A reversible and dual responsive sensing approach for determination of ascorbate ion in fruit juice, biological, and pharmaceutical samples by use of available triaryl methane dye and its application to constructing a molecular logic gate and a set/reset memorized device

Highlights

Notably it is worth mentioning that the present chemosensor has advantages in the fact that:

• A novel probe showed fluorescent/colorimetric response to AscH⁻ was developed.

• This probe was successfully utilized for rapid recognition and monitoring of ascorbate.

• This receptor demonstrates the function of “INHIBITION” logic gate.

• The reversible sensing phenomenon can mimic “write-read-erase-read” logic circuit.

• The proposed method, applied successfully for analysis of juice and biological samples.

Abstract

Since dyes are available in huge quantities and have the well-established chemistry involved in their synthesis, their use in chemosensing could be continued. In the current study, a new and reversible colorimetric and fluorometric chemosensor based on available triaryl methane dye (brilliant green (BG)) - phosphotungstic acid (PTA) complex has been designed for determination of ascorbate (AscH⁻¹) ion in water/DMSO (90:10 v/v, 1.0 mmol L⁻¹ HEPES, pH 7.0). The “ON-OFF” fluorescence and colorimetric responses of this ion association complex to AscH⁻¹ were based on a displacement mechanism. For the detection of AscH⁻¹, the linear ranges achieved for UV–Vis absorbance and fluorescence experiments were 3.9–62.6 μmol L⁻¹ and 1.9–85.4 μmol L⁻¹, respectively. The limits of detection for both of them were also calculated to be 0.4 and 0.2 μmol L⁻¹. The proposed method was also successfully utilized for rapid recognition of ascorbate in juice samples, human serum, and the formulation of supplement products. Moreover, the proposed chemosensor capability of functioning as INHIBITION–type sensor with PTA and AscH⁻¹ as chemical inputs was indicated by the investigation of the molecular logic behavior of this chemosensor. Eventually, a sequential memory unit displaying “Write-Read-Erase-Read” function could be integrated based on the reversible and reproducible system.

Introduction

Sodium ascorbate (AscH⁻¹), otherwise known as Vitamin C or ascorbic acid (AscH₂) at near-neutral pH (pka₁ and pka₂ of AscH₂ are 4 and 11.5, respectively) is a water-soluble organic compound (nutrient) that can be used in many biological processes [1]. It can act as an antioxidant, a cofactor, and an acidity regulator which is important for health maintenance. AscH⁻¹ is naturally occurring in foodstuffs (fresh vegetables such as broccoli, potatoes, cantaloupe, tomatoes and red bell peppers and fruits, namely citruses like oranges, grapefruit, strawberries, and kiwi) [2]. It involves in the absorption of iron in the gut, neurotransmitter formation [3], the synthesis of collagen and norepinephrine and adrenal hormones [4], wound healing and osteogenesis, immune response activation, metabolism of folic acid, tyrosine and tryptophan, carnitine biosynthesis [5], and acts as a reducing agent in cellular metabolism [6]. It also has the ability to eliminate toxic free radicals and other reactive oxygen species [7]. These species are usually formed in cell metabolism. Moreover, AscH₂/AscH⁻¹ can help to protect the immune system and prevent apoplexy, atherosclerotic, cancer, cardiovascular, anemia and mental illness [[8], [9], [10]]. Therefore, according to mentioned points, the normal concentration range of AscH⁻¹ in the human body is necessary. This concentration range in human blood plasma is 40–80 μmol L⁻¹. The highest concentration of AscH⁻¹ that can be achieved in blood plasma is about 200 μmol L⁻¹. In clinical experiments, supraphysiological levels of ascorbate in plasma can be 10,000–30,000 μmol L⁻¹ which is used to treat some human diseases through intravenous administration [11]. Therefore, the excess AscH⁻¹ levels or the lack of it in the body can be harmful and cause various disorders. The lack of AscH⁻¹ leads to develop a well-known syndrome called scurvy [12]. The excess levels of AscH⁻¹ in the body also result in diarrhea, hyperacidity and kidney calculi [13]. Therefore, the detection or determination of the concentration of AscH⁻¹ in biological and pharmacological samples has been considered in recent years.

