Structural Characteristics, Color-Change Mechanisms, and Application Selection of Triphenylmethane Dye-Type Indicators

Triphenylmethane dye-type indicators are a class of organic color-change reagents based on triarylmethane or related lactone/quinoid structures. They are widely used in acid-base titration, non-aqueous titration, complexometric titration, protein assays, histological staining, microbiological staining, and other experimental systems. Their color changes are usually related to the conjugated system, ionization state, and structural ring-opening/ring-closing transformation of the molecule. Therefore, their application should be selected according to pH range, solvent system, sample background color, and detection endpoint.

Keywords: triphenylmethane dye; dye-type indicator; acid-base indicator; phthalein indicator; sulfonphthalein indicator; crystal violet; bromophenol blue; bromocresol green; phenol red; phenolphthalein; non-aqueous titration

1 Basic Characteristics of Triphenylmethane Dye-Type Indicators

1.1 Structural Basis

(1) Triarylmethane skeleton

Triphenylmethane dyes usually have a basic structure in which a central carbon atom is connected to three aromatic rings. The electron-donating, electron-withdrawing, and ionization properties of substituents on the aromatic rings directly affect the degree of conjugation, absorption wavelength, and color performance of the dye.

(2) Phthalein and sulfonphthalein structures

Most commonly used acid-base indicators are phthalein or sulfonphthalein derivatives, such as phenolphthalein, thymolphthalein, bromophenol blue, bromocresol green, bromocresol purple, bromothymol blue, phenol red, and cresol red. These compounds often undergo reversible transformations among lactone, quinoid, and ionic forms, which form the structural basis for their coloration and color change.

(3) Basic triphenylmethane dyes

Crystal violet, methyl violet, and malachite green belong to basic triphenylmethane dyes, which have intense colors and high molar absorptivity. In addition to staining applications, crystal violet is also commonly used in non-aqueous acid-base titration, especially as an endpoint indicator in non-aqueous systems such as glacial acetic acid.

1.2 Color-Change Mechanisms

(1) Protonation and deprotonation

The color change of acid-base indicators is essentially an equilibrium transformation among different protonation states. As pH changes, phenolic hydroxyl groups, sulfonic acid groups, or other ionizable groups in the molecule dissociate, causing changes in electron cloud distribution and the conjugated system, which leads to different colors.

(2) Ring-closing and ring-opening transformation

Phthalein indicators can exist mainly in a colorless closed-ring lactone form under acidic and neutral conditions. Under alkaline conditions, the structure opens and forms a quinoid conjugated system, producing a red or purplish-red color. Under excessively strong alkaline conditions, some indicators may further transform into other colorless or pale-colored structures.

(3) Changes in the conjugated system

The strong color of triphenylmethane dyes mainly originates from the large π-conjugated system formed by aromatic rings, the central carbon, and substituents. Substituents such as halogens, sulfonic acid groups, hydroxyl groups, and alkyl groups can alter electronic effects, enabling indicators to show specific color transitions within different pH ranges.

Table 1 Structural and Color-Change Basis of Triphenylmethane Dye-Type Indicators

Structural Type	Representative Compounds	Main Structural Features	Main Application Direction
Phthalein indicators	Phenolphthalein, thymolphthalein, o-cresolphthalein	Clear transformation between lactone and quinoid structures	Acid-base titration, complexometric titration, alkalinity judgment
Sulfonphthalein indicators	Bromophenol blue, bromocresol green, phenol red, bromothymol blue	Contain sulfonic acid groups, with good water solubility and pH response	Aqueous acid-base indication, culture medium pH monitoring
Basic triphenylmethane dyes	Crystal violet, methyl violet, malachite green	Cationic dyes with intense colors	Non-aqueous titration, histological/microbiological staining
Halogenated sulfonphthaleins	Bromocresol purple, bromochlorophenol blue, tetrabromophenolphthalein derivatives	Halogen substitution regulates absorption and color-change range	Fine pH interval indication, protein-binding analysis

2 Common Types and Representative Indicators

2.1 Phthalein Indicators

(1) Phenolphthalein

Phenolphthalein is one of the most commonly used acid-base indicators in the alkaline range. It is nearly colorless under acidic and neutral conditions and turns pink to red under weakly alkaline to alkaline conditions. It is commonly used for strong acid-strong base titration, weak acid-strong base titration, and alkalinity determination.

