Diagnostic performance of isothermal strand displacement amplification of Mycobacterium tuberculosis IS 6110 in tissue samples

Ultrasensitive multiplexed miRNA detection based on a self-priming hairpin-triggered isothermal cascade reaction

We herein describe an ultrasensitive isothermal strategy to detect miRNAs in a multiplexed manner by utilizing a self-priming hairpin-triggered cascade reaction and the adsorption properties of graphene oxide (GO). In principle, a self-priming hairpin probe (SHP) was designed to be opened through binding to the target miRNA and rearranged to serve as a primer. The following extension displaced the target miRNA to be recycled for opening another SHP and produced a double-stranded (ds) SHP with a longer stem region. The nicking enzyme recognition site within the ds SHP was then subjected to continuous repeated nicking and extension reactions, consequently producing a large amount of the trigger sequence. In the second reaction phase, the trigger also transformed another single-stranded (ss) target template probe (TTP) into ds TTP and simultaneously produced numerous target mimic strands (Target') in the same manner, which could activate the first reaction phase, mimicking the target miRNA. Since the ss portions of the two probes were all transformed to the ds forms (ds SHP and ds TTP), they are resistant to the adsorption by graphene oxide (GO) and then emitted intense fluorescence after the application of GO while the ss forms of the two probes produced a negligible fluorescence signal without the target miRNAs. Based on this unique design principle, we were able to simultaneously identify multiple target miRNAs very sensitively down to attomolar levels (42.63 aM for miRNA let-7a, 13.08 aM for miRNA-141, and 10.14 aM for miRNA-98) within 30 min.

Flap endonuclease-initiated enzymatic repairing amplification for ultrasensitive detection of target nucleic acids

A new isothermal nucleic acid amplification method termed FERA (Flap endonuclease-initiated Enzymatic Repairing Amplification) is developed for the ultrasensitive detection of target nucleic acids. In the FERA method, flap endonuclease (FEN) catalyzes the hydrolytic cleavage at the junction of single- and double-stranded DNAs which is formed only in the presence of target nucleic acids, and releases short oligonucleotides to promote the cyclic enzymatic repairing amplification (ERA) combined with FEN-based amplification. As a result, a large amount of single- and double-stranded DNAs are generated under the isothermal conditions, leading to the high fluorescence intensity from the SYBR I green dye. Relying on the powerful amplification method, we successfully determined the target nucleic acids with a limit of detection as low as 15.16 aM, which corresponds to approximately 180 molecules in 20 μL reaction volume, and verified the practical applicability by detecting long target nucleic acids derived from Chlamydia trachomatis.

Implications of direct amplification for measuring antimicrobial resistance using point-of-care devices

Antimicrobial resistance (AMR) is recognized as a global threat to human health. Rapid detection and characterization of AMR is a critical component of most antibiotic stewardship programs. Methods based on amplification of nucleic acids for detection of AMR are generally faster than culture-based approaches but they still require several hours to more than a day due to the need for transporting the sample to a centralized laboratory, processing of sample, and sometimes DNA purification and concentration. Nucleic acids-based point-of-care (POC) devices are capable of rapidly diagnosing antibiotic-resistant infections which may help in making timely and correct treatment decisions. However, for most POC platforms, sample processing for nucleic acids extraction and purification is also generally required prior to amplification. Direct amplification, an emerging possibility for a number of polymerases, has the potential to eliminate these steps without significantly impacting diagnostic performance. This review summarizes direct amplification methods and their implication for rapid measurement of AMR. Future research directions that may further strengthen the possibility of integrating direct amplification methods with POC devices are also summarized.