Colorimetric pH Indicator Research Articles

A commercially available dye as a highly versatile colorimetric fluoride sensor

Reported herein is the successful use of the commercially available organic dye bromocresol green (compound 1) for high-performing and practical fluoride detection. This dye responds to fluoride anion with high selectivity (virtually no response to other halide anions), excellent sensitivity (limits of detection as low as 0.22 ppm) and rapid response times, and maintains functionality when it is adsorbed on filter paper. Mechanistic studies determined that the fluoride-induced colorimetric changes were due to intermolecular hydrogen bonding between compound 1 and fluoride. Finally, the broad applicability of this sensor was demonstrated through the colorimetric response of compound 1 – functionalized paper to fluoride in commercial mouthwash. These findings underscore compound 1’s potential as a practical and commercially viable fluoride sensor, in addition to compound 1’s better-known role as a colorimetric pH indicator.

Use of Fruit Waste as Natural Dyes in pH-Sensitive Colorimetric Sensors for Tilapia Fillets Quality Decline

Graphical Abstract Highlight Research 1. The use of dragon fruit peel, mangosteen peel and onion peel waste as natural dyes in colorimetric sensors was analyzed in this study. 2. Natural dyes are added to bioplastics with kappa carrageenan polymer, a mixture of corn starch and kappa carrageenan, and corn starch to determine the characteristics of the best bioplastic to be used as a colorimetry sensor. 3. The quality of the fish fillet compared to the color changes in colorimetry sensor was analysed in this study. 4. Mixture of kappa carrageenan and corn starch as bioplastic with casting method was analyzed in this study. Abstract Tilapia fillet aimed to prolonging shelf life, may still experience quality deterioration posing food safety risks. Colorimetric pH indicators offer a simple and affordable solution to the food industry to evaluating fish spoilage. Natural dyes reduce potential health risks associated with synthetic dyes. Anthocyanin sources haven’t been explored like dragon fruit rind, mangosteen rind, and red onion skin serve as real time quality and safety assessment tools for consumers. This study explores the potential of anthocyanin extracted from dragon fruit rind, mangosteen rind, and red onion skin as colorimetric sensors for evaluating the quality and safety of tilapia fillets. The anthocyanin-based sensors developed using kappa carrageenan and corn starch polymers to achieve sustainability fisheries program and were characterized according to the Japanese Industrial Standard for bioplastics. The results show that anthocyanin from dragon fruit skin exhibited the best color change in response to pH changes in the tilapia fillet, indicating its potential as a reliable indicator of spoilage. This research highlights the feasibility of using natural dyes as colorimetric sensors, reducing the risk of health hazards associated with synthetic dyes. This study also shows that different polymers give different characteristic of bioplastic. Carrageenan bioplastic shows best thickness values of 0,118 mm; Carrageenan and corn starch bioplastics shows best tensile strength values of 20,62 MPa; Carrageenan bioplastic shows best elongation values of 254%; and All polymers shows the same biodegradation rate values of 14,29%. Further studies are needed to explore other natural dyes and optimize the polymers for optimal bioplastic characteristics.

Sodium alginate-based indicator film with enhanced physicochemical properties induced by cellulose nanocrystals and monitor the freshness of chilled meat

Intelligent indicator films with colorimetric pH indicator properties were developed, incorporating black soybean seed coat anthocyanin (BA), cellulose nanocrystals (CNC), and sodium alginate (SA) to monitor meat freshness. The effect of different CNC additions on the microstructure, water barrier properties of the films, and BA release kinetics were comprehensively investigated. The results showed that with the increasement of CNC addition, the mechanical properties of SA/BA/CNC films were improved, the water contact angle significantly increased from 51.6° to 69°. Moreover, water solubility, vapor adsorption, and permeability significantly decreased, indicating enhanced water barrier properties. The release kinetic results showed that BA was released rapidly within 72 h and slowly thereafter, and its release process was described by Fick's model. Films with 7 % and 10 % CNC had lower BA diffusion coefficients. Their diffusions were formulated as linear regression equations (y = nx + a), where R2 was >0.80 and n was <0.50. Structural characterization showed that CNC immobilized BA mainly through hydrogen bonding, forming compact network microstructures with SA and BA. Meat freshness monitoring results showed that the film containing 7 % CNC showed visible color changes with increasing total volatile basic nitrogen and pH, along with low BA release, high water barrier and mechanical properties. Therefore, CNC has great potential for improving the physicochemical properties of indicator films, and the intelligent colorimetric indicator film could be applied to various food product.

