Others

pH-Ap-1 is a fluorescent probe used for ratiometric monitoring of pH fluctuations during autophagy in living cells, and it can detect intracellular pH changes in the autophagy process. For fluorescence detection of pH-Ap-1, its excitation wavelength is 475 nm, with an emission wavelength of 538 nm under alkaline conditions and 645 nm under acidic conditions. For intracellular imaging, excitation is performed at 488 nm: the emission light ranging from 500-550 nm is collected via the green channel corresponding to 538 nm, while the emission light ranging from 625-750 nm is collected via the red channel corresponding to 645 nm. pH-Ap-1 exhibits excellent photostability and chemical stability.

FlCFe1 is a ratiometric ferrous ion probe that enables imaging of iron distribution in 3D cell models such as tumor spheroids. Its detection mechanism relies on its structure as a ratiometric analog of calcein AM. It has an excitation wavelength of 405 nm, with emission wavelengths of 490 nm (coumarin emission signal) and 530 nm (fluorescein emission signal).

MBCB is a two-photon Fluorescent probe for dual-detection of mitochondrial SO₂ derivatives and viscosity. For SO₂ derivatives detection, the probe utilizes a Michael addition mechanism: nucleophilic addition of SO₂ derivatives to the C=C bond between the carbazole skeleton and 3-methylbenzothiazolium moiety destroys the strong intramolecular charge transfer (ICT) system between these groups, while enhancing the weak ICT system between the benzothiazole group and carbazole framework; this causes the red emission at 600 nm to decrease and the blue emission at 434 nm to increase, creating a ratiometric response based on the I₄₃₄ₙₘ/I₆₀₀ₙₘ intensity ratio. For viscosity detection, in low-viscosity environments, steric hindrance creates a twisted ICT (TICT) system with weak fluorescence, while in high-viscosity environments, intramolecular rotation is blocked, the TICT state is disrupted, and the strong ICT system is recovered, leading to a strong red emission at 567 nm with negligible change to the short-wavelength emission at 415 nm, creating a ratiometric response based on the I₅₆₇ₙₘ/I₄₁₅ₙₘ intensity ratio that has a logarithmic linear relationship with viscosity. The probe has excitation/emission wavelengths of Ex/Em = 351/434, 600 nm for SO₂ derivatives detection and Ex/Em = 351/567 nm for viscosity detection, with two-photon excitation at 740 nm for bioimaging; it also exhibits good mitochondrial targeting ability with a Pearson's colocalization coefficient of 0.93 when paired with Mito-Tracker Green. The probe shows high sensitivity and selectivity for SO₂ derivatives, has low cell cytotoxicity, and can be applied to detect exogenous/endogenous HSO₃⁻ in living cells and in vivo, as well as visualize mitochondrial viscosity changes induced by nystatin[1].

Biotin-V is a fluorescent probe targeting the biotin receptor (BiR), which can be used to detect changes in intracellular viscosity in cancer cells and tumor tissues. Biotin-V consists of a viscosity-responsive TICT (twisted internal charge transfer) fluorophore and a biotin-targeting moiety. In a high-viscosity environment, intramolecular rotation is restricted, which reduces non-radiative transitions and enhances fluorescence intensity and fluorescence lifetime. Biotin-V enters BiR-positive cancer cells via biotin receptor-mediated uptake, and mainly localizes to mitochondria, enabling dual-modal viscosity imaging (fluorescence intensity imaging and fluorescence lifetime imaging) (Ex/Em = 540/608 nm; cell imaging Ex/Em = 561/570-620 nm).

