Sensitive Detection Of Bacteria Research Articles

Ultrasensitive electrochemical biosensor for bacteria detection based on Fe3O4@COF-AuNPs and trigging isothermal circular amplification

Foodborne bacterial infections pose serious threats to human health, leading to illnesses and even fatalities. The key to solve this problem is to develop fast and effective sensor for sensitive detection of bacteria. In this study, an electrochemical biosensor based on magnetic nanocomposite material Fe3O4@COF-AuNPs and trigging isothermal circular amplification (TICA) was constructed for detection of foodborne bacteria. In this design, a hairpin aptamer probe (HAP)-bound DNA monolayer was designed, serving as the substrate for the electrode to increase surface area. The Escherichia coli (E. coli) was selected as the target. The presence of E. coli caused the configuration change of the HAP and allowed the occurrence of TICA with the use of the Klenow Fragment polymerase (KF-Poly), thus the HAPs were away from the DNA monolayer. After adding the catalytic magnetic nanocomposite material Fe3O4@COF-AuNPs, it was immobilized on the DNA monolayer of the electrode through DNA complementary pairing and exhibited high electrocatalytic behavior towards the reduction of 4-nitrophenol. This enabled ultrasensitive detection of E. coli, with the detection limit (LOD) as low as 10 CFU/mL. The detection time was 1 h. This designed electrochemical sensor showed high selectivity, stability, and reproducibility, which offered a new avenue for detection of foodborne bacteria.

Portable cell imprinted polymer-based microfluidic sensor for bacteria detection in real water

Cell-imprinted polymer (CIP) based optical biosensors have transformed point-of-care detection. However, challenges remain in their portability and detection sensitivity, time, and cost. Herein, we present an imprinted polymer-based low-cost microfluidic device integrated into a portable enclosure that enables rapid and sensitive bacteria detection in real water. A portable 3D-printed platform was custom-designed, housing all essential detection components, i.e., pumping and fluorescent imaging units and the microfluidic sensor. CIP coated magnetic microparticles (MPs) with affinity to bacteria were manipulated inside the magnetophoretic microfluidic device at an optimized flow rate of 0.01 mL/min for bacteria capturing. Fluorescent imaging pre- and post-bacteria capture facilitated quantification of fluorescence intensity changes as bacteria were trapped by the CIP-MPs. The sensor’s dose–response curve established limits of detection (LOD) and quantification (LOQ) at 8 × 103 and 6 × 105 CFU/mL, respectively, within a dynamic range of 103 to 109 CFU/mL. It specifically detected E. coli, distinguishing it from non-specific bacteria like Salmonella and Sarcina. In real pond water tests, our sensor detected 2 × 10⁶ CFU/mL, matching a central lab’s result of 2.33 × 10⁶ CFU/mL, demonstrating its effectiveness for real-water monitoring. While further enhancements are needed for improving the specificity in complex environmental matrices and broader bacterial strain detection, the sensor’s simplicity and portability highlight its potential for practical potential.

A magnetic nanozyme platform for bacterial colorimetric detection and chemodynamic/photothermal synergistic antibacterial therapy.

Rapid, convenient, and sensitive detection of bacteria and development of novel antibacterial materials are conducive to accurate treatment of bacterial infection and reducing the generation of drug-resistant bacteria caused by overuse of antibiotics. A dual-function magnetic nanozyme, Fc-MBL@rGO@Fe3O4, has been constructed with broad-spectrum bacterial affinity and good peroxidase-like activity. Detection signal amplification was realized in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) with a detection limit of 26 CFU/mL. In addition, the excellent photothermal properties of Fc-MBL@rGO@Fe3O4 could realize synergistic chemodynamic/photothermal antibacterial therapy. Furthermore, the good bacterial affinity of Fc-MBL@rGO@Fe3O4 enhances the accurate and rapid attack of hydroxyl radical (·OH) on the bacterial membrane and achieves efficient sterilization (100%) at low concentration (40µg/mL) and mild temperature (47℃). Notably, Fc-MBL@rGO@Fe3O4 has a broad spectrum of antibacterial activity against Gram-negative, Gram-positive, and drug-resistant bacteria. The magnetic nanoplatform integrating detection-sterilization not only meets the need for highly sensitive and accurate detection in different scenarios, but can realize low power density NIR-II light-responsive chemodynamic/photothermal antibacterial therapy, which has broad application prospects.