Application of On-Pack pH Indicators to Monitor Freshness of Modified Atmospheric Packaged Raw Beef

Abstract Three on-pack visual indicators for the real-time monitoring of raw beef steaks in a modified atmospheric packaging (MAP) environment were developed. The indicators were prepared by spray deposition of a nanocellulose (NC) suspension (1.5 wt. %) with the desired concentration of the pH-sensitive indicators, either red cabbage (RC) extract, black carrot (BC) extract, or chlorophenol red (CPR). The responsiveness of the colorimetric pH indicators, assessed visually and by CIE-Lab quantitative analysis, to the freshness of raw beef steaks stored under MAP conditions at 4 °C or 20 °C, was analysed over 7 days. All indicators gave a colour change for beef steak stored at 4 °C for 7 days that was noticeable with the naked eye and had a ΔE value &amp;gt;12. The sensitivity of the RC pH indicator was superior to the BC and CPR pH indicators. A study linking total microbial count (aerobic + Escherichia coli + coliform) and the quantitative colorimetric response of the indicators (ΔE) revealed a strong linear correlation. Thus, it was concluded that the developed colorimetric pH indicators could be used to monitor the freshness of raw beef and as an alternative to the best-before date commonly used in pre-packaged meat.

Development of a novel colorimetric pH-indicator film based on CMC/flaxseed gum/betacyanin from beetroot peels: A powerful tool to monitor the beef meat freshness

A novel indicator film based on carboxymethyl-cellulose (CMC)/flaxseed gum (FG) was developed by introducing betacyanin (BC) from beetroot peel extract. Remarkably, CMC/FG/BC film exhibited a dynamic color transition from pink to yellow in response to pH changes from 1 to 12. Beyond its pH sensitivity, the newly developed film demonstrated exceptional sensitivity to ammonia solution concentrations, detecting variation from 0.125 to 0.5 mg/mL with a significant ΔE (P < 0.05) change when a concentration of 0.5 mg/mL was added. Moreover, the inclusion of BC not only heightened the film's colorimetric capabilities but also enhanced the antioxidant, physical (moisture content, swelling index, thickness and biodegradability), and mechanical (elongation at break) properties. On the other hand, the CMC/FG/BC film's ability to provide real-time monitoring of minced beef meat quality was examined during 14 days of storage at 4 °C. The CMC/FG/BC film displayed a distinctive color change (from light pink to purple) corresponding to changes in meat samples' total volatile basic nitrogen (TVB-N) and microbial count (aerobic plate, psychrotrophic total and Enterobacteriaceae counts) during the storage period. The CMC/FG/BC film could be considered as a novel colorimetric pH indicator to monitor meat and meat derivatives' freshness. Its multifaceted properties make it valuable as an intelligent packaging used in food quality control, offering real-time insights into both pH changes and the freshness of stored meat products.

Chitosan vs chitin: Comparative study of functional pH bioindicators synthesized from natural red dyes and biopolymers as potential packaging additives

In this study, we compare pH-sensitive bioindicators fabricated via the facile one-pot reaction of biopolymers (chitosan or chitin) and natural red dyes (carminic acid and purpurin). The relationship between the biocomponents and the structure, stability, and pH-sensing activity of the resulting materials is also investigated. XPS, FT-IR, SEM and pH assessments confirmed the presence of interactions between the biopolymers and the natural dyes, leading to the formation new functional smart colorants. The type of biopolymer determined the stability of the materials, and the incorporation of natural dyes significantly increased their chemical and thermal stability. All the colorimetric indicators were highly sensitive to HCl and NH3 vapors, changing color after just a few minutes. Their application as new biocolorants for ethylene-norbornene copolymer (EN) resulted in composites with attractive color performance and good photostability. This was evidenced by the lower color changes and carbonyl index increment of the samples containing the new color systems after 50 h, 100 h, and 200 h of UV irradiation compared to pure natural dyes. For the real-time analysis of the application of colorimetric pH indicators, the colored EN composites were applied to colorimetric monitor the freshness of shrimps at room temperature. The findings indicated that the designed biopolymer-dye materials could be used simultaneously as colorants, pH indicators, and additives for polymers, providing protection against unfavorable aging conditions. Importantly, the new colorants also exhibited lower tendency to leach from the polymer matrix compared to natural dyes. This could elegantly overcome the strong migration problems associated with natural dyes and enable widespread application of the new biocolorants in packaging systems.

