Specific chemiluminescent protocol for dual-site recognition of Streptococcus mutans utilizing strong affinity between teicoplanin and Gram-positive bacteria

Phase Transformation and Mechanical Optimization of Eggshell-Derived Hydroxyapatite across a Wide Sintering Temperature Range

Calcium phosphate, particularly hydroxyapatite (HA), bears a close resemblance to human bones, rendering it a prevalent material in biomedical applications. This study focuses on the successful preparation of HA using a precipitation method with eggshell as a raw material. Subsequently, the HA powder was press-formed and sintered at various temperatures to investigate the impact of sintering temperature on the mechanical properties, including hardness, compressive strength, and fracture toughness, of the sintered HA samples (E-HA). Statistical analyses, including one-way ANOVA and Tukey's post-hoc test, were conducted to determine significant differences in these properties at different sintering temperatures. Experimental findings revealed that as the sintering temperature increased, HA partially transformed into β-TCP between 800 and 1300 °C, with α-TCP observed at 1400 °C. The elimination of pores led to an increase in relative density, with a maximum relative density of 94.5% achieved at 1200 and 1300 °C. E-HA sintered at 1200 °C exhibited the highest hardness (5.08 GPa), compressive strength (255.79 MPa), and fracture toughness (1.21 MPa·m0.5). However, at 1400 °C, a slight decrease in apparent density (2.90 g/cm3) was noted due to the presence of α-TCP, along with significant grain growth. This study's objective is clearly aligned with the study design, incorporating detailed statistical analyses to validate the findings. Furthermore, bacterial culture experiments were conducted using sintered E-HA, Chem-HA (HA synthesized from reagent-grade calcium carbonate), and Comm-HA (commercial HA). Streptococcus mutans was cultured on the surfaces of sintered E-HA, Chem-HA, and Comm-HA samples for 20 h. After culturing, the OD values for all samples were below 0.2, indicating significant antibacterial efficacy. The comparable OD values and bacterial counts (p > 0.05) suggest that the source of HA does not impact its antibacterial properties. This underscores the potential of eggshell-derived HA as an effective material for biomedical applications.

Time-resolved fluorescence immunoassay based on glucose oxidase-encapsulated metal-organic framework for amplified detection of foodborne pathogen

BACKGROUND

Fluorescence immunoassays are commonly employed for the detection of pathogenic bacteria as a means of ensuring food safety and preserving public health. However, the challenges such as poor photostability and background interference have limited their sensitivity and accuracy. The emergence of metal-organic frameworks (MOFs) as a label probe offers a promising solution for advancing fluorescence immunoassays owing to their tunable nature. Nonetheless, the low fluorescence efficiency of MOFs and the potential risk of dye leakage pose obstacles to achieving high detection sensitivity. Therefore, there exists a pressing need to fully utilize the potential of MOF composites in fluorescence immunoassays.

RESULTS

We explored the potential of glucose oxidase-encapsulated zeolitic imidazole framework-90 (GOx@ZIF-90) as a label probe to construct a time-resolved fluorescence immunoassay with amplified detection signal. This immunoassay involved functionalizing Fe3O4 nanoparticle with porcine antibody to specifically capture and separate the target bacteria, Staphylococcus aureus (S. aureus). The captured S. aureus was then bound by GOx@ZIF-90 modified with vancomycin, resulting in a fluorescence response in the europium tetracycline (EuTc). The encapsulation of GOx in ZIF-90 provided a confinement effect that significantly enhanced the catalytic activity and stability of GOx. This led to a highly efficient conversion of glucose to H2O2, amplifying the fluorescence signal of EuTc. The immunoassay demonstrated a high sensitivity in detecting S. aureus, with a detection limit of 2 CFU/mL. We also obtained satisfactory results in milk samples. Attractively, the time-resolved detection mode of EuTc allowed the immunoassay to eliminate background fluorescence and enhance accuracy.

SIGNIFICANCE

This study not only presented a new method for detecting foodborne pathogens but also highlighted the potential of enzyme-encapsulated MOF composites as label probes in immunoassays, providing valuable insights for the design and fabrication of MOF composites for various applications.