Molecularly imprinted polymer combined with MOF-assisted redox recycling amplification: A powerful electrochemical sensing strategy for pathogenic bacteria

Rapid and sensitive determination of foodborne pathogenic bacteria at a low cost is crucial for ensuring food safety monitoring and diagnosing bacterial infections. In this protocol, we propose an electrochemical sandwich-type biosensor for highly sensitive detection of bacteria based on a bacterial imprinted polymer film (BIF) and metal-organic frameworks (MOF)-assisted redox recycling amplification. The BIF is formed in-situ through electropolymerization (EP) and template removal on the electrode surface, while aptamers are assembled on nanogold-modified MOF to create signal nanoprobes with target recognition ability. The BIF-modified electrode effectively captures the target bacteria and subsequently forms a sandwich structure through conjugation with signal nanoprobes, enabling efficient adsorption of methylene blue (MB). This facilitates the redox recycling of Fe(II) from the electroactive [Fe(CN)6]3-/4- in testing buffer assisted by MB, thereby generating a significantly amplified anodic current of [Fe(CN)6]3-/4- for precise quantitation. By utilizing the selective BIF interface and MOF-assisted redox recycling amplification, our method demonstrates excellent analytical performance with a low limit of detection (LOD) of 1 CFU mL−1, a broad detection range spanning from 10 to 108 CFU mL−1, and high selectivity. The feasibility of applying this approach for detecting bacteria in complex samples highlights its significant potential in areas related to food safety and public health.

Two birds with one stone: A multi-functional nanoplatform for sensitive detection and real-time inactivation of pathogenic bacteria with NIR-triggered PTT/PDT

Given the increase in public safety incidents due to bacterial infections, sensitive detection and real-time inactivation of pathogenic bacteria have garnered increasing attention in the field of food safety, clinical diagnosis, and environmental monitoring. In this study, we constructed a “two-in-one” PB@DPA-Ce-GMP@Van (PCV) nanoplatform possessing enzyme-like properties and photothermal therapeutic (PTT) and photodynamic therapeutic (PDT) abilities for the detection and inactivation of pathogenic bacteria. PCV was captured on the surface of S. aureus to form a PCV/S. aureus complex. After centrifugation, PCV suspensions could catalyze non-fluorescent Amplex Red (AR) into fluorescent substrates and fluorescent scopolamine (SC) into non-fluorescent substrates. Hence, a ratiometric fluorescence probe with SC/AR reading was constructed for the sensitive detection of bacteria. The detection range reached 101–107 colony-forming unit (CFU)/mL, and the detection limit was as low as 5.0 CFU/mL. Furthermore, approximately 99.7 % of free S. aureus can be inactivated by the PTT and PDT abilities of PCV. Thus, this nanoplatform exhibits a novel advantage in detecting and inactivating bacteria. Moreover, the bacterial infection wound model indicated that PVC exerts good disinfection ability. This study is of immense significance in the application of targeted sensing, eliminating bacterial infection, and even clinical therapy.

Ti3C2T x -AuNP based paper substrates for label-free SERS detection of bacteria and multimodal antibacterials.

Bacterial infections have become a serious global health problem due to the misuse of antibiotics which causes the emergence of antibiotic-resistant strains. Photothermal therapy (PTT) has been widely studied in recent years as a method to combat the development of bacterial resistance. However, PPT may cause damage to the human body due to excessive laser power. Therefore, it is important and urgent to develop a multifunctional platform that can sensitively detect bacteria and effectively inhibit or kill bacteria at low laser power. Herein, a novel multifunctional paper substrate of Ti3C2T x -AuNP was successfully synthesized by a self-assembly and freeze-drying method for bacterial detection and photothermal sterilization at low laser power. The typical Gram-negative Escherichia coli (E. coli) and the Gram-positive Methicillin-resistant Staphylococcus aureus (MRSA) were used as models to perform label-free, rapid and sensitive detection of bacteria based on the surface-enhanced Raman spectroscopy (SERS) method with detection limits as low as 105 CFU mL-1 and 5 × 105 CFU mL-1, respectively, demonstrating the paper substrate's ability to detect bacteria with sensitivity and accuracy. The paper substrate of Ti3C2T x -AuNP exhibits significant antibacterial effects when irradiated with 808 nm light at a low laser power of only 300 mW cm-2 and a short irradiation time of 5 minutes, and the germicidal rates for E. coli and MRSA were 99.94% and 92.71%, respectively. At the same time, the paper substrate of Ti3C2T x -AuNP also produces a variety of reactive oxygen species under 808 nm laser irradiation, resulting in photodynamic therapy (PDT). Accordingly, this paper substrate of Ti3C2T x -AuNP can not only sensitively detect bacteria, but also has photothermal and photodynamic sterilization, providing a promising countermeasure for the clinical treatment of diseases caused by multidrug-resistant bacteria.

