Switching Carbon Nanodots from Single Emission to Dual Emission by One-Step Electrochemical Tailoring in Alkaline Alcohols: Implications for Sensing and Bioimaging

Abstract

Fluorescent carbon nanodots (CNDs) capable of dual emission blue and red light (B-R-CNDs) (460 and 610 nm) have been synthesized by a simple and low cost electrochemical method of discharging indole dissolved in ethanol in the presence of alkali. The presence of alkali played an important role to achieve switching from single blue emission to dual emission (red and blue). The as-synthesized CNDs have been thoroughly characterized by different spectroscopic techniques. Moreover, the origin of the red emission has been investigated by analyzing the intermediate product of CNDs using gas chromatography−mass spectrometry. It was found that 2naphthaleneamine, an intermediate product of B-R-CNDs, achieves an extended π-conjugated system and heteroatom functional groups to B-R-CNDs, which are synergistically responsible for emission at longer wavelength. Moreover, the alkaliethanol system played a pivotal role in structural transition from single emission to dual emission, because surface oxidation is caused by hydroxyl radicals produced in the alkaline system. Surface oxidation creates surface defects thereby giving rise to the surface-state-related red emission. The red emission of B-R-CNDs are found highly pH dependent which makes them a potential candidate for application in pH sensing. Moreover, as-prepared B-R-CNDs have been used in full color bioimaging of HepG2 cells and exhibit an accurate mitochondrial-targeting ability.

Layered Sulfur Nanosheets Prepared by Assembly of Sulfur Quantum Dots: Implications for Wide Optical Absorption and Multiwavelength Photoluminescence

“…A strongly acidic medium led to a blue shift of the absorption peak, while a strongly alkaline medium led to a red shift of the absorption peak. This phenomenon was similar to the effect of pH on a conjugate system . The S-NSs were supposed to contain the π-conjugation system and heteroatoms (O, S).…”

Facile synthesis of dual-emission fluorescent carbon nanodots for a multifunctional probe

“…1B shows the C 1s spectrum. The five peaks at 284.6, 285.6, 286.9, 288.0, and 286.2 eV indicated the presence of C–C/C C, 8 C–N, 18 C–OH, 19 N C–N, 20 and C O, 21 respectively. In the high-resolution N 1s spectrum, peaks at 398.6, 399.6, and 400.4 eV indicated the presence of C–N–C, 2 pyridinic N, 21 and C–(N) 3 (ref.…”

“…The five peaks at 284.6, 285.6, 286.9, 288.0, and 286.2 eV indicated the presence of C–C/C C, 8 C–N, 18 C–OH, 19 N C–N, 20 and C O, 21 respectively. In the high-resolution N 1s spectrum, peaks at 398.6, 399.6, and 400.4 eV indicated the presence of C–N–C, 2 pyridinic N, 21 and C–(N) 3 (ref. 8 , 22 and 23 ) ( Fig.…”

“…S3(C) and (D), † under continuous UV light (254 nm) illumination, the emission fluorescence intensity at 440 nm increased, whereas the emission fluorescence intensity at 510 nm did not changed. According to the report, 21 the photoexcited CDs are capable of producing reactive oxygen species (ROS). We conjectured that CDs generate ROS under UV light illumination.…”

Organophilic Carbon Nanodots with Multi-Band Emission and their Application as a Ratiometric and Colorimetric Fluorescent Sensor

“…7,8 One of the distinctive optical properties of the CNDs is their multi-band emission. [11][12][13][14] This feature can be used for construction of novel optical sensors with improved performance. Generally, single-emission°u orescent probes are easily interfered by various environmental factors, while multi-emission assay with two or more°uorescent signals has advantage of anti-interference and good reproducibility.…”