Fluorescent Probes: A Complete Beginner’s Guide — Definitions & Emission Mechanisms, Signal Readouts, Classification Framework, Selection Roadmap, and Product Tables (Tables 1–4)

1) What is a “fluorescent probe”?

IUPAC defines fluorescence as: a process in which an excited molecule spontaneously emits radiation while preserving the spin multiplicity (simplified: absorb light → emit light shortly after).

Two commonly used related terms:

• Fluorophore (the fluorescent structural unit): a molecular entity that can emit fluorescence.
• Fluorescence quantum yield (quantum yield, Φ): the “efficiency” of a given event (e.g., light emission) per absorbed photon.

A fluorescent probe can be understood as a molecule/material that emits light and can recognize a target, then reports the recognition outcome via a measurable fluorescence change. It is often more than just a dye—it is a chemical/biological sensor featuring both a recognition function and a signal readout mechanism.

2) How is fluorescence produced?

You can think of fluorescence as “a molecule being pushed up a staircase by light, then sliding back down”:

• Excitation (absorption): the molecule absorbs excitation light; an electron transitions from the ground state to an excited state.
• Energy relaxation (non-radiative relaxation): the molecule “shakes off” part of the energy (converted into heat/vibration, etc.) without emitting light.
• Emission: the molecule returns from the excited state to the ground state and emits a photon—this is fluorescence.

Therefore, you typically observe that the emission wavelength is longer (lower energy) than the excitation wavelength. Their difference is often described by the Stokes shift (the difference between absorption and emission peak positions, typically expressed in frequency/wavenumber). In certain mechanisms/systems, anti-Stokes emission (emission at a shorter wavelength) can also occur.

Two fundamental metrics when choosing a probe

• Quantum yield Φ: higher Φ means “more energy-efficient”—absorbed photons are more likely to become emitted photons.
• Molar absorption coefficient ε (molar absorptivity): higher ε means “absorbs light more strongly.”
• Note: IUPAC also mentions that the “brightness” of (laser) dyes is often evaluated by Φ × ε(λ) (at the same excitation wavelength).

3) Why can probes “measure things”? The core is: recognition → converted into a fluorescence change

A typical fluorescent probe can often be conceptually decomposed into three parts (not always physically independent):

Fluorophore + recognition/reaction site (receptor/trigger) + linker/spacer (coupling/regulation element)

When the target (ion/small molecule/enzyme/nucleic acid/environmental parameter) is present, it triggers a photophysical change or a chemical/structural change, producing a measurable fluorescence response.

Common mechanisms that convert “recognition” into “signal” include:

A. “Switch-type” (turn-on / turn-off)

• Turn-on (brightens): lower background; often preferred in biological systems.
• Turn-off (dims): can be useful, but often more sensitive to photobleaching, concentration fluctuations, and optical-path changes.
• Note: Turn-off probes are not rare, but in live-cell/long-term imaging they are more easily affected by bleaching, probe concentration drift, and optical variations. For robust quantification, turn-on or ratiometric readouts are often preferred.

B. “Color ruler / self-calibrating” (ratiometric)

• Instead of using a single-channel intensity, you use the ratio of two emission signals (or the ratio between two wavelength bands from the same probe).
• Advantage: the ratio can resist many non-target interferences (probe concentration, excitation fluctuations, focus changes, partial photobleaching, etc.), making it more suitable for quantitative analysis.

C. “Distance ruler” (FRET: Förster resonance energy transfer)

• FRET reads out distance or conformational change via non-radiative energy transfer between a donor and an acceptor; commonly used for protein interactions, conformational dynamics, and biosensors.
• Note: IUPAC points out that the common phrase “fluorescence resonance energy transfer” is not strictly accurate because no photon emission is involved in the transfer; the more accurate term is Förster resonance energy transfer.

D. Typical “photophysical bottom switches”

• PET (photoinduced electron transfer): target binding/reaction alters electron-transfer pathways, switching from “quenched” to “emissive” or vice versa; PET is a classic cornerstone in probe design.
• ICT (intramolecular charge transfer): changing the strength of intramolecular charge transfer often shifts the emission peak, making it well-suited for ratiometric sensing.
• AIE (aggregation-induced emission): some molecules are “dark when dispersed, bright when aggregated/restricted,” often explained by “restricted intramolecular motion/rotation.”

4) How to classify fluorescent probes?

