Fluorescence detection of malachite green in fish tissue using red emissive Se,N,Cl-doped carbon dots

Highlights

• Highly bright, red emissive Se,N,Cl-doped carbon dots are prepared.

• Carbon dots can be used for trace detection of malachite green in fish tissue.

• The inner filter effect is proposed to be the main detection mechanism.

Abstract

Facile detection of malachite green (MG), a toxic dye, in aquaculture is urgently demanded for environment and food safety. Herein, we design a novel fluorescent probe, namely red emissive Se,N,Cl-doped carbon dots (CDs), to accurately determinate MG. CDs are prepared by hydrothermal treatment of selenourea and o-phenylenediamine in HCl solution. This material exhibits excitation-independent dual emissions at 625 and 679 nm, with a high quantum yield of 23.6%. A selective and sensitive fluorescent sensor toward MG is established based on inner filter effect, because both the excitation and emission light of CDs can be strongly absorbed by MG. The fluorescence quenching of CDs is linear to the MG concentration over the range of 0.07–2.50 μM with a low detection limit of 21 nM. Trace-level analysis of MG in fish tissue is successfully explored, demonstrating the great potential of the proposed sensor for MG monitoring in aquatic products.

Introduction

Malachite green (MG) is a triarylmethane dye that has been extensively used for coloring purpose in leather, silk, cotton and paper industries (Khan et al., 2019). It can also serve as an effective fungicide and parasiticide in aquaculture (Samiey & Toosi, 2010). However, MG is highly toxic. It may cause carcinogenicity and teratogenicity on animal and human body, and thus is explicitly prohibited in fish farming (Yu et al., 2017). But, the illegal use of MG frequently happens in some countries due to its high efficacy and low cost (Zhang et al., 2015). Therefore, the facile detection of MG is in a strong demand for environment and food safety.

Over the past several years, various approaches have been set up to determinate MG, including surface-enhanced Raman scattering (SERS) (Deng et al., 2019, Lai et al., 2019, Zhang et al., 2015, Zhou et al., 2019), high-performance liquid chromatography (HPLC) (Chen & Miao, 2010), immunoassay (Wang et al., 2016), colorimetry (Gavrilenko et al., 2019, Zhao et al., 2019), electrochemical analysis (Wu et al., 2020), molecular imprinting technique (Lin et al., 2016), and fluorescence method (Ju et al., 2018, Luo et al., 2019). Among them, fluorescence method has the great advantages of rapidness, sensitiveness, and easy operation. Very recently, Li group realized a ratiometric fluorescence test of MG based on dual-emissive gold nanoclusters through fluorescence resonance energy transfer (FRET) and dynamic quenching (Ju et al., 2018). Luo et al exploited an RNA aptamer to specially bind with MG for its fluorescence “off–on” detection (Luo et al., 2019). Except for a few impressive cases, the fluorescence assay of MG is rarely explored, due to the limited development of excellent fluorescent sensors toward MG.

Carbon dots (CDs), an emerging photoluminescent nanomaterial, have attracted increasing attention in both fundamental and technological fields because of their fascinating chemical, physical, and optical properties (Dhenadhayalan et al., 2020, Hu et al., 2019, Zhu et al., 2020). The photoluminescence (PL) of CDs, however, is commonly found in blue and green region, while the yellow and red emissive CDs are rather difficult to obtain (Shi et al., 2019, Su et al., 2020, Zhu et al., 2019). Due to the importance of the red light in biological and sensing applications, it is essential to extend the emission of CDs to long-wavelength region, i.e., greater than 600 nm.

In the present paper, we report an acidic hydrothermal synthesis of red emissive Se,N,Cl-doped CDs using selenourea, o-phenylenediamine, and hydrochloric acid as reagents (Fig. 1). The as-prepared CDs exhibits two emission peaks at 625 and 679 nm, with an improved quantum yield of up to 23.6%, which is much higher than that of recently used gold nanoclusters (1.4%) (Ju et al., 2018). Based on an efficient inner filter effect (IFE), the red fluorescence of CDs can be remarkably and selectively quenched by MG. Thus, a fluorescent sensor toward MG is developed. Such a sensor is also applied to detect MG in fish tissue sample, and satisfactory results are achieved.