
==== Front
Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)13511-6
10.1016/j.heliyon.2024.e37480
e37480
Research Article
A novel organic chromo-fluorogenic optical sensor for detecting chromium ions
Saleh Sayed M. E.Saleh@qu.edu.sa
a⁎
Ali Reham a
Algreiby Azizah a
Alfeneekh Bayader a
Ali Ibrahim A.I. b
a Department of Chemistry, College of Science, Qassim University, Buraidah, 51452, Saudi Arabia
b Chemistry Department, Faculty of Science, Suez Canal University, Ismailia, Egypt
⁎ Corresponding author. E.Saleh@qu.edu.sa
07 9 2024
15 9 2024
07 9 2024
10 17 e374801 3 2024
2 9 2024
4 9 2024
© 2024 The Authors
2024
https://creativecommons.org/licenses/by/4.0/ This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Sensing trivalent chromium ion (Cr(III)) is widely applied in different areas, such as clinical analysis, marine, environmental monitoring, or even chemical industry applications. Cr(III) has a significant role in the physiological process of human life. It is classified as an essential micronutrient for living organisms. Herein, we developed and designed a novel optical Cr(III) ions sensor film. The investigated sensor has a relatively small dynamic range of 1.24 × 10−3 to 0.5 μM. We report a highly sensitive optical sensor film for Cr(III) ions based on diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate (3D) probe. The optical characteristics of the chemical probe exhibit substantial emission at 460 nm under 354 nm excitation. Besides, the interaction of the Cr(III) ions with 3D involves a complex formation with a 2:1 (metal: ligand) ratio, which is convoyed by the main peak enhancement that centered at 460 nm of 3D, and the main peak is red-shifted to 480 nm. The easily discernible fluorescence enhancement effect is a defining characteristic of the complexation reaction between the 3D probe and Cr(III). On the basis of the substantial fluorescence mechanism caused by the formation of a (Cr(III)-3D complex, which inhibits the photo-induced electron transfer (PET) process, the devised optical sensor was proposed. This film exhibits exceptional sensitivity and selectivity due to its notable fluorescence properties, stock shift of less than 106 nm, and detection capabilities at a significantly low detection limit of 0.37 × 10−3 μM. The detection procedure is executed by utilizing a physiological pH medium (pH = 7.4) with a relative standard deviation RSDr (1 %, n = 3). In addition, the 3D sensor demonstrates a high degree of affinity for Cr(III), as determined by the calculation of its binding constant to be 1.40 × 106. We present an impressive optical sensor that is constructed upon a three-dimensional molecule.

Keywords

Transition metals
Chromium
Fluorescence
Coordination reactions
Water contamination
Environmental monitoring
==== Body
pmc1 Introduction

Chromium is one of the essential ions that appear as trace levels in living systems and the thirteenth richest metal ion in the earth's crust [1]. It is a hard metal with a high corrosion resistance level. As a result, adding Cr(III) to steel significantly strengthens it against corrosion and discoloration [2] and is mainly employed for chromium plating [3]. It is also used in several important industries [4,5]. This crucial ion is a vital nutrient contributing to numerous biochemical processes. These processes include metabolizing carbohydrates, lipids, proteins, and nucleic acids [6,7]. The ion accomplishes this by reactivating particular metabolic enzymes, preserving proteins and nucleic acids, and producing hemoglobin in red blood cells [8].

However, the effects of chromium (III) are not always beneficial. It has the potential to activate insulin, thereby reducing blood glucose levels. A chromium deficiency (III) has been linked to an increased risk of diabetes and heart disease [9]. On the other hand, elevated concentrations of chromium (III) can disrupt regular enzymatic processes and cellular structures [10]. Furthermore, chromium (III) is an environmental pollutant that has reached hazardous levels due to industrial and agricultural activities. It has been classified as a mutagenic and carcinogenic agent by the US Environmental Protection Agency USEPA [11]. The World Health Organization (WHO) has set the maximum permissible level of chromium in drinking water at 0.1 mg/L (1.9 μM) [12].

When it comes to detecting metal ions, fluorescent probes have emerged as a popular choice due to their ease of preparation, high sensitivity, excellent selectivity, and low cost [13,14]. These probes work by interacting with metal cations through a chromophore, with changes in fluorescence intensity indicating the sensing process [15]. However, developing a fluorescence-based turn-on metal-sensing mechanism is a significant challenge, primarily due to the paramagnetic fluorescence quenching properties of metals like chromium (III) [16]. The paramagnetic property of chromium (III) is well-known for its ability to induce fluorescence quenching. Yet, the lack of a suitable recognition moiety/ligand combination further complicates the detection of chromium (III) using fluorimetric methods [17].

Optical chemical sensors for detecting heavy metals are based on various principles, including fluorescence [[18], [19], [20], [21], [22]], colorimetry [23,24], and surface plasmon resonance [25,26]. The sensing element can comprise various substances, including organic pigments [27,28], nanoparticles [29,30], polymers [31], enzymes [32], antibodies [33], and DNA [34]. Organic molecules are most widely synthesized to achieve this purpose of chemical sensing. They can interact with one another to selectively identify analytes of interest in industry, ecology, and medicine.

Using different types of organic compounds as substantial organic fluorescence probes has attracted much interest recently. As a result of the nitrogen atom that exists in some organic compounds, as in the amine or imine groups serving as π-acceptor [35], they can play an essential part in coordination chemistry. They have been utilized as a detection tool in the analysis of a variety of metal ions. In addition, the number of coordinated atoms is frequently used to classify these compounds. They have a variety of advantageous properties, such as simple synthesis, a broad color scale for the compounds that are formed, stability in metal complexes, and a wide range of potential applications due to their high levels of thermal and mechanical strength. They have various uses, including analytical, bioanalytical chemistry, and material sciences. In addition, different types of organic molecules have emerged as an essential factor in elaborating new structures with a wide range of industrial and biological applications in many different chemical reactions. Another example is organic molecules comprising nitrogen, oxygen, and sulfur atoms that are antipyretic medications [36,37].