PH-sensitive films based on carboxymethyl cellulose/date pits anthocyanins: A convenient colorimetric indicator for beef meat freshness tracking

The pH-sensitive intelligent film is a much-awaited advancement in packaging technology, which uses visually discernible color changes to warn consumers about the freshness or spoilage of perishable food products. This study aims to develop an intelligent indicating film based on carboxymethyl cellulose (CMC), formulated with date pits anthocyanins-rich extract (DPAE) at 1.5 %. The incorporation of DPAE significantly enhanced the physical (moisture content, swelling index, water solubility and biodegradability) and mechanical (thickness, elongation at break and thickness). Developed films exhibited a higher antioxidant and antibacterial activity against food-borne pathogens. Furthermore, the inclusion of DPAE had a noticeable effect on pH-sensitive characteristics of the CMC/DPAE films. Interestingly, the CMC/DPAE film displayed a color change from yellow to dark brownish in response to changes in pH levels, covering a wide range from 1 to 13. The CMC/DPAE films were also capable of detecting ammonia at concentrations ranging from 0.125 to 1 mg/mL. In order to monitor the freshness of minced beef meat stored under refrigerated conditions at 4 °C over 14 days, CMC/DPAE films exhibited noticeable color variations corresponding to the changes in meat quality, which were assessed based on total volatile basic nitrogen, microbial count, and pH during storage. The color alteration on the packaging label shifted from yellow to dark, signifying changes in meat freshness. The obtained results stipulated that the newly developed CMC/DPAE films hold promise as innovative colorimetric pH indicators for tracking the freshness and spoilage meat-products in the food industry and supermarkets.

A nature pH indicator with high colorimetric response sensitivity for pork freshness monitoring

Smart packaging with colorimetric pH indicators is vital for food quality monitoring. However, synthetic pH-sensitive dyes pose safety hazards, and conventional methods to fabricate pH-sensitive films lack real-time detection. In this study, blueberry anthocyanin (Ant) and petunia dye (PD) were chosen among six natural dyes due to their enhanced pH responsiveness. They were utilized as chromogenic agents, while petunia dye composite film (PDCF) and anthocyanin composite film (AntCF) were synthesized using electrostatic spinning that incorporated natural dye, chitosan (CS), trehalose (TRE), and polyvinyl alcohol (PVA). Finally, a “sandwich” structure pH indicator was created by overlaying two layers of PET on the top and bottom of the composite film and perforating one side. The pH indicator based on PD composite film (PDCF-s) demonstrated superior effectiveness and stability compared to the Ant composite film (AntCF-s) in monitoring pork freshness. The indicators exhibited excellent sensitivity to low concentrations of ammonia vapor, completing the reaction within 2 min. As the pork spoiled, the color of PDCF-s changed visibly from pink to purple, with an ΔE value of 40. Moreover, the ΔE variation remained stable across different conditions. This study innovatively designed “sandwich” pH indicators, providing a promising natural safe dye for smart packaging, and promoting the use of pH-responsive indicators.

Innovative Intelligent Cheese Packaging with Whey Protein-Based Edible Films Containing Spirulina

The use of edible and biodegradable films and coatings as active packaging for cheese has recently attracted great attention as it meets the concept of sustainability and ensures safety. Spirulina is a rich source of high-added-value biocompounds, which could be used as functional ingredients. In the present study, spirulina was added in different concentrations (0.5; 1; 2; 4% w/w) to the edible films produced from whey protein concentrate-based solutions. The films were characterized according to their optical parameters (color); they were studied for their total phenolic content, and the viability of the films in simulated gastric juice was investigated. The possible use of the developed films for intelligent food packaging, as colorimetric pH indicators, was also investigated. Finally, a preliminary evaluation of selected films containing spirulina (WPC-based films containing 2% spirulina) as packaging for “kefalotyri” cheese was also assessed. The effect of these films, applied as packaging for “kefalotyri” cheese during two months of refrigerated storage, was evaluated. GC-MS analysis was used to evaluate the effect of the spirulina odor of the film with spirulina incorporated and the cheese products where the film was applied.

