Green Synthesis of CQDs via the Trunks of Bauhinia purpurea as Fluorescence Probes for Rapid and Accurate Detection of Quinoline Yellow.

Carbon quantum dots (CQDs) were greenly synthesized via a single-step hydrothermal method, using the trunks of Bauhinia purpurea as the carbon source. They exhibited good dispersibility, water solubility, high sensitivity, and great stability with a spherical form and a particle size of 2.68 ± 0.32 nm. By utilizing the inner filter effect and dynamic quenching effect, the fluorescence quenching of CQDs can be induced to detect quinoline yellow. Detailed experimental results showed that the change rate of fluorescence intensity of CQDs had a good linear relationship with varying concentrations of quinoline yellow (2-128 µmol/L). It can be clearly observed that the fluorescence quenching occurred within 1 min, its correlation coefficient (R2) is 0.9912, and the detection limit (DL) is 1.7884 µmol/L, substantially lower than the maximum concentration stipulated by the national standard of 209.5 µmol/L. Furthermore, quinoline yellow had been successfully detected in real beverage samples using CQDs, with the recovery rates of 90.6%-110.4% and the relative standard deviation (RSD) ≤ 6.3% and it also showed great anti-interference and selectivity. These findings indicate that the detected quinoline yellow of CQDs possess substantial promise for a wide range of applications within the detected artificial food colors field.

Nitrogen-doped carbon quantum dots as dual mode fluorescence sensors for the determination of food colorant quinoline yellow.

Quinoline yellow (QY), as a food coloring agent, will consume a large number of detoxifying substances in the body after being ingested by the human body, interfering with the normal metabolic functions of the human body, and may cause allergies, diarrhea and other symptoms, as well as a certain degree of carcinogenicity, posing a great threat to human health. As a result, it is critical to develop a fast, sensitive, and effective approach to determining quinoline yellow in food. In this study, carbon dots (N-CQDs) with high fluorescence quantum yield were prepared and used to determine the QY content using the dual mode of internal filtering effect and fluorescence emission shift detection. Both methods showed good linearity in the range of QY concentration of 0.3-3.2 µM, and the detection limits were classified as 2.6 nM and 0.18 µM. In addition, in order to achieve visual detection of QY, fluorescent test strips were constructed using the carbon dots and non-fluorescent qualitative filter paper to make the detection of QY more convenient. This probe presents a novel way for detecting quinoline yellow in food analysis.

Investigating the binding interaction of quinoline yellow with bovine serum albumin and anti-amyloidogenic behavior of ferulic acid on QY-induced BSA fibrils.

Protein aggregation induces profound changes in the structure along with the conformation of the protein, and is responsible for the pathogenesis of a number of neurodegenerative conditions such as Huntington's, Creutzfeldt-Jacob, Type II diabetes mellitus, Alzheimer's, etc. Numerous multi-spectroscopic approaches and in-silico experiments were utilized to investigate BSA's biomolecular interaction and aggregation in the presence of quinoline yellow. The present research investigation evaluated the interaction of BSA with the food colorant (QY) at two different pH (7.4 and 2.0). The development of the BSA-QY complex was established with UV visible and fluorescence spectroscopy. The quenching of fluorescence upon the interaction of BSA with QY revealed the static nature of quenching mechanism. The Kb value obtained from our result is 4. 54 × 10-4 M-1. The results from the competitive site marker study infer that quinoline yellow is binding with the sub-domain IB of bovine serum albumin, specifically on site III. Three-dimensional fluorescence and synchronous fluorescence spectroscopy were applied for monitoring the alterations in the microenvironment of BSA upon the addition of quinoline yellow. The results from turbidity and RLS studies showed that higher concentrations of QY (80-400 µM) triggered bovine serum albumin (BSA) aggregation at pH 2.0. At pH 7.4, QY couldn't manage to trigger bovine serum albumin aggregation, perhaps because of the repulsion between negatively charged dye (QY) and anionic bovine serum albumin. The results from far-UV CD, Congo Red, and scanning electron microscopy implicate that the QY-induced aggregates exhibit amyloid fibril-like structures. Molecular docking results revealed that hydrophobic interactions, hydrogen bonding, and Pi-Sulfur interactions contribute to QY-induced aggregation of BSA. Further, the amyloid inhibitory potential of ferulic acid (FA), a phenolic acid on QY-induced aggregation of BSA, has also been assessed. The QY-induced amyloid fibrils are FA-soluble, as confirmed by turbidity, RLS, and far-UV CD studies. Far-UV CD results showed that FA retains α helix and inhibits cross ß sheet formation when the BSA samples were pre-incubated with increasing concentrations of FA (0-500 µM). Our findings conclude that QY dye successfully stimulates BSA aggregation, but ferulic acid inhibits QY-induced aggregation of BSA. Thus, FA can serve as a therapeutic agent and can help in the treatment of various amyloid-related conditions.