Highly specific and sensitive detection of bacteria by dark-field light-scattering imaging based on bacteriophage-modified magnetoplasmonic nanoparticles

Abstract Bacterial infections pose significant global health concerns, necessitating precise and sensitive detection methods. This study introduces a multifunctional probe for bacterial detection. Bifunctional magnetoplasmonic nanoparticles (NPs) serve a dual purpose as carriers for magnetic separation (MS) and enhancers for light scattering of the target bacteria. We achieved exceptional selectivity at the bacterial species level by bioconjugating them with bacteriophages (phages). Optimal phage coverage was carefully determined to enhance the capture efficiency of the target bacterial cells. Additionally, we identified the ideal mixing ratios of the phage probe to bacteria, ensuring efficient MS and high light-scattering intensity. The use of the phage probe enabled the successful separation of captured target bacteria from other bacterial strains in the sample mixture. Bacterial detection was accomplished through dark-field light-scattering imaging, eliminating the need for additional labeling with other probes. This method showed a remarkable sensitivity, achieving a detection limit of ∼102 colony-forming units ml−1. This value is 2 orders of magnitude lower than that achieved using our previously reported technique using monofunctional plasmonic NPs. These phage probes hold promise for healthcare, biotech, and environmental monitoring owing to their adaptability to diverse bacterial species.

Galvanic Displacement Reaction Enabled Specific and Sensitive Detection of Bacteria with a Digital Photocorrosion GaAs/AlGaAs Biosensor.

The conjugation of ionic gold with bacterial antibodies makes it possible to induce a specific interaction between targeted bacteria and the surface of a GaAs/AlGaAs biochip. The process of immobilization is based on a galvanic displacement reaction (GDR) involving electron transfer between GaAs and Au3+ ions that leads to the formation of a Au-Ga alloy anchoring bacteria to the biochip surface. The GDR-based immobilization of Escherichia coli on biochips comprising a stack of GaAs/AlGaAs nanolayers (dGaAs = 12 nm, dAlGaAs = 10 nm) was confirmed by X-ray photoelectron spectroscopy and atomic force microscopy-based infrared experiments. We report the successful application of this approach for highly sensitive detection of E. coli with a digital photocorrosion (DIP) biosensor. The photoluminescence (PL) monitored DIP of GaAs/AlGaAs nanolayers results in the formation of a PL intensity maximum whose temporal appearance depends on the electric charge transfer between bacteria and the biochip. The formation of a robust bacteria-biochip interface achieved with the GDR process allowed us to observe the role of bacteria on the temporal position of a PL intensity maximum related to the etching of two pairs of GaAs/AlGaAs nanolayers extending up to 24 nm below the biochip surface. We demonstrate the attractive detection of E. coli at 250 CFU/mL, and we discuss the potential of this approach for designing a family of biosensors addressing the quasi-continuous monitoring of a water environment for the presence of pathogenic bacteria.