Axis (Dimension)	Subtype	One-sentence definition	When to prioritize	Typical examples
Axis 1: Probe carrier / physical form	Small-molecule probes	Flexible synthesis, fast diffusion, rapid response	Fast dynamics readout such as ions/ROS/enzyme activity/membrane potential	Fluo-4 AM, DCFH-DA, TMRE, Laurdan
	Biomacromolecule labeling	Antibodies/oligonucleotides/peptides carrying fluorescent tags	When high-specificity recognition is needed (antibody localization, nucleic-acid hybridization)	Antibody–FITC, Oligonucleotide–Cy5
	Genetically encoded fluorescent probes (FP systems)	Expressed in cells; sensing domain + FP (FRET/single-FP/translocation, etc.)	Long-term, trackable live-cell monitoring; organelle targeting	FRET biosensors, single-FP sensors
	Nanoprobes (luminescent nanoprobes)	Quantum dots/polymer dots/upconversion and other luminescent nanoparticles	High brightness/multicolor/time-gated options or in vivo imaging; must also evaluate in vivo metabolism and safety	Quantum dots (QDs), polymer dots (Pdots), upconversion nanoparticles (UCNPs)
Axis 2: Signal output mode	Intensity-based (turn-on/off)	Single-channel intensity change	Easy to start, fast screening; but sensitive to concentration/bleaching/optical-path changes	Most dyes / “turn-on” probes
	Ratiometric	Two-channel ratio is more robust	When closer-to-quantitative readout and resistance to concentration/illumination fluctuation are needed	Fura-2, SNARF, some membrane-environment probes
	Lifetime-based (lifetime/FLIM)	Readout uses fluorescence lifetime rather than intensity	Complex backgrounds, strong intensity artifacts, need a more “absolute” trend	FLIM probes / lifetime sensors
	Time-gated	Delayed acquisition avoids short-lifetime background	Strong tissue autofluorescence, need background suppression (often in long-lifetime systems)	Time-gated readouts are usually built on long-lifetime emitters (e.g., lanthanide complexes, some phosphorescence/delayed fluorescence, or specific luminescent nanomaterials), using delayed collection to bypass short-lifetime autofluorescence.
	Anisotropy / polarization	Reports molecular rotation / binding changes	Studying binding, viscosity, aggregation and other “kinetic/motional” information	Fluorescence anisotropy binding assays (methodology-driven)
Axis 3: Recognition target / trigger	Ions / small molecules	Ca²⁺/H⁺/Zn²⁺ etc.	Cell signaling, homeostasis and dynamic monitoring	Fluo-4, BCECF, etc.
	ROS/RNS	H₂O₂, ONOO⁻, etc.	Oxidative stress, inflammation, mitochondrial function	DCFH-DA, DHE, DAF-FM, etc.
	Enzyme activity / activatable probes	Triggered by enzymatic cleavage or redox activation	“Light up only when the target event occurs”	Substrate-type probes (e.g., Amplex Red family)
	Nucleic acids / structures	DNA/RNA, special structures (e.g., G-quadruplex)	Nuclear staining/hybridization assays/structure studies	Hoechst, DAPI, nucleic-acid dyes
	Microenvironment parameters	Polarity, viscosity, membrane potential, hypoxia, temperature	Imaging physical/chemical microenvironments	Laurdan/PRODAN, membrane potential dyes
Axis 4: Optical window	Visible	Widely available instrumentation, lower cost	Cells/thin samples, controllable background	FITC/TRITC, etc.
	NIR-I (~700–900 nm)	Lower tissue background than visible	Tissue imaging, common in small-animal in vivo imaging	Common near-infrared dyes
	NIR-II (~1000–1700 nm)	Even lower autofluorescence/scattering	Potential for deeper penetration and higher clarity	NIR-II imaging probes
Axis 5: Localization / targeting strategy	Organelle/structure targeting	“Where it lights up” is the key information	Organelle co-localization, functional compartment studies	Mito/Lyso series, membrane/nucleus-targeting probes

5) What technical features should a good fluorescent probe meet?

Dimension	Metric	Why it matters	Quick check / validation
Optical performance	Brightness (ε×Φ)	Whether it is “bright enough” at the same concentration/excitation; weak signals amplify noise and drift	Check datasheet ε and Φ; compare at equal concentration with same exposure/excitation power; watch for environment quenching or binding-induced dimming
Optical performance	Larger Stokes shift is more user-friendly	Reduces excitation leakage, channel crosstalk, self-absorption; more robust multiplexing	Check absorption/emission spectra vs filters; do single-stain → bleed-through (crosstalk) matrix
Optical performance	Photostability (bleach resistance)	Whether it “fades quickly” during long imaging/scanning	Record intensity decay under continuous illumination; compare anti-fade systems (photobleaching is a common microscopy limitation)
Optical performance	Spectral match / multi-channel compatibility	Mismatch with laser lines/filters makes “good on paper, hard in practice”	Back-check instrument channels: excitation lines, dichroics, bandpass filters; verify channels with single-color standards
Background control	Autofluorescence in tissue/complex matrices; choose ratiometric or longer wavelengths if needed	In real samples, background often determines SNR; intensity-based probes are most easily biased by sample variation	Measure sample baseline (no probe); switch to ratiometric or lower-autofluorescence bands (e.g., NIR-II) if necessary
Selectivity & sensitivity	Selectivity / specificity	“Is the signal truly from the target?”	Interferent panel tests; competition inhibitors/scavengers; genetic/pharmacological validation (KO/inhibitors)
Selectivity & sensitivity	LOD & dynamic range	If the sample concentration is outside the range, brightness won’t help	Use calibration curves covering the expected range; confirm no saturation/floor effects
Kinetics	Response speed	Biological processes can be seconds to hours; mismatch means “you won’t see changes”	Record time courses after adding target; distinguish fast-reaction vs slow-accumulation probes
Mechanistic property	Reversible vs irreversible	Reversible for real-time dynamics; irreversible for event recording/end-point accumulation	Check mechanism: coordination/protonation often reversible; covalent reaction/enzymatic cleavage often irreversible (with appropriate controls)
System compatibility	Water solubility / anti-aggregation	Aggregation can cause ACQ or AIE (may dim or brighten)	Run concentration gradients; compare spectra with added protein/serum, surfactants, or organic cosolvents
Biocompatibility	Cell permeability / localization / targeting	If it can’t enter or localizes incorrectly, conclusions drift	Co-localization validation; compartment markers; use targeting motifs or genetic encoding when needed
Biocompatibility	Toxicity / perturbation / phototoxicity	The probe itself may alter the system (esp. strongly lipophilic membrane insertion, ROS-related systems)	Viability/activity controls; separate “dark toxicity” and “light-induced toxicity”
Quantitation & controls	Calibration strategy; whether ratiometric self-calibration is needed	Intensity is sensitive to concentration/optics/bleaching; ratios are more robust	In vitro → intracellular calibration strategy; dual-channel ratio or lifetime methods; clearly state control logic
Quantitation & controls	Negative/competition/mutant controls (recommended)	Key to making conclusions defensible	At minimum include: no-probe control; structurally similar inert probe control; inhibitor/KO/mutant validation (as appropriate)

