Ratiometric PCR in a Portable Sample-to-Result Device for Broad-Based Pathogen Identification

Dual-Mode Biosensor for Simultaneous and Rapid Detection of Live and Whole Salmonella typhimurium Based on Bioluminescence and Fluorescence Detection

Both live and dead Salmonella typhimurium (S.T) are harmful to human health, but there are differences in pathological mechanism, dosage, and security. It is crucial to develop a rapid and simultaneous assay to distinguish and quantify live and dead S.T in foods. Herein, one dual-mode biosensor for simultaneous detection of live and dead S.T was fabricated based on two phage probes, using portable bioluminescence and fluorescent meter as detectors, respectively. Firstly, a magnetic phage capture probe (M-P1) and a phage signal tag (P2-S) labeled with SYTO 13 fluorescent dye were prepared, respectively. Both M-P1 and P2-S can specifically conjugate with S.T to form a magnetic sandwich complex. After magnetic separation, the isolated complex can emit a fluorescent signal under an excited 365 nm laser, which can reflect the total amount of S.T. Afterwards, the lysozyme was added to decompose the captured live S.T, which can release ATP and produce a bioluminescent signal corresponding to the live S.T amount. The dead S.T concentration can be deduced by the difference between total and live examples. The detection limit of 55 CFU/mL for total S.T and 9 CFU/mL for live ones was within 20 min. The assay was successfully employed in milk samples and prospectively for on-site screening of other dead and live bacteria, while changing the phages for the targets.

Sensitive NIR Fluorescence Identification of Bacteria in Whole Blood with Bioorthogonal Nanoprobes for Early Sepsis Diagnosis

Sepsis is one of the leading causes of death worldwide. The disease progression of sepsis is very fast, and there is a 7-9% increase in mortality every hour. Therefore, rapid and sensitive detection of pathogenic bacteria is crucial for the timely treatment of sepsis as well as the reduction of mortality. Herein, we present a sensitive near-infrared (NIR) fluorescence identification and a rapid magnetic capture based on bioorthogonal nanoprobes for the detection of multiple bacteria in whole blood. The nanoprobes with NIR fluorescence/magnetic properties were modified with dibenzocyclooctyne groups and used to capture and recognize the bacteria via bioorthogonal reaction. The magnetic nanoprobes showed superparamagnetic properties with a saturation magnetization as high as 63 emu/g. Through clicking with the azide groups inserted on the bacteria walls by metabolic engineering, the bioorthogonal magnetic nanoprobes allow fast and broad-spectrum capture of both Gram-positive and Gram-negative bacteria. The bioorthogonal NIR fluorescent nanoprobes with a maximum emission at 900 nm can effectively avoid background interference, further enabling sensitive identification of the bacteria in whole blood. The detection limit was as low as 4 CFU/mL in less than 2.5 h and the nanoprobes were successfully applied to the detection of bacteria in blood samples from the patients with sepsis, showing the potential application in early sepsis diagnosis and clinical studies.

Principles and Applications of Loop-Mediated Isothermal Amplification to Point-of-Care Tests

For the identification of nucleic acids, which are important biomarkers of pathogen-mediated diseases and viruses, the gold standard for NA-based diagnostic applications is polymerase chain reaction (PCR). However, the requirements of PCR limit its application as a rapid point-of-care diagnostic technique. To address the challenges associated with regular PCR, many isothermal amplification methods have been developed to accurately detect NAs. Isothermal amplification methods enable NA amplification without changes in temperature with simple devices, as well as faster amplification times compared with regular PCR. Of the isothermal amplifications, loop-mediated isothermal amplification (LAMP) is the most studied because it amplifies NAs rapidly and specifically. This review describes the principles of LAMP, the methods used to monitor the process of LAMP, and examples of biosensors that detect the amplicons of LAMP. In addition, current trends in the application of LAMP to smartphones and self-diagnosis systems for point-of-care tests are also discussed.