Preparation of Co dual atomic site catalysts loaded on defect-engineered MOFs material with superb chemiluminescent enhancement effect for sensitive detection of bacteria

BackgroundDual atomic site catalysts (DASCs) have aroused extensive interest in analytical chemistry on account of the superb catalytic activity caused by the highly-exposed active centers and synergistic effect of adjacent active centers. The reported protocols for preparing DASCs usually involve harsh conditions such as acid/base etching and high-temperature calcination, leading to unfavorable water dispersity and restricted application. It is crucial to develop DASCs with satisfactory water dispersity, improved stability, and mild preparation procedures to facilitate their application as signal probes in analytical chemistry. Results: Formic acid was adopted as a modulator for preparing MOF-808 with abundant defective sites, which was used as the carrier for implanting Co atoms. Co DASCs with a special coordination structure of Co2–O10 and a high loading efficiency of 11.1 wt% were prepared with a mild solvothermal protocol. The resultant Co DASCs can significantly accelerate decay of H2O2 for forming numerous reactive oxygen radicals and boost chemiluminescent (CL) signal. Co DASCs at 1.0 μg mL−1 can enhance the CL signal of luminol-H2O2 system by about 5800 times. Thanks to their satisfactory water dispersity and excellent CL enhancement performance, they were used as ultra-sensitive CL signal probes for monitoring methicillin-resistant Staphylococcus aureus. The method shows a detection range of 102–107 CFU mL−1 and a detection limit of 47 CFU mL−1. Antibiotic susceptibility test was performed with the established CL method to prove its practicality. Significance: The water dispersible Co DASCs prepared with facile and mild solvothermal protocol exhibit prominent peroxidase-like activity and can promote the production of reactive oxygen radicals for boosting CL signal. Therefore, this study paves an avenue for implanting DASCs in defect-engineered carrier to prepare signal probes suitable for development of ultra-sensitive CL analytical methods.

Multifunctional AuAg-doping Prussian Blue-based MOF: Enhanced colorimetric catalytic activities and amplified SERS signals for bacteria discrimination and detection

New strategy of a rapid, sensitive bacteria detection is highly desirable. Constructing a dual-mode colorimetric/surface-enhanced Raman scattering (SERS) biosensor is key to obtain highly sensitive discriminating and detecting of different pathogen bacteria with high accuracy. Herein, we developed a multifunctional colorimetric catalytic nanozyme (AuAg@PB MOF) composed of AuAg-doping Prussian Blue analogue-based metal-organic framework (MOF) that fabricated by self-assembled sheet growth of Ag-etched silver-coated gold nanoparticles (Au@Ag NPs) mediated by addition of ferricyanide (K3[Fe(CN)6]). AuAg@PB MOF displays ultrahigh peroxidase-mimicking activity, enhanced colorimetric signal brightness, and notably SERS enhancement. Through optimizing its Fe-doping level, peroxidase-like activity of AuAg@PB MOF is approximately 1900-fold higher than that of horseradish peroxidase (HRP), while its 3-fold enhancement in SERS signal compared with that of gold nanoparticles (Au NPs). Integrated with nanozyme-based sandwich system that made of bacteria/4-MPBA (4-mercaptophenylboronic acid)/AuAg@PB MOF, this dual-modal biosensor achieves a highly sensitive colorimetric assay of bacteria with a lower limit of detection (6 CFU/mL), and simultaneously discriminate E. coli and S. aureus by bacterial “fingerprints” spectra. Furthermore, this proposed colorimetric assay was combined with a smartphone readout-sensing platform for determining bacteria with ultra-sensitivity (2 CFU/mL). This work exhibits a novel colorimetric nanozyme used in dual-mode colorimetric/SERS sensing of bacteria.

A pH-responsive magnetic resonance tuning probe for precise imaging of bacterial infection in vivo.