Notes:

• ΔΨm dye addendum: For potential-dependent accumulation dyes such as TMRE/TMRM, specify the working mode (non-quenching vs quenching), working concentration, and readout strategy (whole cell vs mitochondrial ROI), and use FCCP/CCCP to define the zero point/dynamic range.
• Addendum: Substrates such as Amplex/Ampliflu Red are often used for HRP/oxidase-coupled H₂O₂ measurements (especially extracellular release). If the goal is intracellular ROS imaging, prioritize probes/sensors specifically designed for intracellular use, together with appropriate controls.

6) Common application areas of fluorescent probes

1. Life sciences and biomedical research

• Live-cell/tissue imaging: see “where and when it happens” (ions, ROS, pH, membrane potential, enzyme activity, metabolism, etc.).
• Protein interactions/conformational changes: FRET sensors and genetically encoded probes are widely used.
• Disease biomarker detection: in vitro assays, tissue staining, intraoperative fluorescence guidance (often more NIR-oriented).

2. Drug discovery and bioanalysis

• High-throughput screening (HTS): fluorescence readouts for enzyme activity, receptor binding, signaling pathways.
• Binding kinetics and cellular signaling: TR-FRET / BRET / FRET methods are well established.

3. Environment, food, and industrial testing

• Heavy metals/pollutants: rapid on-site detection (test strips, smartphone readouts, etc.).
• Food freshness/spoilage indicators: pH, amines, sulfides, etc. can be monitored via fluorescent sensing materials.
• Process monitoring & materials science: monitoring polymerization, stress, defects, and microenvironmental changes.

Table 0 | Quick Selection Guide for Fluorescent Probes: Needs → Corresponding Product Tables (Tables 1–4)

Need / scenario	Typical keywords / probe types to look for	Which table to check first	How to choose (logic)
Live-cell functional readouts: Ca²⁺ dynamics, pH changes, ROS/NO, membrane potential, membrane order/polarity, membrane tracing/endocytosis	Ca²⁺ (Fluo-4 AM / Fura-2 AM); pH (BCECF-AM / SNARF-1 AM); ROS/RNS (DCFH-DA; APF/HPF); NO (DAF-FM DA); membrane potential (TMRE/TMRM or JC-10); membrane environment/order (Laurdan or Flipper-TR); membrane tracing/endocytosis (FM1-43); ions & microenvironment: Cl⁻ (MQAE or SPQ), Zn²⁺ (Zinquin), K⁺ (PBFI-AM); special functions: ¹O₂ (ABDA), viscosity (DCVJ), viability/esterase activity (Calcein AM or FDA), fluorogenic enzyme substrates (4-MUP / MUGal; 4-MU as the common fluorescent core).	Table 1	Table 1 focuses on functional probes for reporting cell physiology/signaling/stress/membrane properties—best for mechanism studies and quantitative imaging/flow readouts.
Only need to label a specific organelle: mitochondrial/lysosomal localization or co-localization, or assess organelle function (mitochondrial ROS/H₂O₂, lysosomal pH)	MitoTracker/MitoScene/MitoMark; MitoSOX, MitoPerOx, MitoPY1; LysoTracker/LysoSensor; Flipper-TR (membrane mechanics/order); ER Flipper-TR, ER PhotoFlipper (ER targeting); HaloFlipper (HaloTag localization + membrane-property readout)	Table 2	Table 2 is the organelle-targeting section: mitochondrial/lysosomal stains and functional probes are grouped together—most time-efficient for co-localization and organelle function assays.
Nuclear/nucleic-acid staining or flow live/dead discrimination: nuclear stains, DNA content, dead-cell exclusion, multicolor panels (far-red/NIR nucleic-acid dyes)	Hoechst 33342/33258, DAPI; PI, 7-AAD, TO-PRO-1/3; DRAQ5 (live-cell nuclear stain), DRAQ7 (dead-cell nuclear stain); EB; acridine orange kits	Table 3	Table 3 is dedicated to nucleic-acid stains & live/dead dyes: includes microscopy nuclear stains, flow live/dead, DNA content/cell-cycle staples, and covers far-red/NIR channels.
Probe construction/labeling/derivatization or general-purpose fluorescent dyes: conjugation to proteins/molecules, method validation, tracer dyes for carriers/materials	FITC, TMR-ITC; carboxyfluorescein / carboxy-TMR (coupling precursors); BODIPY scaffolds; NBD-Cl, dansyl chloride, brominated bimane; general rhodamine/coumarin/sulfonyl “dansyl”-type dyes; NIR-I/NIR-II imaging dyes (ICG, IR-780, IR-1061, NIR-II carboxyl-functionalized dyes)	Table 4	Table 4 covers basic dyes and chemical labeling reagents—ideal for covalent labeling, probe synthesis, derivatization assays, and general tracing/methodology work.
Not sure which category it belongs to: only know the goal is “detection/staining/labeling”	First ask: is it a functional readout, localization stain, nucleic-acid/live-dead, or conjugation/synthesis task?	Check Table 1 → Table 2 → Table 3 → Table 4	Follow a typical research workflow: start with functional probes (Table 1), then organelle localization (Table 2), then nucleic-acid/live-dead (Table 3), and finally labeling/synthesis & general dyes (Table 4).

