Recent advances of fluorescent sensors for bacteria detection-A review

Bacterial infections have become a global public health problem. Rapid and sensitive bacterial detection is of great importance for human health. Among various sensor systems, fluorescence sensor is rapid, portable, multiplexed, and cost-efficient. Herein, we reviewed the current trends of fluorescent sensors for bacterial detection from three aspects (response materials, target and recognition way). The fluorescent materials have the advantages of high fluorescent strength, high stability, and good biocompatibility. They provide a new path for bacterial detection. Several recent fluorescent nanomaterials for bacterial detection, including semiconductor quantum dots (QDs), carbon dots (CDs), up-conversion nanoparticles (UCNPs) and metal organic frameworks (MOFs), were introduced. Their optical properties and detection mechanisms were analyzed and compared. For different response targets in the detection process, we studied the fluorescence strategy using DNA, bacteria, and metabolites as the response target. In addition, we classified the recognition way between nanomaterial and target, including specific recognition methods based on aptamers, antibodies, bacteriophages, and non-specific recognition methods based on biological functional materials. The characteristics of different recognition methods were summarized. Finally, the weaknesses and future development of bacterial fluorescence sensor were discussed. This review provides new insights into the application of fluorescent sensing systems as an important tool for bacterial detection.

Unlocking the power of optical imaging in the second biological window: Structuring near-infrared II materials from organic molecules to nanoparticles

Biomedical imaging techniques play a crucial role in clinical diagnosis, surgical intervention, and prognosis. Fluorescence imaging in the second biological window (second near-infrared [NIR-II]; 1000-1700 nm) has attracted attention recently. NIR-II fluorescence imaging offers unique advantages in terms of reduced photon scattering, deep tissue penetration, high sensitivity, and many others. A host of materials, including small organic molecules, single-walled carbon nanotubes, polymeric and rare-earth-doped nanoparticles, have been explored as NIR-II emitting fluorescent probes. Efficient and viable approaches to design and develop fluorescence probes with tunable photophysical properties without compromising other key features are of paramount importance. Various chemical strategies are explored to increase the quantum yield of these imaging agents without compromising their spatiotemporal resolution, specificity, and tissue penetration capabilities. This review summarizes the strategies implemented to design and synthesize NIR-II emitting nanoparticles and small organic molecule-based fluorescent probes for applications in the biomedical field. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

Fluorescence quenching of MoS2 nanosheets/DNA/silicon dot nanoassembly: effective and rapid detection of Hg2+ ions in aqueous solution

Mercury (Hg) contamination of aquatic sites represents a serious risk for human health and the environment. Therefore, effective and rapid monitoring of Hg in aqueous samples is a challenge of timely importance nowadays. In the present study, a rapid and sensitive mercury sensor based on the fluorescence quenching of MoS₂ nanosheets/DNA/silicon dot nanoassembly has been developed for the efficient detection of mercury(II) in aquatic environments. In this process, silicon dots were synthesized through one-step high-temperature calcinations and thermomagnesium reduction method at 900 °C using rice husk as a silicon source, which demonstrates superior photophysical properties and excitation-dependent fluorescence behavior. The interaction between MoS₂ nanosheets/DNA/silicon dot nanoassembly and Hg²⁺ ions was studied using photoluminescence spectroscopy. The addition of Hg²⁺ ions to the assay solution induced the detachment of fluorescent probe from the surface of MoS₂ nanosheets. Thus, the fluorescent probes sustained its fluorescence intensity. The developed sensor was tested on various concentrations of Hg²⁺ ions ranging from 0 to 1000 nM as well as on various metal ions. In addition, MoS₂ nanosheets/DNA/silicon dot nanoassembly fluorescent Hg sensor efficiently detected the presence of Hg²⁺ ions in real-time water samples, which was comparably detected by the conventional atomic absorbance spectrometer (AAS). Overall, our results highlighted the high reliability of the present approach for environmental monitoring of Hg²⁺ ions, if compared to that of the customary method with a lowest detection limit of 0.86 nM.

Graphene oxide coating core–shell silver sulfide@mesoporous silica for active targeted dual-mode imaging and chemo-photothermal synergistic therapy against tumors

FA-modified-GO coated core–shell Ag₂S@mesoporous silica where DOX was loaded for active targeting FL/PA imaging and synergistic chemo-photothermal therapy of tumors.

Reviving near infra-red emission of Ag2 S nanoparticles using interfacial defects in the Ag2 S@CdS core-shell structure

Ag₂ S@CdS core-shell particles were synthesized with different Cd source content as a measure of shell thickness using a pulsed microwave irradiation method. The particles were verified structurally using X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscopy. Optical spectroscopy revealed that core-shells show an absorption peak at 750 nm and an emission peak located around 800 nm after 6 min of microwave irradiation. With continued microwave treatment, the NIR luminescence first vanished but it was revived after 12 min of irradiation, which was 100 nm red shifted. This new type of NIR emission in Ag₂ S with sizes greater than 5 nm is due to the proximity of a highly deficient CdS shell with strong red emission that was stable for more than 6 months in water. A mechanism has been suggested for this type of emission.