A trifunctional split dumbbell probe coupled with ligation-triggered isothermal rolling circle amplification for label-free and sensitive detection of nicotinamide adenine dinucleotide

Construction of a label-free fluorescent biosensor for homogeneous detection of m6A eraser FTO in breast cancer tissues

Fat mass and obesity-associated protein (FTO) is a crucial eraser of RNA N6- methyladenosine (m6A) modification, and abnormal FTO expression level is implicated in pathogenesis of numerous cancers. Herein, we demonstrate the construction of a label-free fluorescent biosensor for homogeneous detection of m6A eraser FTO in breast cancer tissues. When FTO is present, it specifically erases the methyl group in m6A, inducing the cleavage of demethylated DNA by endonuclease DpnII and the generation of a single-stranded DNA (ssDNA) with a 3'-hydroxyl group. Subsequently, terminal deoxynucleotidyl transferase (TdT) promotes the incorporation of dTTPs into the ssDNA to obtain a long polythymidine (T) DNA sequence. The resultant long poly (T) DNA sequence can act as a template to trigger hyperbranched strand displacement amplification (HSDA), yielding numerous DNA fragments that may be stained by SYBR Gold to produce an enhanced fluorescence signal. This biosensor processes ultrahigh sensitivity with a detection limit of 1.65 × 10-10 mg/mL (2.6 fM), and it can detect the FTO activity in a single MCF-7 cell. Moreover, this biosensor can screen the FTO inhibitors, evaluate enzyme kinetic parameters, and discriminate the FTO expression levels in the tissues of breast cancer patients and healthy persons.

Signal Amplification-Based Biosensors and Application in RNA Tumor Markers

Tumor markers are important substances for assessing cancer development. In recent years, RNA tumor markers have attracted significant attention, and studies have shown that their abnormal expression of post-transcriptional regulatory genes is associated with tumor progression. Therefore, RNA tumor markers are considered as potential targets in clinical diagnosis and prognosis. Many studies show that biosensors have good application prospects in the field of medical diagnosis. The application of biosensors in RNA tumor markers is developing rapidly. These sensors have the advantages of high sensitivity, excellent selectivity, and convenience. However, the detection abundance of RNA tumor markers is low. In order to improve the detection sensitivity, researchers have developed a variety of signal amplification strategies to enhance the detection signal. In this review, after a brief introduction of the sensing principles and designs of different biosensing platforms, we will summarize the latest research progress of electrochemical, photoelectrochemical, and fluorescent biosensors based on signal amplification strategies for detecting RNA tumor markers. This review provides a high sensitivity and good selectivity sensing platform for early-stage cancer research. It provides a new idea for the development of accurate, sensitive, and convenient biological analysis in the future, which can be used for the early diagnosis and monitoring of cancer and contribute to the reduction in the mortality rate.

Rapid and Ultrasensitive Approach for the Simultaneous Detection of Multilocus Mutations to Distinguish Rifampicin-Resistant Mycobacterium tuberculosis

The untested empirical medications exacerbated the development of multidrug-resistant Mycobacterium tuberculosis (MDR-TB). Here, we develop a rapid and specific method based on loop-mediated isothermal amplification and duplex-specific nuclease for distinguishing rifampicin-resistant M. tuberculosis. Three probes were designed for the codons 516, 526, and 531 on the RNA polymerase β-subunit (rpoB) gene. These three sites accounted for more than 90% of the total mutations of the ropB gene in the rifampicin-resistant strain. The approach can perform simultaneous and sensitive detection of three mutant sites with the actual detection limit as 10 aM of DNA and 62.5 cfu·mL^-1 of bacteria in 67 min under isothermal conditions. Moreover, the positive mode of the approach for MDR-TB can not only deal with the randomness and diversity of mutations but also provide an easier way for medical staff to read the results. Therefore, it is a particularly valuable method to handle major and urgent MDR-TB diagnostics.

Carbon nanodots combined with loop-mediated isothermal amplification (LAMP) for detection of African swine fever virus (ASFV)

The spread of African swine fever virus (ASFV) caused huge economic costs, so early detection is particularly important. Here, we established a fluorescence biosensor based on carbon nanodots (CNDs) and loop-mediated isothermal amplification (LAMP) to ultra-sensitively detect ASFV. LAMP with high efficiency produced a large amount of pyro phosphoric acid and caused pH change in a short time. CNDs with strong light stability had a large fluorescence response at the emission wavelength of 585.5 nm to small pH change by the excitation wavelength of 550 nm. The biosensor realized “turn-off–on” mode for ASFV detection with the detection limit as low as 15.21 copies μL⁻¹. In addition, the biosensor had high accuracy in the actual sample assay. Therefore, the biosensor achieved rapid, sensitive, low-cost, and simple detection for ASFV. Moreover, the biosensor broadened the detection pathway of LAMP as a tool with great development prospect.

The fluorescent biosensor for detecting N6 methyladenine FzD5 mRNA and MazF activity

N⁶ methyladenine (m⁶A) modification of the FzD5 mRNA, an important post-transcriptional regulation in eukaryotes, is closely related to the occurrence and development of breast cancer. Here, we developed an ultra-sensitive biosensor based on MazF combining with cascaded strand displacement amplification (C-SDA) and CRISPR/Cas12a to detect m⁶A FzD5 mRNA. MazF toxin protein is a vital component of the bacterial mazEF toxin-antitoxin system that is sensitive to m⁶A RNA. Take advantage of it, the biosensor achieved antibody-independent and gene-specific detection for m⁶A RNA. Moreover, compared with traditional amplification methods, the more efficient C-SDA and the CRISPR/Cas12a system with trans-cleavage activity gave the fluorescent biosensor an excellent sensitivity with the detection limit of 0.64 fM. In addition, MazF, as a new antibacterial target, was detected by the biosensor based on C-SDA and CRISPR/Cas12a with the detection limit of 1.127 × 10^-4 U mL^-1. More importantly, the biosensor has good performance in complex samples. Therefore, the biosensor is a potential tool in detecting m⁶A FzD5 mRNA and MazF activity.