nanoparticle (MNP)-based pretreatment has drawn attention owing to the unique properties of MNP, such as high magnetic susceptibility, superparamagnetism, and biocompatibility. After target bacteria are captured by recognition molecule-functionalized MNPs, bacteria-MNP complexes can be easily separated and enriched by applying an external magnetic field. Various devices, such as optical, electrochemical, and magnetoresistance sensors, can be used to detect target bacteria, and their detection principles have been discussed in numerous review papers. Herein, we focus on recent research advances and challenges in magnetic pretreatment of pathogenic bacteria using microfluidic devices, which offer the advantages of process automation and miniaturization.

Autonomous Internal Reflux of Magnetic Nanoparticle Chains in a Flow Channel for Efficient Detection of Waterborne Bacteria

Herein, we developed a novel method for the efficient capture of waterborne bacteria by creating an autonomous internal reflux of the magnetic nanoparticle chains (MNCs) inside a flow channel. A glass tube containing positively charged polyethyleneimine-coated MNCs (PEI-MNCs) was placed at the center of a Halbach ring, generating a strong and uniform magnetic field inside the ring. When a bacteria-spiked solution was injected into the tube, the target bacteria bound to the PEI-MNCs via an electrostatic interaction remained in the tube, whereas the unbound bacteria left the tube. Some PEI-MNC-bacteria complexes left the glass tube at high flow rates because of the drag force, which reduced the capture efficiency of the device. The loss of the PEI-MNC-bacteria complexes at high flow rates was suppressed by placing a k₀ ring behind the Halbach ring. The k₀ ring was used to apply a magnetic force in the opposite direction of the solution flow and create an autonomous reflux of the PEI-MNCs inside the glass tube, reducing their loss and increasing their capture efficiency. The capture efficiency of Escherichia coli O157 was determined based on the cell count to be greater than 90% at a flow rate of 15 mL/min. E. coli O157 was detected using quantitative polymerase chain reaction, and the limits of detection were 2 and 3 cfu/mL in deionized water and river water, respectively.

Magnetic Nanoparticles for Biomedical Applications: From the Soul of the Earth to the Deep History of Ourselves

Precisely engineered magnetic nanoparticles (MNPs) have been widely explored for applications including theragnostic platforms, drug delivery systems, biomaterial/device coatings, tissue engineering scaffolds, performance-enhanced therapeutic alternatives, and even in SARS-CoV-2 detection strips. Such popularity is due to their unique, challenging, and tailorable physicochemical/magnetic properties. Given the wide biomedical-related potential applications of MNPs, significant achievements have been reached and published (exponentially) in the last five years, both in synthesis and application tailoring. Within this review, and in addition to essential works in this field, we have focused on the latest representative reports regarding the biomedical use of MNPs including characteristics related to their oriented synthesis, tailored geometry, and designed multibiofunctionality. Further, actual trends, needs, and limitations of magnetic-based nanostructures for biomedical applications will also be discussed.