Mussel‐inspired polydopamine‐encapsulated carbon dots with dual emission for detection of 4‐nitrophenol and Fe³⁺

Abstract

Carbon dots (CDs) with excellent optical properties are widely used in biomedicine, fluorescence sensing, and light‐emitting diodes (LEDs). However, it is still a challenge to prepare CDs that can stably emit red fluorescence in the water environment. In this study, polydopamine‐encapsulated luminescent carbon dots (CDs@PDA) with an encapsulating structure were synthesized at room temperature from p‐phenylenediamine‐derived red‐light CDs as the core and using mussel‐inspired chemical properties of polydopamine (PDA). In the binary system of water:ethanol = 1: 3 (volume ratio), the as‐prepared CDs@PDA had a dual emission of ultraviolet light (330 nm) and red light (640 nm) with the fluorescence quantum yields of 8.0 and 15.5%, respectively, at the same time under 285 nm light excitation. The as‐prepared CDs@PDA could be directly used for fluorescence selective sensing of 4‐nitrophenol (4‐NP) and Fe3+ through simultaneously quenching of ultraviolet and red fluorescence based on the internal filtration effect mechanism with detection limits of 3.44 and 3.75 μM, respectively. This research showed that PDA‐coated CDs can significantly improve the photoluminescence stability of CDs with new optical features. This means that the encapsulated structure of mussel chemistry is very helpful for expanding the application range of CDs in the water environment.

A Review on Carbon Dots: Synthesis, Characterization and Its Application in Optical Sensor for Environmental Monitoring

“…Carbon sources based on non-acid reagents, namely graphite oxide [ 198 ], poly(ethylene glycol) [ 199 , 200 ], 3-(3,4-dihydroxyphenyl)-L-alanine [ 201 ], ethanolamine [ 202 ], polyimide [ 203 ], polyethyleneglycol bis(3-aminopropyl) [ 204 ], ethanol [ 205 ], 3-bromophenol [ 206 ], azidoimidizole [ 207 ], activated carbon [ 208 ], glucose [ 209 ], N-methylethanolammonium thioglycolate [ 209 ], chitosan [ 210 ], chlorophyll [ 211 ], microcrystalline cellulose [ 212 ], o-phenylenediamine [ 213 ], carbon paper [ 214 ], papain [ 215 ], dextrose solution [ 216 ], etc. [ 217 , 218 , 219 , 220 , 221 , 222 , 223 , 224 , 225 , 226 , 227 , 228 , 229 , 230 ], have also been reviewed, as shown in Table 9 . 3-Bromophenol is the first insecticide adopted to be a potential precursor, thus suggesting that carbon sources are not limited in typical chemical reagents with high purity or low toxicity [ 206 ].…”

“…Due to the concerns about improving and protecting living organisms, more optical detection methods that utilize CDs as a sensing element have been developed to detect Fe 2+/3+ [ 13 , 22 , 38 , 40 , 72 , 78 , 87 , 124 , 135 , 142 , 151 , 159 , 166 , 169 , 219 , 226 ], Cu 2+ [ 53 , 66 , 97 , 141 , 227 , 239 ], Pb 2+ [ 65 , 87 , 181 , 240 ], Cr 6+/4+ [ 23 , 85 , 193 , 241 ], and Co 2+ [ 51 ]. For instance, Shamsipur et al (2018) prepared green-emitting CDs instead of common blue-emitting CDs for selective and sensitive detection of Fe 3+ [ 159 ].…”

“…The rules are as follows: (i) the absorption spectrum of the quencher (phenols) should overlap with the emission spectrum fluorophore and (ii) there is a change in the fluorescence lifetime of CDs before and after the addition of the quencher. Furthermore, the inner filter effect (IFE) is also considered important and has been applied as a developing novel fluorescent assay in recent studies [ 34 , 136 , 170 , 218 , 219 , 226 ]. This approach offers more simplicity and expediency because IFE-based sensors use fluorophore and the receptor directly rather than chemically interacting with each other.…”

“…Recently, the aggregated N,S-CDs as a dual-excitation ratiometric fluorescent probe have proven to be an effective approach for the quantitative determination of chlorogenic acid [ 184 ]. Apart from dual excitation, Liu et al (2021) observed the dual-color fluorescence emission of ultraviolet and red light when detecting 4-nitrophenol using CDs@PDA [ 226 ]. The detection limits obtained for the ultraviolet and red-light emission were 3.44 µM and 7.29 µM, respectively.…”

Fluorescence ‘off–on’ probe for lead (II) detection based on Atractylodes III CQDs and bioimaging

“…There have been many studies on the use of CQDs for Pb(II) or other metal ion detection. [29][30][31] Compared with traditional methods, fluorescence CQD sensors have the superiority of low cost and rapid determination. Regrettably, most of the CQDs usually have disadvantages such as a single sensing platform and narrow linear range.…”