(2) Thymolphthalein

The color-change range of thymolphthalein is more alkaline than that of phenolphthalein. It is colorless under acidic to neutral conditions and blue under alkaline conditions. This indicator is suitable for endpoint judgment at higher pH values and has application value in certain alkalinity determinations and alkaline buffer system evaluations.

(3) o-Cresolphthalein

o-Cresolphthalein can be used as an acid-base indicator and is also often combined with metal ion complexation reactions for analytical systems involving calcium, magnesium, and related ions. The phenolic hydroxyl groups and aromatic ring substituents in its structure play important roles in color development and complexation response.

2.2 Sulfonphthalein Indicators

(1) Bromophenol blue

Bromophenol blue is an indicator for acidic ranges. It is commonly used for pH judgment from strongly acidic to weakly acidic ranges and can also be used as an electrophoresis tracking dye and in protein-binding-related experiments. Its yellow to blue-purple transition is distinct and suitable for endpoint observation in low-pH ranges.

(2) Bromocresol green

Bromocresol green is suitable for weakly acidic ranges and is commonly used in serum albumin detection, culture medium pH judgment, and acid-base titration. Its color changes from yellow to blue-green, and it is sensitive to sample background color and protein-binding status.

(3) Bromocresol purple

Bromocresol purple is suitable for weakly acidic to near-neutral ranges. It is commonly used for pH monitoring in microbial culture media, fermentation systems, and cell culture-related applications. Its yellow to purple change is suitable for judging acid production or alkalization processes.

(4) Bromothymol blue

The color-change range of bromothymol blue is close to neutral. It is commonly used in biological culture systems, carbonate balance studies, respiration experiments, and water quality pH monitoring. It appears yellow under acidic conditions, green near neutrality, and blue under alkaline conditions.

(5) Phenol red

Phenol red is commonly used for pH monitoring in cell culture media. It appears yellow under acidic conditions and red or purplish-red under neutral to weakly alkaline conditions. Its advantage is intuitive color change, but interpretation should be cautious in systems containing serum, phenolic substances, or strong background colors.

2.3 Basic Triphenylmethane Dyes

(1) Crystal violet

Crystal violet is a typical basic triphenylmethane dye and is commonly used in Gram staining, cell staining, and non-aqueous titration. As a non-aqueous titration indicator, crystal violet can undergo clear color changes in strongly acidic non-aqueous environments and is suitable for determining the content of weakly basic organic compounds.

(2) Methyl violet

Methyl violet is structurally close to crystal violet and is a representative of basic triphenylmethane dye mixtures. It is commonly used in staining and some acid-base indicator systems, but its color is significantly affected by composition, solvent, and acidity.

(3) Malachite green

Malachite green has an intense color and is commonly seen in staining and colorimetric systems. Because of its biological toxicity and environmental risk, experimental use should pay attention to application limitations, salt-form differences, waste liquid disposal, and alternative method selection.

Table 2 Application Characteristics of Common Triphenylmethane Dye-Type Indicators

Indicator Type	Representative Indicator	Typical Color Change	Main Application
Phthalein	Phenolphthalein	Colorless → pink/red	Acid-base titration, alkalinity determination
Phthalein	Thymolphthalein	Colorless → blue	Endpoint judgment in high-pH ranges
Phthalein	o-Cresolphthalein	Pale color → reddish-purple/purple	Acid-base indication, complexometric analysis
Sulfonphthalein	Bromophenol blue	Yellow → blue-purple	Acidic-range pH indication, electrophoresis tracking
Sulfonphthalein	Bromocresol green	Yellow → blue-green	Weakly acidic-range pH indication, albumin detection
Sulfonphthalein	Bromocresol purple	Yellow → purple	Culture medium pH monitoring, fermentation acidification judgment
Sulfonphthalein	Bromothymol blue	Yellow → green → blue	Near-neutral pH indication, water quality and culture systems
Sulfonphthalein	Phenol red	Yellow → red	Cell culture medium pH monitoring
Basic triphenylmethane dye	Crystal violet	Acidity-related change within a purple system	Non-aqueous titration, staining
Basic triphenylmethane dye	Methyl violet	Purple to yellow-green change	Non-aqueous titration, staining systems
Basic triphenylmethane dye	Malachite green	Green coloration	Staining, colorimetric analysis

3 Selection Logic in Acid-Base Indicator Applications

3.1 Selection by Color-Change Range

(1) Acidic range

For low-pH titration or acidic system monitoring, indicators such as bromophenol blue, bromochlorophenol blue, and methyl violet can be selected. These indicators are suitable for judging strong acid systems, weakly acidic buffer systems, or acid-generating processes, but they are not suitable for titration systems with clearly alkaline endpoints.

