Stimuli-Responsive Dendritic Macromolecules for Optical Detection of Metal Ions and Acidic Vapors by the Photoinduced Electron Transfer Mechanism: Paper-Based Indicator for Food Spoilage Sensing

Abstract

Visual detection of analytes has been a significant challenge in the design and development of optical chemosensors. Sensing of analytes in aqueous solution by organic molecules has encountered some issues, such as poor water solubility and quenching of optical properties. In this study, a new category of smart dendritic macromolecules was designed and synthesized by functionalization of the poly(amidoamine) (PAMAM) dendrimer with spiropyran molecules to afford a photoluminescent dendritic structure (SP-PAMAM). Smart optical sensors were prepared by physical incorporation of four different oxazolidine derivatives containing hydroxyl and nitro substituted groups into the SP-PAMAM structure. Investigation of optical properties demonstrated photoinduced electron transfer (PET) between the spiropyran end group of SP-PAMAM and oxazolidine derivatives (in a concentration of about 0.0002 M), which can result in quenching of fluorescence emission of spiropyran photoswitch in the form of merocyanine (MC). Treatment of the oxazolidinedoped SP-PAMAM samples with metal ions resulted in changes in the PET mechanism (switching on or off), as observed in the case of Fe 3+ , Pb 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Co 2+ , and Ni 2+ by different oxazolidine derivatives through various mechanisms (increase or decrease of fluorescence emission). These smart photoluminescent dendritic macromolecules have potential applications for photodetection of metal ions in aqueous media as optical chemosensors. In addition, the smart macromolecules displayed disconnection of PET between MC and oxazolidine and also showed red fluorescence emission under acidic conditions (pH 1−5). It is due to the protonation of the MC to MCH form and demonstrates a remarkable red shift in fluorescence spectra. The pH-responsivity of smart macromolecules was used for designing a paper-based pH indicator for visual detection of spoilage in the food industry, especially in the case of milk. The prepared papers applied on cap of the milk bottles did not show any fluorescence emission in the case of fresh milk; however, a red fluorescence emission was observed after milk spoilage as a result of adsorption of acidic volatile components generated by bacterial degradation and oxidation process on the paper surface. The reported smart papers can serve as optical portable pH indicators for timely detection of spoilage in food materials, which are usable in food packaging as smart indicator tags.

Biogenic amine sensors using organic π-conjugated materials as active sensing components and their commercialization potential

“…43 In addition to change in emission intensity, a response can also be determined by a change in emission wavelength, thus exhibiting a color change in emissive light. How the fluorescent sensing materials see these types of responses can differ greatly, where aggregation, 44,86,94,95 charge transfer, [96][97][98][99] and acid-base reactions 100 have been used to achieve this.…”

Water treatment using stimuli-responsive polymers

“…With a similar structure to spiropyran, oxazolidine molecules have also been used in ion detection and removal from aqueous solutions. [154][155][156] He and coworkers reported methacrylic acid (MAA) copolymerization with a fluorescent BODIPY monomer via RAFT polymerization, and used the product in the sensitive and selective recognition of Fe 3+ . 54 They reported a detection limit of 1.2 μM even with a BODIPY content of 0.5%, which provides a method to develop water soluble high performance polymer sensors.…”

Thermal-Induced Chromism and Fluorescence Emission of Rhodamine B-Containing Polymers with Different Polarities: Tracking Temperature and Development of Thermochromic Labels

“…In order to prevent from environmental degradation of the chromic compounds and improve their chromic properties, great efforts have been devoted to prepare chromic polymers. , This type of smart polymers is generally prepared by different methods, where embedding of thermochromic dyes in a polymer matrix is one of the most significant methods . This technique is accomplished by two chemical or physical incorporation methods. − Physical incorporation has frequently been used because of the ease of the preparation method and also high preservation of the thermochromic properties of the dye. − The polymeric matrix not only plays the carrier role for the thermochromic compounds and increases their lifetime but also has great effects on thermochromic properties, such as color purity and absorption intensity, due to the different polarity of the matrix originating from its different functional groups. , In addition, incorporation of thermochromic dyes into a polymer carrier reduces their consumption, which is highly important in different applications, such as temperature sensors and anticounterfeiting inks .…”