Table 1 | Functional Fluorescent Probes for Cells (Ca²⁺/pH/ROS & NO/membrane potential/membrane environment & tracing)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / purity	Key features / function
Ca²⁺ probe (AM ester, single-channel)	273221-67-3	F746068	Fluo-4 AM (calcium fluorescent probe)	BioReagent, ≥90% (HPLC), 2 mM	A commonly used Ca²⁺ probe for live-cell loading (AM enters cells, then is cleaved by esterases and retained); suitable for microscopy/high-throughput readouts; use ionophore/chelator controls to verify dynamic range.
Ca²⁺ probe (AM ester, ratiometric)	108964-32-5	F131042	Fura-2, AM, fluorescent calcium indicator	≥95% (HPLC)	Classic ratiometric Ca²⁺ indicator (more robust against probe amount/illumination fluctuations), suitable for quantitative trends and calibration; higher demands on instrument channels/excitation.
Ca²⁺ probe (AM ester, ratiometric; common in flow)	112926-02-0	I1455253	Indo-1 AM	_	Ratiometric Ca²⁺ indicator commonly used in flow cytometry and microscopy; better suited for designs needing relative quantification and interference resistance.
Mg²⁺ probe (AM ester, ratiometric; also Ca²⁺ sensitive)	130100-20-8	M1453637	Mag-Fura-2 AM	——	Often used for intracellular Mg²⁺ changes (but can be affected by Ca²⁺); recommended to include Ca²⁺ controls/chelation controls.
K⁺ probe (AM ester)	124549-23-1	P1437664	PBFI-AM	——	Live-cell K⁺ indicator (AM loading); suitable for intracellular K⁺ fluctuations (e.g., apoptosis/ion channels); calibration and ionic-strength effects require attention.
Cl⁻ probe (commonly quenching-type)	162558-52-3	M131144	MQAE [1-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide]	For fluorescence analysis, ≥97%	Classic dye for intracellular Cl⁻/halide studies (often collisional quenching readout); suitable for Cl⁻ channel/transport studies; requires ion-substitution and calibration schemes.
Cl⁻ probe (commonly quenching-type)	83907-40-8	S1499702	SPQ	Moligand™, 10 mM in Water	Common halide/Cl⁻-sensitive dye (often quenching-type); suitable for methodology and ion-substitution experiments; strict positive/negative and background controls recommended.
Zn²⁺ probe (labile zinc)	181530-09-6	Z274867	Zinquin ethyl ester	≥99%	Zinquin-type probe for labile Zn²⁺ distribution/changes; recommended to pair with chelator (e.g., TPEN) and zinc-addback controls.
Metal-sensitive probe (signal affected by multiple metals)	234075-45-7	P647966	Phen Green SK diacetate (5/6-mixture)	≥91%	Cell-loadable metal-sensitive probe (multiple metal ions can alter fluorescence; see product description for selectivity); useful for screening/controls, but be cautious for single-metal quantification.
pH probe (AM ester)	117464-70-7	B273262	BCECF-AM	≥90% (HPLC)	Classic intracellular pH probe (often with ratiometric/dual-excitation strategies); suitable for pH calibration and live-cell imaging; nigericin/high-K⁺ calibration is recommended when permissible.
pH probe (AM ester, red-shifted / dual-channel advantage)	126208-13-7	C273271	5(6)-Carboxy SNARF-1, acetoxymethyl ester, acetate	≥90%	Red-shifted, ratiometric pH probe; useful for multicolor experiments alongside green channels; commonly used for intracellular or organelle pH trend comparisons.
NO probe (AM ester, low NO levels)	254109-22-3	D131469	DAF-FM DA, reagent for low-level NO detection and quantification	≥98% (HPLC)	Widely used for detecting NO production (DA form improves cell loading); controls and interference management are critical (pair with NO donors/inhibitors and blanks).
ROS probe (overall oxidation / trend)	4091-99-0	H131224	2′,7′-Dichlorodihydrofluorescein diacetate (DCFH-DA)	≥97%	Common for screening overall oxidative-stress trends (limited selectivity); suitable for between-group comparisons; recommended to pair with more specific probes and scavenger/inhibitor controls.
ROS probe (peroxides/peroxynitrite, etc.)	109244-58-8	D755415	Dihydrorhodamine 123	Cell-permeable fluorogenic probe that is useful for the detection of reactive oxygen species (ROS) such as peroxide and peroxynitrite.	Oxidized intracellularly into a fluorescent form; suitable for monitoring ROS-related changes; control illumination and auto-oxidation background.
ROS probe (superoxide-related)	104821-25-2	D113494	Dihydroethidium	≥95%	Commonly used for superoxide-related detection (products can be complex; interpret cautiously); recommended to include specific inhibition/scavenging controls and appropriate analytical methods.
HOCl / strong oxidant probe	359010-70-1	A356800	APF	≥95%, ~5 mM in dimethyl formamide	Often used for HOCl studies (may also respond to ·OH/ONOO⁻); frequently paired with HPF for discrimination/control design.
·OH / ONOO⁻ probe	359010-69-8	R336295	HPF	Moligand™, ≥98%, a solution in methyl acetate	Often used as a control counterpart to APF, more oriented toward ·OH/ONOO⁻; suitable for “HOCl vs other strong oxidants” control logic (see product documentation).
Fluorogenic substrate for H₂O₂ / oxidase systems	119171-73-2	A131064	10-Acetyl-3,7-dihydroxyphenoxazine (Ampliflu Red)	For fluorescence analysis, ≥98% (HPLC)	Representative “Amplex/Ampliflu Red” substrate: generates a fluorescent product in HRP/oxidase-coupled systems; suitable for microplate quantification and sensitive detection.
Singlet oxygen (¹O₂) indicator	5471-63-6	D122454	1,3-Diphenylisobenzofuran	≥97%	DPBF: commonly used to verify ¹O₂ generation (easily oxidized; protect from light); more for system validation/methodology.
Singlet oxygen (¹O₂) indicator	307554-62-7	A131481	9,10-Anthracenediyl-bis(methylene)dimalonic acid	≥90%	ABDA: commonly used for ¹O₂ detection/validation; suitable for evaluating photosensitization/photo-oxidation systems.
Microenvironment viscosity probe (molecular rotor)	58293-56-4	D131255	9-(2,2-Dicyanovinyl)julolidine	≥97% (HPLC)	DCVJ: classic molecular rotor; signal varies with restriction/viscosity; suitable for trend comparisons of viscosity/microenvironment changes.