Numerous established methodologies are commonly employed for detecting Cr(III) ions in diverse samples. These techniques encompass atomic absorption spectroscopy (AAS) [38], inductively coupled plasma atomic emission spectroscopy (ICP-AES) [39], instrumental neutron activation analysis [40], electrochemical methods [41], X-ray fluorescence spectroscopy [42], electrothermal atomic absorption spectrometry (ETAAS) [43], and flame atomic absorption spectroscopy (FAAS) [44]. Nevertheless, the current methods employed for detection exhibit a high degree of technological intricacy and need the use of costly apparatus. Furthermore, these approaches could be more satisfactory regarding sensitivity since they show a lack of responsiveness at elevated concentration levels. Additionally, the sample preparation process associated with these methods is time-consuming [45]. The optical responses of the sensors are illustrated by a variety of mechanisms, such as chelation-enhanced fluorescence (CHEF) [46], intermolecular charge transfer (ICT) [47], fluorescence resonance energy transfer (FRET) [48], metal-to-ligand charge transfer (MLCT) [49], photoinduced electron transfer (PET) [50], excited state intermolecular proton transfer (ESIPT), aggregation-induced emissions (AIE) [51], and photoinduced charge transfer (PCT) [52].

This study presents a newly developed optical sensor film that utilizes a diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate (3D) organic fluorophore to detect Cr(III) ions. The mechanism can be ascribed to metal-ligand chelation, where a highly sensitive 3D probe and Cr(III) ions combine to create a metal complex. The metal complex's structure is accompanied by a significant increase in fluorescence owing to the creation of a metal: ligand complex, which prevents the PET process [53,54]. The detection mechanism of Cr(III) in the presence of 3D has been analyzed by UV–Vis and fluorescence measurements. The new optical sensor exhibits exceptional selectivity, a substantial limit of detection (LOD), sensitivity, and rapid reversibility for detecting Cr(III) metal ions.

2 Materials and methods

Sigma-Aldrich was the purchase source for all the chemicals employed. Other chemical ingredients and solvents were of analytical quality and were administered in the same manner as they were received. Methanol was of HPLC grade. Before any experiments, every metal nitrate stock solution was newly made with bi-distilled water and utilized immediately.

2.1 Instruments

NMR spectra were obtained using a JEOL JNMECA 600 spectrometer capable of operating at 600-MHz for 1H and 150-MHz for 13C. The TMS was used as an internal standard. A Kofler Microhot Stage Instrument was utilized to determine melting points. An API QSTAR pulsar mass spectrometer was utilized to record the mass spectrum of the separated chemical. Using an Evolution™-200-series/UV–Visible spectrophotometer. In a quartz cell measuring 1 cm in diameter, fluorometric measurements were taken using a JASCO FP-6300 spectrofluorometric. These measurements included excitation and emission spectra.

2.2 Synthesis of 3D probe

A mixture of 0.5 mol (69.0 g) oven dried potassium carbonate (K2CO3) and 0.1 mol (6.6 g) of the malononitrile in 100 mL DMF was stirred at room temperature for 1 h, then the mixture was cooled to 0 °C and 0.1 mol (6.0 mL) carbon disulfide were added dropwise under vigorous stirring. After 30 min, the mixture was cooled to 0 °C again and 0.2 mol (22.0 mL) ethyl bromacetate was added in 20 min. The reaction mixture was then stirred for 5 h at 50 °C, 3 h at 90 °C and poured into 300 mL of cold water. The precipitate was collected and washed 3 times with 100 mL of water. The crude diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate obtained were purified by crystallization in 83 % yield (see Scheme 1). 1H NMR (300 MHz, CDCl3) δ = 4.79 (s, 4H, 2NH2), 3.96 (q, J = 7.1 Hz, 4H, 2OCH2), 0.98 (t, J = 7.1 Hz, 6H, 2CH3) (Fig. S1). 13C NMR (75.0 MHz, CDCl3) δ = 161.2, 144.8, 136.8, 127.0 (C-Ar), 121.4 (Olefinic), 61.2 (2OCH2), 14.0 (2CH3). Ms data; m/z: 314(100 %), 258, 222, 170, 166 (Fig. S2) [55].Scheme 1 Synthesis of 3D compound.

Scheme 1

2.3 Fabrication of 3D film

Mixing 2.0 mg of 3D, 34.5 mg of polyvinyl chloride PVC, and 69.0 mg of bis(2-ethylhexyl) phthalate (DOP) plasticizer in 3.2 mL of tetrahydrofuran (THF) resulted in the chemical sensor film for fabrication. After that, for around 8 h, the net solution was agitated until it became transparent. A polyester polymer support was used to disseminate the resulting cocktail using a knife coater [56]. Air was allowed to dry the optical sensor film. Based on the materials composition, it was determined that the sensor layer had a thickness of 3–4 μm as shown in Scheme 2.Scheme 2 3D optical sensor film for Cr(III)ions.

Scheme 2

2.4 Optical measurements

An experiment series was carried out to investigate the 3D chromophore optical characteristics. Experiments were conducted with a concentration of 0.5 μM 3D in a buffered medium based on H2O:ethanol (5:95) and a constant pH of 7.4 to measure UV–Vis absorbance. The buffered medium contained 20 mM HEPES. The Cr(III) concentration range was between 0 and 130 nM. At 25 °C, the net volumes of the solutions collected from the 3D chemical probe and the Cr(III) aliquots were maintained at a constant 2 mL throughout the titration phases. The fluorimetric studies for the 3D probe were carried out in the presence of Cr(III) under the identical circumstances studied. In addition, the optical characteristics of the 3D probe were investigated in the presence of 0–1.1 μM Cr(III) to assess the chemical sensor's effectiveness.

2.5 Binding study

We used Job's approach [5,7], [57]. [58] to measure the stoichiometry of the 3D chromophore and Cr(III) ions. At a buffer solution with a pH of 7.4, the complexation process was conducted by combining Cr(III) metal ions with a 0.5 μM 3D chemical probe at equal molar concentrations. From 9:1 to 9:1, the molar ratios of the reactants were changed. At 480 nm, the 3D probe exhibited its greatest fluorescence.

