Direct and rapid quantum dots labelling of Escherichia coli cells

A simple and efficient fluorescent labeling method in Staphylococcus aureus for real-time tracking of invasive bacteria

Bacterial fluorescent labeling is a powerful tool for the diagnosis and treatment of bacterial infections. Here, we present a simple and efficient labeling strategy for Staphylococcus aureus. Intracellular labeling of bacteria was achieved by heat shock using Cyanine 5.5 (Cy5.5) near-infrared-I dyes in S. aureus (Cy5.5@S. aureus). Several key factors, such as Cy5.5 concentration and labeling time, were systematically evaluated. Further, the cytotoxicity of Cy5.5 and the stability of Cy5.5@S. aureus was evaluated by flow cytometry, inverted fluorescence microscopy, and transmission electron microscopy. In addition, Cy5.5@S. aureus were used to explore the phagocytic behavior of RAW264.7 macrophages. These results proved that Cy5.5@S. aureus had a uniform fluorescence intensity and high luminance; additionally, our method had no significant adverse effects on S. aureus compared to unlabeled S. aureus infections. Our method provides researchers with a useful option for analyzing the behavior of S. aureus as an infectious agent. This technique can be broadly applied to study host cell-bacteria interactions at the molecular level, and to in vivo tracing of bacterial infections.

Direct conjugation of fluorescent quantum dots with E. coli via surface-displayed histidine-containing peptides

Biocompatible approaches to labeling bacteria with fluorescent nanoparticles are essential in order to create living bacterial bioconjugates for imaging, biosensors, medicine, and other applications. Herein we report the direct conjugation of carboxyl quantum dots (QDs) with E. coli outer membrane via surface-displayed binding peptides. The histidine-containing peptide H6G9 was displayed at the N-terminus of membrane-embedded enhanced circularly permuted outer membrane protein X (eCPX) scaffold, which was expressed upon chemical induction. The presence of the binding peptide creates an environment distinct from the negatively charged E. coli surface and provides strong binding affinity to carboxyl quantum dots (QDs). Transmission electron microscopy (TEM) analysis of E. coli-QD bioconjugates revealed high loading densities of these QDs immobilized on the cell surface, even when adding a very low concentration (10 μg/mL) of QDs in order to reduce the cell exposure. These hybrid cells strongly fluoresce with each of the distinct colors of loaded QDs with different emission wavelengths, which can be easily visualized by fluorescence microscopy or differentiated using flow cytometry. Importantly, the E. coli-QD bioconjugates were highly viable and maintained the ability to grow and divide. This study demonstrates a simple, direct, and highly efficient method for labelling bacteria with QDs, without significantly compromising the vitality of the cells.

Superior Properties and Biomedical Applications of Microorganism-Derived Fluorescent Quantum Dots

Quantum dots (QDs) are fluorescent nanocrystals with superb photo-physical properties. Applications of QDs have been exponentially increased during the past decade. They can be employed in several disciplines, including biological, optical, biomedical, engineering, and energy applications. This review highlights the structural composition and distinctive features of QDs, such as resistance to photo-bleaching, wide range of excitations, and size-dependent light emission features. Physical and chemical preparation of QDs have prominent downsides, including high costs, regeneration of hazardous byproducts, and use of external noxious chemicals for capping and stabilization purposes. To eliminate the demerits of these methods, an emphasis on the latest progress of microbial synthesis of QDs by bacteria, yeast, and fungi is introduced. Some of the biomedical applications of QDs are overviewed as well, such as tumor and microRNA detection, drug delivery, photodynamic therapy, and microbial labeling. Challenges facing the microbial fabrication of QDs are discussed with the future prospects to fully maximize the yield of QDs by elucidating the key enzymes intermediating the nucleation and growth of QDs. Exploration of the distribution and mode of action of QDs is required to promote their biomedical applications.

Study of Physico-Chemical Changes of CdTe QDs after Their Exposure to Environmental Conditions

The irradiance of ultraviolet (UV) radiation is a physical parameter that significantly influences biological molecules by affecting their molecular structure. The influence of UV radiation on nanoparticles has not been investigated much. In this work, the ability of cadmium telluride quantum dots (CdTe QDs) to respond to natural UV radiation was examined. The average size of the yellow QDs was 4 nm, and the sizes of green, red and orange QDs were 2 nm. Quantum yield of green CdTe QDs-MSA (mercaptosuccinic acid)-A, yellow CdTe QDs-MSA-B, orange CdTe QDs-MSA-C and red CdTe QDs-MSA-D were 23.0%, 16.0%, 18.0% and 7.0%, respectively. Green, yellow, orange and red CdTe QDs were replaced every day and exposed to daily UV radiation for 12 h for seven consecutive days in summer with UV index signal integration ranging from 1894 to 2970. The rising dose of UV radiation led to the release of cadmium ions and the change in the size of individual QDs. The shifts were evident in absorption signals (shifts of the absorbance maxima of individual CdTe QDs-MSA were in the range of 6–79 nm), sulfhydryl (SH)-group signals (after UV exposure, the largest changes in the differential signal of the SH groups were observed in the orange, green, and yellow QDs, while in red QDs, there were almost no changes), fluorescence, and electrochemical signals. Yellow, orange and green QDs showed a stronger response to UV radiation than red ones.

