Application Guide to Super Fluor 680 / 750 Near-Infrared Dyes for In Vivo Small-Animal Fluorescence Imaging

In cell imaging, flow cytometry, and tissue sections, we are most familiar with “visible” dyes such as 488, 555, and 647. However, once we move to whole-body small-animal imaging (in vivo), the situation becomes quite different: we need to penetrate skin and tissues and visualize whole-body distribution. In this context, the 680 / 750 nm near-infrared channels offer clear advantages.

Super Fluor 680 / 750 is a domestically developed series of near-infrared dyes that are spectrally equivalent to the Alexa Fluor 680 / 750 channels. They are suitable for labeling antibodies, small-molecule drugs, and proteins, and can be used for in vivo fluorescence imaging in small animals such as mice and nude mice.

This article is organized around a single practical question: “If I have Super Fluor 680 / 750 in hand and want to perform in vivo fluorescence imaging in small animals, what key points should I pay particular attention to?”

Why Choose the 680 / 750 Near-Infrared Channels?

1. Close to the “tissue optical window”: low background and deep penetration

Within the 650–900 nm near-infrared window (NIR-I), tissue scattering and absorption of light are markedly reduced compared with the visible range, and autofluorescence is greatly suppressed. As a result, both signal-to-noise ratio and effective penetration depth are improved, making this window highly suitable for whole-body small-animal imaging.

(1) Super Fluor 680: excitation/emission approximately 680 / 702 nm, with spectra similar to Alexa Fluor 680 and Cy5.5.

(2) Super Fluor 750: excitation/emission approximately 750 / 775 nm, with spectra similar to Alexa Fluor 750 and Cy7.

Both channels fall within the near-infrared window, where tissue autofluorescence is low and the background is clean, making them particularly suitable for imaging tumors, vasculature, and deep tissues.

2. Compatible with common imaging systems and laser lines

Most small-animal imaging systems support Cy5.5 / Cy7 or Alexa Fluor 680 / 750 channels, with typical excitation/emission filter sets as follows:

(1) 680 channel: Ex ~ 670–690 nm, Em ~ 700–720 nm

(2) 750 channel: Ex ~ 730–770 nm, Em ~ 780–800 nm (or 790 nm long-pass)

The spectra of Super Fluor 680 / 750 substantially overlap with these dyes, so they can be directly assigned to existing Cy5.5 / Cy7 channels without the need to customize filters specifically for these dyes.

3. Broad pH tolerance, high brightness, and suitable for in vivo use

In general, the Super Fluor series features:

(1) Fluorescence that is essentially stable in the pH 4–10 range;

(2) High molar extinction coefficients (ε ~ 1.8×10⁵–2.4×10⁵ L·mol⁻¹·cm⁻¹), providing strong brightness;

(3) Good photostability, suitable for multi-time-point imaging;

(4) Supplied as NHS esters, allowing convenient coupling to primary amines on antibodies, proteins, peptides, polysaccharides, and small-molecule drugs to generate “target-specific probes”.

Common Probe Formats: More Than Just “Injecting Dye into the Mouse”

In in vivo imaging, Super Fluor 680 / 750 can be carried by different “vehicles”:

1. Free dye (unconjugated)

(1) Water-soluble near-infrared dyes are dissolved directly in buffer and then injected;

(2) Advantages: very simple to handle and useful for verifying instrument channels;

(3) Features: for hydrophilic small-molecule Super Fluor dyes, clearance is typically rapid via the kidneys, with transient accumulation in the bladder. They are often used as fast tracers for renal clearance or vascular angiography.

2. Labeled BSA, serum albumin, and other “blood-pool probes”

(1) For example, BSA–Alexa Fluor 680/750 contrast agents are commonly used in the literature for vascular and blood-pool imaging;

(2) Super Fluor 680 / 750 can likewise be used to label BSA as a “long-circulating” vascular contrast agent.

3. Labeled antibodies, receptor ligands, or small-molecule drugs

(1) The most common approach is to label tumor-targeting antibodies or peptides with Super Fluor 750 for tumor imaging and monitoring the distribution of targeted drugs;

(2) The in vivo distribution of such probes is jointly determined by target expression, pharmacokinetics, and probe size. The signal typically evolves over a time window of several hours to several days.