3 Results and discussion

3.1 Optical characterization of the 3D probe

The chemical sensor displays unique optical properties in its prepared state. UV–Vis spectroscopy was measured. The UV–vis spectrum of ligand displayed a characteristic absorption peak at 220, 268, and 366 nm correspondingly (see Fig. 1a). In addition, the 3D chromophore exhibits an apparent peak at 460 nm under excitation with 354 nm (see Fig. 1b).Fig. 1 (a) Absorbance spectrum of 3D, (b) Fluorescence spectrum of 3D (λem 460; λexc 354 nm).

Fig. 1

3.2 Sensing measurements

The fluorescence emission intensity of 3D was measured at a wavelength of 460 nm upon excitation at 354 nm; it was observed that the 3D molecule has a weak fluorescence. This can be attributed to the photoinduced electron transfer (PET) process, where the lone pair of electrons of the N atom on the amine group, which acts as an electron donor, transfer to the adjacent fluorophore (thiophene ring), which acts as an acceptor; as a result, a weak fluorescence is obtained. When Cr(III) is added to the 3D probe, it exhibits a significant increase in fluorescence because it forms a 1:2 complex (3D-Cr(III)) where the amino group acts as a receptor for the Cr(III) ions, and the formation of Cr(III)-3D complex prevents the PET process, resulting in the fluorescence enhancement of 3D probe [53,54]. Alkali, alkaline, and other transition metal ions did not impact the fluorescence. This suggests that the 3D compound is a highly specific Cr(III) fluorescent sensor. Cr(III) ion was introduced into a combination including 3D and other potentially competitive metal ions indicated above. The mixture was prepared using a buffered medium of H2O: C2H5OH (5:95) and maintained at a constant pH of 7.4 using a 20 mM HEPES solution. This increased fluorescence intensity, as seen in Fig. 2. These data indicate that 3D can potentially serve as a highly sensitive and specific fluorescence optical sensor for Cr(III) ions.Fig. 2 Fluorescence spectra of 3D probe in the presence of different metal ions.

Fig. 2

The reaction between ligand and chromium ions was analyzed using absorbance and fluorescence techniques. 3D ligand's UV–vis spectrum displayed characteristic absorption peaks, which possibly will be attributed to π-π* and n-π* transitions [59]. With the gradual addition of Cr(III) ions to the 3D, we note an enhancement in the peak, and the absorbance was at 422 nm, with an isosbestic point at 390 nm. The intensity of the spectrum displayed crucial quenching at (363 nm) (Fig. 3a). It is interesting to note that the reaction of the 3D chromophore UV–vis spectra confirms the binding process comprising the Cr(III) ions and the functional groups, which contain oxygen and nitrogen atoms of the 3D [60]. Notably, there is a correlation between the absorption ratio of the 3D probe at 422 and 363 nm and the concentration of Cr(III) across the dynamic range of 0–130 nM (Fig. 3b). In particular, when the Cr(III) concentration rises to a molar ratio of ligand to Cr(III) of 1:2, the absorption ratios become constant at higher molar ratios. Consequently, this could be attributed to encapsulating the Cr(III) ions via coordination with the chemical ligand's oxygen and nitrogen donor sites [61].Fig. 3 (a) The absorbance spectra of 3D with the addition of Cr(III) ions; (b) The absorbance band ratios (A422/A363) versus Cr(III) ion concentrations.

Fig. 3

The Cr(III) was detected by the ligand in the fluorescence spectra with the gradual addition of Cr(III) concentration, as shown in (Fig. 4a). A pH 7.4 buffer system tuned to 20 mM HEPES was used to study the fluorimetric titration response between the chemical probe 3D and concentrations of Cr(III). When excited at 354 nm, the 3D chemical probe shows a maximal fluorescence band at 460 nm (Fig. 4a). The addition of Cr(III) ions to the buffered solution at a molar ratio of 7.9 × 10−3 to 1.1 μM Cr(III) ions immediately increased the emission of the major 3D peak at 460 nm. The appearance of a strong fluorescence peak at 480 nm with a 20 nm red shift from the 3D main peak proves the formation of Cr(III)- 3D complex. An increase in the concentration of Cr(III) metal ions, with a dynamic range of 7.9 × 10−3 to 1.1 μM, significantly brightened the fluorescence band at 480 nm, providing further proof that the 3D chemical probe had complexed with Cr(III) ions. This suggests that the Cr(III)-3D chelation has an equivalent ratio of 2:1 Cr(III):3D, as the 3D fluorescence remained unchanged upon repeated addition of Cr(III) at a molar concentration of >2 equivalent (Fig. 4b).Fig. 4 (a) The fluorescence emission spectra of 3D in the presence of various [Cr(III)]; (b) the Fluorescence spectra of 3D versus molar concentration of Cr(III) ions.

Fig. 4

Fig. 5a shows the results of determining the 3D sensing film's fluorescence spectra in the presence of different Cr(III) ions concentrations. A significant increase in the emission band at 458 nm, accompanied by a 26 nm red shift (to 484 nm), was noted during the fluorescence titration. An increase in the primary emission peak's fluorescence intensity at 458 nm with a red shift at 484 nm was evidence of complex development. For confirmation of the production of the Cr(III)-3D complex, Fig. 5b shows that (F484) is dependent on [Cr(III)] through correlation. One possible explanation for the complexation process is that 3D acts as a donor chelator and binds to Cr(III) as a receptor. Amazing sensitivity to Cr(III) was shown in the 3D probe molecule throughout a concentration range of 1.24 × 10−3 to 0.5 μM. The LOD was determined using the 3D fluorimetric titration with Cr(III). Assuming an accuracy of ±1 % in perceiving fluorescence intensity, the LOD is predicted to be 0.37 × 10−3 μM Cr(III). Therefore, the 3D chemical probe is an optical chemosensor that detects Cr(III) with great impact. Memorably, the response time of the optical sensor film was determined to be 1.18 min.Fig. 5 (a) The fluorescence spectra of the 3D sensor film in the presence of various Cr(III) ion concentrations; (b) the fluorescence intensities of 3D sensor film versus molar concentration of Cr(III) ions.