Colorimetric pH indicators based on well-defined amylose and amylopectin matrices enriched with anthocyanins from red cabbage

This study aimed to prepare a novel colorimetric indicator film from virtually pure (99 %) amylose (AM) and anthocyanins extracted from red cabbage (RCA). The AM used was a unique engineered bulk material extracted from transgenic barley grains. Films produced by solution casting were compared to normal barely starch (NB) and pure barley amylopectin (AP), with amylose contents of 30 % and 0 %, respectively. The pH-indicator films were produced by incorporation of RCA into the different starch support matrices with different amylose contents. Barrier, thermal, and mechanical properties, photo degradation stability, and release behavior data revealed that RCA interact differently through the glucan matrices. Microstructural observations showed that RCA were evenly dispersed in the glucan matrix, and AM+RCA indicator films showed high UV-barrier and mechanical performance over normal starch. FTIR revealed that RCA was properly affected by the AM matrix. Moreover, the AM+RCA films showed sensitive color changes in the pH range (2–11) and a predominant Fickian diffusion release mechanism for RCA. This study provides for the first time data regarding AM films with RCA and their promising potential for application as support matrices in responsive food and other industrial biodegradable packaging materials.

Synthesis and Spectrophotometric Studies of Heterocyclic Bay-Substituted Naphthalenediimide Colorimetric pH Indicators

Four naphthalenediimide colorimetric pH indicators were synthesized with N,N-dimethylethyleneamine at the imide positions and with 5- to 7-membered heterocyclic rings at the bay positions, namely pyrrolidine, morpholine, piperidine and azepane. The pH indicators are constructed in a modular receptor–spacer–fluorophore–spacer–receptor format based on a photoinduced electron transfer (PET) design. The compounds were studied by UV–visible absorption and steady-state fluorescence spectroscopy in 1:1 (v/v) methanol/water. Brilliant colour changes are observed between pH 2 and 4 due to an internal charge transfer (ICT) mechanism. Fluorescence turn-on enhancements range from 10–37 fold; however, the maximum fluorescence quantum yield in the presence of acid is &lt;0.004, which is below naked eye detection. Hence, from the viewpoint of a human observer, these chemosensors function as colorimetric YES logic gates, and fluorimetric PASS 0 logic gates.

Cross-linked CMC/Gelatin bio-nanocomposite films with organoclay, red cabbage anthocyanins and pistacia leaves extract as active intelligent food packaging: colorimetric pH indication, antimicrobial/antioxidant properties, and shrimp spoilage tests

Multifunctional food packaging films were produced from crosslinked carboxymethyl cellulose/gelatin (CMC/Ge) bio-nanocomposites incorporated with Ge-montmorillonite (OM) nanofiller, anthocyanins (ATH) from red cabbage as colorimetric pH-indicator, and pistacia leaves extract (PE) as active agent. The influence of additives on the structural, physical, and functional properties of the films was investigated. The results showed that ATH and PE caused color alteration and reduced transparency. However, they improved the UV light barrier ability by 98 %, with less impact from OM, despite its well-dispersed state in the matrix. Increasing PE content in the bio-nanocomposite films caused an increase in compactness and surface roughness, reduction in moisture content (15.10–12.33 %), swelling index (354.55–264.58 %), surface wettability (contact angle 80.1–92.49°), water vapor permeability (7.37–5.69 × 1010 g m−1s−1Pa−1), and nano-indentation mechanical parameters, without affecting the thermal stability. ATH-included films demonstrated color pH-sensitivity with improved ATH color stability through the ATH-Al3+ chelates formation. PE-added films exhibited effective antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, reaching 93 % of inhibition, and antimicrobial properties with biocidal effects for PE-rich film. The shrimp spoilage test showed that the T-1.5PE film offered the strongest active intelligent response. The CMC/Ge-based bio-nanocomposite films endowed with antioxidant/antimicrobial properties and colorimetric pH-sensitivity have promising potential for food packaging application.