Highly Sensitive Voltammetric Method for Quinoline Yellow Determination on Renewable Amalgam Film Electrode.

A novel electrochemical method for the determination of quinoline yellow (QY) was developed using the renewable amalgam film electrode (Hg(Ag)FE). The sensors used can be characterized by good stability and long lifespan. Irreversible QY reduction peaks were recorded in 0.05 mol L-1 HCl with a potential of about -630 mV. The use of the Hg(Ag)FE electrode with a regulated working surface allowed the QY limit of detection to be as low as 0.48 nmol L-1. The obtained result is the lowest in comparison to other voltammetric methods described in the literature. The effects of parameters such as the size of the working electrode surface, influence of the pH value, accumulation time, and potential were investigated to provide precision and high sensitivity of the performed measurements. This new procedure was applied for the highly sensitive determination of quinoline yellow in different beverages, pre-workout supplements, and throat lozenges. The process of sample preparation was relatively simple. Calculated recoveries (96-107%) suggest that the method can be considered accurate.

MoS2 quantum dots-based optical sensing platform for the analysis of synthetic colorants. Application to quinoline yellow determination.

In this work, a novel fluorescence sensor has been designed to solve the actual need of new fast and inexpensive sensing platforms for the analysis of synthetic colorants. It is based on MoS2 quantum dots obtained by a hydrothermal method and incorporated as fluorophore into the matrix of PVC membranes, which are deposited on quartz substrates by spin-coating. It was proven, as in these conditions, MoS2 quantum dots maintain the fluorescent properties that they present in solution. Experiments carried out in solution displayed a maximum emission when they were excited under 310 nm. This initial fluorescence decreases linearly in presence of increasing concentrations of various synthetic colorants namely quinoline yellow, tartrazine, sunset yellow, allura red, ponceau 4R and carmoisine. The two possible mechanisms that can explain this quenching effect, colorants absorbing photons emitted by quantum dots and/or competing with the nanomaterial for photons coming from the excitation source, were evaluated. The most pronounced effect was observed with quinoline yellow, as a result of a mixed mechanism. The optimized methodology developed for the determination of quinoline yellow showed a linear concentration range between 5.4 and 55.0 µg with a limit of detection of 1.6 µg. The sensor was applied to the determination of quinoline yellow in a food colour paste obtaining results in good agreement with those obtained by HPLC-UV-vis measurements.

Effects of two food colorants on catalase and trypsin: Binding evidences from experimental and computational analysis.

Recently, growing concern has been paid to the toxicity of additives in food. The present study investigated the interaction of two commonly used food colorants, quinoline yellow (QY) and sunset yellow (SY), with catalase and trypsin under physiological conditions by fluorescence, isothermal titration calorimetry (ITC), ultraviolet-vis absorption, synchronous fluorescence techniques as well as molecular docking. Based on the fluorescence spectra and ITC data, both QY and SY could significantly quench the intrinsic fluorescence of catalase or trypsin spontaneously to form a moderate complex driven by different forces. Additionally, the thermodynamics results demonstrated QY bind more tightly to both catalase and trypsin than SY, suggesting QY poses more of a threat to two enzymes than SY. Furthermore, the binding of two colorants could not only lead to the conformational and microenvironmental alterations of both catalase and trypsin, but also inhibit the activity of two enzymes. This study provides an important reference for understanding the biological transportation of synthetic food colorants in vivo, and enhancing their risk assessment on food safety.

Dye removal with emulsion liquid membrane: experimental design and response surface methodology.