Fig. 5

3.3 PH effect on the sensing process and time response

Most metal cations are detected by influencing the fluorescence of an optical sensor, which is associated with hydrogen proton transfer. Variations in the pH of the surrounding solution impact this phenomenon. The study investigated how pH levels ranging from 2 to 11 affect the selectivity and responsiveness of the chemical sensor towards Cr(III) ions. By manipulating the pH of the liquid solution using 20 M HEPES buffer solutions at a specific concentration of Cr(III) ions (0.5 μM) and stimulating it with light at a wavelength of 354 nm, we successfully measured the concentration of Cr(III) ions (as shown in Fig. 6a). Within the pH range of 2.0–7.0, the response of the chemical sensor is directly proportional to the pH value. This is because the 3D probe remains protonated without forming any complexes. The proton's attachment to the nitrogen and oxygen atoms of the active groups hinders the creation of complexes to some extent. The observed elevation in 3D sensor fluorescence when exposed to alkaline pH or pH levels over 7 results from forming Cr(III) hydroxide from the liquid solution. The study examined the reactivity and selectivity of the 3D sensing molecule for Cr(III) ions in various pH 7.4 buffered systems, such as the HEBES buffer.Fig. 6 (a) The alteration in fluorescence intensity with the pH of the sensors 3D with Cr3+; (b) the response time of the optical sensor to Cr(III) ions.

Fig. 6

In order to measure the response time of the sensor film to Cr(III) ions, a fluorimetric technique was employed to detect the luminescence intensity of the optical sensor subsequent to immersed the sensor film in 0.5 μM Cr(III). The primary peak fluorescence intensity of the 3D probe exhibited a gradual increase until it reached a constant value approximately 1.08 min. There is no alteration observed in the blue fluorescence of 3D upon the introduction of Cr (III) (See Fig. 6b). The stability of the chemosensor was assessed by submerging it in an aqueous solution for a duration of 12 h. During this time, neither the emission of 3D fluorescence nor the leaching of the 3D probe content were observed.

3.4 Binding efficiency

Based on the Benesi-Hildebrand equation and the plotting 1/(Fo-F) against 1/[Cr(III)] in (Fig. 7), the binding constant (Kb) for 3D was estimated to be 1.4 × 106.Fig. 7 Benesi-Hildebrand plot for the Cr(III)-3D complex.

Fig. 7

Benesi-Hildebrand equation:

Where Fo is the fluorescence intensity of the ligand in the absence of the Cr(III), and F is the fluorescence intensity in the presence of the Cr(III). K is the binding constant, and Fmax is the fluorescence intensity in the presence of added [M]max (max. metal concentration). The slope of the linear graph of 1/(F-Fo) against 1/[M]n allowed for the determination of the association constant (Ka). More importantly, the plot was linear (R2 = 0.9949) in this range, submitting that 3D ligand can be employed to estimate Cr(III) concentration. The affinity of the 3D probe for Cr(III) directly affects the sensitivity of the corresponding sensor. The Cr(III)-3D complex has a high affinity for binding, suggesting that 3D will possess greater sensitivity. Even low concentrations of the ligand will trigger a response. Conversely, the sensor sensitivity will be reduced if the chemosensor has low binding efficiency. Thus, Higher ligand concentrations will be required to elicit a response.

3.5 Interference investigation

In interference studies, has been added of various metal ions at a concentration of 0.5 μM. However, in the presence of Cr(III), the sensor film exhibits enhancement of fluorescence emission intensity without any interference from other competitive metal ions present in the solution, as evident in (Fig. 8a). Therefore, the sensor film has the potential to function as a very precise sensor for Cr(III). Herein, our findings indicate that Cr(III) can greatly increase the fluorescence intensity of the 3D probe. This allows us to effectively detect and estimate even small amounts of Cr(III) in a water-based solution. However, we have observed that Cr(VI) does not impact the fluorescence intensity of the 3D probe. Therefore, to detect Cr(VI), we have to convert Cr(VI) into Cr(III) by utilizing suitable reducing agents [62]. For the determination of stoichiometry between ligand and Cr(III), Job's plot analyses [63] were applied (Fig. 8b). The Job's plot was produced by altering the [Cr(III)]. A maximum fluorescence was when the molar fraction of Cr(III) reached approximately 0.65, indicating that the stoichiometric binding ratio among Cr(III) ions and 3D ligand is 2:1.Fig. 8 (a) the selectivity of 3D ligand toward other competing ions in the absence or the presence of Cr(III) ions; (b) Job's plot for the stoichiometry detection of the Cr(III)-3D complex.

Fig. 8

3.6 Reversibility

Reversibility is a very significant feature of an optical sensor. Ethylenediaminetetraacetate (EDTA), an extremely potent chelating agent for Cr(III) ions, was utilized to examine the sensor reversibility. EDTA solution considerably enhances the luminescence of the Cr(III)-3D complex because Cr(III) ions interact with the active groups of EDTA molecules. The emission intensity of the optical sensor was enhanced in the presence of Cr(III); upon the addition of EDTA, an immediate Cr-EDTA complex formed. Intriguingly, the fluorescence of the 3D chemical probe decreases after the exchange chelation process. We can observe that the emission intensity of the 3D quenched with EDTA addition and reached its original maximum after coordinating to the EDTA with 1:1 metal/3D ligand; the luminescence of ligand after six cycles reaches ≈92 % from its starting fluorescence as seen in (Fig. 9).Fig. 9 Reversibility of 3D-Cr(III) and EDTA mutually, λex = 354 nm and λem = 384 nm, respectively.

Fig. 9

3.7 Quantum yield

Fluorescence quantum yields (QY) were calculated using quinine sulfate as a standard and reference; in sulfuric acid, a solution of quinine sulfate with a QY of 55 % was established. Using

the following equation, the fluorescence QY of the ligand was calculated [64].QX=QRARIsns2AXIRns2

While.• X and R point to the ligand and reference solutions

• η is a refractive index at room temperature

• I the integrated area under the peak

• A is the maximum absorbance peak.

Both the free (3D) and Cr(III)-3D complexes were found to have estimated quantum yield values of 0.173 and 0.285, respectively.