Membrane-environment probe (polarity/order)	74515-25-6	L131299	6-Dodecanoyl-N,N-dimethyl-2-naphthylamine (Laurdan)	For fluorescence analysis, ≥97% (HPLC)	Classic probe for membrane phase state/order (often used for GP analysis); suitable for comparing membrane order and phase-transition trends.
Membrane-environment probe (PRODAN type)	70504-01-7	P131289	N,N-Dimethyl-6-propionyl-2-naphthylamine	≥98%	PRODAN: sensitive to environmental polarity; often used to study microenvironment changes in membranes/protein hydrophobic pockets.
Membrane potential dye (voltage-sensitive)	90134-00-2	D768599	4-(2-(6-(Dibutylamino)-2-naphthyl)vinyl)-1-(3-sulfopropyl)pyridinium hydroxide, inner salt	≥95% (HPLC)	Typical styryl-type voltage-sensitive dye; used for plasma-membrane potential imaging (manage phototoxicity and staining conditions).
Membrane/organelle stain (lipophilic cyanine)	53213-82-4	D1455411	3,3′-Dihexyl oxacarbocyanine iodide; iodide 3,3′-dihexyloxycarbonyl cyanine	≥99%	Lipophilic cyanine dye; commonly used for membrane/organelle staining or potential-related assays (see product documentation for specific use).
Membrane potential/distribution-related dye	70363-83-6	D141163	Bis(1,3-dibutylbarbituric acid) trimethine oxonol	≥95%	Oxonol-type dye often used for membrane potential/distribution studies (optimize staining and controls).
Mitochondrial membrane potential probe (ΔΨm)	115532-52-0	T131055	TMRE [tetramethylrhodamine ethyl ester perchlorate]	For fluorescence analysis, ≥90% (HPCE)	Classic ΔΨm probe: cationic dye that accumulates in mitochondria in a potential-dependent manner; recommended to include FCCP/CCCP depolarization controls.
Mitochondrial membrane potential probe (ΔΨm)	115532-50-8	T768877	Tetramethylrhodamine methyl ester perchlorate	≥98%	TMRM: commonly used ΔΨm probe; low-concentration conditions are better for quantitative trend comparisons (avoid self-quenching).
Mitochondrial membrane potential probe (ΔΨm)	62669-70-9	R299309	Rhodamine 123	≥98%	Classic mitochondria-enriching dye for ΔΨm/mitochondrial function studies (controls are essential).
Mitochondrial membrane potential probe (ΔΨm)	_	J141206	JC-10, mitochondrial membrane potential fluorescent probe	≥95%	JC series: aggregate/monomer signals change with ΔΨm; suitable for microscopy/flow comparisons of potential changes.
Lipid/hydrophobic environment stain	7385-67-3	N121291	Nile Red	BioReagent, for fluorescence analysis, ≥95% (HPLC)	Common for lipid droplet/neutral lipid staining; also indicates hydrophobic environments (control background and permeability).
Membrane tracing / endocytosis probe	149838-22-2	T1373392	FM 1-43	_	Inserts into membranes and enters vesicles via endocytosis; widely used for membrane cycling/synaptic vesicle tracing.
Live-cell esterase/activity probe	596-09-8	F109384	Fluorescein diacetate	≥97%	FDA: cell-permeable; cleaved by esterases to fluorescein; used for live-cell/esterase activity and rapid viability assessments (often paired with PI, etc.).
Live-cell viability / tracer probe	148504-34-1	C131116	Calcein acetoxymethyl ester	For fluorescence analysis, ≥96% (HPLC)	Calcein AM: cleaved intracellularly, fluorescent and retained; used for live-cell labeling, toxicity assessment, and paired with dead-cell dyes (PI, etc.).
Cell tracking (long-term / proliferation tracking)	150347-59-4	C131127	5(6)-Carboxyfluorescein diacetate succinimidyl ester (CFDA)	For fluorescence analysis, ≥90% (HPLC)	Common route for cell/proliferation tracking (converted intracellularly and can form stable labeling); suitable for immune-cell proliferation/migration tracking, etc.
Fluorogenic enzyme substrate (phosphatases)	3368-04-5	M1499707	4-Methylumbelliferyl phosphate	Moligand™, 10 mM in Water	4-MUP: hydrolyzed by phosphatases to release fluorescent 4-MU; used for alkaline/acid phosphatase activity assays.
Fluorogenic enzyme substrate (β-Gal)	6160-78-7	M171181	4-Methylumbelliferyl-β-D-galactopyranoside	≥98%	MUGal: β-galactosidase hydrolysis → 4-MU; used for reporter-gene/enzyme activity detection.
Fluorogenic enzyme substrate (β-GUS)	6160-80-1	M194210	4-Methylumbelliferyl-β-D-glucuronide	≥98%	MUGlcA: β-glucuronidase hydrolysis → 4-MU; used for enzyme assays/microbial detection, etc.
Fluorescent reporter core (substrate aglycone)	90-33-5	M106701	4-Methylumbelliferone (4-MU)	≥98%	Shared fluorescent core for many 4-MU substrates; used for standard curves, methodology controls, and reaction-system calibration.
Fluorogenic esterase substrate	2747-05-9	A151699	7-Acetoxy-4-methylcoumarin	≥98%	Esterase hydrolysis releases 4-MU; used for esterase activity and substrate screening.
Protein aggregation/amyloid probe	2390-54-7	T168914	Thioflavin T	_	Commonly shows enhanced signal upon binding amyloid/β-sheet structures; suitable for aggregation kinetics and screening (include blank/protein controls).
Membrane-property probe (Flipper-TR family, general)	2081888-04-0	F1452957	Flipper-TR 5	_	Flipper-TR family: reports membrane properties (often mechanics/order-related); commonly combined with lifetime/intensity strategies for membrane biophysics studies.
Membrane-property probe (Flipper-TR family, general)	_	F1455208	Flipper-TR probe	_	General Flipper-TR probe version; used for membrane-property imaging and readouts.
Membrane-property probe (Flipper derivative)	2804069-31-4	A1451998	Arg-Flipper 34	_	Flipper derivative (Arg functionalization); used for membrane-property imaging/studies (see product documentation).
Membrane-property probe (Flipper derivative)	2804069-30-3	E1450064	EE-Flipper 33	_	Flipper derivative (EE functionalization); used for membrane-property assays (as specified in the product documentation).
Supramolecular/assembly-related membrane probe (Flipper derivative)	_	S1453269	SupraFlipper 31	_	SupraFlipper: oriented toward supramolecular/assembly contexts for membrane-related readouts (see product documentation), suitable for more chemistry/materials-leaning membrane studies.

