The effective monitoring, identification, and quantification of pathogenic bacteria is essential for addressing serious public health issues. In this study, we present a universal and facile one-step strategy for sensitive and selective detection of pathogenic bacteria using a dual-molecular affinity-based Förster (fluorescence) resonance energy transfer (FRET) platform based on the recognition of bacterial cell walls by antibiotic and aptamer molecules, respectively. As a proof of concept, Vancomycin (Van) and a nucleic acid aptamer were employed in a model dual-recognition scheme for detecting Staphylococcus aureus (Staph. aureus). Within 30 min, by using Van-functionalized gold nanoclusters and aptamer-modified gold nanoparticles as the energy donor and acceptor, respectively, the FRET signal shows a linear variation with the concentration of Staph. aureus in the range from 20 to 10 cfu/mL with a detection limit of 10 cfu/mL. Other nontarget bacteria showed negative results, demonstrating the good specificity of the approach. When employed to assay Staph. aureus in real samples, the dual-recognition FRET strategy showed recoveries from 99.00% to the 109.75% with relative standard derivations (RSDs) less than 4%. This establishes a universal detection platform for sensitive, specific, and simple pathogenic bacteria detection, which could have great impact in the fields of food/public safety monitoring and infectious disease diagnosis.

In the modern era of molecular evidence-based medicine and advanced biomedical technologies, the rapid, sensitive and specific assay of multiple pathogens is critical to, but largely absent from, clinical practice. Therefore, to improve the current ordinary separation and collection method, we report herein a strategy of magnetism-resolved separation and fluorescence quantification for near-simultaneous detection of multiple pathogens, followed by the direct antimicrobial susceptibility testing (AST). To accomplish this strategy, we utilized aptamer-modified fluorescent-magnetic multifunctional nanoprobes (apt-FMNPs). FMNPs with intriguing different magnetic responses and excellent fluorescence quality were first self-assembled based on metal coordination interaction using (3-mercaptopropyl) trimethoxysilane, magnetic γ-FeO, and fluorescent quantum dots as matrix components. Then, aptamers, which specific to target pathogens of Escherichia coli O157:H7 ( E. coli) and Salmonella typhimurium ( S. typ), were conjugated with FMNPs to yield apt-FMNPs nanoprobes for multiple pathogens assay. Based on the discrepant magnetic response of pathogen@nanoprobes complex under the identical external magnetic field, the model bacteria were fished out by magnetic adsorption at different time points and subjected to fluorescence quantification with good linear ranges and detection limits within 1h. Multiple pathogens spiked in real samples were also effectively detected by the apt-FMNPs and sequentially fished out for AST assay, which showed similar results to that for pure pathogens. The apt-FMNPs-based strategy of near-simultaneous detection of multiple pathogens shows promise for the potential application in the diagnosis and treatment of pathogen-related infectious diseases.

The intracellular invasion and survival of a pathogen like Staphylococcus aureus (S. aureus) within host cells enable them to resist antibiotic treatment and colonize long-term in the host, which leads to a series of clinical issues. Rapid and specific detection of intracellular bacteria is important in diagnosis of infection and guiding antibiotic administration. Herein, this work reports a simple one-step fluorescence resonance energy transfer (FRET) platform-based strategy to achieve specific and rapid detection of S. aureus in specimens of phagocytic cells. The aptamer modified quantum dots (Aptamer-QDs) and antibiotic molecule of Teicoplanin functionalized-gold nanoparticles (Teico-AuNPs) dual-recognition units to S. aureus are employed as energy donor and acceptor, respectively. Based on the "off" to "on" signal readout mode, when in the presence of target S. aureus, the donor and acceptor are close to each other and bring high FRET efficiency, which is suitable for analysis of intracellular S. aureus. After it was incubated with the sample for 2 h, the as-prepared FRET sensor showed selectivity to the target S. aureus, and the changed fluorescence signal shows an obvious variation with increasing concentration of S. aureus in pure buffer. When the FRET strategy was further applied to assay intracellular S. aureus, there was an obvious fluorescence signal change obtained both by spectrum analysis and visual fluorescence microscope observation when the average number of S. aureus in one host cell (N S. aureus/cell ) was as low as 1, which can be attributed to the high fluorescence quenching efficiency of about 41.3%. It could be envisioned that this FRET nanoprobe with high fluorescence quenching efficiency may provide a simple approach for the facile, selective, and rapid diagnosis of an intracellular bacterial infection.

Tumor cell heterogeneity leads to differences in tumor proliferation and invasiveness, as well as drug sensitivity. These factors affect the diagnosis, treatment, and monitoring of tumor progression. Thus, analysis of tumor cell subpopulations is crucial for tumor diagnosis and individualized treatment. This study describes an approach to capture and sequentially isolate tumor cells subpopulations based on antibody-mediated recognition and magnetic gradient separation, using biomimetic immuno-fluorescent magnetic multifunctional nanoprobes, consisting of magnetic γ-Fe 2 O 3 and fluorescent quantum dots as the core, and leukocyte membrane vesicles with antibodies as the shell. Upon binding with leukocyte membrane-coated fluorescent magnetic nanoparticles with antibodies (LFMNPs-Ab), the model of three types of breast cancer cells with different expression levels of Her2 marker on the cell surface, namely, BT474 Her2+++ , MDA-MB-453 Her2++ , and MDA-MB-231 Her2+ , develop different magnetic susceptibilities. Based on the differences in their magnetic response under constant external magnetic field, the three tumor cell subpopulations in blood samples are magnetically separated and collected sequentially at 90, 120, and 180 s, respectively, as confirmed by a subsequent fluorescent imaging assay. The magnetic gradient separationbased strategy described in the present study is a simple, fast, and feasible method for targeted separation of tumor cell subpopulations, and shows great potential for clinical study.

Despite the significant advances of imaging techniques nowadays, accurate diagnosis of bacterial infections and real‐time monitoring the efficacy of antibiotic therapy in vivo still remain huge challenges. Herein, a self‐assembling peptide (FFYEGK) and vancomycin (Van) antibiotic molecule co‐modified gadolinium (Gd) MRI nanoaggregate probe (GFV) for detecting Staphylococcus aureus (S. aureus) infection in vivo and monitoring the treatment of S. aureus‐infected myositis by using daptomycin (Dap) antibiotic as model are designed and fabricated. The as‐prepared GFV probe bears Van molecules, making itself good bacteria‐specific targeting, and the peptide in the probe can enhance the longitudinal relaxivity rate (r1) after self‐assembly due to the π–π stacking. The study showed that, based on the GFV probe, bacterial infections and sterile inflammation can be discriminated, and as few as 105 cfu S. aureus can be detected in vivo with high specificity and accurately. Moreover, the T1 signal of GFV probe at the S. aureus‐infected site in mice correlates with the increasing time of Dap treating, indicating the possibility of monitoring the efficacy of antibacterial agents for infected mice based on the as proposed GFV probe. This study shows the potential of GFV probe for diagnosis, evaluation, and prognosis of infectious diseases in clinics.