MitoAIE1 is a Fluorescent probe for mitochondrial viscosity detection. MitoAIE1 contains a pyridinium structural unit, which endows it with mitochondria-targeting specificity. The detection mechanism of this probe is based on aggregation-induced emission (AIE): in low-viscosity media such as PBS buffer, intramolecular rotation leads to non-radiative energy dissipation, resulting in only weak fluorescence; however, in high-viscosity environments such as the mitochondrial matrix or the vicinity of the inner mitochondrial membrane, such intramolecular motion is restricted, thereby significantly enhancing its fluorescent signal; in addition, this probe is not interfered by changes in microenvironment polarity and pH. Its emission wavelength is 625 nm, with absorption peaks at 325 nm and 450 nm; when transferred from low-viscosity PBS to high-viscosity 99% glycerol, its fluorescence intensity at 625 nm can be increased by 38-fold. It can be used to monitor changes in mitochondrial viscosity during processes such as Stauroporine (HY-15141)-induced apoptosis and starvation-induced mitophagy in live cells, and has good biocompatibility.

LysoAIE2 is a Fluorescent probe for lysosomal viscosity detection and live-cell imaging. Its detection mechanism relies on the aggregation-induced emission effect: it exhibits only weak fluorescence in non-viscous media; in viscous environments, restricted intramolecular motion inhibits non-radiative energy dissipation pathways, thereby significantly enhancing fluorescence intensity. It achieves specific targeting of lysosomes through the proton acceptor property of its indole ring structure, while its hydroxyl group endows it with excellent water solubility. This probe is basically unaffected by microenvironmental polarity and pH within the range of pH 4.0 to pH 8.0, which avoids interference from these factors in viscosity measurement. LysoAIE2 has an emission wavelength of 570 nm. It can be used to monitor lysosomal viscosity changes during processes such as Dexamethasone (HY-14648)-induced lysosomal migration and starvation-induced mitophagy in live cells; at concentrations up to 40 μM, cell viability remains above 80%, demonstrating excellent biocompatibility.

Mem-RhoNox is a fluorescent probe used to detect labile Fe (II) on the plasma membrane surface and inside endosomes during iron uptake in live cells. Mem-RhoNox can anchor to the extracellular surface of the plasma membrane; upon contact with Fe (II), its N-oxide group undergoes a deoxygenation reaction, converting weakly fluorescent Mem-RhoNox into strongly fluorescent Mem-Rhodamine. During transferrin-mediated endocytosis, Mem-RhoNox enters endosomes together with the transferrin-transferrin receptor complex, and reacts with Fe (II) released by transferrin to enable detection of endosomal Fe (II).

Gol-SiRhoNox is a Golgi apparatus-targeted fluorescent probe with high selectivity for Fe (II), with a limit of detection of 50 nM. Gol-SiRhoNox integrates a myristoyl motif for Golgi apparatus targeting and a silicon-fused rhodamine N-oxide as the Fe (II)-sensitive moiety. Gol-SiRhoNox is non-fluorescent in its native state; Fe (II)-mediated deoxygenation of the N-oxide triggers fluorescence recovery. Its fluorescent product, Gol-SiR, has excitation/emission wavelengths of 630/665 nm and a maximum absorption wavelength of 655 nm.

NtHzBtd is a fluorescent probe for detecting Fe³⁺. NtHzBtd is applicable to the selective fluorescent detection of Fe³⁺ ions and live cell imaging studies. NtHzBtd can selectively coordinate with Fe³⁺ to form a 1:1 complex, triggering chelation enhanced quenching (CHEQ) and intramolecular charge transfer (ICT) processes, which result in fluorescence turn-off, thereby enabling sensitive detection of Fe³⁺ and live cell fluorescence imaging. After binding to Fe³⁺, NtHzBtd reduces fluorescence intensity, exhibits a rapid response property, with a limit of detection of 0.036 μM and a response time of approximately 55 s. The detection wavelengths are Ex/Em = 334/401 nm (solution system).

IOPBA is a fluorescent probe that can be used for the detection and bioimaging of trivalent iron ions Fe³⁺ and fluoride ions F^- in living cells. IOPBA emits blue fluorescence in its native state, but upon the introduction of Fe³⁺, it forms a Fe³⁺-IOPBA π-complex, where Fe³⁺ ions coordinate with two phenyl groups of IOPBA, resulting in fluorescence quenching. IOPBA returns to its free state and recovers its original fluorescence after F^- sequesters Fe³⁺ to form the more stable [FeF₆]^3- and dissociates the Fe³⁺-IOPBA complex. The excitation wavelength of IOPBA is 342 nm, and its emission wavelength is 458 nm.