Tip: TMRM/TMRE can be used in non-quenching (low nM) or quenching (higher concentration) modes. Depending on the mode, interpretations such as “signal increases vs decreases upon depolarization” and whether you analyze whole-cell vs mitochondrial ROI can be opposite. For ΔΨm trend quantification, low-concentration non-quenching conditions are often preferred, together with FCCP/CCCP depolarization controls to define the dynamic range.

Table 2 | Organelle-Targeting and Localization Probes (Mitochondria + Lysosomes)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / purity	Key features / function
ER-targeted membrane probe	2334078-37-2	E1451345	ER Flipper-TR 28	_	Endoplasmic reticulum (ER)-targeted Flipper membrane probe for ER membrane-property imaging/readouts (often used in membrane biophysics studies).
ER-targeted photo-controllable membrane probe	_	E1454254	ER PhotoFlipper 32	_	ER-targeted PhotoFlipper for light-controlled/photoactivation strategies in membrane readouts (mechanism/usage per product documentation).
HaloTag-localized membrane probe	_	H1451916	HaloFlipper 30	_	HaloTag chemical probe that covalently binds HaloTag-fusion proteins, enabling a semi-synthetic strategy: localize to a specific membrane/organelle first, then read out membrane properties.
Mitochondria-targeted membrane probe	2334078-40-7	M1449714	Mito Flipper-TR 27	——	Mitochondria-targeted Flipper membrane probe for mitochondrial membrane-property imaging/studies.
Lysosome-targeted membrane probe	2324152-35-2	L1452333	Lyso Flipper-TR 29	——	Lysosome-targeted Flipper membrane probe for lysosomal membrane properties and functional-state studies.
Mitochondrial localization stain (far-red)	——	M748085	Mito-Tracker Far-Red (far-red mitochondrial fluorescent probe)	BioReagent, ≥95%	Mitochondrial localization/co-localization (far-red channel), suitable for combining with green/orange channels.
Mitochondrial localization stain (deep red)	873315-86-7	M1455700	MitoTracker Deep Red FM	≥99%	Deep-red mitochondrial stain, suitable for multicolor panels.
Mitochondrial localization stain (orange)	199116-50-2	M1455293	MitoTracker Orange CMTMRos	——	Orange-channel mitochondrial staining/co-localization.
Mitochondrial localization stain (green)	201860-17-5	M288856	MitoScene™ Green I (green mitochondrial fluorescent probe)	——	Green mitochondrial localization stain.
Mitochondrial localization stain (red)	167095-09-2	M287728	MitoMark Red I, red fluorescent mitochondrial stain	≥90% (HPLC)	Red mitochondrial staining/co-localization use.
Mitochondrial superoxide probe	1003197-00-9	M647069	MitoSOX Red	≥95%	Mitochondria-targeted superoxide-related probe for mitochondrial ROS studies (optimize conditions and include controls).
Mitochondrial lipid peroxidation probe	1392820-50-6	M275561	MitoPerOx, mitochondria-targeted lipid peroxidation probe (cis/trans isomer mixture)	≥95%	Reports mitochondrial membrane lipid peroxidation; useful for oxidative stress/ferroptosis-related studies (strict controls recommended).
Mitochondrial H₂O₂ probe	1041634-69-8	M286913	MitoPY1, fluorescent mitochondrial hydrogen peroxide indicator	——	Mitochondria-targeted H₂O₂ indicator for monitoring mitochondrial H₂O₂ changes.
Mitochondria-targeted dye/platform	——	M1424518	Mito-Rh-S	——	Mitochondria-targeted dye/platform-type probe (specific applications per product documentation).
Lysosomal localization stain (green)	——	L747762	Lyso-Tracker Green (green lysosomal fluorescent probe)	For immunofluorescence (IF), BioReagent, biological stain, molecular biology grade, 1 mM	Enriches in acidic organelles; commonly used for lysosome/acidic vesicle localization and co-localization.
Lysosomal localization stain (red)	——	L747763	Lyso-Tracker Red (red lysosomal fluorescent probe)	——	Lysosome localization (red channel).
Lysosomal localization stain (red)	231946-72-8	L647096	LysoTracker Red	≥97%	Lysosome localization stain (red channel), suitable for multicolor co-localization.
Lysosomal localization stain (blue)	215247-93-1	L1455325	LysoTracker Blue DND-22	——	Lysosome localization stain (blue channel).
Lysosomal localization stain (yellow)	1064123-31-4	L1455226	LysoTracker Yellow HCK 123	≥98%	Lysosome localization stain (yellow channel), convenient for pairing with green/red channels.
Lysosome-targeted red probe	——	L1452172	LysoSR-549	——	Lysosome-targeted red probe for co-localization applications.
Lysosomal functional probe (pH / acidic-environment sensitive)	——	L1455145	LysoSensor PDMPO	≥98%	LysoSensor family: sensitive to acidic environments; used for lysosomal function/acidification-state studies.

