Quantitatively Switchable pH-Sensitive Photoluminescence of Carbon Nanodots

Abstract

pH sensing plays a key role in the life sciences as well as the environmental, industrial, and agricultural fields. Carbon nanodots (C-dots) with small size, low toxicity, and excellent stability hold great potential in pH sensing as nanoprobes due to their intrinsic pHsensitive photoluminescence (PL). Nonetheless, the undesirable sensitivity and response range of C-dot PL toward pH cannot meet the requirements of practical applications, and the unclear pH-sensitive PL mechanism makes it difficult to control their pH sensitivity. Herein, the quantitative correlation of pH-sensitive PL with specific surface structures of Cdots is uncovered for the first time, to our best knowledge. The association of carboxylate and H + increases the ratio of nonradiation to radiation decay of C-dots through excited-state proton transfer, resulting in the decrease of PL intensity. Meanwhile, the dissociation of α-H in β-dicarbonyl forming enolate increases the extent of delocalization of the C-dots conjugated system, which induces the PL broadening to the red region and a decreasing intensity. Based on the understanding of the pH-sensitive PL mechanism, the pHsensitive PL of C-dots can be switched by quantitative modulation of carboxyl and β-dicarbonyl groups to achieve a desirable pH response range with high sensitivity. This work contributes to a better understanding of the pH-sensitive PL of C-dots and therefore presents an effective strategy for controllably tuning their pH sensitivity, facilitating the rational design of C-dot-based pH sensors.

Red/Green Tunable-Emission Carbon Nanodots for Smart Visual Precision pH Sensing

“…Previous reports showed that the protonation and deprotonation of functional groups on the surface of CDs could change the energy level, aggregation, and electron/proton transfer, giving rise to a change in the PL properties. ,− Here, the fluorescence decay curves of CDs 1 at different pH values were recorded to further study the possible mechanism of the unique pH-sensitive PL. For the emission site with an ∼500 nm peak, which is sensitive toward pH (ranging from 1.6 to 3.0), the fluorescence lifetime (τ) increased from 2.95 ns (pH 1.6) to 7.54 ns (pH 3.0) as the pH increased from 1.6 to 3.0 (Figure a and Table S2).…”

Tunable fluorescent amino-functionalized Ti3C2Tx MXene quantum dots for ultrasensitive Fe3+ ion sensing

“…Under extreme pH conditions, the rapid oxidation or inactivation of N-MQDs is responsible for the decreased PL emission. 41,42…”

“…Under extreme pH conditions, the rapid oxidation or inactivation of N-MQDs is responsible for the decreased PL emission. 41,42 In addition, the emission wavelength of the N-MQDs exhibited very small redshift (∼5 nm) when the pH decreased from 12.1 to 2.0 under excitation at 320 nm. When excited at 365 nm, the fluorescence peak of the N-MQDs showed a pronounced redshift of 50 nm from 464 to 514 nm (Fig.…”

“…S12 †). 41 These two detection ranges can be employed for different applications with the corresponding requirements.…”

Self-assembly of carbon nanodots induced by liquid–liquid phase separation in a surface microdroplet

“…1,2 C-dots have sparked enormous research interest due to their advanced physical and chemical properties, including ultra-small size, excellent solvent solubility, biocompatibility, continuous and broad absorption spectra, high luminescent activity, significantly improved photostability, and environmental friendliness. [3][4][5][6][7][8] As the alternative to metal and semiconductor based luminescent nanomaterials, C-dots with their pronounced and tuneable photophysical properties [9][10][11] have been widely used for bioimaging, [12][13][14] drug delivery, [14][15][16] sensing, [17][18][19] catalysis [20][21][22] and optoelectronic applications. 3,[23][24][25][26][27] The functionalities of C-dots are connected with their structures.…”