Near-Infrared Fluorescence Probe for Specific Detection of Acetylcholinesterase and Imaging in Live Cells and Zebrafish

Acetylcholinesterase (AChE) is a pivotal enzyme that is closely related with multiple neurological diseases, such as brain disorders or alterations in the neurotransmission and cancer. The development of convenient methods for imaging AChE activity in biological samples is very important to understand its mechanisms and functions in a living system. Herein, a fluorescent probe exhibiting emission in the near-infrared (NIR) region is developed to detect AChE and visualize biological AChE activities. This probe exhibits a quick response time, reasonable detection limit, and a large Stokes shift accompanied by the NIR emission. The probe has much better reactivity toward AChE than butyrylcholinesterase, which is one of the significant interfering substances. The outstanding specificity of the probe is proved by cellular imaging AChE activity and successful mapping in different regions of zebrafish. Such an effective probe can greatly contribute to ongoing efforts to design emission probes that have distinct properties to assay AChE in biological systems.

A Golgi Apparatus-Targeting, Naphthalimide-Based Fluorescent Molecular Probe for the Selective Sensing of Formaldehyde

Formaldehyde (FA) is a colorless, flammable, foul-smelling chemical used in building materials and in the production of numerous household chemical goods. Herein, a fluorescent chemosensor for FA is designed and prepared using a selective organ-targeting probe containing naphthalimide as a fluorophore and hydrazine as a FA-binding site. The amine group of the hydrazine reacts with FA to form a double bond and this condensation reaction is accompanied by a shift in the absorption band of the probe from 438 nm to 443 nm upon the addition of FA. Further, the addition of FA is shown to enhance the emission band at 532 nm relative to the very weak fluorescent emission of the probe itself. Moreover, a high specificity is demonstrated towards FA over other competing analytes such as the calcium ion (Ca²⁺), magnesium ion (Mg²⁺), acetaldehyde, benzaldehyde, salicylaldehyde, glucose, glutathione, sodium sulfide (Na₂S), sodium hydrosulfide (NaHS), hydrogen peroxide (H₂O₂), and the tert-butylhydroperoxide radical. A typical two-photon dye incorporated into the probe provides intense fluorescence upon excitation at 800 nm, thus demonstrating potential application as a two-photon fluorescent probe for FA sensing. Furthermore, the probe is shown to exhibit a fast response time for the sensing of FA at room temperature and to facilitate intense fluorescence imaging of breast cancer cells upon exposure to FA, thus demonstrating its potential application for the monitoring of FA in living cells. Moreover, the presence of the phenylsulfonamide group allows the probe to visualize dynamic changes in the targeted Golgi apparatus. Hence, the as-designed probe is expected to open up new possibilities for unique interactions with organ-specific biological molecules with potential application in early cancer cell diagnosis.

Palladium Probe Consisting of Naphthalimide and Ethylenediamine for Selective Turn-On Sensing of CO and Cell Imaging

An assay to detect carbon monoxide (CO), one of the gaseous signaling molecules, has been prepared using a new palladium complex probe. The ethylenediamine group linked to the naphthalimide fluorophore coordinates to Pd(II) which intramolecularly quenches the emission. Upon treatment with CO, the absorbance of the turn-on fluorescent sensor changes due to the formation of a complex between Pd(II) and CO at room temperature in a phosphate buffer. As the concentration of CO increases, the probe peak emission intensity at 527 nm gradually increases. Other analyte controls, such as K⁺, Mg²⁺, Al³⁺, Zn²⁺, Cr³⁺, Hg²⁺, Fe³⁺, alanine, glycine, leucine, lysine, serine, threonine, tyrosine, F^-, Cl^-, Br^-, NO, NO₂^-, NO₃^-, HCO₃^-, CH₃COO^-, H₂O₂, ^•OH, and ^tBuOO^•, exhibit no significant effect on emission intensity. The response time of the probe to CO was quite fast because of the relatively weak coordination of Pd(II) to the pendent ethylenediamine group. The Pd probe is capable of detecting CO in aqueous buffer as well as in living cells with high selectivity and stability, providing a potential real-time indicator for studying CO-involved reactions in biological systems.

A cancer cell-specific benzoxadiazole-based fluorescent probe for hydrogen sulfide detection in mitochondria

The present work describes the design and biological applications of a novel colorimetric and fluorescence turn-on probe for hydrosulfide detection. The probe was designed to introduce hemicyanine as the fluorescent skeleton and 7-nitro-1,2,3-benzoxadiazole as the recognition site. The optical properties and responses of the probe towards HS^-, anions and some biothiols indicate an impressively high selectivity of the probe towards HS^- such that it can be effectively used as an indicator for monitoring the level of HS^- in living cells. In biological experiments using the probe, the H₂S levels are found to be higher in cancer cells than in normal cells. In addition, the probe is shown to specifically and rapidly detect endogenous H₂S, which is produced primarily in the mitochondria of cancer cells, as demonstrated by a co-localization experiment using specific trackers for the detection of cellular organelles in pharmacological inhibition or stimulation studies, without any significant cytotoxic effects. Thus, the results of the chemical and biological experiments described herein demonstrate the potential of this novel probe to specifically, safely, and rapidly detect H₂S to distinguish cancer cells from normal cells by targeting it specifically in mitochondria.