3.8 Assessment of Cr(III) in real samples

To validate the suggested approach, the synthesized probe 3D was utilized to quantify the concentration of Cr(III) in drinking and tap water samples. Because the examined samples did not contain any Cr(III), it may be concluded that this metal ion was not present. The recovery investigations were performed on additional water samples tainted with known concentrations of Cr(III). Each spike sample was subjected to three separate tests; the results of these findings are shown in Table 1. The additional data and the estimated values were found to be in good agreement with one another, as can be seen in the table, which demonstrates that our suggested technique is accurate. It is clear from the low relative standard deviation (RSD) percentage and the high recoveries that 3D has the potential to be used as a sensor for correctly identifying Cr(III) in actual samples. The obtained results were compared to the ICP-MS data, indicating that this method effectively detects Cr(III) in the analyzed materials.Table 1 Detection of Cr(III) in various water.

Table 1Sample	added (μM)	ICP-MS (μM)	Found (μM)	RSD (%,n = 3)	Recovery (%)	
Tap Water	0	0.00002	0	2.95	–	
0.05	0.0502	0.053	2.35	106.0	
0.2	0.201	0.211	2.19	105.5	
0.4	0.402	0.435	2.08	108.8	
Mineral Water	0	0.00001	0	2.63	–	
0.05	0.0501	0.052	2.21	104.0	
0.2	0.203	0.207	2.12	103.5	
0.4	0.402	0.411	2.02	102.8	

3.9 Comparison

The 3D chemosensor designed for fluorescence detection of Cr3+ is quite impressive. Furthermore, we conducted a comparison between the current sensor and previously documented chemosensors for Cr3+ as shown in Table 2. Chemosensor 3D demonstrated a comparatively superior response.Table 2 Comparative analysis of chemosensor 3D with previously reported sensors.

Table 2Chemosensor	Analytes	Method	Mechanism	Medium	LOD (M)	Ref.	
Carbazole-based Schiff base (1-(5-(9-hexyl-9H-carba-zol-3-yl)thiophen-2-yl)-N-(3-nitrophenyl) methanimine	Fe3+ and Cr3+	Turn-on
Fluorescence	C=N isomerization inhibits ESIPT	CH3CN	2.75 × 10−6	[65]	
A Schiff base based on triphenylamine and thiophene	Cr3+	Turn- off-on
Fluorescence	PET	THF/H2O (1:1, v:v)	1.5 × 10−6	[66]	
A thiophene-coumarin hybrid molecule	Cr3+	Turn-on
Fluorescence	Complex formation inhibits PET	CH3CN-HEPES (0.02 M) (4:6, v/v)	1 × 10−6	[67]	
Imine-linked, benzimida-zole-based chemosensor	Mg2+ and Cr3+	Turn-on
Fluorescence	Cr3+ complex enhances Keto-tautomer	CH3CN/H2O (8:2, v/v)	7.94 × 10−5	[68]	
2,3-dimethyl-4-(3-oxo-1,3-diphenylpropylidene-amino)-1-phenyl-1,2- dih-ydropyrazol-5-one	Al3+ and Cr3+	Turn-off-on
Fluorescence	PET	CH3OH/H2O (8:2, v/v)	0.73	[69]	
2-((quinolin-8-ylimino) methyl) naph-thalen-1-ol	Al3+ and Cr3+	Colorimetric	Complex formation Inhibits C=N isomerization	CH3OH	1.1 × 10−5	[70]	
N,N0-bis(salicylidene)-2-(6-(2-aminophenyl)-4-phenylpyridin-2-yl)	Cr3+	Turn-on
Fluorescence	PET and CHEF	CH3CN/H2O (95/5 %)	2.2 × 10−7	[71]	
Diethyl 3,4-diaminothie-no[2,3-b]thiophene-2,5-dicarboxylate	Cr3+	Turn-on
Fluorescence	Complex formation inhibits PET	H2O: C2H5OH (5:95)
20 mM HEPES	0.37 × 10−9	This work	

4 Conclusion

In this study, we have created a novel optical sensor film using diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate (3D) to detect Cr(III). The 3D molecules exhibited preferential recognition of Cr(III) ions compared to other metal cations. Unlike the typical phenomenon of metal-induced fluorescence amplification, the presence of Cr(III) ions resulted in a notable increase in the fluorescence of the ligand mentioned. The optical film properties of the 3D molecules were studied in the presence of Cr(III) in a combination of H2O: ethanol (5:95) based buffered medium with a constant pH of 7.4 using (20 mM HEPES). The investigation focused on the dependence of the film features on fluorescence. The 3D optical sensor film has excellent selectivity and sensitivity towards Cr(III) ions, with a low limit of detection (LOD) of 0.37 × 10−3 μM. It does not show any interference from neighboring cations in the medium. The ligand's complexation with Cr(III) ions demonstrated reversibility when treated with EDTA, allowing the regeneration of the free ligand for further sensing of Cr(III). Based on the plot of Job's analysis, the binding stoichiometry between Cr(III) and the ligand, as determined by the fluorescence approach, was found to be 2:1. The Benesi-Hildebrand equation was employed to determine the binding constant (Kb) of Cr(III) to the ligand, yielding a value of 1.4 × 106. This optical sensor can be a notable tool for detecting Cr(III) in real water samples.

Data availability statement

Data is included in the article/supp. material/referenced in the article.

CRediT authorship contribution statement

Sayed M. Saleh: Writing – review & editing, Writing – original draft, Validation, Supervision, Methodology, Data curation, Conceptualization. Reham Ali: Writing – original draft, Supervision, Methodology, Conceptualization. Azizah Algreiby: Validation, Investigation. Bayader Alfeneekh: Visualization, Validation, Methodology, Data curation. Ibrahim A.I. Ali: Visualization, Validation, Methodology.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Sayed M. Saleh reports financial support was provided by 10.13039/501100007414 Qassim University , 10.13039/501100023674 Deanship of Scientific Research . If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A Supplementary data

The following is/are the supplementary data to this article:Multimedia component 1

Multimedia component 1

Acknowledgment

“The author(s) gratefully acknowledge 10.13039/501100007414 Qassim University , represented by the Deanship of Scientific Research, on the financial support for this research under the number (2023-SDG-1-BSRC35366 ) during the academic year 1445 AH/2023 AD.”