Separation process characteristics of phenolic compounds from organic purple‐fleshed sweet potatoes (Ipomoea batatas L.) leaves using macroporous resins

AbstractCurrent trends have been noticed in to study of unedible parts of food as sources of phytochemicals or as ingredients in order to develop new uses for discarded materials and to promote sustainability. This study aimed to evaluate the performance of six macroporous resins (XAD 16, XAD 7HP, XAD 2, XAD 4, DAX 8, and XAD 1180 N) in purification of phenolic compounds from organic purple‐fleshed sweet potatoes. Static adsorption and desorption showed that XAD16 and XAD7HP had the highest adsorption and desorption ratio and recovery yield. The process temperature did not affect the adsorption capacity of XAD16. However, XAD7HP showed higher adsorption capacity when performed at 30°C, compared with 40 and 50°C. The process of equilibrium adsorption isotherms for phenolics was better described using Freundlich isotherm model. Dynamic adsorption process on XAD7HP resin showed that phenolic compounds in the water extracts of leaves started to break through after 4.5 bed volumes of extract was loaded. The purification of phytochemicals using adsorption is an alternative to replace organic solvents and provide a safety process for industrial application.Practical ApplicationsRecently, phenolic compounds have been explored due to their significant biological and antioxidant properties; phenolic compounds are also related to decreasing the risk of cardiovascular diseases, cancer, oxidative stress, diabetes, fatness, cancer, and several degenerative diseases. In addition, there is the potential use of phenolic compounds such as anthocyanin as safe colorimetric pH indicators in innovative packaging due to the relationship between levels of pH and anthocyanin colors. Therefore, using advanced processing technologies, phenolic compound purification can be essential for many applications related to food safety, quality, nutrition, and food waste. Furthermore, purified phenolic compounds can be used as raw materials in the pharmaceutical area and food industries.

Monitoring food quality ‐ effect of curcumin in the development of polyethylene/thermoplastic starch based smart packaging

AbstractSmart packaging relies on the one‐to‐one interaction of food with its packaging or its environment to monitor food quality and safety. Colorimetric pH indicators (synthetic, natural) working in a smart food packaging system are particularly striking when used with fresh foodstuffs such as fish and meat that perish quickly and require real‐time freshness monitoring. In this study, curcumin (Cur) was used as a natural pH indicator to produce sustainable smart packaging material. Towards this objective, low‐density polyethylene (LDPE) and thermoplastic starch (TPS) blend‐based films containing Cur were prepared using a twin screw extrusion and hot‐pressing processes. Besides, two different compositions of LDPE/TPS mixture (50/50 and 70/30) were used as the matrix. Thermal, mechanical, morphological properties, an affinity for water, and color change properties of LDPE/TPS/Cur films were investigated. They showed a significant color change from yellow to brown at pH: 10 at the end of the seventh day, especially in the 50 LDPE/50 TPS mixture. 50 LDPE/50 TPS mixture with 7% curcumin content gave the highest tensile strength of 8.03 Mpa. When the same mixture was used to monitor chicken meat spoilage at 25°C, meat samples have shown color changes from light yellow to light brown due to the increased content of total volatile basic amines. As a result, it has been suggested that 50 LDPE/50 TPS mixture containing 7% Cur can be used as a smart packaging material.

Encapsulated Colorimetric Indicators used as Additives During the Polymerization of Smart Polyethylene

AbstractA number of colorimetric pH indicators (phenolphthalein, bromocresol green, 4‐nitrophenol, phenol red, and bromothymol blue) are encapsulated within silica particles via an acid‐catalyzed sol–gel process. The fabricated indicator is added during ethylene polymerization with a metallocene (Cp2ZrCl2) catalyst. Introduction of the indicator into the silica matrix affects the surface area, probably by partially blocking some of the pores. The encapsulated pH indicator reduces the catalytic activity by up to 17%, whereas adding a solution of the indicator reduced the catalytic activity by up to 34%. The crystallinities of the samples containing the silica‐encapsulated pH indicators are lower than those of the samples to which the pH indicator is added in solution form. The prepared encapsulated colorimetric pH indicators are analyzed by diffuse reflectance UV‐vis spectroscopy. The measured color values are distributed according to the CIE Lab lightness psychometric color space. Addition of the indicator in solution form (free) to the ethylene polymerization reaction does not result in indicator activity in acidic or alkaline media. The pH indicators incorporated into the polyethylene show color changes when exposed to acidic and alkaline media. Samples to which the unencapsulated pH indicators (free) are added exhibit lower catalytic activities and higher crystallinities than the samples containing the encapsulated pH.