(2) Near-neutral range

Near-neutral systems are suitable for bromothymol blue, phenol red, or bromocresol purple. Cell culture media, microbial fermentation, water quality monitoring, and carbonate buffer systems often require visual judgment around pH 6–8.

(3) Alkaline range

Phenolphthalein and thymolphthalein are commonly used for alkaline endpoints. Phenolphthalein is suitable for most weak acid-strong base titrations, while thymolphthalein is suitable for higher-pH endpoints. If the pH change near the endpoint is not obvious, potentiometric titration or spectrophotometric detection should be prioritized instead of relying only on visual indicators.

3.2 Selection by Sample System

(1) Aqueous titration

Aqueous titration should prioritize indicators with good water solubility and a color-change range close to the stoichiometric point. Sulfonphthalein indicators usually contain sulfonic acid groups and are therefore easier to use in aqueous systems.

(2) Non-aqueous titration

Non-aqueous titration is commonly used for weakly basic organic compounds, pharmaceutical raw materials, and amine compounds. Crystal violet, methyl violet, and other basic triphenylmethane dyes can be used for endpoint indication in glacial acetic acid and perchloric acid-glacial acetic acid systems.

(3) Biological and culture systems

In biological culture systems, the effects of indicators on cells or microorganisms should be considered. Phenol red, bromocresol purple, and bromothymol blue are often used as pH indicators in culture media, but the dye concentration should not be too high to avoid affecting culture status or reading interpretation.

3.3 Selection by Detection Method

(1) Visual endpoint

Visual endpoints are suitable for systems with clear color transitions, light sample background color, and large titration curve jumps. If the sample is dark, turbid, or contains precipitates, relying solely on color changes should be avoided.

(2) Spectrophotometric detection

Some triphenylmethane dyes have high molar absorptivity and can be quantitatively analyzed through absorbance changes. Such methods are suitable for experimental systems where endpoints are difficult to observe visually, sample volumes are small, or higher reproducibility is required.

(3) Color cards or automated readings

Culture systems, environmental water samples, and micro-detection scenarios can use color cards, microplate readings, or image analysis. In these cases, light source, path length, sample volume, and reading time should be standardized to reduce subjective color judgment errors.

Table 3 Indicator Selection for Different pH Ranges

Application Range	Suitable Indicators	Main Color Change	Applicable Scenarios
Strong acid to weak acid	Bromophenol blue, bromochlorophenol blue	Yellow → blue-purple	Acidic titration, acidification process judgment
Weak acid to near neutral	Bromocresol green, bromocresol purple	Yellow → blue-green/purple	Fermentation systems, culture media, weakly acidic buffers
Near neutral	Bromothymol blue, phenol red	Yellow → green/red → blue/purplish-red	Water quality, cell culture, carbonate balance
Weakly alkaline to alkaline	Phenolphthalein	Colorless → pink/red	Weak acid-strong base titration, alkalinity determination
Stronger alkaline range	Thymolphthalein	Colorless → blue	High-pH endpoint judgment
Non-aqueous strong acid system	Crystal violet, methyl violet	Clear color change within a purple system	Non-aqueous titration of weakly basic organic compounds

4 Typical Application Scenarios

4.1 Acid-Base Titration

(1) Weak acid-strong base titration

The stoichiometric point of weak acid-strong base titration is usually alkaline, making phenolphthalein a common choice. A stable pale pink color near the endpoint usually indicates that the titration is close to completion. If the sample contains buffering components or has a deep color, potentiometric verification should be used.

(2) Strong acid-weak base titration

The endpoint of strong acid-weak base titration is usually acidic, so an acidic-range indicator such as bromophenol blue, bromocresol green, or a methyl violet-related system should be selected. If phenolphthalein is used, endpoint deviation may occur because its color-change range does not match the stoichiometric point.