Appendix A Supplementary data to this article can be found online at https://doi.org/10.1016/j.heliyon.2024.e37480.
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References

1 Maity M.B. Talukdar D. Dutta B. Bairy G. Murmu N. Das G. Sinha C. Application of a Rhodamine-chromone Schiff base probe for sensing Fe3+, Al3+, and Cr3+ at low concentration and exploring the anticancer activity and bio-imaging Inorg. Chim. Acta. 545 2023 121276
2 Kamali S. Arabahmadi R. Orojloo M. Amani S. A new azo Schiff base probe for detection of Cr3+, HSO4−, and CN−: computational studies, 4-to-2 encoder, and integrated molecular logic circuits Microchem. J. 184 2023 108204
3 Singh J. Kaur V. Singh R. Bhardwaj V.K. Exploration of solvent responsive Cr3+-Schiff base conjugates formonitoring Cr3+ ions and organophosphates: fabrication of spot-testingdevices Spectrochim. Acta Mol. Biomol. Spectrosc. 201 2018 46 53
4 Jebnouni A. Teka S. Bahrouni Y. Jaballah N.S. Bechambi O. Majdoub M. Highly selective turn-on fluorescent chemosensor for the detection of Cr(III) ion in drinking water Opt. Mater. 134 2022 113091
5 Musikavanhu B. Zhang Y. Zhu D. Xue Z. Yuan R. Wang S. Zhao L. Turn-off detection of Cr (III) with chelation enhanced fluorescence quenching effect by a naphthyl hydrazone Shiff base chemosensor Spectrochim. Acta Mol. Biomol. Spectrosc. 281 2022 121599
6 Wang M. Wang J. Xue W. Wu A. A benzimidazole-based ratiometric fluorescent sensor for Cr3+ and Fe3+ in aqueous solution Dyes Pigments 97 3 2013 475 480
7 Chalmardi G.B. Tajbakhsh M. Hasani N. Bekhradnia A. A new Schiff-base as fluorescent chemosensor for selective detection of Cr3+: an experimental and theoretical study Tetrahedron 74 18 2018 2251 2260
8 Sunnapu O. Kotla N.G. Maddiboyina B. Asthana G.S. Shanmugapriya J. Sekar K. Singaravadivel S. Sivaraman G. Rhodamine based effective chemosensor for Chromium (III) and their application in live cell imaging Sensor. Actuator. B Chem. 246 2017 761 768
9 Lee S.Y. Bok K.H. Kim J.A. Kim S.Y. Kim C. Simultaneous detection of Cu2+ and Cr3+ by a simple Schiff-base colorimetric chemosensor bearing NBD (7-nitrobenzo-2-oxa-1, 3-diazolyl) and julolidine moieties Tetrahedron 72 35 2016 5563 5570
10 Amitha G.S. Rajan V.K. Amritha B. Muraleedharan K. Vasudevan S. Betti base and its modified phthalonitrile derivative for the turn on fluorimetric detection of Hg2+ and Cr3+ ions J. Photochem. Photobiol. Chem. 382 2019 111904
11 Shrivastava R. Upreti R.K. Seth P.K. Chaturvedi U.C. Effects of chromium on the immune system FEMS Immunol. Med. Microbiol. 34 1 2002 1 7 12208600
12 EFSA Panel on Contaminants in the Food Chain (CONTAM) Scientific Opinion on the risks to public health related to the presence of nickel in food and drinking water EFSA J. 13 2 2015 4002
13 Zhang M. Gong L. Sun C. Li W. Chang Z. Qi D. A new fluorescent-colorimetric chemosensor based on a Schiff base for detecting Cr3+, Cu2+, Fe3+ and Al3+ ions Spectrochim. Acta Mol. Biomol. Spectrosc. 214 2019 7 13
14 dos Santos Carlos F. Nunes M.C. De Boni L. Machado G.S. Nunes F.S. A novel fluorene-derivative Schiff-base fluorescent sensor for copper(II) in organic media J. Photochem. Photobiol. Chem. 348 2017 41 46
15 Baslak C. Kursunlu A.N. A naked-eye fluorescent sensor for copper (II) ions based on a naphthalene conjugate Bodipy dye Photochem. Photobiol. Sci. 17 2018 1091 1097 29947409
16 Das B. Ghosh A. Dorairaj D.P. Dolai M. Karvembu R. Mabhai S. Im H. Dey S. Jana A. Misra A. Multiple ion (Al3+, Cr3+, Fe3+, and Cu2+) sensing using a cell-compatible rhodamine-phenolphthalein-derived Schiff-base probe J. Mol. Liq. 354 2022 118824
17 Yang Y. Xue H. Chen L. Sheng R. Li X. Li K. Colorimetric and highly selective fluorescence" turn‐on" detection of Cr3+ by using a simple schiff base sensor Chin. J. Chem. 31 3 2013 377 380
18 Ali R. Ghannay S. Messaoudi S. Alminderej F.M. Aouadi K. Saleh S.M. A reversible optical sensor film for mercury ions discrimination based on isoxazolidine derivative and exhibiting pH sensing Biosensors 12 11 2022 1028 36421146
19 Saleh S.M. El-Sayed W.A. El-Manawaty M.A. Gassoumi M. Ali R. Microwave-assisted rapid synthesis of luminescent tryptophan-stabilized silver nanoclusters for ultra-sensitive detection of Fe(III), and their application in a test strip Biosensors 12 6 2022 425 35735572
20 Saleh S.M. Almotiri M.K. Ali R. Green synthesis of highly luminescent gold nanoclusters and their application in sensing Cu(II) and Hg(II) J. Photochem. Photobiol. Chem. 426 2022 113719
21 Saleh S.M. El-Sayed W.A. El-Manawaty M.A. Gassoumi M. Ali R. An eco-friendly synthetic approach for copper nanoclusters and their potential in lead ions sensing and biological applications Biosensors 12 4 2022 197 35448257
22 Ali R. Alfeneekh B. Chigurupati S. Saleh S.M. Green synthesis of pregabalin‐stabilized gold nanoclusters and their applications in sensing and drug release Arch. Pharmazie 355 4 2022 2100426