DCA-Mln is a Fluorescent probe for ferric iron (Fe³⁺) detection. The probe works via an internal charge transfer (ICT) process from its diethylamino group to its dicyano group, which produces bright pink fluorescence in its unbound state; when Fe³⁺ is present, two molecules of DCA-Mln chelate with one Fe³⁺ ion, with one cyano group of each DCA-Mln participating in the complexation, and this binding triggers a photoinduced electron transfer (PET) process that provides a nonradiative deactivation pathway, resulting in fluorescence quenching; additionally, the probe exhibits a visible color change from purple to peach pink upon Fe³⁺ binding, enabling dual-channel detection. The probe has an excitation wavelength of 570 nm and an emission wavelength of 670 nm, and it shows a rapid response, with fluorescence stabilizing within 15 seconds of Fe³⁺ addition. DCA-Mln is cell-membrane-permeable, nontoxic at the imaging concentration of 10 μM, and can be used for Fe³⁺ detection in actual water samples, Fe³⁺ imaging in living cells, and as an anti-counterfeiting ink[1].

Mito-RhFe is a Fluorescent probe for mitochondrial labile Fe³⁺ monitoring via imaging and flow cytometry. This probe is a rhodamine-based construct with a spirolactam fluorescence signaling group and an N2-hydroxyethyldiethylenetriamine chelator; its delocalized positive charge enables mitochondria-targeting ability in live cells, and it exhibits fine cell membrane permeability. In its native state, it exists in the non-fluorescent spirolactam form, but upon binding to Fe³⁺, it undergoes a ring-opening conversion to the fluorescent rhodamine form, triggering a turn-on fluorescent response; this process is reversible, as the addition of the metal chelator TPEN removes Fe³⁺ and converts the probe back to its non-fluorescent spirolactam form, and re-addition of Fe³⁺ restores fluorescence. The probe shows high selectivity for Fe³⁺ over most other metal cations present in living systems, with a ~90-fold fluorescence enhancement upon binding to 20 equiv of Fe³⁺. Mito-RhFe has excitation/emission wavelengths of Ex/Em = 540/578 nm, with an ~8 nm bathochromic shift in emission upon Fe³⁺ binding, and it can also be excited at 543 nm for confocal imaging with emission detected at 570-620 nm[1].

Ratio-pHCL-1 is a fluorescent probe for quantitative ratiometric pH imaging in biological systems. Ratio-pHCL-1 consists of an acrylamide 1,2-dioxetane chemiluminescent scaffold and a linked pH-sensitive carbon fluorescein fluorophore, and functions via chemically initiated electron exchange luminescence (CIEEL) decomposition and chemiluminescence resonance energy transfer (CRET). Ratio-pHCL-1 can cross cell membranes and accumulate intracellularly, enabling pH measurement within the range of 6.8-8.4.

Mem-pH is a ratiometric fluorescent probe used for measuring vesicular pH. Mem-pH inserts into the plasma membrane bilayer and localizes to the vesicular lumen, switching between its basic and acidic forms via protonation during vesicular acidification to enable ratiometric pH readout. In aqueous media, Mem-pH forms non-emissive aggregates through aggregation-induced quenching, and then depolymerizes and recovers its fluorescent activity upon binding to the plasma membrane. The excitation/emission wavelengths of the basic form of Mem-pH are 405/450-550 nm, while those of the acidic form are 488/500-700 nm.

Lyso-MPCB is a two-photon fluorescent probe used for lysosomal pH detection and autophagy monitoring. Lyso-MPCB integrates a benzimidazole pH-responsive group and a morpholine lysosome-targeting group, enabling specific localization to lysosomes. The fluorescence properties of Lyso-MPCB change with protonation, exhibiting blue fluorescence under alkaline conditions and green fluorescence under acidic conditions.