This work aims to removing anionic food dyes, Acid Red18 (E124) and Quinoline Yellow WS (E104), from their aqueous solutions. The Emulsion Liquid Membrane (ELM) technique was used. ELM consists of diluent (kerosene), nonionic surfactant (0.5 wt. % Triton X-45), Aliquat 336 as an extractant. Sulfuric acid (H2SO4) solution was used as an internal aqueous phase. The key parameters impacting the stability of liquid membrane and the efficiency of dye removal were investigated; Almost 98% of E124 at 50 mg/L are successfully extracted under optimum conditions. The extraction of a mixture of the two dyes at equal concentrations (25 mg/L) was conducted and their extraction showed more than 95% of efficiency. The experimental results of dye mixture (E124, E104) extraction were expressed by the following three quantities: The concentration of Triton X-45, the concentration of Aliquat 336, and the internal phase concentration of H2SO4, represented on three dimensional plots using the Box-Behnken design and the response surface methodology. For each of the parameters, the values of which were determined by experimental design, these results were subjected to empirical smoothing. The values, thus calculated, are consistent with the measurements.

Hypersensitivity of azo dyes in urticaria patients based on a single-blind, placebo-controlled oral challenge.

Introduction: The role of azo dyes in urticaria is not fully understood. Aim: To assess the incidence rate of hypersensitivity reactions to food azo dyes based on a placebo-controlled oral challenge in a group of patients with suspected urticaria exacerbation after consuming food additives. Material and methods: The study included patients over 18 years of age with chronic urticaria, in whom hypersensitivity to food additives was suspected based on a questionnaire and medical history. Patients suspected of urticaria exacerbations after ingestion of azo dyes were enrolled in a placebo-controlled single-blind oral challenge (OC) with a mixture of azo food dyes: tartrazine, Quinoline Yellow, Sunset Yellow, Cochineal Red, Allura Red, and azorubine. Results: Out of 110 patients (76 women and 34 men, mean age 46.1 (20-76 years), 39 patients were qualified for the oral challenge. We observed two subjects (5.1%) with a positive result. Conclusions: Azo dyes ingested in food or medications incidentally cause urticaria but may exacerbate its course. Oral challenge-confirmed hypersensitivity to azo dyes is much less common than reported by patients.

Identification of Tartrazine adulteration and evaluating exposure to synthetic dyes of sunset yellow and Quinoline yellow through consumption of food products among children.

Excessive consumption of synthetic food dyes by children may raise concerns about their health. These dyes may aggravate the hyperactivity symptoms and exacerbate asthma in sensitive children. The purpose of this study was to determine the presence of sunset yellow and quinoline yellow dyes, as well as tartrazine in dairy-free fruit ice cream, freeze pop, jelly, and candy. Additionally, we evaluated the amount of two food dyes consumed by children. To do so, a total of 150 food samples, including 20 dairy-free fruit ice creams, 25 freeze pops, 57 jelly products, and 48 types of candy were randomly selected from stores in Shiraz, Iran. Then, using the high-performance liquid chromatography (HPLC) method and an ultraviolet (UV) detector, we measured the amounts of sunset yellow and quinoline yellow dyes and identified the use of tartrazine. Also, the per capita consumption (grams per day) of the mentioned foods was calculated using a checklist in two groups of male and female primary schoolchildren aged 6-9 years and 10-13 years in Shiraz, Iran. According to the results, 11 (7.33%) samples contained only tartrazine and 107 (71.33%) samples contained quinoline yellow and sunset yellow synthetic dyes. In addition, of 107 samples that used quinoline yellow and sunset yellow, 102 (95.33%) contained unauthorized tartrazine. Only seven (6.54%) samples contained exceedingly high concentrations of authorized quinoline yellow and sunset yellow synthetic dyes. However, the exposure assessment showed that the intake of quinoline yellow and sunset yellow was at average levels and the 95th percentile in both age groups was less than the associated acceptable daily intake (ADI). For synthetic dyes, the target hazard quotient (THQ) and hazard index (HI) were less than one, indicating that ingestion of these two dyes via food products does not pose a risk to children's overall health.

Enhanced reactivity of the CuO-Fe2O3 intimate heterojunction for the oxidation of quinoline yellow dye (E104).

This research work describes the degradation of quinoline yellow (QY) in aqueous solutions by the heterogeneous Fenton and photo-Fenton processes in the presence of CuO/Fe2O3 photocatalyst. CuO/Fe2O3 derived from LDH structure was synthesized by the co-precipitation method. The physiochemical characteristics of CuO/Fe2O3 were described by XRD, TEM/SEM, BET surface area, and FTIR techniques. The effects of pH, H2O2 concentration, dye concentration, catalyst dose, reaction temperature, and reusability of catalyst on the QY decolorization efficiency were studied. The results indicated that a complete removal of QY was achieved within 150 min, when the H2O2 and QY concentrations were 27.6 mM and 100 mg/L, respectively. The rate constants for QY removal by the heterogeneous Fenton system were calculated, and the experimental data were found to fit the pseudo-first order model. Under optimal conditions, the rate constants were, respectively, 0.02032 and 0.01715 min-1 for the photo-Fenton and Fenton systems; this means that the addition of light has not a noticeable effect.