(3) Polyprotic acid-base systems

Polyprotic acids, carbonates, phosphates, and mixed alkali systems may show multiple titration jumps. In such cases, a multi-indicator method can be used, such as phenolphthalein for the first endpoint and methyl orange or another low-pH indicator for the second endpoint. If triphenylmethane dyes are used, the meaning of the corresponding endpoint should be clearly defined.

4.2 Non-Aqueous Titration

(1) Determination of weakly basic organic compounds

Many amines, nitrogen-containing heterocyclic compounds, and weakly basic drugs do not show strong basicity in water and are suitable for non-aqueous titration. Crystal violet can indicate endpoints in glacial acetic acid-perchloric acid systems, with relatively sensitive color changes.

(2) Solvent effects

In non-aqueous systems, the indicator color-change range cannot be simply matched to aqueous pH. Solvent acidity/basicity, dielectric constant, hydrogen bonding, and ionization ability can all affect dye color. Therefore, indicators should be selected according to specific method conditions.

(3) Endpoint confirmation

Color changes in non-aqueous titration may be affected by the sample background color and solvent system. For dark-colored samples, weak jump systems, or high-precision detection, potentiometric titration is recommended for endpoint confirmation.

4.3 Biological Culture and Microbiological Detection

(1) pH monitoring in cell culture media

Phenol red is commonly used as a pH indicator in cell culture media. The medium turns more yellow when acidified, and becomes deeper red or purplish-red as pH increases. It can quickly reflect CO₂ balance, metabolic acid production, and contamination risk, but it should not replace accurate pH measurement with a pH meter.

(2) Fermentation acid production judgment

Bromocresol purple, bromothymol blue, and bromocresol green can be used to judge microbial acid or alkali production. In fermentation systems, carbon source consumption, metabolite accumulation, and buffer capacity all affect color changes.

(3) Selective culture media

Some selective or differential media use pH indicators to display acidification or alkalization zones around colonies. In such systems, indicator concentration, incubation time, and substrate composition can affect result interpretation.

4.4 Staining and Colorimetric Analysis

(1) Gram staining

Crystal violet is the primary stain in Gram staining. It forms a complex with iodine solution and shows differential retention due to differences in cell wall structure. In this context, the role of crystal violet is not pH indication, but staining and cellular structural differentiation.

(2) Protein-binding colorimetry

Bromocresol green can bind to albumin and produce spectral changes, and is commonly used for albumin content determination. This application differs from traditional pH indication; the core mechanism is a change in absorption characteristics caused by dye-protein binding.

(3) Electrophoresis tracking

Bromophenol blue is commonly used as a tracking dye in electrophoresis loading buffer. Its migration speed and clear color are suitable for monitoring the electrophoresis front, but it does not represent the migration position of target molecules in the sample.

Table 4 Application Scenarios of Triphenylmethane Dye-Type Indicators

Application Scenario	Common Indicators	Mode of Action	Main Notes
Aqueous acid-base titration	Phenolphthalein, bromothymol blue, bromocresol green	Color changes according to pH jump	Color-change range should be close to the stoichiometric point
Non-aqueous titration	Crystal violet, methyl violet	Color change under non-aqueous acid-base conditions	Aqueous pH color-change ranges cannot be directly applied
Cell culture	Phenol red	Culture medium pH indication	Affected by CO₂ concentration, metabolic acids, and serum
Fermentation detection	Bromocresol purple, bromothymol blue	Acid/alkali production indication	Should be interpreted together with the buffering capacity of the medium
Protein assay	Bromocresol green, bromophenol blue	Dye-protein binding color development	Protein type and interfering substances can affect results
Gram staining	Crystal violet	Cell structure staining	Different from pH indicator use
Electrophoresis tracking	Bromophenol blue	Migration front tracking	Does not represent the actual position of target molecules

