Fast-responsive and multi-applicable fluorescent turn-off chemodosimeter for monitoring hypochlorite: application to test strips, water samples, disinfectants and bioimaging

Due to the twin-demic of COVID-19 and flu virus, disinfectants containing ClO- have been widely used nowadays. Therefore, it is urgent to develop a sensor capable of efficiently detecting toxic hypochlorite. We present the invention and assessment of a fast-responsive and multi-applicable chemodosimeter sensor ETA (2-(2-((1E,2E)-3-(4-(dimethylamino)phenyl)allylidene)hydrazineyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) for monitoring ClO‑. In pure water, adding ClO- to ETA caused a turn-off fluorescence within 2 sec. These changes made it possible to quickly detect ClO- with a high level of selectivity. ETA displayed a low detection limit (0.68 μM) to ClO-. Using UV-vis titrations, ESI-MS and DFT calculations, we were able to demonstrate the detection mechanism, in which ETA was cleaved by ClO-. In particular, we established the possibility for reliable ClO- detection in environmental systems such as actual water samples, disinfectants, living cells, zebrafish and celery, in addition to confirming the practicality of ETA utilizing test strips.

Detection of environmentally hazardous hypochlorite in pure water with a novel fluorescent chemosensor: Application to water samples, commercial disinfectants, test strips, and zebrafish

With the increasing use of chlorinated disinfectants or bleaches such as sodium hypochlorite in the coronavirus disease 2019 (COVID-19) pandemic, the effectual detection of toxic hypochlorite is very important. In this study, a novel hydrazide-based fluorescence chemosensor DHT-Cl ((E)-2-(2-(3,5-dichloro-2-hydroxybenzylidene)hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) was synthesized. DHT-Cl could selectively detect environmentally hazardous hypochlorite in pure water through a fluorescence turn-off process. The detection limit for hypochlorite was determined to be 0.57 μM. DHT-Cl can monitor hypochlorite with little interference even in the presence of other analytes. Practically, DHT-Cl detected hypochlorite in water samples, commercial disinfectants, test strips, and living zebrafish. The hypochlorite detection mechanism through cleavage of the CN bond was illustrated by 1H NMR spectroscopy titration, ESI-mass spectrometry and quantum calculations.

Biosensors Based on Bivalent and Multivalent Recognition by Nucleic Acid Scaffolds

Several biological macromolecules adopt bivalent or multivalent interactions to perform various cellular processes. In this regard, the development of molecular constructs presenting multiple ligands in a specific manner is becoming crucial for the understanding of multivalent interactions and for the detection of target macromolecules. Nucleic acids are attractive molecules to achieve this goal because they are capable of forming various, structurally well-defined 2D or 3D nanostructures and can bear multiple ligands on their structures with precisely controlled ligand–ligand distances. Thanks to the features of nucleic acids, researchers have proposed a wide range of bivalent and multivalent binding agents that strongly bind to target biomolecules;consequently, these findings have uncovered new biosensing strategies for biomolecule detection. To date, various bivalent and multivalent interactions of nucleic acid architectures have been applied to the design of biosensors with enhanced sensitivity and target accuracy. In this review, we describe not only basic biosensor designs but also recently designed biosensors operating through the bivalent and multivalent recognition of nucleic acid scaffolds. Based on these designs, strategies to transduce bi- or multivalent interaction signals into readable signals are discussed in detail, and the future prospects and challenges of the field of multivalence-based biosensors are explored.

Combining recombinase polymerase amplification and DNA-templated reaction for SARS-CoV-2 sensing with dual fluorescence and lateral flow assay output.

The early phase of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic was exacerbated by a diagnostic challenge of unprecedented magnitude. In the absence of effective therapeutics or vaccines, breaking the chain of transmission through early disease detection and patient isolation was the only means to control the growing pandemic. While polymerase chain reaction (PCR)-based methods and rapid-antigen tests rose to the occasion, the analytical challenge of rapid and sequence-specific nucleic acid-sensing at a point-of-care or home setting stimulated intense developments. Herein we report a method that combines recombinase polymerase amplification and a DNA-templated reaction to achieve a dual readout with either fluorescence (microtiter plate) or naked eye (lateral flow assay: LFA) detection. The nucleic acid templated reaction is based on an SN Ar that simultaneously transfers biotin from one Peptide Nucleic Acid (PNA) strand to another PNA strand, enabling LFA detection while uncaging a coumarin for fluorescence readout. This methodology has been applied to the detection of a DNA or RNA sequence uniquely attributed to the SARS-CoV-2.