Table 3 | Nucleic-Acid Stains and Live/Dead Dyes (Nucleus/DNA–RNA/Flow Cytometry Essentials)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / purity	Key features / function
Nucleic-acid stain (DNA, nucleus; cell-permeable)	23491-52-3	O1501802	Hoechst 33342 Staining Solution	For immunofluorescence (IF), BioReagent, ready-to-use, biological stain, for fluorescence analysis, dye grade, for microscopy, for cell culture, 1.0 mg/mL in H₂O	Ready-to-use Hoechst 33342: cell-permeable DNA stain (preferentially binds AT-rich regions); used for nuclear staining/counting/IF.
Nucleic-acid stain (DNA; cell-permeable)	875756-97-1	H288601	Hoechst 33342 Trihydrochloride	≥98% (HPLC)	Powder form of Hoechst 33342; used for live-cell nuclear staining/counting/IF (prepare and use at working concentration).
Nucleic-acid stain (DNA; cell-permeable)	23491-45-4	B755381	Bisbenzimide H 33258 Fluorochrome, Trihydrochloride	Membrane-permeable, adenine-thymine-specific fluorescent stain.	Hoechst 33258: DNA stain (AT-preferential); commonly used for nuclear staining, microscopy, and quantification.
Nucleic-acid stain (DNA; DAPI)	28718-90-3	D106471	4′,6-Diamidino-2-phenylindole dihydrochloride	≥98% (HPLC)	DAPI: classic blue nuclear stain (AT-preferential); widely used for fixed cells/tissues; under some conditions can also be used in live cells.
Nucleic-acid stain (DNA/RNA; intercalating)	1239-45-8	E119045	Ethidium bromide (EB)	Molecular biology grade, ≥95% (HPLC), powder	Intercalating nucleic-acid dye; commonly used for DNA/RNA gel staining (note: strong mutagenic hazard—use proper PPE and compliant disposal).
Nucleic-acid stain (live/dead; flow)	7240-37-1	A131295	7-Aminoactinomycin D (7-AAD)	Moligand™, ≥97% (HPLC)	7-AAD: typically does not readily cross intact plasma membranes; used for dead-cell exclusion/live–dead discrimination and DNA-content analysis (common in flow cytometry).
Nucleic-acid stain (DNA; dead cells/flow)	25535-16-4	P266304	Propidium iodide (PI)	≥98% (HPLC)	PI: enters when membrane integrity is compromised and binds DNA/RNA; used for dead-cell staining and as a control in cell cycle/apoptosis assays (flow).
Nucleic-acid stain (dead cells/flow)	157199-59-2	T1427933	TO-PRO 1	_	TO-PRO-1: typically membrane-impermeant; used for dead-cell nucleic-acid staining/live–dead discrimination (green channel).
Nucleic-acid stain (dead cells/flow, far-red)	157199-63-8	T1454780	TO-PRO-3 iodide	_	TO-PRO-3: dead-cell nucleic-acid stain (far-red/NIR channel); used for live–dead exclusion in multicolor flow panels.
Nucleic-acid stain (DNA; cell-permeable, far-red)	254098-36-7	D1427942	DRAQ5	_	DRAQ5: cell-permeable nuclear DNA stain (far-red); commonly used for live-cell nuclear staining and flow cytometry.
Nucleic-acid stain (DNA; cell-permeable, far-red)	——	D266292	DRAQ5 Fluorescent Probe	_	Same use class as above: far-red nuclear stain, helpful for multicolor panels to reduce channel crowding.
Nucleic-acid stain (dead-cell DNA; near-infrared)	——	D266297	DRAQ7 Fluorescent Probe	_	DRAQ7: typically membrane-impermeant; used for dead-cell nuclear staining/live–dead discrimination (near-infrared channel, suitable for multicolor).
Nucleic-acid staining kit (often for microscopy/counting)	_	A1456513	Acridine Orange Fluorescent Staining Kit	BioReagent, biological stain, for microscopy	Acridine orange–type nucleic-acid stain (DNA/RNA) often used for cell staining/counting/morphology observation (following kit instructions and controls is more robust).
Nucleic-acid stain (YO/oxazole yellow family)	152068-09-2	O598365	Oxazole Yellow	1 mM in DMSO	A common class of dyes whose fluorescence increases markedly upon binding nucleic acids (YO-type/related structures); used for nucleic-acid staining/methodology (permeability depends on structure and conditions).