5 Product and Reagent Selection

Table 5 Selection of Common Triphenylmethane Dye-Type Indicators

Product Type	Product Name	CAS No.	Typical Use	Selection Points
Phthalein acid-base indicator	Phenolphthalein	77-09-8	Weak acid-strong base titration, alkalinity determination	Suitable for alkaline endpoints; nearly colorless under acidic and neutral conditions
Phthalein acid-base indicator	Thymolphthalein	125-20-2	Endpoint judgment in high-pH ranges	Color-change interval is more alkaline than phenolphthalein
Phthalein complexometric/indicator reagent	o-Cresolphthalein	596-27-0	Acid-base indication, complexometric analysis	Can be used in specific metal ion analysis systems
Sulfonphthalein acid-base indicator	Bromophenol blue	115-39-9	Acidic-range pH indication, electrophoresis tracking	Suitable for low-pH ranges with distinct color change
Sulfonphthalein acid-base indicator	Bromocresol green	76-60-8	Weakly acidic pH indication, albumin determination	Can bind proteins; interference must be controlled in detection systems
Sulfonphthalein acid-base indicator	Bromocresol purple	115-40-2	Culture medium pH indication, fermentation acid production judgment	Suitable for observing weakly acidic to near-neutral changes
Sulfonphthalein acid-base indicator	Bromothymol blue	76-59-5	Near-neutral pH indication, water quality and culture systems	Can show continuous yellow-green-blue changes
Sulfonphthalein acid-base indicator	Phenol red	143-74-8	Cell culture medium pH indication	Significantly affected by CO₂ balance and cell metabolism
Sulfonphthalein acid-base indicator	Cresol red	1733-12-6	pH indication, culture system analysis	Suitable for specific weakly acidic to weakly alkaline ranges
Sulfonphthalein acid-base indicator	Chlorophenol red	4430-20-0	pH indication, culture system analysis	Suitable for weakly acidic to near-neutral ranges
Basic triphenylmethane dye	Crystal violet	548-62-9	Non-aqueous titration, Gram staining	Strong color; suitable for endpoint observation in non-aqueous strong acid systems
Basic triphenylmethane dye	Methyl violet	8004-87-3	Non-aqueous titration, tissue staining	Often a mixed dye; composition and batch differences should be considered
Basic triphenylmethane dye	Malachite green	569-64-2	Staining, colorimetric analysis	Salt form, purity, toxicity, and waste disposal should be considered
Basic triphenylmethane dye	Brilliant green	633-03-4	Staining, antibacterial selective systems	Mostly used in staining and selective culture systems
Basic triphenylmethane dye	Basic fuchsin	632-99-5	Tissue staining, microbiological staining	Prominent staining use; composition differences should be noted
Acidic triarylmethane dye	Acid fuchsin	3244-88-0	Tissue staining, counterstaining systems	An acidic triarylmethane dye; mainly used for staining
Protein dye / tracking dye	Coomassie Brilliant Blue G-250	6104-58-1	Bradford protein assay	Triarylmethane dye; color development depends on dye-protein binding
Protein dye / tracking dye	Coomassie Brilliant Blue R-250	6104-59-2	Protein gel staining	Suitable for post-electrophoresis protein staining analysis

Table 6 Selection of Triphenylmethane Dye-Based Indicator Preparations and Solution Products

Cat. No.	Product Name	Specification/Concentration	Corresponding Category	Application Notes
D196473	Diphenylcarbazone-bromophene blue mixed indicator		Mixed indicator containing bromophenol blue	Can be used as a mixed endpoint indicator system containing a sulfonephthalein dye
N299244	α-naphthol phthalide indicator	0.1% in 50% Ethanol	Phthalein acid-base indicator	Suitable for acid-base indication in the alkaline range
X299243	Xylenol Blue Indicator	0.05%	Sulfonephthalein acid-base indicator	Suitable for pH indication and colorimetric interpretation
X299389	Xylenol Orange indicator	indicator	Sulfonephthalein/complexometric indicator	Can be used in metal complexometric analysis systems
M1520393	Malachite Green Indicator	BioReagent,Suitable for microbiology,Biological Stain,for microscopy	Basic triphenylmethane dye	Suitable for microbial staining and microscopic observation
B406276	Bromocresol Green - Methyl Red Solution [Mixed Indicator for Neutralization Titration]		Mixed indicator containing bromocresol green	Suitable for endpoint indication in neutralization titration
B299161	Bromophenol red indicator	0.4%	Sulfonephthalein acid-base indicator	Suitable for pH indication in the acidic to weakly acidic range
R299257	Rosolic acid Indicator	0.5% in 50% Ethanol	Triarylmethane acid-base indicator	Suitable for colorimetric judgment in the alkaline range
M196491	Methyl Orange-Xylene Cyanol Mixed Indicator	0.1% ethanol solution	Mixed indicator containing a sulfonephthalein dye	Can serve as a supplementary composite pH color-change system
C299259	Chromeazurol S indicator	0.02%	Triarylmethane complexometric chromogenic reagent	Suitable for metal ion color development and spectrophotometric analysis
M196490	m-Cresol purple indicator	0.4%	Sulfonephthalein acid-base indicator	Suitable for pH indication in the weakly acidic to near-neutral range
M196488	m-Cresol purple indicator	0.04%(w/v) in water	Sulfonephthalein acid-base indicator	Suitable for low-concentration pH indication in aqueous systems
M196489	m-Cresol purple indicator	0.1%(w/v) in water	Sulfonephthalein acid-base indicator	Suitable for pH interpretation in culture systems or aqueous systems