In practical applications, the 680 channel is often used as a vascular/background reference, while the 750 channel is used for the targeting probe, enabling dual-channel imaging and comparison.

General Workflow for Small-Animal Experiments: From Administration to Imaging

Below is a simplified example workflow using “Super Fluor 750-labeled antibody for tumor imaging”. Detailed procedures for anesthesia, dosing, and other steps must follow the animal ethics regulations of each institution. The steps here are provided only as a conceptual guide.

1. Animal preparation

(a) It is recommended to use nude mice or hairless mice: less fur, less light scattering, and better imaging quality;

(b) Typically, male or female nude mice weighing 18–25 g;

(c) Animals may be given food and water ad libitum before experiments; if fasting is required, follow the guidance from the animal facility.

2. Probe preparation and injection

(1) Probe preparation

(a) Super Fluor 680 / 750 is usually supplied as a powder and should be stored at −20 ℃ in a dry, light-protected environment;

(b) For labeled antibodies or proteins, it is recommended to:

(i) Dissolve them in normal saline or PBS. If necessary, add a small amount of organic solvent within a tolerable range (such as a small amount of ethanol, PEG, or a small amount of DMSO);

(ii) When needed, a small amount of DMSO or other organic solvents may be added to aid dissolution. The final DMSO concentration is recommended to be kept below 10% (and below 2% for nude or frail animals). The specific upper limit must strictly follow institutional SOPs and ethical requirements to avoid intravenous toxicity risks associated with high DMSO levels.

(2) Route and volume of injection

(a) In small-animal near-infrared imaging, the most common route is tail-vein injection;

(b) A typical single injection volume is about 5–10 mL/kg body weight (approximately 100–200 μL for a 20 g mouse); the specific upper limit must follow the guidance from the animal facility;

(c) The exact dose (mg/kg) should be determined based on:

(i) Probe toxicity;

(ii) Expected level of targeting;

(iii) Instrument sensitivity: a small pilot study is usually performed first with 2–3 dose levels.

3. Anesthesia and imaging time points

(a) Anesthesia: inhaled isoflurane or an injectable regimen recommended by the institution can be used. It is not recommended to copy mg/kg doses directly from other studies. Always follow animal ethics and SOPs.

(b) Common imaging time points:

(i) Free dyes or vascular contrast agents: within a few minutes after injection, the signal quickly distributes throughout the body, then rapidly accumulates in the kidneys/bladder. Imaging can be performed at 0, 5, 15, 30, and 60 minutes, etc.;

(ii) Antibodies or targeting probes: typically require several hours or even 24–48 hours to accumulate at the target. Imaging can be performed at 1, 4, 8, and 24 hours, or at even later time points.

During imaging, place the mouse in a prone or supine position on the imaging stage, maintain stable body temperature and respiration, and avoid positional changes that could introduce differences in signal.

Imaging System and Parameter Settings: How to “Use the Channels Correctly”

Although the user interfaces of different small-animal imaging systems vary by brand, several core parameters are essentially the same.

1. Channel settings (example: Super Fluor 750 / Cy7 channel)

Using common Cy7 / Alexa Fluor 750 imaging parameters as a reference:

(a) Excitation filter: 700–770 nm band-pass (or a central wavelength of ~740–750 nm)

(b) Emission filter: ~790 nm long-pass or 780–820 nm band-pass

(c) If the 680 channel is used simultaneously:

(i) Ex ~ 660–690 nm

(ii) Em ~ 700–720 nm

When choosing parameters, simply identify the preset channels corresponding to Alexa Fluor 680 / 750 or Cy5.5 / Cy7 and map the Super Fluor 680 / 750 probes onto those channels.

2. Exposure time and sensitivity

(a) Exposure time: typically ranges from a few hundred milliseconds to several seconds. Start with a short exposure for preview to avoid saturation in bright regions, then extend the exposure time as needed;

(b) Gain/sensitivity: increase as much as possible without introducing obvious noise;

(c) For multi-time-point imaging or multi-animal comparisons, keep imaging parameters as consistent as possible to facilitate subsequent quantitative analysis.