23 Ali R. Ali I.A. Messaoudi S. Alminderej F.M. Saleh S.M. An effective optical chemosensor film for selective detection of mercury ions J. Mol. Liq. 336 2021 116122
24 Saleh S.M. Ali R. Hegazy M.E.F. Alminderej F.M. Mohamed T.A. The natural compound chrysosplenol-D is a novel, ultrasensitive optical sensor for detection of Cu(II) J. Mol. Liq. 302 2020 112558
25 Dhara P. Kumar R. Binetti L. Nguyen H.T. Alwis L.S. Sun T. Grattan K.T. Optical fiber-based heavy metal detection using the localized surface plasmon resonance technique IEEE Sensor. J. 19 19 2019 8720 8726
26 Bakhshpour M. Denizli A. Highly sensitive detection of Cd(II) ions using ion-imprinted surface plasmon resonance sensors Microchem. J. 159 2020 105572
27 Ali R. Elshaarawy R.F. Saleh S.M. Turn-on ratiometric fluorescence sensor film for ammonia based on salicylaldehyde-ionic liquid J. Environ. Chem. Eng. 5 5 2017 4813 4818
28 Saleh S.M. Ali R. Ali I.A. A novel, highly sensitive, selective, reversible and turn-on chemi-sensor based on Schiff base for rapid detection of Cu(II) Spectrochim. Acta Mol. Biomol. Spectrosc. 183 2017 225 231
29 Ali R. Saleh S.M. Elshaarawy R.F. Turn-on pH nano-fluorosensor based on imidazolium salicylaldehyde ionic liquid-labeled silica nanoparticles RSC advances 6 90 2016 86965 86975
30 Saleh S.M. Ali R. Wolfbeis O.S. Quenching of the luminescence of upconverting luminescent nanoparticles by heavy metal ions Chem.--Eur. J. 17 51 2011 14611 14617 22106007
31 Skorjanc T. Shetty D. Valant M. Covalent organic polymers and frameworks for fluorescence-based sensors ACS Sens. 6 4 2021 1461 1481 33825458
32 Unnikrishnan B. Lien C.W. Chu H.W. Huang C.C. A review on metal nanozyme-based sensing of heavy metal ions: challenges and future perspectives J. Hazard Mater. 401 2021 123397
33 Wang Y. Zhang C. Liu F. Antibody developments for metal ions and their applications Food Agric. Immunol. 31 1 2020 1079 1103
34 He Z. Yin H. Chang C.C. Wang G. Liang X. Interfacing DNA with gold nanoparticles for heavy metal detection Biosensors 10 11 2020 167 33172098
35 Yeldir E.K. Erdener D. Kaya İ. Synthesis and characterization of a pyrene-based Schiff base and its oligomer: investigation of fluorescent Cr3+ probe React. Funct. Polym. 170 2022 105097
36 Aroua L.M. Ali R. Albadri A.E. Messaoudi S. Alminderej F.M. Saleh S.M. A new, extremely sensitive, turn-off optical sensor utilizing schiff base for fast detection of Cu (II) Biosensors 13 3 2023 359 36979571
37 Patil D.Y. Patil A.A. Khadke N.B. Borhade A.V. Highly selective and sensitive colorimetric probe for Al3+ and Fe3+ metal ions based on 2-aminoquinolin-3-yl phenyl hydrazone Schiff base Inorg. Chim. Acta. 492 2019 167 176
38 Zhong W.S. Ren T. Zhao L.J. Determination of Pb (Lead), Cd (Cadmium), Cr (Chromium), Cu (Copper), and Ni (Nickel) in Chinese tea with high-resolution continuum source graphite furnace atomic absorption spectrometry J. Food Drug Anal. 24 1 2016 46 55 28911408
39 Zhang L. Li Z. Du X. Li R. Chang X. Simultaneous separation and preconcentration of Cr (III), Cu (II), Cd (II) and Pb (II) from environmental samples prior to inductively coupled plasma optical emission spectrometric determination Spectrochim. Acta Mol. Biomol. Spectrosc. 86 2012 443 448
40 Kumar R. Alamelu D. Acharya R. Rai A.K. Determination of concentrations of chromium and other elements in soil and plant samples from leather tanning area by Instrumental Neutron Activation Analysis J. Radioanal. Nucl. Chem. 300 2014 213 218
41 Jin W. Wu G. Chen A. Sensitive and selective electrochemical detection of chromium (VI) based on gold nanoparticle-decorated titania nanotube arrays Analyst 139 1 2014 235 241 24191278
42 Marguí E. Zawisza B. Sitko R. Trace and ultratrace analysis of liquid samples by X-ray fluorescence spectrometry TrAC, Trends Anal. Chem. 53 2014 73 83
43 Sardans J. Montes F. Penuelas J. Electrothermal atomic absorption spectrometry to determine As, Cd, Cr, Cu, Hg, and Pb in soils and sediments: a review and perspectives Soil Sediment Contam. 20 4 2011 447 491
44 Yildiz Z. Arslan G. Tor A. Preconcentrative separation of chromium (III) species from chromium (VI) by cloud point extraction and determination by flame atomic absorption spectrometry Microchim. Acta 174 2011 399 405
45 Ulusoy H.I. Gürkan R. Yılmaz Ö. Akçay M. Development of a cloud point extraction and preconcentration method for chromium (III) and total chromium prior to flame atomic absorption spectrometry J. Anal. Chem. 67 2012 131 139
46 Saleh S.M. Ali R. Ali I.A. A novel, highly sensitive, selective, reversible and turn-on chemi-sensor based on Schiff base for rapid detection of Cu (II) Spectrochim. Acta Mol. Biomol. Spectrosc. 183 2017 225 231
47 Saleh S.M. Ali R. Elshaarawy R.F. A ratiometric and selective fluorescent chemosensor for Ca (II) ions based on a novel water-soluble ionic Schiff-base RSC advances 6 73 2016 68709 68718