Accurate and sensitive detection of bacteria is essential for treating bacterial infections. Herein, a pH-responsive magnetic resonance tuning (MRET) probe, whose T1-weighted signal is activated in the bacteria-infected acid microenvironment, is developed for in situ accurately magnetic resonance imaging (MRI) of bacterial infection in vivo. The MRET probe (MDVG-1) is an assembly of paramagnetic enhancer (gadolinium-modified i-motif DNA3, abbreviated as Gd-DNA3-Gd) and the precursor of superparamagnetic quencher (DNA and vancomycin-modified magnetic nanoparticle, abbreviated as MDV). The T1-weighted signal of Gd-DNA3-Gd is quenched once the formation of MDVG-1 (MRET ON). Interestingly, the MDVG-1 probe was disassembled into the monomers of Gd-DNA3-Gd and MDV under the bacteria-infected acid microenvironment, resulting significantly enhanced T1-weighted signal at the infected site (MRET OFF). The pH-responsive MRET probe-based enhanced MRI signal and bacteria targeting significantly improve the distinction between bacterial infectious tissues and sterile inflamed tissues, which provides a promising approach for accurately detecting bacterial infection in vivo. STATEMENT OF SIGNIFICANCE: : Detecting pathogenic bacteria in vivo based on magnetic resonance imaging (MRI) strategy has been exploring recently. Although various bacterial-targeted MRI probes have been developed to image bacteria in vivo, the MRI signal of these MRI probes is always "on", which inevitably generates nonspecific background MRI signals, affecting the accuracy of MRI to a certain extent. In the current study, based on the magnetic resonance tuning (MRET) phenomenon, we present a pH-responsive MRET probe (MDVG-1) with T2-weighted imaging to T1-weighted imaging switchable properties to achieve in situ precise imaging of bacterial infection in vivo.

Highly sensitive detection of bacteria (E. Coli) endotoxin using novel PANI-benzimidazole-Ag nanocomposite by DMMB dye displacement assay

In the present study, a new biochemical biosensor material of conductive Silver (Ag) reinforced polyaniline (PANI)-Benzimidazole copolymer nanocomposite was fabricated via in situ chemical oxidative polymerization method for the detection of endotoxin. The fabricated PANI-Benz-Ag nanocomposite was characterized by FTIR, XRD, UV–visible spectrometer, DSC, TGA, Zeta-potential, SEM, TEM, and Confocal fluorescence imaging microscopy. The measured particle size, zeta-potential, and conductivity of the PANI-Benz-Ag nanocomposite were 4.942 nm, −10.4 mV, and 73.7 μS cm−1 respectively. The crystallite size of Ag nanoparticles was around 67 nm calculated by XRD analysis and TGA analysis was carried out to determine weight loss and thermal stabilities of PANI-Benz and PANI-Benz-Ag nanocomposite. The endotoxin (E. coli) bacteria detection ability of the synthesized PANI-Benz-Ag nanocomposite-based biochemical biosensor using DMMB dye displacement assay through the hitchhiking method by confocal fluorescence microscopy was found to be simple and effective. Endotoxin (E. coli) can form a stable interaction with other bioactive molecules and thus it binds readily with Ag-doped PANI-Benzimidazole nanocomposite. Further, the DMMB dye displacement assay method is more accurate and sensitive than the other existing methods for the detection of endotoxin.

Enzymatic Catalysis in Size and Volume Dual-Confined Space of Integrated Nanochannel-Electrodes Chip for Enhanced Impedance Detection of Salmonella.

Nanochannel-based confinement effect is a fascinating signal transduction strategy for high-performance sensing, but only size confinement is focused on while other confinement effects are unexplored. Here, a highly integrated nanochannel-electrodes chip (INEC) is created and a size/volume-dual-confinement enzyme catalysis model for rapid and sensitive bacteria detection is developed. The INEC, by directly sandwiching a nanochannel chip (60µm in thickness) in nanoporous gold layers, creates a micro-droplet-based confinement electrochemical cell (CEC). The size confinement of nanochannel promotes the urease catalysis efficiency to generate more ions, while the volume confinement of CEC significantly enriches ions by restricting diffusion. As a result, the INEC-based dual-confinement effects benefit a synergetic enhancement of the catalytic signal. A 11-times ion-strength-based impedance response is obtained within just 1min when compared to the relevant open system. Combining this novel nanoconfinement effects with nanofiltration of INEC, a separation/signal amplification-integrated sensing strategy is further developed for Salmonella typhimurium detection. The biosensor realizes facile, rapid (<20min), and specific signal readout with a detection limit of 9 CFU mL-1 in culturing solution, superior to most reports. This work may create a new paradigm for studying nanoconfined processes and contribute a new signal transduction technique for trace analysis application.

Recent advances of Raman spectroscopy for the analysis of bacteria.