Development of Quantum Dots-Labeled Antibody Fluorescence Immunoassays for the Detection of Morphine

Quantum dots (QDs)-labeled antibody fluorescence immunoassays (FLISA) for the detection of morphine were developed. Quantum dots (CdSe/ZnS), which contained carboxyl, were used to label antimorphine antibody by 1-ethyl-3-(3-dimethylaminoprophyl) carbodiimide hydrochloride/N-hydroxysulfosuccinimide, which were used as coupling reagents. The CdSe/ZnS QDs labeled antimorphine antibody (QDs labeled Ab) was characterized by fluorescence spectrum and gel electrophoresis. Plate-based FLISA and nitrocellulose membrane-based flow-through FLISA were developed and applied to quantitative and qualitative detection of morphine. Under the optimal conditions for plate-based FLISA, the linear range spanned from 3.2 × 10^-4 to 1 mg/L (R² = 0.9905), and the detection limit was 2.7 × 10^-4 mg/L. The visual detection limit for morphine by membrane-based flow-through FLISA was 0.01 mg/L. These results demonstrated that the developed fluorescence immunoassays could be applied as highly sensitive and convenient tools for rapid detection of morphine, which make it ideally suited for on-site screening of poppy shell added illegally in hot pot soup base.

Recent Advancements in Nanobioassays and Nanobiosensors for Foodborne Pathogenic Bacteria Detection

Bacterial pathogens are one of the leading causes of food safety incidents and product recalls worldwide. Timely detection and identification of microbial contamination in agricultural and food products is crucial for disease prevention and outbreak investigation. In efforts to improve and/or replace time-consuming and laborious "gold standards" for pathogen detection, numerous alternative rapid methods have been proposed in the past 15 years, with a trend toward incorporating nanotechnology and nanomaterials in food pathogen detection. This article is a review of the use of nanotechnology in various detection and sample preparation techniques and advancements in nanotechnology applications in food matrices. Some practical considerations in nanobioassay design are discussed, and the gaps between research status quo and market demands are identified.

Silica-based matrices: State of the art and new perspectives for therapeutic drug delivery

Colloidal carriers based on silica (Si) matrices are an innovative approach within the context of therapeutic drug delivery systems. These carriers are emerging as a great promise for diagnosis and treatment of a wide range of injuries, particularly in cancer and infectious diseases. In addition, bioencapsulation for biosensing and cell therapy in silica sol-gel allows the survival of enzymes and cells for a long period of time. Owing to their porosity, large surface area, and high capability of functionalization, silica nanoparticles (SiNP) have been considered as an attractive option for several bioanalysis applications, such as selective bioseparation, imaging, and drug and gene delivery. However, although great advances are achieved in the biomedical fields, some toxicity effects can be associated with the use of SiNP. This article aims to present a comprehensive review of recent technological advances for silica matrices in biomedical applications, as well as the potential impact of silica-based materials on human health and environment.

Antibacterial potential of rutin conjugated with thioglycolic acid capped cadmium telluride quantum dots (TGA-CdTe QDs)

Quantum dots not only act as nanocarrier but also act as stable and resistant natural fluorescent bio markers used in various in vitro and in vivo photolabelling and biological applications. In this study, the antimicrobial potential of TGA-CdTe QDs and commercial phenolics (rutin and caffeine) were investigated against Escherichiacoli. UV absorbance and fluorescence quenching study of TGA-CdTe QDs with rutin and caffeine complex was measured by spectroscopic technique. QDs-rutin conjugate exhibited excellent quenching property due to the -OH groups present in the rutin structure. But the same time caffeine has not conjugated with QDs because of lacking of -OH group in its structure. Photolabelling of E. coli with QDs-rutin and QDs-caffeine complex was analyzed by fluorescent microscopic method. Microbe E. coli cell membrane damage was assessed by atomic force (AFM) and confocal microscopy. Based on the results obtained, it is suggested that QDs-rutin conjugate enhance the antimicrobial activity more than the treatment with QDs, rutin and caffeine alone.