A Ratiometric Fluorescent Sensor for Cd2+ Based on Internal Charge Transfer

Abstract

This work reports on a novel fluorescent sensor 1 for Cd2+ ion based on the fluorophore of tetramethyl substituted bis(difluoroboron)-1,2-bis[(1H-pyrrol-2-yl)methylene]hydrazine (Me4BOPHY), which is modified with an electron donor moiety of N,N-bis(pyridin-2-ylmethyl)benzenamine. Sensor 1 has absorption and emission in visible region, at 550 nm and 675 nm, respectively. The long wavelength spectral response makes it easier to fabricate the fluorescence detector. The sensor mechanism is based on the tunable internal charge transfer (ICT) transition of molecule 1. Binding of Cd2+ ion quenches the ICT transition, but turns on the π − π transition of the fluorophore, thus enabling ratiometric fluorescence sensing. The limit of detection (LOD) was projected down to 0.77 ppb, which is far below the safety value (3 ppb) set for drinking water by World Health Organization. The sensor also demonstrates a high selectivity towards Cd2+ in comparison to other interferent metal ions.

Green Hydrothermal Synthesis of N-doped Carbon Dots from Biomass Highland Barley for the Detection of Hg2+

“…In the range of 10–160 μM the linear equation of FL intensity versus the concentration was FL = −16.74 × C Hg 2+ + 541.5, R 2 = 0.995. According to three times the standard deviation regulation [25], we figured out that the limit of detection (LOD) was equal to 0.48 μM, which was higher than the safety level stipulated by the EPA (0.01 μM) for drinking water. We compared the properties of our N-CDs with some reported CDs for Hg 2+ as shown in Table 1.…”

“…Hg 2+ is one of the most toxic and threatening heavy metal ions in the environment, can easily bioaccumulate in the human body and seriously damage the central nervous and endocrine systems [23,24,25]. Nowadays, complicated instruments and tedious procedures are obvious disadvantages of methods for Hg 2+ detection [26,27,28].…”

Sensing mechanism of a ratiometric near-infrared fluorescent chemosensor for cysteine hydropersulfide: Intramolecular charge transfer

“…Until now, numerous sensing mechanisms have been proposed and elucidated for designing fluorescent chemosensors, including the intramolecular charge transfer (ICT) 17,22,[30][31][32][33][34][35][36] , the photoinduced electron transfer (PET) 8,9,[37][38][39][40] , the excited state proton transfer (ESPT) 16,[41][42][43][44][45] , and the fluorescence resonance energy transfer (FRET) [46][47][48][49][50] . Thereinto, ICT mechanism is usually adopted to design the ratiometric fluorescent chemosensors 17,21,22,29,34,51,52 . An ICT-based ratiometric fluorescent chemosensor can lead to the fluorescence spectrum displacement by enhancing or suppressing such an ICT process accompanying with partial charge transfer 7,32,53 .…”

Development of selective high-affinity fluorescent sensors for imaging neurotransmitters and application in cells and tissue

“…7 Shown below is an example of a fluorescent sensor that applies an internal charge transfer mechanism and makes use of fused BODIPY dye with an extended conjugation system (Figure 1-1). 8 When there is no analyte (metal ion), the nitrogen atom donates its low pair electrons to the extended π system of the fluorophore, providing fluorescence at 675 nm, from strong ICT. When the metal ion (cadmium ion) binds to the fluorescent sensor, it coordinates with the three nitrogen atoms of dipicolylamine, the lone pair of electrons of the nitrogen will interact with the d orbital of cadmium ion such that it's not available to donate to the π system.…”

“…Among them, several macrocyclic structures, such as cyclodextrins, calixarene and cucurbiturils, are very popular encapsulation tool to detect neurotransmitters. [49][50][51] One example presented here is using cucurbit [8]uril (CB [8]) complexation with a 2,7-dimethyldiazapyrenium dication (Me 2 DAP 2+ ) (Figure 1-14). 52 This stable complex was confirmed by NMR and mass spectrometry.…”