Bacterial metabolism-triggered-chemiluminescence-based point-of-care testing platform for sensitive detection and photothermal inactivation of Staphylococcus aureus

Post-operative pathogenic infections in liver transplantation seriously threaten human health. It is essential to develop novel methods for the highly sensitive and rapid detection of Staphylococcus aureus (S. aureus). Interestingly, the combination of the property of bacteria to secrete hydrogen peroxidase, bacterial metabolism-triggered-chemiluminescence (CL)-based bioassays can be as a candidate point-of-care testing (POCT) for the detection of S. aureus against the CL substrate Luminol and hydrogen peroxide without excitation light sources. Here, a CL-based strategy with stable and visualized CL intensity was fabricated according to a hybrid biomimetic enzyme of copper-Hemin metal-organic framework, which enhances the biological enzyme activity while improving the stability and sensitivity of the assay. By further integrating S. aureus-specific capture and one-step separation of the antibody-modified Fe3O4 NPs (Fe3O4 NPs@Ab), the portable device integrated smartphone enables CL-based POCT for specific detection of S. aureus in the range of 101-106 CFU/mL with a limit of detection as low as 1 CFU/mL. Specifically, S. aureus can be eliminated after detection with high antibacterial efficiency due to the excellent photothermal properties of Fe3O4 NPs@Ab. The developed multifunctional platform has the advantages of simplicity of operation and low cost, indicating great potential in clinical applications.

Highly selective and sensitive detection of Hg2+ by a novel fluorescent probe with dual recognition sites

A novel thionocarbonate-coumarin-thiourea triad-based probe with dual recognition sites for sensing mercury (Hg²⁺) ion was developed. The synthesized probe possessed both fluorogenic ("off-on") and chromogenic (from colorless to blackish brown) sensing performance towards Hg²⁺ ions. The fluorescence intensity was increased by 70 fold after the addition of Hg²⁺. As expected, the probe exhibited excellent selectivity and sensitivity for Hg²⁺ compared to other common competitive metal ions. The fluorescence intensity of the probe improved linearly with the increase of the concentration of Hg²⁺ (0-40 μM). Also, the minimum limit of detection (LOD) of the synthesized probe was 0.12 μM. Considering the importance of test feasibility in the harsh environment, the developed probe was applicable for detecting Hg²⁺ ions over a broad working pH range of 3-11. It is reliable and qualifies for the quantitative determination of Hg²⁺ concentrations in actual water samples. Finally, the probe achieved the bioimaging performance of Hg²⁺ in living cells and plants with good biocompatibility.

Dual recognition strategy and magnetic enrichment based lateral flow assay toward Salmonella enteritidis detection

As a rapid and facile means for foodborne bacteria detection in situ, lateral flow immunoassay (LFA) still has intrinsic limitations in the construction of the existing sandwich LFA format, e.g. screening difficulties of paired antibodies (Abs), poor stability of Ab probe, etc. Here, combined the strong affinity of antibiotic with the superior specificity of antibody molecules, a novel and robust LFA based on a dual recognition strategy and magnetic separation was designed to achieve specific and sensitive determination of Salmonella enteritidis (S. enteritidis). In this work, ampicillin (Amp), a broad-spectrum antibiotic against bacteria, was employed as an ideal Ab replacer to anchor cells of target bacteria. By coating Amp on magnetite nanoparticles (MNPs), the Amp-MNPs showed remarkable binding, separation and enrichment capacities toward bacteria even under complex sample matrices. To ensure the selectivity of this protocol, anti-S. enteritidis monoclonal antibody was then adopted as the second anchoring agent to form a sandwich complex with Amp-MNPs. Based on these facts, S. enteritidis, as low as 10²-10³ CFU/mL, could be detected by naked eyes in food samples. Therefore, this creative antibiotic-bacteria-antibody LFA sandwich pattern shows great application potential in the monitoring of food contamination and infectious diseases caused by pathogenic bacteria. Compared to the common paired Abs based sandwich method, the proposed approach was cost-effective, non-labor intensive, stable, sensitive and efficient.