Development and validation of the HPLC-DAD method for the quantification of 16 synthetic dyes in various foods and the use of liquid anion exchange extraction for qualitative expression determination.

Synthetic dyes can cause many health problems, and their use as food additives is rigorously regulated worldwide. Two methods for the determination of synthetic dyes in food are described in this article. The visual qualitative expression method was based on the extraction of synthetic dyes using a liquid anion exchanger (0.01 M solution of trioctylmethylammonium chloride in chloroform). Using this reagent, an optimal transition of 15 anionic synthetic dyes from the aqueous to the organic phase was achieved (R > 99.8%). It was applicable for testing food that must not contain synthetic dyes (wines, juices, etc.) in a very short time (5-10 min). In the case of colouring of the organic phase, identification and quantification was carried out using the HPLC-DAD method described. The rapid and simple method allows for simultaneous determination of 16 synthetic dyes from all food types. The LOD and LOQ ranged from 0.026 to 0.086 µg mL-1 and from 0.077 to 0.262 µg mL-1 respectively, and recovery was 83.7-107.5%. Hypothesis: anionic synthetic dyes have hydrophobic properties, as a result they are retained on the non-polar stationary phase of the chromatographic column and are easily extracted from aqueous solutions by liquid anion exchangers.

Quinoline yellow dye stimulates whey protein fibrillation via electrostatic and hydrophobic interaction: A biophysical study.

Amyloid fibril formation of proteins is associated with a number of neurodegenerative diseases. Several small molecules can accelerate the amyloid fibril formation in vitro and in vivo. However, the molecular mechanism of amyloid fibrillation is still unclear. In this study, we investigated how the food dye quinoline yellow (QY) induces amyloid fibrillation in α-lactalbumin (α-LA), a major whey protein, at pH 2.0. We used several spectroscopy techniques and a microscopy technique to explore how QY provokes amyloid fibrillation in α-LA. From turbidity and Rayleigh light scattering experiments, we found that QY promotes α-LA aggregation in a concentration-dependent manner; the optimal concentration for α-LA aggregation was 0.15 to 10.00 mM. Below 0.1 mM, no aggregation occurred. Quinoline yellow-induced aggregation was a rapid process that escaped the lag phase, but it depended on the concentrations of both α-LA and QY. We also demonstrated that aggregation switched the secondary structure of α-LA from α-helices to cross-ß-sheets. We then confirmed the amyloid-like structure of aggregated α-LA by transmission electron microscopy measurements. Molecular docking and simulation confirmed the stability of the α-LA-QY complex due to the formation of 1 hydrogen bond with Lys99 and 2 electrostatic interactions with Arg70 and Lys99, along with hydrophobic interactions with Leu59 and Tyr103. This study will aid in our understanding of how small molecules induce aggregation of proteins inside the stomach (low pH) and affect the digestive process.

Determination of optimization parameters based on the Box-Behnken design for cloud point extraction of quinoline yellow using Brij 58 and application of this method to real samples.

Quinoline yellow (E104) dye is a food additive and generally used in cosmetics and drugs. In this work, polyethylene glycol hexa decyl ether (Brij 58) was used for the spectrophotometric determination of quinoline yellow (QY) in food and drug samples after cloud point extraction (CPE). Some parameters such as extraction temperature and time, pH, centrifuge speed, Brij 58 (surfactant) concentration, and Na2SO4 concentration were optimized using Box-Behnken design. The limit of detection (LOD) of this method was 0.0019 µg mL-1 for QY while the relative standard deviation (RSD) at low concentration levels (0.03 µg mL-1) was 1.32% (n = 5). Findings indicated that, this novel CPE method can be used quickly for the reproducible, selective and sensitive determination of QY dye in ordinary analysis.

Tiered intake assessment for food colours.