Table 4 | General Fluorescent Dyes and Labeling/Derivatization Reagents + NIR Imaging Dyes

Category	CAS No.	Aladdin Cat. No.	Name	Spec / purity	Key features / function
General fluorescent dye (fluorescein core)	2321-07-5	F104053	Fluorescein	Indicator	Classic fluorescein scaffold; used as a tracer/indicator and as a foundational building block for derivatization and probe construction.
Covalent labeling reagent (amine coupling)	3326-32-7	F272903	Fluorescein 5-isothiocyanate (isomer I) [5-FITC (isomer I)]	Ex: 498 nm, Em: 517 nm, ≥95% (HPLC)	FITC: classic labeling reagent for conjugation to primary amines on proteins/antibodies; widely used for general fluorescent labeling.
Covalent labeling reagent (amine coupling)	95197-95-8	T131567	Tetramethylrhodamine-5(6)-isothiocyanate	For fluorescence analysis, Ex: 552 nm, Em: 578 nm, mixture of isomers	TMR-ITC: commonly used for protein/antibody labeling in the orange–red channel; suitable for multicolor combinations.
General fluorescent dye (carboxyl precursor / conjugatable)	91809-67-5	C115506	6-Carboxytetramethylrhodamine	For fluorescence analysis, ≥90%	Carboxy-TMR precursor: often used to prepare active esters and other conjugation derivatives.
General fluorescent dye (carboxyl precursor / conjugatable)	91809-66-4	C272928	5-Carboxytetramethylrhodamine	≥97%	Carboxy-TMR precursor commonly used in probe synthesis/conjugation.
General fluorescent dye (carboxyl precursor / conjugatable)	72088-94-9	C107883	5(6)-Carboxyfluorescein	≥95% (HPLC), mixture of 5- and 6-isomers	Carboxyfluorescein: general conjugation precursor (isomer mixture).
General fluorescent dye (carboxyl precursor / conjugatable)	76823-03-5	C105530	5-Carboxyfluorescein	≥95%	5-Carboxyfluorescein: commonly used for conjugation/probe construction.
General fluorescent dye (carboxyl precursor / conjugatable)	3301-79-9	C105327	6-Carboxyfluorescein	≥95%	6-Carboxyfluorescein: commonly used for conjugation/probe construction.
General fluorescent dye (rhodamine)	989-38-8	R105623	Rhodamine 6G	Biological stain	High-brightness general dye; used for methodology, tracing, and fluorescence instrument checks/calibration.
General fluorescent dye (rhodamine)	81-88-9	R104961	Rhodamine B	Premium grade, ≥95% (HPLC)	General red dye; commonly used for tracing/staining/method development.
General fluorescent dye (coumarin)	38215-36-0	C100929	Coumarin 6	≥98% (HPLC)	Lipophilic green dye; often used for tracing in materials/carriers/membrane systems.
General fluorescent dye (red tracer)	60311-02-6	S131262	Sulforhodamine 101	≥98%	Common red tracer/staining dye (e.g., for materials/tissue tracing and other methodological use cases).
Probe scaffold (BODIPY core)	121207-31-6	D154725	[[(3,5-Dimethyl-1H-pyrrol-2-yl)(3,5-dimethyl-2H-pyrrol-2-ylidene)methyl]methane]difluoroborane	≥98% (HPLC)	BODIPY scaffold: narrow bands, high brightness, highly tunable; widely used for building probes/dyes.
Fluorescent derivatization reagent (amines)	605-65-2	D133513	Dansyl chloride (DNSCl)	Moligand™, ≥98% (HPLC)	Reacts with amines to form fluorescent derivatives; commonly used for HPLC/analytical derivatization.
Fluorescent derivatization reagent (NBD)	10199-89-0	C113202	4-Chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl)	≥98%	Common for derivatization of amines/thiols and for probe synthesis; a staple reagent in analytical chemistry.
Thiol labeling reagent (bimane)	71418-44-5	M131292	Monobromobimane	≥95%	Bimane-type thiol labeling/derivatization reagent; often used for thiol (e.g., GSH) analyses and probe construction.
NIR-I imaging dye	3599-32-4	I107931	Indocyanine green (ICG)	Moligand™, ≥75%	Classic near-infrared I dye for in vivo/tissue imaging and methodology validation (sensitive to instrumentation and solution conditions).
NIR-I imaging dye	207399-07-3	I302749	IR-780 iodide	Dye content ≥95%	Near-infrared cyanine dye; used for NIR imaging and system evaluation (targeting/enrichment depends on experimental system).
NIR-II imaging dye	155614-01-0	I478357	IR-1061	Dye content 80%	Common candidate for near-infrared II imaging systems; suitable for deep-tissue imaging methods and detector matching/validation.
NIR-II imaging dye (conjugatable)	_	N485341	NIR-II dye	Carboxyl-functionalized	NIR-II dye with a carboxyl group: convenient for conjugation to amines/carriers for targeting and probe construction (per product documentation).

Note: The items above are representative Aladdin products. For additional specifications and more products, please refer to the full product list at the end of the article or search the Aladdin website by product name/CAS.

Aladdin: https://www.aladdinsci.com/