Spring Red is a fluorescent probe for mitochondrial pH detection (Ex/Em = 530/680 nm) that can be taken up by live cells and mitochondria. The detection mechanism of Spring Red depends on pH changes and mitochondrial membrane potential. Fluorescence intensity increases with elevated pH, and a significant pH-dependent fluorescent response is observed in the pH range of 5.0‑8.0. Spring Red is suitable for long-term live-cell imaging and in vivo imaging, and can be used to monitor dynamic mitochondrial pH changes.

HS-CyBz is a Fluorescent probe for H₂S detection, enabling ratiometric optical/photoacoustic dual-modality in/ex vivo imaging. Its detection mechanism relies on nucleophilic substitution of its benzoic ester group by HS⁻, which releases an enolic meso-hydroxyltricarboheptamethine cyanine that then undergoes keto-enol tautomerization to form Cy-ketone; this tautomerization causes distinct shifts in absorption and emission spectra, producing a ratiometric response that reduces interferences from tissue scattering, autofluorescence, and probe concentration. In its initial state, HS-CyBz has an excitation wavelength of 595 nm, with emission bands centered at 805 nm (main) and 630 nm (minor); upon reaction with H₂S, the 805 nm emission band decreases while the 630 nm band drastically increases, and its absorption spectrum shows a sharp band at 775 nm and a shoulder band at 708 nm, which decrease upon H₂S reaction with a minor increase at 850 nm and an isosbestic point at 825 nm. For in vivo optical imaging, excitation at 560 nm is used with emission channels at 620 nm and 790 nm, while in vivo photoacoustic imaging uses excitation at 775 nm and 825 nm. The detection limit of HS-CyBz for H₂S is 0.5 μM, and it shows high selectivity, with only H₂S inducing a distinct enhancement of the emission ratio F₆₃₀/F₈₀₅ and PA ratio PA₈₂₅/PA₇₇₅, while other biochemical species including cations, anions, reactive oxygen species, biothiols, and carboxylesterase trigger only minor changes and do not interfere with H₂S sensing. Tail intravenous injection of HS-CyBz leads to accumulation in the liver of mice, and it can be used to verify endogenous H₂S upregulation triggered by S-adenosyl-L-methionine via ratiometric optical/photoacoustic imaging.

Pinkment-OAc is an AND logic gate-based dual-analyte-dependent fluorescence inducer (Ex/Em = 545 nm/590 nm) that can be used for the simultaneous detection of hydrogen peroxide (H₂O₂) and esterases (e.g., porcine liver esterase PLE). Pinkment-OAc triggers a fluorescent response only when both esterase and hydrogen peroxide are present.

TPE-Ph-In is a mitochondria-targeted voltage-sensitive probe that can be used for mitochondrial membrane potential detection, mitochondrial imaging of animal and plant cells and tissues, mouse sperm activity indication, and detection of mitochondrial membrane potential changes associated with early apoptosis. TPE-Ph-In is non-fluorescent in solution, but emits strong fluorescence when aggregated via restriction of intramolecular rotation/movement, and its fluorescence intensity is directly correlated with local probe concentration or mitochondrial membrane potential level. TPE-Ph-In can penetrate cell membranes, target mitochondria through charge-dependent accumulation, has low cytotoxicity and high photostability, and enables super-resolution imaging of plant mitochondrial fission, fusion and cristae structures. The excitation wavelengths of TPE-Ph-In include 450 nm, 488 nm, and 489 nm, while its emission wavelengths include 551-661 nm, 660 nm, and 694 nm. TPE-Ph-In can be used for studies on mitochondrial dysfunction associated with early apoptosis.

NRh-Cu is a highly sensitive near-infrared fluorescence turn-on indicator and Cu²⁺-selective probe (λ_ex=680 nm, λ_em=740 nm). When NRh-Cu interacts with Cu²⁺, it undergoes a structural transition from a non-fluorescent spirocyclic state to a fluorescent ring-opened state, which drives the enhancement of fluorescence emission. NRh-Cu can be used for Cu²⁺ imaging in live cells and in vivo.