So far, various techniques have been reported for the determination of AscH₂/AscH⁻¹, including HPLC [14], electrochemical methods [[15], [16], [17]], capillary zone electrophoresis [18], Raman spectroscopy [19], optical paper- based method [20], Amperometry [21], sequential injection redox [22], colorimetric [23], fluorescence [[24], [25], [26], [27], [28]], and enzymatic method [29,30]. However, despite these analytical methods and other available techniques employed for the quantitative determination of AscH₂/AscH⁻¹, scientists constantly continue their research to achieve better methods to overcome the limitations of the present methods for the detection of AscH₂/AscH⁻¹ concentration. For instance, among the techniques mentioned above, HPLC requires specific operating skills, expensive and specialized equipment, and sample preparation. Moreover, this analytical method is relatively labor-intensive and time-consuming. Similarly, electrochemical methods also encounter problems such as slow electron-transfer kinetics of ascorbic acid, time-consumption, and complicated synthesis of the sensor. The electrode is also fouled by its oxidized form. The colorimetric method presented requires the longtime synthesis and preparation of the sensor (24 h) and the long time for the determination of the analyte (40–60 min). It also has the poor selectivity that is unable to discriminate AscH₂/AscH⁻¹ from some interferes. About fluorescence methods, they suffer from the sample interference, synthesis of the sensor, and use of organic solvent. The enzymatic method also requires a series of enzymatic reactions and special equipment. There are also some difficulties in some other available methods such as costly and time-consuming synthesis and separation processes, chemical modifications, and use of sophisticated instrumentations. Therefore, needs for a new rapid response, simple and cost-effective analytical technique for selective determination of ascorbate still exist.

So far, various molecules have been utilized as chemosensors. Among them, dyes have significant importance due to their structural type as well as their physic-chemical characteristics in the context of ICT. Dyes are not only applicable to chemistry, material science, coloration, medical diagnostics, etc. [31] but they can also be used in the field of chemosensing due to the ease in their availability in huge quantities among different chemical classes of chromophores [32].

In this study, we report the use of Brilliant Green ((4‑(4‑(diethylamino)‑alpha‑phenyl benzylidene)‑2,5‑cyclohexadiene‑1‑ylidene) diethyl ammonium sulfate, BG) (Scheme 1), a commercially available triaryl methane dye, as a sensing probe for the fluorimetric and colorimetric detection of ascorbate (AscH⁻¹) ion by the interaction of this dye with phosphotungstic acid (A heteropoly acid with the chemical formula H₃PW₁₂O₄₀, PTA) in water/DMSO (90:10 v/v, 1.0 mmol L⁻¹ 4‑(2‑hydroxyethyl)‑1‑piperazine ethane sulfonic acid (HEPES) buffer pH 7.0). Since brilliant green is an organic compound and was not dissolved completely in absolute water, DMSO/water (10:90 v/v) mixture was used as the experiment media. Despite increasing the solubility, this organic solvent has some moderate toxic effect. Therefore, suitable concentration of this organic solvent was used to decrease its toxic effect (90:10 v/v water/DMSO mixture).

This aniline-based basic dye can form a bond with PTA. According to the studies carried out on the cytochemical properties, phosphotungstic acid has been considered as the electron-opaque moiety. This compact and roughly spherical molecule can react chemically as a strong tribasic anion. Moreover, the symmetrical and undirected distribution of the negative charge causes that the directional forces don't limit the reactivity of the molecule [33].

At the first step of this study, the production of (BG⁺)₃·PTA³⁻ ion pair led to change in the absorption spectra and color and increase in the fluorescence intensity (fluorescence switch “ON”). Then, the response of the complex toward sodium ascorbate was studied in vitro through PTA displacement mechanism. In this mechanism, sodium ascorbate as a competitive analyte with a stronger binding affinity for the PTA displaces the ligand BG. This displacement, in turn, is accompanied by changes in colorimetric or/and fluorescence signal [34]. In this way, such a simple and rapid “ON-OFF” fluorescence and colorimetric sensory system for AscH⁻¹ was designed.

It should also be noted that our group has developed easily available dyes-based high selective chromogenic/fluorescent probes for detection of cations and anions in the previous efforts [[35], [36], [37], [38], [39]]. The proposed method was successfully applied as a practical chemosensor to determine the quantitative levels of sodium ascorbate in real samples (pharmaceutical, biological, and juice samples). Moreover, the behavior of BG as an “off-on-off” reversible switch (the “ON-OFF” states of BG could be repeated for many times) by the sequential inputs of PTA and AscH⁻¹ can be considered as a “Write-Read-Erase-Read” memory function for information storage. This functional set-reset circuit outputs signals in one channel with one feedback loop. Herein, two analytes just act one role (pen or eraser) in this system. PTA (set input) could act a pen and AscH⁻¹ (reset input) act an eraser in the feedback loop.