Quercetin-Mediated Silver Nanoparticle Formation for the Colorimetric Detection of Infectious Pathogens Coupled with Loop-Mediated Isothermal Amplification

Plant-Assisted Synthesis of Ag-Based Nanoparticles on Cotton: Antimicrobial and Cytotoxicity Studies

The syntheses of Ag-based nanoparticles (NPs) with the assistance of plant extracts have been shown to be environmentally benign and cost-effective alternatives to conventional chemical syntheses. This study discusses the application of Paliurus spina-christi, Juglans regia, Humulus lupulus, and Sambucus nigra leaf extracts for in situ synthesis of Ag-based NPs on cotton fabric modified with citric acid. The presence of NPs with an average size ranging from 57 to 99 nm on the fiber surface was confirmed by FESEM. XPS analysis indicated that metallic (Ag0) and/or ionic silver (Ag2O and AgO) appeared on the surface of the modified cotton. The chemical composition, size, shape, and amounts of synthesized NPs were strongly dependent on the applied plant extract. All fabricated nanocomposites exhibited excellent antifungal activity against yeast Candida albicans. Antibacterial activity was significantly stronger against Gram-positive bacteria Staphylococcus aureus than Gram-negative bacteria Escherichia coli. In addition, 99% of silver was retained on the samples after 24 h of contact with physiological saline solution, implying a high stability of nanoparticles. Cytotoxic activity towards HaCaT and MRC5 cells was only observed for the sample synthetized in the presence of H. lupulus extract. Excellent antimicrobial activity and non-cytotoxicity make the developed composites efficient candidates for medicinal applications.

Rapid and specific detection of Enterococcus faecium with an isothermal amplification and lateral flow strip combined method

Enterococcus faecium is responsible for a highly contagious, drug-resistant nosocomial infection that often causes serious illness. In this study, a rapid and sensitive RPA-LFS (recombinase polymerase amplification-lateral flow strip) method for the detection of E. faecium was established based on specific primers and probes designed using the ddl gene. To verify the specificity and sensitivity of the method, 26 specific strains and 100-106 CFU/μL E. faecium were selected for detection. The results show that the proposed method can specifically detect E. faecium, and the minimum detection limit is 100 CFU/μL. To compare the clinical application of the method with qPCR, 181 clinical samples were collected for testing. RPA-LFS and qPCR had the same practical applicability, and 61 parts of E. faecium were detected in 183 clinical samples. The methods developed in this study not only have the advantages of rapid sensitivity and specificity but also meet the needs of remote areas with scarce medical resources.

Nitrogen- and Sulfur-Codoped Strong Green Fluorescent Carbon Dots for the Highly Specific Quantification of Quercetin in Food Samples

Carbon dots (CDs) doped with heteroatoms have garnered significant interest due to their chemically modifiable luminescence properties. Herein, nitrogen- and sulfur-codoped carbon dots (NS-CDs) were successfully prepared using p-phenylenediamine and thioacetamide via a facile process. The as-developed NS-CDs had high photostability against photobleaching, good water dispersibility, and excitation-independent spectral emission properties due to the abundant amino and sulfur functional groups on their surface. The wine-red-colored NS-CDs exhibited strong green emission with a large Stokes shift of up to 125 nm upon the excitation wavelength of 375 nm, with a high quantum yield (QY) of 28%. The novel NS-CDs revealed excellent sensitivity for quercetin (QT) detection via the fluorescence quenching effect, with a low detection limit of 17.3 nM within the linear range of 0-29.7 μM. The fluorescence was quenched only when QT was brought near the NS-CDs. This QT-induced quenching occurred through the strong inner filter effect (IFE) and the complex bound state formed between the ground-state QT and excited-state NS-CDs. The quenching-based detection strategies also demonstrated good specificity for QT over various interferents (phenols, biomolecules, amino acids, metal ions, and flavonoids). Moreover, this approach could be effectively applied to the quantitative detection of QT (with good sensing recovery) in real food samples such as red wine and onion samples. The present work, consequently, suggests that NS-CDs may open the door to the sensitive and specific detection of QT in food samples in a cost-effective and straightforward manner.

A paper-embedded thermoplastic microdevice integrating additive-enhanced allele-specific amplification and silver nanoparticle-based colorimetric detection for point-of-care testing

This study introduces a thermoplastic microdevice integrated with additive-enhanced allele-specific amplification and hydrazine-induced silver nanoparticle-based detection of single nucleotide polymorphism (SNP) and opportunistic pathogens. For point-of-care testing of SNP, an allele-specific loop-mediated isothermal amplification reaction using nucleotide-mismatched primers and molecular additives was evaluated to discriminate single-nucleotide differences in the samples. The microdevice consists of purification and reaction units that enable DNA purification, amplification, and detection in a sequential manner. The purification unit enables the silica-based preparation of samples using an embedded glass fiber membrane. Hydrazine-induced silver nanoparticle formation was employed for endpoint colorimetric detection of amplicons within three min at room temperature. The versatile applicability of the microdevice was demonstrated by the successful identification of SNPs related to sickle cell anemia, genetically-induced hair loss, and Enterococcus faecium. The microdevice exhibited a detection limit of 103 copies per μL of SNP targets in serum and 102 CFU mL-1 of Enterococcus faecium in tap water within 70 min. The proposed microdevice is a promising and versatile platform for point-of-care nucleic acid testing of different samples in low-resource settings.

Pipette-Free and Fully Integrated Paper Device Employing DNA Extraction, Isothermal Amplification, and Carmoisine-Based Colorimetric Detection for Determining Infectious Pathogens

A pipette-free and fully integrated device that can be used to accurately recognize the presence of infectious pathogens is an important and useful tool in point-of-care testing, particularly when aiming to decrease the unpredictable threats posed by disease outbreak. In this study, a paper device is developed to integrate the three main processes required for detecting infectious pathogens, including DNA extraction, loop-mediated isothermal amplification (LAMP), and detection. All key reagents, including sodium dodecyl sulfate (SDS), NaOH, LAMP reagents, and carmoisine, are placed on the paper device. The paper device is operated simply via sliding and folding without using any bulky equipment, and the results can be directly observed by the naked eye. The optimized concentrations of sodium dodecyl sulfate (SDS), sodium hydroxide (NaOH), and carmoisine were found to be 0.1%, 0.1 M, and 0.5 mg/mL, respectively. The paper device was used to detect Enterococcus faecium at concentrations as low as 102 CFU/mL within 60 min. Also, E. faecium spiked in milk was successfully detected using the paper device, demonstrating the feasible application in real sample analysis.