Signal Dynamics and Data Interpretation: What Will You See?

Based on publicly available data on Super Fluor 680 / 750 and similar Alexa Fluor dyes, the following patterns are typically observed:

1. Free dyes / small-molecule probes

(a) Within a few minutes after injection, near-infrared signals appear throughout the systemic blood pool and major organs;

(b) Over time, the signal gradually fades from the whole body and concentrates in the kidney and bladder, showing a characteristic renal-clearance profile;

(c) These probes can be used to assess renal function, blood perfusion, and related parameters.

2. BSA or other macromolecular “blood-pool agents”

(a) Signals remain in blood vessels and high-blood-flow tissues (heart, lungs, tumor vasculature, etc.) for an extended period;

(b) They are suitable for vascular tracing and for evaluating tumor vascular leakage (EPR effect), among other applications.

3. Super Fluor 750-labeled antibodies/targeting molecules

(a) At early time points, the signal is dominated by the blood-pool component;

(b) Over several hours to 1–2 days, a progressively enhanced signal appears in tumors or tissues expressing the target molecule;

(c) Signals in non-target tissues gradually decline, resulting in an increased target-to-non-target ratio.

Frequently Asked Questions (FAQ)

1) What types of mice are most suitable for in vivo fluorescence imaging?

Nude mice or hairless mice are preferred. Fur causes significant light scattering and blockage, and it especially affects skin reflectance in the near-infrared range.

2) How should I choose injection volume and solvent?

(a) For mice of around 20 g, the single tail-vein injection volume is typically kept in the hundred-microliter range (for example, 100–200 μL). The exact upper limit should follow the regulations of your animal facility;

(b) Use normal saline or PBS as the primary solvent whenever possible, and keep the volume fraction of organic solvents (such as DMSO) as low as you reasonably can;

(c) If the probe is poorly soluble, it can first be dissolved in a small amount of DMSO and then diluted with buffer to an acceptable final proportion.

3) What DOL (F/P ratio) should I aim for when labeling antibodies?

(a) For antibodies labeled with NIR dyes, many empirical reports recommend a DOL in the range of approximately 2–5. For in vivo imaging, a more conservative range of 1.5–3 is often preferred to balance brightness with acceptable in vivo behavior;

(b) If the DOL is too low, the signal will be too weak; if it is too high, it may lead to:

(i) Reduced antibody affinity;

(ii) Increased nonspecific binding;

(iii) Dye self-quenching and reduced fluorescence.

Therefore, it is advisable to test 2–3 DOL conditions spanning a reasonably broad range and then select the one that offers the best signal-to-noise ratio.

4) What happens if free dye is not removed thoroughly?

(a) You will see a high whole-body background and very strong bladder signals at early imaging time points;

(b) This can easily be misinterpreted as “the whole animal is glowing”, whereas in reality most of the signal comes from unbound dye;

(c) It is recommended to carefully remove free dye using G-25 / P-30 desalting columns or dialysis, repeating the process if necessary.

5) Can Super Fluor 680 / 750 be used together with bioluminescence imaging?

Yes. Many systems support dual-modality fluorescence + bioluminescence imaging. For example, Super Fluor 750-labeled probes can be combined with the D-luciferin / luciferase system, with different channels used to visualize structural versus functional signals.

Safety and Compliance Notes

(a) Super Fluor 680 / 750 and their labeled probes are for research use only and must not be used in humans or for clinical diagnosis or treatment;

(b) All animal experiments must be approved by your institutional animal ethics committee. Anesthesia, administration, and euthanasia procedures must follow the institution’s official SOPs;

(c) When handling dyes and organic solvents, wear gloves and safety goggles to avoid contact with skin and eyes;

(d) Waste liquids and animal carcasses must be disposed of as biological hazardous waste in accordance with relevant regulations.

