Multifunctional nanoprobes for pathogen-selective capture and detection

Photoluminescent inorganic nanoprobe-based pathogen detection

Pathogens are serious threats to human health, and traditional detection techniques suffer from various limitations. The unique optical properties of photoluminescent inorganic nanomaterials, such as high photoluminescence quantum yields, good photostability, and tunable spectrum, make them ideal tools for the detection of pathogens with high specificity and sensitivity. In this review, the design strategies, working mechanisms, and applications of photoluminescent inorganic nanomaterial-based probes in pathogen detection are introduced. In particular, the design and construction of stimuli-responsive nanoprobes and their potential in these fields are highlighted.

Engineering Phage Tail Fiber Protein as a Wide-Spectrum Probe for Acinetobacter baumannii Strains with a Recognition Rate of 100

As a multidrug-resistant pathogen, Acinetobacter baumannii has long been identified as one of the most common nosocomial bacteria. High-performance recognition probes for wide-spectrum detection of A. baumannii are highly desired to achieve efficient diagnosis and timely treatment of infectious diseases induced by this pathogen. An engineering tail fiber protein (ETFP) named as Gp50 encoded by lytic phage Abp9 was expressed in Escherichia coli and identified as a binding protein for A. baumannii. According to the results of genome sequencing of an A. baumannii wild strain and phage-resistant strains, the binding receptor of ETFP Gp50 is inferred to be a lipopolysaccharide distributed on the bacterial surface. The engineering protein did not show lytic activity to A. baumannii, which facilitates the development of reliable diagnosis kits and biosensors with high flexibility and low false-negative rate. The results of specificity study show that ETFP Gp50 is a species-specific binding protein with a recognition rate of 100% for all tested 77 A. baumannii strains, while that of the natural phage Abp9 is only 27.3%. With the engineering protein, a fluorescence method was developed to detect A. baumannii with a detection range of 2.0 × 10² to 2.0 × 10⁸ cfu mL^-1. The method has been used for the quantification of A. baumannii in a diverse sample matrix with acceptable reliability. The work demonstrates the application potential of ETFP Gp50 as an ideal recognition probe for rapid screening of A. baumannii strains in a complicated sample matrix.

Highly Specific Bacteriophage-Affinity Strategy for Rapid Separation and Sensitive Detection of Viable Pseudomonas aeruginosa

A virulent bacteriophage highly specific to Pseudomonas aeruginosa (P. aeruginosa) was isolated from hospital sewage using a lambda bacteriophage isolation protocol. The bacteriophage, named as PAP1, was used to functionalize tosyl-activated magnetic beads to establish a bacteriophage-affinity strategy for separation and detection of viable P. aeruginosa. Recognition of the target bacteria by tail fibers and baseplate of the bacteriophage led to capture of P. aeruginosa onto the magnetic beads. After a replication cycle of about 100 min, the progenies lysed the target bacteria and released the intracellular adenosine triphosphate. Subsequently, firefly luciferase-adenosine triphosphate bioluminescence system was used to quantitate the amount of P. aeruginosa. This bacteriophage-affinity strategy for viable P. aeruginosa detection showed a linear range of 6.0 × 10² to 3.0 × 10⁵ CFU mL^-1, with a detection limit of 2.0 × 10² CFU mL^-1. The whole process for separation and detection could be completed after bacteria capture, bacteriophage replication, and bacteria lysis within 2 h. Since the isolated bacteriophage recognized the target bacteria with very high specificity, the proposed strategy did not show any signal response to all of the tested interfering bacteria. Furthermore, it excluded the interference from inactivated P. aeruginosa because the bacteriophage could replicate only in viable cells. The proposed strategy had been applied for detection of P. aeruginosa in glucose injection, human urine, and rat plasma. In the further work, this facile bacteriophage-affinity strategy could be extended for detection of other pathogens by utilizing virulent bacteriophage specific to other targets.

Ultrasensitive detection of microbial cells using magnetic focus enhanced lateral flow sensors

We report on an improved lateral flow immunoassay (LFIA) sensor with a magnetic focus for ultrasensitive naked-eye detection of pathogenic microorganisms at a near single cell limit without any pre-enrichment steps, by allowing the magnetic probes to focus the labelled pathogens to the target zone of the LF strip.

Gram-positive antimicrobial activity of amino acid-based hydrogels

Antimicrobial hydrogels are prepared based on the co-assembly of commercial Fmoc-phenylalanine and Fmoc-leucine, which act as the hydrogelator and antimicrobial building block, respectively. This co-assembled antimicrobial hydrogel is demonstrated to exhibit selective bactericidal activity for gram-positive bacteria while being biocompatible with normal mammalian cells, showing great potential as an antimicrobial coating for clinical anti-infective applications.

Chiral, fluorescent microparticles constructed by optically active helical substituted polyacetylene: preparation and enantioselective recognition ability

Novel chiral fluorescent microparticles derived from helical substituted polyacetylene were prepared. The microparticles showed enantioselective recognition ability in both heterogeneous and homogeneous systems.

Double-site recognition of pathogenic bacterial whole cells based on an antibiotic-affinity strategy

An antibiotic-affinity strategy was designed for direct assaying whole cells of a pathogenic bacterium based on the strong affinity of the antibiotic agent to bind to the cell wall of the bacterium.

Nanoparticle approaches against bacterial infections

Despite the wide success of antibiotics, the treatment of bacterial infections still faces significant challenges, particularly the emergence of antibiotic resistance. As a result, nanoparticle drug delivery platforms including liposomes, polymeric nanoparticles, dendrimers, and various inorganic nanoparticles have been increasingly exploited to enhance the therapeutic effectiveness of existing antibiotics. This review focuses on areas where nanoparticle approaches hold significant potential to advance the treatment of bacterial infections. These areas include targeted antibiotic delivery, environmentally responsive antibiotic delivery, combinatorial antibiotic delivery, nanoparticle-enabled antibacterial vaccination, and nanoparticle-based bacterial detection. In each area we highlight the innovative antimicrobial nanoparticle platforms and review their progress made against bacterial infections.

A new nanoprobe based on FRET between functional quantum dots and gold nanoparticles for fluoride anion and its applications for biological imaging

A new nanoprobe was designed for the fluorescence imaging of fluoride anion (F(-)) in living cells with high sensitivity and selectivity. The design is based on the fluorescence resonance energy transfer (FRET) between CdTe quantum dots (CdTe QDs) and gold nanoparticles (AuNPs) through the formation of cyclic esters between phenylborinic acid and diol. In the presence of F(-), the boronate ester, a "hard acid", strongly reacts with F(-), a "hard base". Therefore, the boronate ester is converted to trifluoro borate, which causes the breakage of the linkage and disassembles CdTe QDs from AuNPs, resulting in the fluorescence recovery of the quenched CdTe QDs. The interaction mechanism was investigated by (19)FNMR on a model that was constructed by a small molecule and F(-). Quantum chemical calculations also testify the reactivity of boronate ester to F(-) and the sensing mechanism. Experimental results show that the increase in fluorescence intensity is proportional to the concentration of F(-) in the range of 5.0-45 μM. The detection limit and the relative standard deviation were 50 nM and 2.6%, respectively. Fluorescence imaging of F(-) in macrophages cells indicates good cell membrane penetration ability and low cytotoxicity of the nanoprobe, providing a viable alternative to detection of F(-) in biological or environmental samples.