48 Saleh S.M. Müller R. Mader H.S. Duerkop A. Wolfbeis O.S. Novel multicolor fluorescently labeled silica nanoparticles for interface fluorescence resonance energy transfer to and from labeled avidin Anal. Bioanal. Chem. 398 2010 1615 1623 20446080
49 Wang X. Wang Q. Chen Y. Li J. Pan R. Cheng X. Ng K.W. Zhu X. He T. Cheng J. Tang Z. Metal-to-ligand charge transfer chirality-based sensing of mercury ions Photon. Res. 9 2 2021 213 221
50 de Silva A.P. Luminescent photoinduced electron transfer (PET) molecules for sensing and logic operations J. Phys. Chem. Lett. 2 22 2011 2865 2871
51 Gao M. Tang B.Z. Fluorescent sensors based on aggregation-induced emission: recent advances and perspectives ACS Sens. 2 10 2017 1382 1399 28945357
52 Li X. Rajasree S.S. Yu J. Deria P. The role of photoinduced charge transfer for photocatalysis, photoelectrocatalysis and luminescence sensing in metal-organic frameworks Dalton Trans. 49 37 2020 12892 12917 32990707
53 Chalmardi G.B. Tajbakhsh M. Bekhradnia A. Hosseinzadeh R. A highly sensitive and selective novel fluorescent chemosensor for detection of Cr3+ based on a Schiff base Inorg. Chim. Acta. 462 2017 241 248
54 Batista R.M. Costa S.P. Raposo M.M.M. Naphthyl-imidazo-anthraquinones as novel colorimetric and fluorimetric chemosensors for ion sensing J. Photochem. Photobiol. Chem. 259 2013 33 40
55 He W.W. Yang G.S. Tang Y.J. Li S.L. Zhang S.R. Su Z.M. Lan Y.Q. Phenyl groups result in the highest benzene storage and most efficient desulfurization in a series of isostructural metal–organic frameworks Chem.--Eur. J. 21 27 2015 9784 9789 26015079
56 Ali R. Alminderej F.M. Messaoudi S. Saleh S.M. Ratiometric ultrasensitive optical chemisensor film based antibiotic drug for Al(III) and Cu(II) detection Talanta 221 2021 121412
57 Saleem M. Lee K.H. Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species Rsc Advances 5 88 2015 72150 72287
58 Facchiano A. Ragone R. Modification of Job's method for determining the stoichiometry of protein-protein complexes Anal. Biochem. 313 1 2003 170 172 12576074
59 Chen X.C. Tao T. Wang Y.G. Peng Y.X. Huang W. Qian H.F. Azo-hydrazone tautomerism observed from UV-vis spectra by pH control and metal-ion complexation for two heterocyclic disperse yellow dyes Dalton Trans. 41 36 2012 11107 11115 22864773
60 Tajbakhsh M. Chalmardi G.B. Bekhradnia A. Hosseinzadeh R. Hasani N. Amiri M.A. A new fluorene-based Schiff-base as fluorescent chemosensor for selective detection of Cr3+ and Al3+ Spectrochim. Acta Mol. Biomol. Spectrosc. 189 2018 22 31
61 Dhineshkumar E. Iyappan M. Anbuselvan C. A novel dual chemosensor for selective heavy metal ions Al3+, Cr3+ and its applicable cytotoxic activity, HepG2 living cell images and theoretical studies J. Mol. Struct. 1210 2020 128033
62 Tawfik S.M. Farag A.A. Kobisy A.S. Elged A.H. Abusaif M.S. Ammar Y.A. Ragab A. Blue-green emitting cationic thiazole surfactants-based paper devices for highly sensitive and selective fluorescence detection of chromium oxyanions in wastewater Microchem. J. 193 2023 108988
63 Deshapande N. Belavagi N.S. Panchamukhi S.I. Rabinal M.H. Khazi I.A.M. Synthesis and optoelectronic properties of thieno [2,3-b] thiophene based bis 1,3,4-oxadiazole derivatives as blue fluorescent material for use in organic light emitting diodes Opt. Mater. 37 2014 516 519
64 Elshaarawy R.F. Ali R. Saleh S.M. Janiak C. A novel water-soluble highly selective “switch-on” ionic liquid-based fluorescent chemi-sensor for Ca (II) J. Mol. Liq. 241 2017 308 315
65 Zhu W. Yang L. Fang M. Wu Z. Zhang Q. Yin F. Huang Q. Li C. New carbazole-based Schiff base: colorimetric chemosensor for Fe3+ and fluorescent turn-on chemosensor for Fe3+ and Cr3+ J. Lumin. 158 2015 38 43
66 Kolcu F. Erdener D. Kaya İ. A Schiff base based on triphenylamine and thiophene moieties as a fluorescent sensor for Cr (III) ions: synthesis, characterization and fluorescent applications Inorg. Chim. Acta. 509 2020 119676
67 Guha S. Lohar S. Banerjee A. Sahana A. Hauli I. Mukherjee S.K. Matalobos J.S. Das D. Thiophene anchored coumarin derivative as a turn-on fluorescent probe for Cr3+: cell imaging and speciation studies Talanta 91 2012 18 25 22365674
68 Saluja P. Sharma H. Kaur N. Singh N. Jang D.O. Benzimidazole-based imine-linked chemosensor: chromogenic sensor for Mg2+ and fluorescent sensor for Cr3+ Tetrahedron 68 10 2012 2289 2293
69 Kumawat L.K. Mergu N. Asif M. Gupta V.K. Novel synthesized antipyrine derivative based “Naked eye” colorimetric chemosensors for Al3+ and Cr3+ Sensor. Actuator. B Chem. 231 2016 847 859
70 Jang Y.J. Yeon Y.H. Yang H.Y. Noh J.Y. Hwang I.H. Kim C. A colorimetric and fluorescent chemosensor for selective detection of Cr3+ and Al3+ Inorg. Chem. Commun. 33 2013 48 51
71 Chalmardi G.B. Tajbakhsh M. Bekhradnia A. Hosseinzadeh R. A highly sensitive and selective novel fluorescent chemosensor for detection of Cr3+ based on a Schiff base Inorg. Chim. Acta. 462 2017 241 248
