Label-free and ratiometric detection of nuclei acids based on graphene quantum dots utilizing cascade amplification by nicking endonuclease and catalytic G-quadruplex DNAzyme

Herein, we report a ratiometric fluorescence assay based on graphene quantum dots (GQDs) for the ultrasensitive DNA detection by coupling the nicking endonuclease assisted target recycling and the G-quadruplex/hemin DNAzyme biocatalysis for cascade signal amplifications. With o-phenylenediamine acted as the substrate of G-quadruplex/hemin DNAzyme, whose oxidization product (that is, 2,3-diaminophenazine, DAP) quenched the fluorescence intensity of GQDs (at 460nm) obviously, accompanied with the emergence of a new emission of DAP (at 564nm). The ratiometric signal variations at the emission wavelengths of 564 and 460nm (I564/I460) were utilized for label-free, sensitive, and selective detection of target DNA. Utilizing the nicking endonuclease assisted target recycling and the G-quadruplex/hemin DNAzyme biocatalysis for amplified cascade generation of DAP, the proposed bioassay exhibited high sensitivity toward target DNA with a detection limit of 30fM. The method also had additional advantages such as facile preparation and easy operation.

Cancer cell-targeted two-photon fluorescence probe for the real-time ratiometric imaging of DNA damage

A sequential ICT fluorescence probe (ANF–Glu) was successfully utilized to spatially and temporally image DNA damage in cancer cells.

Cascade DNA logic device programmed ratiometric DNA analysis and logic devices based on a fluorescent dual-signal probe of a G-quadruplex DNAzyme

Two fluorescence sensitive substrates of G4 DNAzyme with inverse responses were simultaneously used to a cascade advanced DNA logic device based DNA analysis for the first time.

Mitochondria-targeting ratiometric fluorescent probe for γ-glutamyltranspeptidase and its application to colon cancer

An indocyanine-based probe for γ-glutamyltranspeptidase exhibited ratiometric fluorescence in mitochondria through an enzyme-mediated amide-to-amine transformation reaction applicable for colon cancer detection.

A two-photon fluorescent sensor revealing drug-induced liver injury via tracking γ-glutamyltranspeptidase (GGT) level in vivo

Currently drug-induced liver injury (DILI) has become a major and challenging public health issue in terms of medicine development and clinical therapy. The level of γ-glutamyl transpeptidase (GGT) has long been regarded as a preclinical/clinical biomarker for prediction of DILI. Herein, we report a two-photon fluorescent sensor for tracking GGT level changes resulted from DILI in vivo. The sensor was prepared by linking a glutamic acid to a dicyanomethylene-4H-pyran (DCM) derivative; and the presence of GGT cleaves γ-glutamyl amide group from the sensor and thereby restores the fluorescence emission (at 635 nm) of DCM moiety under femtosecond pulses at 800 nm. This two-photon sensor exhibits superior sensing performance such as red emission, high photostability and low detection limit (∼0.057 U/L). On a two-photon microscope, the sensor shows a bright red fluorescence in GGT-overexpressing A2780 cells; and it can fluorescently respond to the GGT generated in the liver of zebrafishes as a result of clinical drug (phenytoin) treatment. These findings demonstrate that a commonly-used clinical drug phenytoin can cause remarkable elevation in GGT level in liver, and this sensor may be useful as a marker to detect clinical drug-induced organ damages.

DNA-regulated silver nanoclusters for label-free ratiometric fluorescence detection of DNA

Two kinds of DNA-regulated Ag nanoclusters were one-pot synthesized on an oligonucleotide, and delicately utilized in the design of a label-free ratiometric fluorescence strategy for DNA detection with simplicity and high sensitivity.

An optimized ratiometric fluorescent probe for sensing human UDP-glucuronosyltransferase 1A1 and its biological applications

This study aimed to develop a practical ratiometric fluorescent probe for highly selective and sensitive detection of human UDP-glucuronosyltransferase 1A1 (UGT1A1), one of the most important phase II enzymes. 4-Hydroxy-1,8-naphthalimide (HN) was selected as the fluorophore for this study because it possesses intramolecular charge transfer (ICT) feature and displays outstanding optical properties. A series of N-substituted derivatives with various hydrophobic, acidic and basic groups were designed and synthesized to evaluate the selectivity of HN derivatives toward UGT1A1. Our results demonstrated that the introduction of an acidic group to HN could significantly improve the selectivity of UGT1A1. Among the synthesized fluorescent probes, NCHN (N-3-carboxy propyl-4-hydroxy-1,8-naphthalimide) displayed the best combination of selectivity, sensitivity and ratiometric fluorescence response following UGT1A1-catalyzed glucuronidation. UGT1A1-catalyzed NCHN-4-O-glucuronidation generated a single fluorescent product with a high quantum yield (Φ=0.688) and brought remarkable changes in both color and fluorescence in comparison with the parental substrate. The newly developed probe has been successfully applied for sensitive measurements of UGT1A1 activities in human liver preparations, as well as for rapid screening of UGT1A1 modulators, using variable enzyme sources. Furthermore, its potential applications for live imaging of endogenous UGT1A1in cells have also been demonstrated.

Enzymatic synthesis of γ-glutamylmethylamide from glutamic acid γ-methyl ester and methylamine catalyzed by Escherichia coli having γ-glutamyltranspeptidase activity

A new method for the synthesis of γ-glutamylmethylamide is presented. Glutamic acid γ-methyl ester was used as substrate for γ-glutamylmethylamide synthesis catalyzed by Escherichia coli with γ-glutamyltranspeptidase activity. Reaction conditions were optimized by using 300 mM glutamic acid γ-methyl ester and 3,000 mM methylamine at pH 10 and 40 °C. Bioconversion rate of γ-glutamylmethylamide reached 87 % after 10 h. γ-Glutamyltranspeptidase was reversibly inhibited only when glutamic acid γ-methyl ester was above 300 mM.

A highly selective long-wavelength fluorescent probe for the detection of human carboxylesterase 2 and its biomedical applications

A highly selective long-wavelength fluorescent probe for the detection of human carboxylesterase 2 (hCE2) has been developed and well characterized. The probe can be used for measuring the real activities of hCE2 in complex biological systems.