Rapid and sensitive bacteria detection and identification are becoming increasingly important for a wide range of areas including the control of food safety, the prevention of infectious diseases, and environmental monitoring. Raman spectroscopy is an emerging technology which provides comprehensive information for the analysis of bacteria in a short time and with high sensitivity. Raman spectroscopy offers many advantages including relatively simple operation, non-destructive analysis, and information on molecular differences between bacteria species and strains. A variety of biochemical properties can be measured in a single spectrum. This short review covers the recent advancements and applications of Raman spectroscopy for bacteria analysis with specific focuses on bacteria detection, bacteria identification and discrimination, as well as bacteria antibiotic susceptibility testing in 2022. The development of novel substrates, the combination with other techniques, and the utilization of advanced data processing tools for the improvement of Raman spectroscopy and future directions are discussed.

Semi-automated water sampling module for repeated sampling and concentration of Bacillus cereus group spores

Monitoring the presence of pathogenic Bacillus spores is important for industrial applications, as well as necessary for ensuring human health. Bacillus thuringiensis is used as a biopesticide against several insect pests. Bacillus cereus spores are a significant cause of food poisoning, and Bacillus anthracis is a recognized biosecurity threat. Laboratory-based methods, such as polymerase chain reaction, enzyme-linked immunosorbent assay, or matrix-assisted laser desorption ionization spectroscopy provide sensitive detection of bacteria and spores, but the application of those methods for quasi-continuous environmental monitoring presents a significant challenge requiring frequent human intervention. To address this challenge, we developed a workstation for quasi-autonomous monitoring of water reservoirs for the presence of bacteria and spores, and designed and validated the functionality of a microprocessor-controlled module capable of repetitive collection and pre-concentration of spores in liquid samples tested with fiberglass (FG), polyether sulfone and polyvinylidene fluoride filters. The best results were obtained with FG filters delivering a 20× concentration of B. thuringiensis and B. cereus spores from saline suspensions. The successful 20× pre-concentration of Bacillus spores demonstrated with FG filters could be repeated up to 3 times when bleach decontamination is applied between filtrations. Taken together, our results demonstrate an attractive instrument suitable for semi-automated, quasi-continuous sampling and pre-processing of water samples for biosensing of bacterial spores originating from a complex environment.

Amikacin- and AuNP-mediated colorimetric biosensor for the rapid and sensitive detection of bacteria

Bacterial contamination has been recognized as a major public health concern worldwide, leading to putrefaction of food and endanger human health. In this study, we proposed a novel biosensing strategy for bacterial sensing based on modified gold nanoparticles (AuNPs) combined with amikacin as the molecular recognition element. Amikacin, an antibacterial drug, acts not only as a specific binder for bacteria but also as an aggregator for AuNPs. Without bacteria, amikacin combined with AuNPs, once target bacteria existed, they bound to bacteria that rendered the AuNPs free, providing a colorimetric readout of the binding event. The biosensor shows a good linear correlation with the concentration of bacteria ranging from 10 to 106 CFU/mL, with a limit of detection at 104 CFU/mL and 2.9 log CFU/mL by naked eyes and simple spectroscopic analysis of bacterial, respectively. Furthermore, the detection time was within 10 min without any expensive reagents or complex instruments. Briefly, we proposed a novel, easy, and rapid method, and it could be promising for the on-site detection of bacterial in food processing plant.

Sensitive Methicillin-Resistant Staphylococcus Aureus (MRSA) Detection Using Gold Nanoparticle-Based Satellite Network With Potential For Early Diagnosis of Diabetes-Related Infection

Background: As pathogenic bacteria account for the leading cause of diabetes-related infections, sensitive detection of bacteria from clinical samples has attracted abundant attention. Methods: We propose an innovative DNA-AuNP-based sensing system that integrates low-speed centrifugal bacteria isolation, detection and protein analysis. In the method, RCA (rolling circle amplification) is utilized to produce a long-ssDNA (single-strand DNA), which can form a hairpin structure comprising repeats of functional domains, such as PBP2a aptamer. When aptamers bind to target bacteria, the hairpin structure in the RCA product changes its conformation, exposing the AuNP binding sequence. As a result, the probe on the surface of AuNP hybridizes with AuNP binding sequence in RCA product by strand displacement reaction, releasing the fluorescent-labeled complementary probe as the detection signal. The simultaneous formation of the bacteria-DNAAuNP satellite network enables the isolation of target bacteria by low-speed centrifugation. Results: Eventually, we applied the method for MRSA (methicillin-resistant Staphylococcus aureus) detection and obtained a favorable detection performance with a limit of detection of 275 cfu/μL. Conclusion: We believe the method has potential application in the early diagnosis of diabetesrelated infections.