A tiered intake assessment approach, ranging from the conservative default and refined budget method to refined dietary exposure assessments using national food consumption surveys is presented and applied to derive maximum potential global colour intake estimates. The US and UK markets served as representative for the world and the EU, respectively, to determine the maximum potential exposure ceilings for eleven colours in various sub-populations, including brand-loyal consumers. Industry-reported global use levels were assigned as the maximum level. Conservative intake assessments for food colours used in non-alcoholic beverages were estimated for the general population 2 + y, toddlers, children 3-9 y, adolescents 10-17 y, adults 18-64 y, elderly 65-74 y, very elderly 75 + y based on assumed uses in high intake markets. Refined dietary exposures were estimated using either the 2-day food consumption data from the 2013-2016 US National Health and Nutrition Examination Survey or the 4-day food consumption data from the 2008-2016 U.K. National Diet and Nutrition Survey Rolling Programme. In the most refined market-share adjusted assessment, brand-specific market volume data were used to place appropriate weight on corresponding beverage type uses. Strong concordance between the refined budget method and the brand-loyal deterministic approach was shown, in which the latter assumes that the maximum use level of the colour is present in 100% of non-alcoholic beverages. This study shows that safety of colours - both synthetic and natural - in beverages at proposed use levels can be supported for any geography, with all intake estimates falling below the acceptable daily intake in refined assessments. Importantly, this study demonstrates that the refined budget method is a valid first-tier screening assessment to prioritise food colours that may benefit from more refined intake assessments when warranted.

Quinoline yellow (food additive) induced conformational changes in lysozyme: a spectroscopic, docking and simulation studies of dye-protein interactions.

Quinoline yellow (QY) is a synthetic yellow dye widely used as a coloring agent for various foodstuffs. In the current study, we have examined the role of QY on the aggregation propensity of hen egg-white lysozyme (HEWL) under physiological conditions. The dye induced conformational changes in HEWL leading to aggregate formation were identified by circular dichroism (CD), turbidity analysis, fluorescence measurement and microscopic (TEM) imaging. Molecular docking and molecular dynamics simulation studies were also employed to strengthen binding and aggregation results. Our results indicate that 25-100 µM of QY induces aggregation in HEWL, while lower QY concentrations (5 and 10 µM) does not have any effect on the aggregation propensity of HEWL. The kinetics of HEWL aggregation demonstrate nucleation independent aggregation of HEWL without lag phase. On the other hand, far UV-CD analysis illustrated the loss of α-helical structure with the increasing concentration of QY. TEM results also support the formation of aggregate structures in HEWL when exposed to QY. Molecular docking and simulation studies revealed that the HEWL-QY complex is stable as compared to individual entities. In silico analysis also illustrated that QY-induced aggregation of HEWL proceeds through the formation of hydrogen bonds, electrostatic (Pi-Anion) and Pi-Sulfur interactions. The above-mentioned results highlight the possible detrimental effect by food additive dyes, particularly in protein misfolding.

Determination of sulphonated quinophthalones in Quinoline Yellow and its lakes using high-performance liquid chromatography.

Quinoline Yellow (QY, Colour Index No. 47005) is internationally used as a colour additive in foods, drugs, and cosmetics. The manufacture of QY requires sulphonating quinophthalone, and depending on the degree of sulphonation, various forms of QY result, containing different proportions of quinophthalone mono-, di-, and trisulfonic acid sodium salts (monoSA, diSA, and triSA, respectively). Regulations on the specific composition and uses of QY differ across countries with associated differences in names for QY. The QY form certified for use in the U.S. in drugs and cosmetics is known as D&C Yellow No. 10 (Y10). The Code of Federal Regulations (CFR) specifies that Y10 and its lakes consist of predominantly monoSA's, the sum of whose levels is ≥ 75%, and that the sum level of diSA's is ≤ 15%, with one of them (6'8'diSA) at ≤ 3%. The present work reports the development of an HPLC method for determining those CFR-specified values and the level of a non-CFR-specified component, 6'8'5triSA. The selected analytes, 6'SA, 6'5diSA, 6'8'diSA, and 6'8'5triSA, were quantified by using five-point-calibration curves (R2 > 0.999) with data-point ranges of 9.96-96.53%, 0.54-21.69%, 0.10-5.00%, and 0.11-5.53% by weight, respectively. The method was found to be precise (relative standard deviation values, 0.55-0.80%) and accurate (recovery values, 91.07-99.45%). LOD and LOQ values, respectively, were as follows: 1.23 and 3.70%, 6'SA; 0.42 and 1.26%, 6'5diSA; 0.11 and 0.34%, 6'8'diSA; and 0.01 and 0.04%, 6'8'5triSA. The HPLC method was applied successfully to the analysis of 20 Y10 and eight Y10 lake samples. It can be extended to other QY forms such as E104 and Yellow 203 because it enables analysis of 6'8'5triSA. This paper also addresses the implications of the varying structure depictions and CAS numbers of the QY components that are due to the existence of three tautomeric forms of quinophthalone.