Natural dye modified hemp fibrous foam for colorimetric NH3 sensing

Environmental pH monitoring through color change has attracted much attention, especially for the application as food freshness indicator. However, how to unlock its safety by using natural resources has not been taken into account. Herein, a colorimetric pH foam indicator was developed by loading the natural dye anthocyanin onto hemp fiber (Anth-foam). Anth-foam made from biomass presented advantageous properties such as nontoxicity, low density, and high porosity. The colorimetric response of as-prepared Anth-foam to acidity and alkalinity in both aqueous and vaporous conditions were investigated using UV-Vis spectroscopy and CIELab analyses. All the color changes in pH range from 2 to 10 were perceivable by naked eyes. Compared with film-based indicator, the colorimetric responsive time was significantly shortened by 60% due to the porous structure of Anth-foam. The Anth-foam exhibited a greatly increased color change as NH 3 concentration increased to 250 ppm and an excellent cycling performance for retaining 89.5% of the original colorimetric response over several cycles. These properties made the Anth-foam a promising material for practical applications as a colorimetric pH indicator. • A porous colorimetric indicator was prepared from all natural resources. • Foam indicator responds faster than film indicator under the same conditions. • Sensitivity to different ammonia concentration was quantitatively investigated. • Color change of the foam indicator is reversible, leading to excellent reusability.

DESIGN AND DEVELOPMENT OF POLYLACTIDE BASED NANOFIBROUS pH INDICATOR

In this study, a colorimetric pH indicator was developed using nanofibrous mats of polylactide (PLA) including turmeric, a natural dye. Firstly, nanofibrous mats were produced by dissolving PLA at different concentrations in chloroform (CHL)/dimethylformamide (DMF) at various volume ratios, and morphological analysis was performed. Subsequently, turmeric was added at a concentration of 2% wt. to the polymer solution having a PLA concentration of 10% in 75/25 CHL/DMF, and nanofibrous pH indicators were produced. Then, pH indicators containing turmeric were immersed into pH buffer solutions (pH 1, 4, 7 and 10), and color variations were measured using a spectrophotometer. It was foreseen that the produced pH indicators have the potential to be used in intelligent food packaging applications.

Development and evaluation of sumac (Rhus coriaria) incorporated guar gum films as colorimetric pH indicator with antioxidant and antimicrobial potential

Development and evaluation of sumac (Rhus coriaria) incorporated guar gum films as colorimetric pH indicator with antioxidant and antimicrobial potential

Design and Preparation of a Biobased Colorimetric pH Indicator from Cellulose and Pigments of Bacterial Origin, for Potential Application as Smart Food Packaging.

Nowadays, worldwide challenges such as global warming, pollution, unsustainable consumption patterns, and scarcity of natural resources are key drivers toward future-oriented bioeconomy strategies, which rely on renewable biobased resources, such as bacterial pigments and bacterial cellulose (BC), for materials production. Therefore, the purpose of this study was to functionalize bacterial cellulose with violacein, flexirubin-type pigment, and prodigiosin and test their suitability as pH indicators, due to the pigments’ sensitivity to pH alterations. The screening of the most suitable conditions to obtain the BC-pigment indicators was achieved using a full factorial design, for a more sustainable functionalization process. Then, the pH response of functionalized BC to buffer solutions was assessed, with color changes at acidic pH (BC-violacein indicator) and at alkaline pH (BC-violacein, BC-prodigiosin, and BC-flexirubin-type pigment indicators). Moreover, the indicators also revealed sensitivity to acid and base vapors. Furthermore, leaching evaluation of the produced indicators showed higher suitability for aqueous foods. Additionally, color stability of the functionalized BC indicators was carried out, after light exposure and storage at 4 °C, to evaluate the indicators’ capacity to maintain color/sensitivity. Thus, BC membranes functionalized with bacterial pigments have the potential to be further developed and used as pH indicators.

Spiroindeno-pyridineindoles (SIPIs) as new visible colorimetric pH indicators

Some new, highly selective, and sensitive colorimetric pH indicators, spiro[4H-indeno-[1,2-b]pyridine-4,3’-[3H]indoles] (SIPIs) in aqueous solution were developed. SIPIs were synthesized via a one-pot four-component condensation of isatin derivatives, β-diketones 1,3-indandione, and ammonium acetate using FSi-PrNH-BuSO3H as a nanocatalyst in EtOH. According to the experimental evaluations, it was found that SIPI derivatives are pH indicators for naked-eye detection of OHˉ ion with intense color changes from orange to purple in the pH range of 10.3–12.