Abstract
Fluorescent carbon quantum dots (CDs) are synthesized and employed as fluorescent nanochemosensors for selective detection of amino acids. A detailed investigation of excitation–emission maps revealed that the fluorescence properties of CDs are intensely and strongly influenced by the interaction at the surface with different amino acids. The discrimination capability was demonstrated by tensor rank decomposition of the differences induced by the surface reaction in the excitation–emission maps and by means of a common machine learning approach based on artificial neural networks.
Highlights
Carbon quantum dots (CDs) are carbon nanoparticles smaller than 10 nm having attractive photoluminescence properties, good water solubility, high stability, and biocompatibility
The chemical−physical mechanism underlying CD fluorescence is not yet fully understood,[13] it is found in the literature that fluorescence can be modulated through several factors: particle size, surface groups, surface defects, and fluorophores with different degrees of π conjugation and electron holes located between the sp[2] carbons of the clusters and the sp[3] carbons of the matrices.[14−16] Recent studies have shown that the optical properties vary considerably depending on the synthesis methodology used, passivation, doping, and size of the CDs.[17−22] This suggests that fluorescence may depend on the surface of the nanoparticles, in particular on the ′′surface defects′′ that may be responsible for absorption at certain wavelengths.[23]
CDs are synthesized by hydrothermal decomposition that produces at their surface hydroxy, carbonyl, carboxylic, ether, and epoxy groups, and these nanoparticles are suitable for reaction with amine groups.[24]
Summary
Carbon quantum dots (CDs) are carbon nanoparticles smaller than 10 nm having attractive photoluminescence properties, good water solubility, high stability, and biocompatibility. The name CDs, reflects the composition and property of emitting light at different wavelengths from the incident Since their discovery by Xu et al in 2004,1 CDs have been applied for different basic research circumstances and very technical applications ranging from molecular communication[2−5] to theranostics,[6] as well as for the detection of specific analytes[7,8] with particular reference to metal ions.[9−11] as demonstrated by Sun et al, CD fluorescence yield is greatly increased through surface passivation.[12] the chemical−physical mechanism underlying CD fluorescence is not yet fully understood,[13] it is found in the literature that fluorescence can be modulated through several factors: particle size (quantum effect), surface groups, surface defects, and fluorophores with different degrees of π conjugation and electron holes located between the sp[2] carbons of the clusters and the sp[3] carbons of the matrices.[14−16] Recent studies have shown that the optical properties vary considerably depending on the synthesis methodology used, passivation, doping, and size of the CDs.[17−22] This suggests that fluorescence may depend on the surface of the nanoparticles, in particular on the ′′surface defects′′ that may be responsible for absorption at certain wavelengths.[23] the functionalization of the surface of CDs can change the fluorescence characteristics in terms of emission intensity and excitation and emission wavelengths. What we propose to overcome these limitations is a chemosensor strategy, shown in Scheme 1, through the combined use of bare CDs and the application of multivariate analysis and fluorescent nanochemosensors
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