Aladdin Near-Infrared Fluorescent Dyes and D-Luciferin / Luciferase Bioluminescence System

Category	Product name	Aladdin Cat. No.	Grade or Purity	CAS	Main function / Application scenario
NIR dye	Super Fluor 680, SE (NHS Ester)	S266352	≥90%	–	Near-infrared fluorescent dye, Ex ≈ 680 nm / Em ≈ 702 nm, ε ≈ 1.84×10⁵; used to label antibodies, proteins, and small molecules; suitable for small-animal NIR imaging and as a substitute for Cy5.5 / AF680.
NIR dye	Super Fluor 750, SE (NHS Ester)	S266401	Ex: 752 nm; Em: 776 nm; ≥95% (HPLC)	–	Near-infrared dye, Ex ≈ 752 nm / Em ≈ 776 nm, with spectra similar to Alexa Fluor 750 / Cy7; stable over pH 4–10; suitable for deep-tissue imaging and in vivo tracking in small animals.
NIR reference dye	Alexa Fluor 680 NHS ester	A1452612	–	407628-15-3	Classical near-infrared dye, Ex/Em ≈ 679/702 nm; used as a control or “equivalent channel” for Super Fluor 680, for labeling antibodies/proteins in both in vivo and in vitro imaging.
NIR reference dye	Aladdin Fluor 790 NHS Ester	A638848	Ex: 784 nm; Em: 814 nm	–	For small-animal imaging systems equipped with a 780/800 nm NIR channel, Aladdin offers Aladdin Fluor 790 NHS Ester (A638848), Ex/Em ~ 784/814 nm. Its spectra are similar to Alexa Fluor 790 and IRDye 800, enabling construction of longer-wavelength NIR channels to further reduce tissue autofluorescence, and can be combined with Super Fluor 680 / 750 for multi-channel NIR imaging.
NIR reference dye	Super Fluor 647, SE (NHS Ester)	S266349	Ex: 650 nm; Em: 671 nm; ≥95% (HPLC)	–	Fluorescent dye in the far-red / near-infrared border region; Ex ≈ 651 nm / Em ≈ 668 nm, with spectra similar to Alexa Fluor 647 and Cy5. Used to label antibodies, proteins, and nucleic acids; suitable for flow cytometry, confocal imaging, and as a “transition channel” preceding Super Fluor 680 / 750.
NIR comparator dye	Cyanine5.5 NHS ester	C276343	≥95%	2375105-86-3	Far-red / near-infrared fluorescent dye, suitable for imaging and signal detection under strong background autofluorescence. Serves as a traditional comparator for Super Fluor 680 / AF680 to demonstrate “Super Fluor 680 as a replacement for Cy5.5”.
NIR comparator dye	Cyanine7 NHS ester	C171360	≥95%	2408482-09-5	Classical near-infrared dye with spectra similar to Alexa Fluor 750; suitable for in vivo imaging and for comparison with Super Fluor 750 / AF750.
Bioluminescent substrate	D-Luciferin potassium salt	D1375449	Molecular biology grade ≥99.9% (HPLC)	115144-35-9	Natural substrate of firefly luciferase; forms a luminescent system with firefly luciferase; used for in vivo small-animal bioluminescence imaging, reporter gene assays, and ATP measurement.
Bioluminescent substrate	D-Luciferin, Sodium Salt	D1375459	Molecular biology grade ≥99.9% (HPLC)	103404-75-7	Highly water-soluble; suitable for in vivo injection, in vivo mouse bioluminescence imaging, and luc reporter gene experiments.
Bioluminescent substrate	D-Luciferin	D115508	≥98%	2591-17-5	Classical D-luciferin reagent for in vitro luc reporter assays, cell viability assays, and ATP-based fluorescence hygiene monitoring. Can be prepared as a high-concentration stock solution prior to use.
Bioluminescent substrate	Coelenterazine	C131248	≥94%	55779-48-1	Classical coelenterazine-type bioluminescent substrate; the substrate for apoaequorin and Renilla luciferase. Used for Ca²⁺ imaging, small-animal bioluminescence imaging, and as the luminescent donor in BRET (bioluminescence resonance energy transfer) systems; also serves as a chemiluminescent probe for superoxide anion and peroxynitrite.

Aladdin: https://www.aladdinsci.com/