6 Method Establishment and Quality Control

6.1 Indicator Concentration Control

(1) Concentration too low

If the indicator concentration is too low, the endpoint color may be unclear, especially in systems with dark or turbid sample backgrounds, making delayed endpoint judgment more likely. In such cases, the concentration can be appropriately increased or instrumental readings can be used.

(2) Concentration too high

Excessively high concentration increases background color and may consume a small amount of titrant or affect system equilibrium. For microtitration and low-concentration samples, the amount of indicator added should be strictly controlled.

(3) Stability of stock solution

Most indicators are prepared as stock solutions in ethanol, water, or mixed solvents. Long-term storage may cause photodegradation, precipitation, or solvent evaporation. Suitability for continued use should be judged according to color, clarity, and blank test results.

6.2 Control of System Interference

(1) Sample color

Dark-colored samples can mask endpoint color changes. For stained samples, plant extracts, pharmaceutical intermediates, or fermentation broths, potentiometric titration, spectrophotometry, or blank correction should be prioritized.

(2) Proteins and surfactants

Some triphenylmethane dyes can bind proteins, surfactants, or polymers, causing changes in color and absorption peaks. When used for pH indication, binding-induced coloration should not be mistaken for acid-base color change.

(3) Solvent and ionic strength

Indicator color change is affected by solvent polarity, ionic strength, and temperature. In non-aqueous systems, high-salt systems, and systems with a high proportion of organic solvent, endpoints should be verified using standard samples rather than judged directly according to aqueous-system experience.

6.3 Endpoint Interpretation Control

(1) Blank test

Blank tests can exclude the influence of solvents, reagents, and the indicator itself on the endpoint. Blank correction is especially important for microanalysis and weak-color endpoints.

(2) Standard sample validation

During method establishment, standard substances or samples with known concentrations should be used to verify the consistency between the indicator endpoint and the theoretical endpoint. If significant deviation occurs, the indicator should be adjusted or an instrumental endpoint method should be used.

(3) Batch-to-batch consistency

Dye-type indicators are sensitive to purity, isomer composition, and moisture. When reagents from different batches are used, standard titration, absorption spectra, or control samples should be used to confirm consistent color performance.

Table 7 Common Problems and Optimization Directions for Triphenylmethane Dye-Type Indicators

Problem	Possible Cause	Impact on Results	Optimization Direction
Endpoint color is unclear	Low indicator concentration, deep sample background color	Delayed or unstable endpoint judgment	Add controls and use instrumental readings
Background color is too deep	Excessive indicator or dye adsorption by sample	Premature endpoint or tailing	Reduce indicator amount and set blank control
Color-change range does not match	Indicator pH range inconsistent with stoichiometric point	Increased systematic error	Re-select indicator or use potentiometric titration
Abnormal color in non-aqueous system	Solvent effect changes ionization state	Cannot interpret according to aqueous-system experience	Verify endpoint according to non-aqueous titration method
Biased readings in protein samples	Dye-protein binding	Color change does not only come from pH	Distinguish pH indication from binding color development
Stock solution color changes	Light exposure, oxidation, solvent evaporation, or degradation	Indicator failure or reduced sensitivity	Store away from light and verify regularly

The value of triphenylmethane dye-type indicators lies in their sensitive response to acid-base status, solvent environment, and molecular binding states through their structural characteristics. Phthalein and sulfonphthalein indicators are more suitable for acid-base indication and pH monitoring in biological systems. Crystal violet and methyl violet are more suitable for non-aqueous titration and staining systems. Triarylmethane dyes such as Coomassie Brilliant Blue are more commonly used for protein color development.

For more related articles, please see below:

[1] Principles and methods of smear staining, microbiological staining, and fundamental dye systems

[2] Biological Stain