pH-Dependent surface properties of N–Cdots obtained by the hydrothermal method with multicolored emissions

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Ratiometric intracellular pH sensors based on nitrogen-doped graphene oxide quantum dots

Intracellular pH (pHi) is very essential for the function of cells and organisms. Thus, it is of great scientific and technical significance to develop nanosensors for probing pHi. In this work, nitrogen-doped graphene oxide quantum dots (N-GOQDs) with fluorescent efficiency of 54% are prepared. The fluorescent spectrum excited at 340 nm contains two remarkable bands at 430 and 520 nm. Interestingly, when pH value increases from 3.6 to 10.5, the blue band at 430 nm slightly changes, while the green band at 520 nm significantly quenches. The change of fluorescent intensities also can be reflected by the variation of fluorescent color. The dual-emissive N-GOQDs are developed as ratiometric fluorescent probes for pHi, which can avoid the influence of several deviations, such as probe concentration, optical path length, and detector efficiency. As a proof of concept, pHi of Hela cells is monitored successfully. This work demonstrates the construction of nano-biosensors based on N-GOQDs with bright fluorescence, high-stability, and good biocompatibility.