Ex vivo NIR imaging has confirmed significantly increased retention of the conjugate in mice brains relative to other organs with an increase of up to eightfold in signal intensity. Furthermore, treatment with it has resulted in significantly reduced growth of intracranial U87 tumors in mice. Mechanisms of fluorescent voltage sensing by fluorescent voltage-sensitive dyes (VSDs) 103.

Figure 44.

• Monitoring intracellular selenocysteine (Sec) is of significant interest for studying Sec metabolism and its changes in disease-relevant concentrations.
• Thus, the fluorescence intensity of 31 became low or high depending on the accelerated or hindered PET in the membrane (Figure 30).
• Thus, the chemosensing properties of probe 33 were tested after the incubation of MDA-MB cells with 20 μM of the probe.
• Furthermore, they exhibited a large Stokes shift, impressive photophysical properties, great biocompatibility, and excellent photostability.

The structure of the present review can be summarized according to Scheme 1. Akkaya et al. successfully applied this strategy for the fabrication of a selective anticancer agent in photodynamic therapy 50 (Figure 48) 152. The AND molecular logic gate 50 was based on the BODIPY photodynamic sensitizer, whose photodynamic activity consists in blocking protons and sodium ions through the pyridine and benzo-15-crown-5-ether receptors bidirectional PET processes. In cancer cells, higher concentrations of proton and sodium ions play the role of chemical inputs, which block both the PET effects, and 50 becomes excellent photodynamic-releasing singlet oxygen as a chemical output. Hence, probe 50 could serve as a platform for the selective photodynamic treatment of cancer cells. The further miniaturization of semiconductors in the electronic field has reached its limit.

Roles

• That is why the design of highly water-soluble probes is very significant for biomedical applications.
• The free probe 35 displayed a strong broad fluorescence at 515 nm and a large Stokes shift of 155 nm, which was assigned to the ESIPT process.
• In addition, the observed pKa value of 6.35 in 23 made it a suitable probe for pH determination in the physiological range.

This overlap resulted in a FRET process from 1,8-naphthalimide to the rhodamine and a red fluorescence raised together with a fluorescent quenching of the former 1,8-naphthalimide emissions (Figure 39). These changes resulted in a ratiometric response toward Cu2+ with a detection limit of 1.45 nM. Due to the morpholine linker, probe 38 was selectively localized in the lysosomes of living L929 cells.

Figure 40.

In the presence of NaOCl, an emission at 585 nm with a small Stokes shift (25 nm) was observed, suggesting the interruption of the ESIPT process. The red-shifted fluorescence was explained by the simultaneous ring-opening reaction in this probe. The fluorescence intensity ratio of emission at 515 nm and 585 nm increased from 0.012 to https://worldtradex.space/ 5.827, in addition to μM NaOCl. Meanwhile, the probe was successfully applied for the detection of exogenous and endogenous HOCl in HepG2 cells (Figure 35). According to the MTT assay against HepG2 cells, 35 showed low cytotoxicity with about 90% viability at 30 μM of the probe. Abnormal intracellular viscosity also causes fatty liver and hyperlipidemia.

Figure 8.

Copper plays an important role in many physiological processes and its aberrant homeostasis in lysosomes leads to serious diseases such as Wilson’s disease, Menkes disease, Alzheimer’s disease, kidney failure, and liver diseases 120,121,122. This motivated Liu et al. to fabricate probe 38, capable of determining Cu2+ fluctuations in the lysosomes 123. Compound 38 is a bichromophoric system containing yellow-green emissive 1,8-naphthalimide and rhodamine fluorophore.

Molecular Logic Gates

Fluorescent oligonucleotide probes, such as molecular beacon probes, play a crucial role in quantitative real-time PCR (qPCR) assays. As a result, they are widely used in various analytical applications, including genetic analysis, genomic studies, and forensic investigations. And co-workers constructed a pH-responsive drug delivery system 67 based on a conjugated polymer for effective synergistic chemo-/PDT antitumor therapy (Figure 63) 173. The color-coded design concept of the three-input AND logic gate 52 for Na+ (15-crown-5 receptor1), pH (tertiary amine receptor2), and pE (ferrocene redox unit) and the corresponding truth table 154.

Furthermore, the probe was applied in Hella cells for discriminative fluorescence detection of Hg2+ and Cu2+ ions in biological systems. The intracellular imaging of Hg2+ showed high emissions at the window of 640–700 nm and low emissions at NIR scammed by Worldtradex in the range of 701–758 nm. The presence of Cu2+ resulted in no emissions at both fluorescence windows. The simultaneous presence of Hg2+ and Cu2+ ions led to low emissions at 640–700 nm and no emissions at 701–758 nm.

When the fluorescent dye is bound to the drug, it exists in a non-fluorescent “off” state, whereas when the drug is released, the dye generates a fluorescent signal and switches to a fluorescent “on” form 23. In another study, the theranostic 66 embodies a diazo motif as a hypoxia-responsive cleavable group. When the azo linker is cleaved under hypoxia, a chromophore (66-NH2) is generated with red-shifted absorption and the active drug nitrogen mustard (a classic alkylating agent) is released as well. 66-NH2 shows prominent absorption at around 680 nm and strong fluorescence at about 710 nm, which makes it an ideal contrast agent for detecting and imaging tumor hypoxia both fluorescently and optoacoustically. Molecule 66, encapsulated into liposomes with particle sizes in the range of 60 ≈ 100 nm, ensures permeability and a retention effect.

Fluorophores

Probe 37 was cell membrane permeable and showed localization in the endoplasmic reticulum. It showed low toxicity and was used in 3D ratiometric Zn2+ imaging of zebrafish larvae’s heads. Based on 37, new ratiometric protocols for monitoring labile Zn2+ homeostasis were realized. Over the last few years, the development of fluorescent probes has received considerable attention.

NHS esters are especially useful in situations where the equivalent phosphoramidites exhibit instability to the conditions of oligonucleotide synthesis and/or deprotection. Photophysical behavior of probe 53 as a function of pH and truth table for operation of 53-based digital comparator 156. The proposed mechanism of 39 for sensing HOCl 124. Sensing mechanism of 33 towards Mg2+ and Zn2+ ions. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

As a result, the system showed blue fluorescence with maximum emissions at 415 nm. The introduction of fluoride removed the TBS group through Si-O bond cleavage resulting in a proton-containing hydroxyl fragment. The obtained ESIPT fluorescence of 34 in the presence of F− was centered at 586 nm (Figure 34). This dual channel response of 34 toward F− was utilized for ratiometric analysis.

The nerve signals were changed using rapid potential difference that was set up in a cell membrane by an imbalance of cations such as Ca2+, Na+, and K+ across a lipid bilayer. Miller et al. have integrated a PET fluorophore in the lipid bilayer of the neuron as the fluorophore signaling part stayed outside on the membrane surface while the PET receptor was placed in the membrane. The fluorescent signaling was off due to the PET process that could be modulated from the electric field created by the membrane potential interacting with the electron-donating amino receptor. Thus, the fluorescence intensity of 31 became low or high depending on the accelerated or hindered PET in the membrane (Figure 30).