Dual-channel fluorescence dye: Fluorescent color-dependent visual detection of microplastics and selective polyurethane

A cost-effective and efficient fluorescence staining agent for the identification of microplastics in environmental samples and zebrafish (Danio rerio)

Microplastics (MPs) are recognized as a significant environmental hazardous material. Therefore, identifying and tracking microplastics are crucial to understand their harmfulness. Herein, we introduce (Z)-N'-(pyren-1-ylmethylene)pyrazine-2-carbohydrazide (PPC) as a cost-effective and efficient fluorescence staining agent. Unique properties of PPC, including aggregation-induced emission (AIE) and solvatochromism, were verified by spectroscopic studies and theoretical calculations. PPC selectively stained eight types of MPs with green fluorescence in water/tetrahydrofuran (THF) solution (97/3, v/v). Interestingly, only polyurethane (PU) was selectively stained both in green and blue channel using 50 % ethanol (EtOH) treatment. Moreover, with 30 % EtOH treatment, PU and polyethylene terephthalate (PET) were distinctly stained in the blue channel, highlighting their selective fluorescence. These results suggested that changes in solvent polarity induced by different EtOH amounts might alter the binding strength between PPC and MPs, resulting in varying fluorescence responses. In addition, the adsorption interaction of PPC to MPs was proposed, based on thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and non-covalent interaction (NCI) analysis. PPC could identify MPs without any influence in the size, aging and pH difference. Successfully, PPC could stain eight types of MPs and selectively PU and PET in artificial environmental samples like seawater, river water and soil. Moreover, PPC-labeled MPs could be tracked in biological system such as Danio rerio (zebrafish) to monitor the transit and accumulation of MPs. These results underscore the potential of PPC for efficient detection of MPs in environmental and biological systems.

An AIE-based fluorescent dye for selective staining of polyamide microplastics without pretreatment: Applications to environmental samples and zebrafish

A novel staining dye, BEM ((1E,1'E)-1,1'-([2,2'-bithiophene]-5,5'-diyl)bis(N-(9-ethyl-9H-carbazol-3-yl)methanimine)) was synthesized for selective identification of polyamide (PA) micrplastics. BEM showed unique photophysical properties such as solvatochromism, intramolecular charge transfer (ICT), and aggregation induced emission (AIE) which were demonstrated through spectroscopic analysis and density functional theory (DFT) calculations. The optimal staining conditions for selective staining of PA by BEM were established by evaluating the staining efficiency according to the variation of the solvent compositions, concentrations of BEM, and staining durations. BEM demonstrated outstanding selective staining of PA among 11 types of microplastics (MPs) and 5 types of non-plastics through the emission of green fluorescence. BEM successfully identified PA without any noticeable influence on the size change of PA, aging of PA, and pH alteration of the solvent. In addition, BEM was practically applied to environmental samples like river water, seawater, and soil for selective identification of PA without pretreatment. In particular, the cost-effective technique of BEM-labeled PA allowed to monitor the location and accumulation of PA in living zebrafish. The interaction between PA and BEM was investigated through scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), which suggested that BEM might be adsorbed onto the surface of PA. Moreover, non-covalent interaction (NCI) analysis demonstrated that the intermolecular hydrogen bonds and van der Waals interactions would play a significant role in the adsorption process between PA and BEM.

Selective visual staining of polyurethane microplastics by novel colorimetric and near-infrared (NIR) fluorescent dye: Application to environmental water and natural soil samples

Microplastics can cause environmental pollution and ecosystem destruction as well as human health problems. Among the types of microplastics, polyurethane (PU) is particularly resistant to heat and difficult to decompose, causing disposal problems, and is evaluated as one of the most hazardous polymers. We present a novel colorimetric and near-infrared (NIR) fluorescence dye, (E)-N-(2-((4-(diphenylamino)benzylidene)amino)phenyl)- 7-nitrobenzo[c][1,2,5]oxadiazol-4-amine (DPNA), designed for selective visual PU microplastic staining. The intramolecular charge transfer (ICT) properties of DPNA are demonstrated through density functional theory (DFT) calculations along with solvatochromic shift. DPNA exhibits red color and red fluorescence emission, showing promising potential as a staining dye. To achieve selective PU microplastic staining, we establish an optimized experimental procedure with the staining dye DPNA by evaluating the staining efficiency under different staining solvent compositions and staining times. DPNA can distinguish PU by both red fluorescence signal and red coloration among different types of microplastics. In addition, DPNA well stain fresh PUs with diverse sizes and at various pH range of 5-9, and the aged PUs can also be dyed as effectively as the fresh PU. Most importantly, DPNA selectively stains PU among 11 types of microplastics and 5 types of natural particles in environmental water and soil with and without any pre-treatments. The adsorption mechanism of DPNA on PU microplastic is demonstrated through field emission scanning electron microscopes (FE-SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and non-covalent interaction (NCI)-reduced density gradient (RDG) analyses, and proposed that intermolecular hydrogen bonding has a significant effect.