Plasmon-Mediated Peroxidase-like Activity on an Asymmetric Nanotube Architecture for Rapid Visual Detection of Bacteria.

Rapid and sensitive detection of bacteria from a complex real media remains a challenge. Herein, we report a visual bacterial sensing assay with excellent specificity, anti-interference ability, and sensitivity based on a surface plasmon resonance (SPR)-enhanced peroxidase (POD) mimetic. The POD mimetic based on Pt nanoparticles (NPs) asymmetrically decorated on Au/TiO2 magnetic nanotubes (Au/Pt/MTNTs) is designed by combining the intrinsic photocatalytic activity of TiO2 and the limited transport depth of light. It is revealed that the localized surface plasmon resonance (LSPR) effect of the asymmetric nanotubes is more effective in facilitating the generation of hot electrons, which are subsequently transferred to Pt and MTNTs, thus greatly promoting the catalytic performance. Using Staphylococcus aureus (S.aureus) as a model of Gram-positive bacteria, the dependence of the colorimetric reaction on the active sites of the POD mimetic is used for the sensing of target bacteria. Owing to the specific recognition between S.aureus and peptide, the fluorescein isothiocyanate (FITC) labeled peptide probes are captured by S.aureus and removed from the Au/Pt/MTNTs, leading to the recovery of POD-like activity and fluorescence emission of S.aureus. Particularly, benefiting from the Au-SPR effect and the magnetic feature of the Au/Pt/MTNTs, the recovery of catalytic activity induced an improved colorimetric assay with a wider linear response for S.aureus qualification and a detection limit of four cells, as well as satisfactory selectivity and feasibility for application in real samples. The plasmon-enhanced POD activity would provide a simple-yet-effective approach to achieve a colorimetric bioassay with high efficiency and sensitivity. This asymmetric design can also be utilized to engineer nanozymes in colorimetric assays for the specific detection of biotoxins, biomarkers, and cancer cells.

Simplified Fabrication of Magnetic Nanoparticles With Directly Adsorbed Antibodies for Bacteria Detection

Antigen–antibody reactions with conjugated magnetic nanoparticles (MNPs) are widely used for detecting viruses, bacteria, and proteins. In this study, we proposed a novel method for adsorbing antibodies directly on the surface of MNPs without coating any proteins. MNPs (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ; average size 4 nm) were synthesized by a thermal decomposition method using oleyl amine as a surfactant, the fabricated MNPs exhibit superparamagnetic characteristics, and the antibodies (anti- <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>Bifidobacterium longum</i></b> ) were adsorbed. We found that 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> /mg of antibody adsorbed to MNPs and were able to detect the bacteria bound to the produced antibody-MNPs based on the antigen–antibody reaction, offering potential for highly sensitive bacteria detection.

Enzyme-Activated, Chemiluminescent Siderophore-Dioxetane Probes Enable the Selective and Highly Sensitive Detection of Bacterial Pathogens.

The sensitive detection of bacterial infections is a prerequisite for their successful treatment. The use of a chemiluminescent readout was so far hampered by an insufficient probe enrichment at the pathogens. We coupled siderophore moieties, that harness the unique iron transport system of bacteria, with enzyme‐activatable dioxetanes and obtained seven trifunctional probes with high signal‐to‐background ratios (S/B=426‐859). Conjugates with efficient iron transport capability into bacteria were identified through a growth recovery assay. All ESKAPE pathogens were labelled brightly by desferrioxamine conjugates, while catechols were weaker due to self‐quenching. Bacteria could also be detected inside lung epithelial cells. The best probe 8 detected 9.1×103 CFU mL−1 of S. aureus and 5.0×104 CFU mL−1 of P. aeruginosa, while the analogous fluorescent probe 10 was 205–305fold less sensitive. This qualifies siderophore dioxetane probes for the selective and sensitive detection of bacteria.