Food additive dye (quinoline yellow) promotes unfolding and aggregation of myoglobin: A spectroscopic and molecular docking analysis.

Protein aggregation leads to vast conformational changes and plays a key role in the pathogenesis of various neurodegenerative diseases including Alzheimer's and Parkinson's. In the current piece of work, we have explored the interaction of quinoline yellow (QY) with myoglobin (Mb) at two different pH (3.5 and 7.4). Various spectroscopic techniques such as turbidity, Rayleigh light scattering (RLS), UV-Vis absorbance, fluorescence resonance energy transfer (FRET), far UV-CD along with transmission electron microscopy (TEM) and molecular docking have been utilized to characterize dye-induced aggregation in Mb. Binding results showed that interaction between QY and myoglobin is spontaneous and static in nature with high KSV value of 2.14 × 104 M-1. On the other hand, thermodynamics studies (∆H & ∆S) revealed that complex formation was driven by hydrogen and Van der Walls forces. Molecular docking analysis showed strong binding affinity (Kd = 4.95 × 104 M-1) between QY and Mb at Pro100, Ile101, Lys102, Glu105, Glu136, Arg139, Lys140, and Ala143 residues. The intrinsic fluorescence and circular dichroism studies indicated that QY induced conformational changes in Mb at pH 3.5. Turbidity and RLS studies showed aggregation of Mb in the presence of QY (0.2-5 mM). Moreover, kinetics data revealed nucleation independent aggregation of myoglobin in the presence of QY. TEM analysis further established amorphous nature of Mb aggregate induced by QY. At pH (7.4), QY was unable to induce aggregation in myoglobin; it might be due to repulsive nature of negatively charged dye and myoglobin or partially altered states of protein could be pre-requisite for binding and aggregation.

Copper nanoclusters: an efficient fluorescence sensing platform for quinoline yellow.

Fluorescence quenching behavior of artificial food colorant quinoline yellow (QY), on interaction with l-cysteine stabilized copper nanoclusters (l-Cys-CuNCs) is investigated in this work. For this purpose, l-cysteine stabilized CuNCs were synthesized and characterized using various analytical techniques. Results demonstrated that the synthesized probe (size ~2 nm) had very promising optical features such as bright blue fluorescence, significant quantum yield and excellent photostability. l-Cys-CuNCs can function as a fluorescence sensor by selectively sensing QY among other yellow colorants, giving a detection limit as low as 0.11 µM. The developed sensor exhibited a linear concentration range from 5.50 to 0.20 µM. The developed fluorescence assay was successfully applied for testing commercial samples, thereby making this sensing strategy significant for quality control of food stuffs.

Interaction between quinoline yellow and human serum albumin: spectroscopic, chemometric and molecular docking studies.

BACKGROUND: Quinoline yellow (QY), a synthetic colourant widely used in the food industry, has caused extensive concerns because of its potentially harmful effects on human health. In the present work, the interactions between QY and human serum albumin (HSA) were characterized by multiple spectroscopic methods, a chemometric algorithm, and molecular modelling studies. RESULTS: The concentration profiles and pure spectra obtained for the components (QY, HSA and QY-HSA complex) from analyses of the expanded UV-visible absorption data matrices by multivariate curve resolution alternating least squares confirmed the QY-HSA interaction process. QY quenched the fluorescence of HSA through formation of a QY-HSA complex that was stabilized by moderate affinity. Hydrophobic forces and hydrogen bonding play major roles in the binding of QY to HSA. Site-specific marker-induced displacement results suggest that QY binds to subdomain IIA of HSA. This was corroborated by the molecular docking results. Decreases in HSA surface hydrophobicity and free sulfhydryl group content indicate that QY causes a contraction of the peptide strand in HSA, hiding the hydrophobic patches of the protein. Analyses by UV-visible absorption, circular dichroism, and three-dimensional fluorescence spectroscopy found that QY causes microenvironmental perturbations around the fluorophores and secondary structure changes in HSA. CONCLUSION: This work shows that QY binds to HSA, affecting its structural and functional properties, and provides new insights into the binding mechanism and a comprehensive understanding of the toxicity of QY to biological processes. © 2018 Society of Chemical Industry.